26. slovenski kolokvij o betonih PROJEKTIRANJE MIKROARMIRANIH BETONSKIH KONSTRUKCIJ IN NJIHOVE APLIKACIJE ZBORNIK GRADIV IN REFERATOV LJUBLJANA, 16. MAJ 2019 IRMA Inštitut za raziskavo materialov in aplikacije Ljubljana Založnik: IRMA inštitut za raziskavo materialov in aplikacije Ljubljana, Slovenčeva 95, 1000 Ljubljana, Slovenija Redakcija: doc.dr. Andrej Zajc Znanstveni komite: dr. Jakob Šušteršič, IRMA, Ljubljana - predsednik člani: Prof. Dr.Joaquim António Oliveira de Barros, University of Minho, ISISE, Department of Civil Engineering, Portugal Prof. Dr. Marco di Prisco, Politecnico di Milano, Department of Civil and Environmental Engineering Italy Prof. Dr.Johan L. Silfwerbrand, KTH Royal Institute of Technology, Stockholm, Sweden Prof. Dr. Andrzej Garbacz, Warsaw University of Technology, Poland Prof. Dr. Dimitrije Zakić, Građevinski fakultet Univerziteta u Beogradu, Srbija Prof.Dr. Naser Kabashi, University of Pristina, Kosovo Doc. Dr. Jože Lopatič, Univerza v Ljubljani, Fakulteta za gradbeništvo in geodezijo, Ljubljana Doc. Dr. Andrej Zajc, IRMA Organizacijski komite: doc. dr. Andrej Zajc - predsednik člani: dr. Jakob Šušteršič Mitja Bernik David Polanec Martina Habat Rok Ercegovič Tisk: KOPI TIM d.o.o., Slovenčeva ulica 97, 1000 Ljubljana Naklada: 200 izvodov Leto izida: 2019 CIP - Kataložni zapis o publikaciji Narodna in univerzitetna knjižnica, Ljubljana 624.012.45(082) SLOVENSKI kolokvij o betonih (26 ; 2019 ; Ljubljana) Projektiranje mikroarmiranih betonskih konstrukcij in njihove aplikacije: zbornik gradiv in referatov / 26. slovenski kolokvij o betonih, Ljubljana, 16. maj 2019 ; [redakcija Andrej Zajc]. - Ljubljana : IRMA, Inštitut za raziskavo materialov in aplikacije, 2019 ISBN 978-961-93671-5-5 1. Gl. stv. nasl. 2. Zajc, Andrej, 1938- COBISS.SI-ID 299846144 Spoštovani! Na 1. slovenskem kolokviju o betonih, leta 1994, z naslovom: »Mikroarmirane malte in betoni« smo obravnavali lastnosti malt in betonov z različnimi vrstami vlaken ter nekatere pionirske aplikacije teh kompozitov pri izdelavi konstrukcijskih elementov. Od takrat pa do danes je na osnovi rezultatov raziskav in ugotovitev opazovanj številnih novih aplikacij postal mikroarmirani beton (MAB) material, uporaben za proizvodnjo konstrukcijskih elementov ob upoštevanju pravil projektiranja, ki so na voljo v številnih državah. Pripravljen pa je že osnutek priloge L k »Eurocodu 2«. Na letošnjem 26. kolokviju o betonih z naslovom: »Projektiranje mikroarmiranih betonskih konstrukcij in njihove aplikacije« bomo obravnavali ta pravila projektiranja, nekatere nove aplikacije, pri katerih se želi povečati predvsem trajnost konstrukcijskih elementov, nekaj pa bo govora o trajnosti MAB konstrukcij, ki so že vrsto let v uporabi. Kot predavatelji bodo na kolokviju nastopili aktivni strokovnjaki različnih mednarodnih in nacionalnih komisij, ki obravnavajo predmetno problematiko in pripravljajo pravila projektiranja MAB konstrukcij. Ker prihajajo iz različnih držav, pa bo možno spoznati tudi različne poglede pri reševanju te problematike, kakor tudi ugotovitve raziskav in aplikacij MAB konstrukcij. Za njihov trud pri pripravi gradiv za Zbornik predavaj in njihovo prisotnost na kolokviju se jim iskreno zahvaljujem. Ker je med udeleženci kolokvija veliko strokovnjakov, ki imajo bogate izkušnje pri razvoju, pripravi in uporabi MAB, pričakujem, da se bodo med in po kolokviju razvile plodne razprave in morda porodile nove ideje, ki jih bomo lahko uporabljali pri svojem vsakdanjem delu. S tem bi bil uresničen tudi glavni namen tega kolokvija in prepričan sem tudi vseh naslednjih. Tako kot vedno, bi se želel še enkrat zahvaliti za prisotnost in interes vseh udeležencem, iz Slovenije in iz naše bližnje ter širše okolice. Prav tako pa se moram zahvaliti vsem našim poslovnim prijateljem, ki ste z objavami oglasov v Zborniku gradiv in referatov ali z razstavnimi paneli finančno podprli naš kolokvij in omogočili njegovo izvedbo. Ljubljana, maj 2019 Direktor dr.Jakob Šušteršič, univ.dipl.ing.grad. Sponzorji CGP, d.d., Novo mesto DARS Družba za avtoceste Slovenije, Celje DELTABLOC, varnostne in protihrupne ograje d.o.o., Murska Sobota Elea iC, projektiranje in svetovanje d.o.o., Ljubljana Form + Test Seidner + Co. GmbH, Riedlingen, ZR Nemčija Gorenjska gradbena družba d.d., Kranj Hidroelektrarne na Spodnji Savi, d.o.o., Brežice HSE Invest d.o.o., Maribor Hidrotehnik Vodnogospodarsko podjetje d.d., Ljubljana IBE, d.d., svetovanje, projektiranje in inženiring, Ljubljana IZS Inženirska zbornica Slovenije, Ljubljana IRI d.d., Ljubljana Kostak d.d., Krško Lespatex d.o.o., Ljubljana Map-trade d.o.o., Slovenska Bistrica Rafael, gradbena dejavnost d.o.o., Sevnica RGP Rudarski gradbeni programi d.o.o., Velenje Salonit Anhovo d.d., Anhovo Saning, sanacije in gradnja objektov d.o.o., Kranj SGD Strdin d.o.o., Lovrenc na Pohorju Stanovanjski sklad Republike Slovenije, javni sklad, Ljubljana Šuštar Trans d.o.o., Kresnice TEB Termoelektrarna Brestanica, Brestanica TKK Proizvodnja kemičnih izdelkov Srpenica ob Soči d.d., Srpenica Zavod za gradbeništvo Slovenije, Ljubljana ZBS, Združenje za beton Slovenije Vsebina Recent developments on the design of FRC structures Joaquim António Oliveira de Barros 1 FRC Structures in the next EC2: advances and open questions Marco di Prisco 19 Fibre Concrete – Tests, Design and Applications Johan L. Silfwerbrand 23 Basalt fibers and basalt-carbon fiber reinforced polymers for reinforcement of concrete structures Andrzej Garbacz, Marta Kosior-Kazberuk, Kostiantyn Protchenko, Marek Urbański, Maria Włodarczyk, Elżbieta Szmigiera 37 Primena cementnih kompozita na bazi sintetičkih vlakana za prefabrikovane fasadne panele Tijana Vojnović Ćalić, Dragica Jevtić, Dimitrije Zakić 51 Effect of types and length of fibres in reinforcement concrete structures Naser Kabashi, Cene Krasniqi, Enes Krasniqi, Hysni Morina 61 Krčenje mikroarmiranih betonov visoke trdnosti v zgodnjem obdobju Drago Saje, Jože Lopatič 69 Možnost uporabe mikroarmiranega betona za izdelavo zabojnika za NSRAO Jakob Šušteršič, Rok Ercegovič, Franc Sinur, Boštjan Duhovnik, Aljoša Šajna, Teja Török Resnik 81 Ocena trajnosti prednapetih betonskih pragov iz mikroarmiranega betona Andrej Zajc, Jakob Šušteršič in David Polanec 91 Recent developments on the design of FRC structures Najnovejši razvoji projektiranja MAB konstrukcij Joaquim António Oliveira de Barros University of Minho, ISISE, Department of Civil Engineering, Portugal Abstract In this work, two models are presented for the design of fibre reinforced concrete (FRC) structural elements. These elements also include conventional flexural reinforcement, and are herein designated by the acronym R/FRC. The first model is dedicated to the evaluation of the flexural capacity of R/FRC elements, by considering the constitutive laws of the intervenient materials, where the post-cracking tensile capacity of the FRC is simulated by a tensile-crack width multi-branch diagram. The model accounts for the sliding between conventional flexural reinforcement and surrounding FRC. It estimates a moment-rotation relationship for the cross section, as well as the moment-crack width. The good predictive performance of this model is demonstrated by simulating experimental tests with R/FRC beams. The second model is dedicated to the evaluation of the shear capacity of R/FRC beams, and it considers the fibre distribution profile, the fibre pull-out resistance and the modified compression field theory by using a comprehensive integrated strategy. To assess the performance of the developed model, a database consisting of 122 steel fibre reinforced and prestressed concrete beams failing in shear was assembled. The model predictions are shown to correlate well with the test data, and better the ones obtained with the two approaches of fib Model Code 2010. Povzetek V tem prispevku sta predstavljena dva modela za projektiranje konstrukcijskih elementov iz mikroarmiranega betona (MAB). Ti elementi vključujejo tudi običajno upogibno armaturo in so tukaj označeni z akronimom A/MAB. Prvi model je namenjen oceni upogibne nosilnosti A/MAB elementov z upoštevanjem zakonov sestavljanja vnesenih materialov, pri katerih je natezna nosilnost MAB po razpokanju simulirana z večdelnim diagramom nateg - širina razpoke. Model upošteva drsenje med konvencionalno upogibno armaturo in obdajajočim MAB. Ocenjuje se razmerje moment-rotacija za prečni prerez, kakor tudi moment-širina razpoke. Dobra napovedna učinkovitost tega modela je prikazana s simulacijo eksperimentalnih preskusov A/MAB nosilcev. Drugi model je namenjen vrednotenju strižne nosilnosti A/MAB nosilcev, pri čemer upošteva profil porazdelitve vlaken, odpornost vlakna na izvlek in modificirano teorijo tlačnega polja z uporabo celovite integrirane strategije. Za oceno uspešnosti razvitega modela je bila sestavljena baza podatkov iz 122 prednapetih MAB nosilcev, ki so se strižno porušili. Predvidevanja modela se dobro ujemajo s testnimi podatki in boljše od tistih, ki so bili pridobljeni z dvema pristopoma fib Model Code 2010. Keywords: Fibre reinforced concrete, flexural capacity, crack width, shear capacity Ključne besede: mikroarmirani beton, upogibna nosilnost, širina razpoke, strižna nosilnost applications. As an alternative reinforcement to 1. INTRODUCTION conventional ones, discrete fibres have been used, mainly, for flooring [1,2] and tunnelling [3-5]. Fibre reinforcement has been investigated and used as However, even in these applications, there are zones of an alternative and a complement to traditional steel high tensile strain gradients that require the use of both reinforcements in several structural and non-structural conventional and fibre reinforcement, which will be 26. slovenski kolokvij o betonih – Projektiranje mikroarmiranih betonskih konstrukcij in njihove aplikacije, Ljubljana, 16.5.2019 2 J. Barros hereafter designated by R/FRC. Several models have resistance, and interaction between these resisting been proposed to estimate the flexural capacity of mechanisms. The model that is proposed in the present R/FRC elements [6-11]. However, few of them are work integrates the relevant shear resisting mechanisms capable of estimating the crack width by considering in an integrated framework, thereby has higher potential simultaneously the possibility of occurring debond of providing better and more reliable predictions than between conventional reinforcement and surrounding the available ones. FRC [6]. This aspect is fundamental in the objective of estimating with more rigour the crack width, flexural 2 – APPROACH FOR THE DESIGN OF FRC stiffness and capacity, and ductility at failure, which are MEMBERS IN BENDING essential features when designing for attending the requisites at serviceability and ultimate limit state (SLS, 2.1 – Formulation ULS) conditions. The model that are presented in this In the section a model is briefly described for the work has these potentialities and is simple of evaluation of the flexural capacity and crack width of implementing in a excel data sheet of similar tool, R/FRC elements submitted to bending moment. The therefore very convenient for serving as a design possibility of occurring sliding between conventional method. reinforcement and surrounding FRC is accounted for. This model assumes that failure of the elements only Fibres are also being explored for the replacement of occur by bending. It will be used to determine not only steel stirrups in reinforced concrete (RC) beams [12- the flexural capacity at SLS and ULS conditions, but 17], due to the relatively high costs for the preparation also the bending moment vs crack width relationship, and installation of this type of reinforcement, and its and therefore verify its potential for being a design tool susceptibility to be corroded, since in general, it is the for crack width estimation. This capability will be reinforcement closest to the external surface of RC assessed by simulating some available experimental elements. However, estimating the contribution of fibre results, and compared to the predictive performance reinforcement for the shear capacity of a R/FRC beam assured by fib Model Code 2010 (MC2010) [18] and includes several challenges due to the complex RILEM TC 162-TDF [19]. The detailed description of phenomena it involves, such it the case of the influence this model can be found in [20]. of fibre orientation, the mobilized fibre pull-out Fig 2.1: - Idealized representation of flexural deformation of R/FRC beams and crack spacing. a) b) Fig. 2.2 Constitutive law for the FRC in compression: a) pre-peak stress-strain response, b) post-peak stress deformation response. Recent developments on the design of FRC structures 3 Fig. 2.1 represents a segment of a R/FRC subjected to where E is the elasticity modulus of steel and f the s sy pure bending, where is it assumed that cracks are yield stress. formed at a distance L . cs For modelling the bond behaviour between Fig. 2.2 shows the constitutive law adopted for the conventional reinforcement and surrounding FRC, a concrete in compression. The compressive response is linear bond stress-slip relationship,  ( x)  k s( x) , bs decomposed in two phases: a pre-peak phase where k is the bond stress-slip stiffness. bs characterized by a stress-strain law (   ) , as cc cc represented in Fig. 2.2a; and a post peak phase The overall deformational response of the beam can be simulated by a stress-deformation relationship obtained by using the moment-rotation response of each (  u ) , as shown in Fig. 2.2b. prism, M  , as depicted in Fig. 2.4. A symmetric cc cross section that can have a width varying along its In tension, the FRC is assumed described by the linear depth (Fig. 2.4b), and a height h, is discretized in n stress-strain diagram,     E  0     layers in order to take into account the appropriate ct ct c ct ct cr  constitutive law for each concrete layer during the , Fig. 2.3a, while after crack initiation, the tensile loading procedure. The width, the thickness and the behaviour is simulated by a stress-crack width diagram depth of the ith layer (with respect to the beam’s top (   w ) that can be formed by several linear branches surface) is designated, respectively, by b , t , and d . (Fig. 2.3b). i i i For the concrete layer at the level of the reinforcement For simulating both the tension and compression ( d  d ) , the total width of this layer ( b ) is i s i behaviour of steel reinforcement is assumed a bilinear decomposed in the part corresponding to the diagram formed by a linear elastic stress-strain branch reinforcement b ( A / t ) and to the concrete bc up to yield initiation (  ), followed by a perfectly s s i sy ( b  b ) . plastic regime up to the ultimate strain (  ), above i s su which rupture is assumed, i.e. The equations of the constitutive laws of the   E  (   );  f      ;  0    intervenient materials are provided comprehensively in st s st st sy st sy sy st su st  st su  , [20], being introduced in Table 2.1 with the flowchart shown in Fig. 2.5 for the understanding how the M  a) b) Fig. 2.3 Tensile behaviour of FRC: a) linear stress-strain relationship before cracking, b) Post-cracking stress-crack width response. a) b) Fig. 2.4 - a) Cracked R/FRC segment of length cs L submitted to pure bending, b) layered approach to discretize the cross section. 4 J. Barros Table 2.1: Equations of the model (the subscript i represent a generic ith layer of the cross section, while the superscript k represents a generic loading step) Main equation Eq. nº Dependent Eq. and physical meaning of the variables in Fig.2.5 2 (4)   L  L L ps ps cs    k    ; A  2.5 cb , L is the s bs   c, ef ps s A E E A  s s c c, ef  perimeter of the steel reinforcement, c =concrete cover; b =width of the cross section k D   d  d (16) k D =axial displacement; d = distance of the neutral axis i k i NA i NA 2 D effective strain ef i   (17) i Lcs    ef   ef b t if     (18a) compressive force cc i i i i cc, p c F   (18b) i    u  ef b t if    cc i i i i cc, p ef       2 u / L  0 (19a)   =compressive strain of the layer when subjected to the i cc, i  i cs  cc, i   (19b) u       axial displacement u cc  i  cc   0 cc, i  i  c    b t if   (20a) F = tensile force; =strain at concrete crack initiation i cr c  ef  ef ct i i i i cr F   (20b) i    w  ef b t if   ct i i i i cr    w   (21) Crack width w  2 ct i D  L  i i cs E  c  s F  b t   ef  (22) Force in the reinforcement when in perfect bond conditions i s i st i  A E w E w (23) Force in the reinforcement when sliding occurs. s ( / 2)  0.76 ( ) F  s s s s c ct s i 0.76 Ec n Bending moment of the cross section c s M   F d F  d k i i i s i 1  is obtained together with the other relevant results (see concrete between cracks is considered negligible for the also Figs. 2.1 to 2.4 for the physical meaning of the evaluation of the average crack width). variables). The model requires the following data: h, n, The beams are designated by B1, B2 and B3, and their t , b , d , A ,   ,  ( u) ,   ,  w ct   ct  ct  cc  cc  i i i s cc respective steel fibre reinforced self-compacting ,   and k . concrete (SFRSCC) was reinforced with 45, 60 and 90 st  st  bs kg/m3 of hooked end steel fibres, respectively, planned to have a compressive strength at 28 days of, 2.2 – ASSESSMENT OF THE PREDICTIVE respectively, 15, 25, and 45 MPa, therefore the PERFORMANCE OF THE MODEL designation of C15f45, C25f60, and C45f90 was attributed to these SFRSCC. The predictive performance of the proposed model is evaluated by simulating the experimental program Tables 2.2 indicates the average compressive strength ( formed by three series of three R/FRC beams, each f ) obtained experimentally at 28 days according to beam with a cross section of a width of 150 mm and a cm EN 206-1 [21] recommendations, while the average height of 110 mm reinforced flexurally with a steel bar of 8 mm diameter. The beams were tested in four point tensile strength ( f ), and the average Young’s ctm bending configuration, as represented in Fig. 2.6. To modulus ( E ) where determined according the cm obtain the average value of crack width formed along equations proposed by MC2010 [18], using f . To cm the central pure bending zone, the elongation of the pure characterize the toughness class of the developed bending zone of the beam, measured by LVDT1 in Fig. SFRSCCs, three-point notched beam bending tests 2.6, was divided by the number of cracks formed at the (TPBT) were performed on representative notched stabilized cracking process (the elastic deformation of beams of 600×150×150 mm, following the recommendations of MC2010 [18]. The obtained Recent developments on the design of FRC structures 5 characteristic and average values of flexural residual (  and  ) and ultimate stress and strain (  and  sy sy su su strengths corresponding to the crack mouth opening ) were determined: E =204.8GPa,  =  =575MPa, displacement (CMOD) of 0.5 and 2.5 mm, designated s sy su by f and f , respectively, and the corresponding  =2.8‰,  =32‰. R 1, k R 3, k sy su toughness class of the SFRSCCs are also included in In Fig. 2.8 the average moment-crack opening Table 2.2. relationship predicted by the proposed model is The post-cracking response of the used SFRSCCs was compared to the one obtained experimentally, characterized by inverse analysis applied to the force- according which it can be concluded that the proposed deflection responses registered in the performed TPBT. model has predicted with high accuracy the The adopted inverse approach is detailed elsewhere experimental results. In Fig. 2.8 is also included the [22]. The post-cracking response of the SFRSCCs is predictions according to the formulations recommended depicted in Fig. 2.7, according which the intervening by MC2010 [18] and RILEM TC 162-TDF [19], where parameters defining the stress-crack width constitutive it is verified that these approaches lead to moment-crack law of Fig. 2.3 are summarized in Table 2.3. width responses noticeably lower (predicted higher crack width) than the ones measured in the tested The tensile stress-strain of the steel bar was obtained beams. through direct tensile tests conducted according to the recommendations of ASTM A370 [23], according to which the mechanical properties of steel bar including, modulus of elasticity ( E ), stress and strain at yielding s Fig. 2.5 - Flowchart of the algorithm of the model. 6 J. Barros Table 2.2: Mechanical properties of the SFRSCCs used in the experimental program Designation FRC f f E f f f f Toughness cm ctm cm 1 R , k 1 R , m R 3, k R 3, m class indication [MPa] [MPa] [GPa] [MPa] [MPa] B1 C15f45 13.12 1.31 23.31 2.97/4.02 2.05/3.20 2 c 23.57 28.62 B2 C25f60 1.74 4.14/7.36 3.54/6.44 4 e 44.42 35.23 B3 C45f90 2.53 8.73/11.59 7.40/9.70 8 d represents the contribution of concrete ( V ) and the 3 – APPROACHES FOR PREDICTING THE Rd , c SHEAR CAPACITY OF R/FRC BEAMS one provided by fibre reinforcement ( R V d, f ): 3.1 - Introduction k p v k  with f  8 MPa (3.3) In this chapter is concisely described an approach R V d, c fck w zb  ck recently developed for predicting the shear capacity of c R/FRC beams. This approach, which is described in F   fuk  uv w  u w  detail in [24], was named as Integrated Shear Model  V  (3.4) (ISM), and is based on the following strategy: (i) Rd , f  F evaluation of fibre distribution profile (FOP) according to the approach proposed in [25]; (ii) determination of while Rd V corresponds to the contribution of steel , s the resisting stress assured by fibres bridging the critical stirrups: diagonal crack, CDC, ffuk ( w), by considering the fibre pull-out resistance according to the recommendations in sw A [26, 27]; and (iii) evaluation of crack width at mid depth      (3.5) R V d, s zf ywd cot cot sin of the CDC, at shear failure conditions, w s u, by using the w modified compression field theory (MCFT) [28]. being sw A , sw , f ywd and  the, respectively, cross 3.2 – Formulation sectional area, spacing, yield stress and orientation of the stirrups towards the axis of the beam, z  0.9 d the 3.2.1 – Main frame effective shear depth (d is replaced by deq, Eq. (3.11), The shear resistance of R/FRC beams is obtained from: when using passive and prestressed reinforcement), and  is the inclination of the CDC in relation to the axis of   R V d R V d, F R V d, s (3.1) the beam. where: In Eq. (3.2) kf is a parameter to take into account the extra contribution for the shear resistance the   propagation of the shear failure crack through the web- Rd V , F k f  Rd V , c Rd V , f  (3.2) flange interface in case of a I or a T cross-section RC beam (Fig. 3.1): Fig. 2.6- Four point bending test setup and position of LVDT to measure the horizontal elongation in the pure bending region at the level of the reinforcement (dimensions in mm). Recent developments on the design of FRC structures 7 Table 2.3: Mechanical properties of intervening materials of the simulated beams C15f45 C25f60 C45f90 f [MPa] 13.12 23.57 44.42 cm f [MPa] 1.31 1.74 2.39 ctm  [-] 1.22 1.15 1.21 1  [-] 0.95 1.32 1.55 2  [-] 0.88 1.15 0.67 3  [-] 0.42 0.34 0.38 4  [-] 0.19 0.29 0.29 5 w [mm] 0.01 0.01 0.065 1 w [mm] 0.2 0.03 0.2 2 w [mm] 0.7 1.0 3.5 3 w [mm] 3.0 4.6 5.1 4 w [mm] 5.0 6.5 6.5 5 w [mm] 9.5 9.0 9.0 u      c b A 1 c  cb w b  2 A c h , eq c h n , eq c 2 k  1    1.5 b  f (3.6) c, eq s     (3.9) w b d  eq  A 1 c c A 2  h A  h A c b , eq w b b 1 c 1 c c 2 c 2  n   3  n  3 w (3.7) c h , eq A  (3.10) A c h , eq c h , eq 1 c c 2   2, T-section dl l A d p Ap s   (3.8) d  eq 6, I-section  (3.11) l A Ap where c b , eq and c h , eq are the equivalent of the width being l A and l d , and Ap and d p the cross sectional and height of the flange, and internal arm of the area and internal arm of passive (subscript “l”) and reinforcement (Fig. 3.1): prestressed (subscript “p”) reinforcements, and bw the width of the web’s cross section. 5 C15f45 4.5 C25f60 4 C45f90 [MPa] t 3.5 σ, s 3 rests 2.5 e lis 2 enT 1.5 1 0.5 0 0 1 2 3 4 5 6 7 8 9 10 Crack width, w [mm] Fig. 2.7- Tensile stress-crack width relationship of the SFRSCCs). 8 J. Barros In Eq. (3.3) k     p is a parameter that simulates the where N A 0.2 cp sd c fck c is the average favourable effect of prestress in terms of extra shear stress acting on the concrete cross section, Ac, for an capacity, adapted from [14]: axial force, Nsd, due to loading or prestressing actions ( Nsd > 0 for compression).  cp k  1 2.0 In Eq. (3.3) k p (3.12) v is a parameter aiming to simulate the fctk influence of cross section dimension and the favourable effect of the aggregate interlock for the shear resistance:  0.4 1300 ... for   0.08  w fck flyk 1  1500 1000  x zkdg  k    0.0 v  0.4 ... for   0.08  w fck flyk 1  1500   x (3.13) where  is the longitudinal strain determined at the x mid-depth of the section (Fig. 3.2):  1  M V cot  1   Ed Ed e   N  for RC beams   Ed   2 E A   z 2  2 l l z    M V cot  1   0    0.003  Ed Ed e x    N   Ed    z 2  2 z   for PC beams   z z  p  2 l (a)   l E l A E p Ap   z z    5 (3.14) Experimental Model Prediction In this equation, MEd, VEd and NEd are the design values 4 RILEM TC 162-TDF [10] of the bending moment, shear and axial forces acting on ] fib Model Code 2010 [9] the cross section, respectively. The bending moment .mN and shear force are taken as positive; the axial force is 3 [k positive for tension and negative for compression. The M , t eccentricity of the beam axis with respect to section en 2 m mid-depth ( e  ), shown in Fig. 3.2, is a positive value Mo when positioned above the centre of gravity of the cross 1 section. For R/SFRC hybrid flexurally reinforced beams, with passive and prestressed reinforcements, the effective shear depth, z, is evaluated from: 0 0.0 0.1 0.2 0.3 0.4 0.5 2 2 Crack opening, w [mm]  l z l A z p Ap z  (3.15) (b)  l z l A z p Ap 5 where z  0.9  l l d and z 0.9 p d p (Fig. 3.2). 4 ] Experimental .m In Eq. (3.13) Model Prediction kdg parameter aims to simulate the N 3 [k RILEM TC 162-TDF [10] aggregate interlock effect: M , t fib Model Code 2010 [9]  32 en 2  0.75 ... for normal-weight concrete with f  70MPa  ck m 16  d k  g dg  Mo  2.0 ...for f  70MPa and for light-weight concrete  ck 1 (3.16) where d 0 g is maximum dimension of aggregates (in mm). 0.0 0.1 0.2 0.3 0.4 0.5 In Eq. (3.13)   A  is the w sw  b s sin w w  Crack opening, w [mm] percentage of steel stirrups, and flyk is the characteristic (c) value of the yield strength of the main longitudinal bars: Fig. 2.8- Moment-crack width response of (a) B1, (b)     l E lyk l A  Ep pyk fpo  A B2, (c) B3 R/SFRSCC beams (in the legends [9] and p f  (3.17) lyk [10] correspond to references [18] and [19],  l A Ap respectively. Recent developments on the design of FRC structures 9 where for the case of beams reinforced with passive and In Eq. (3.4)  F is the partial safety factor for the parcel prestressed longitudinal reinforcements,  lyk and corresponding to the contribution of the fibre  reinforcement for the shear resistance of R/FRC beam, pyk are their respective characteristic value of the which according to the MC2010 should be considered yield strain, while f po is the applied prestress. The equal to 1.5 [18]. evaluation of the inclination of the CDC, , an updated The design shear resistance cannot be greater than the version of the MCFT is adopted, by considering the crushing capacity of FRC in the web: recommendations of [14] for taking into account the beneficial effects of fibre reinforcement and the f cot  cot  ck      compressive axial load in the prestressed R/SFRC (3.19) R V d,max kc w b z 2    beams: c 1 cot  where:     for V  0 29 7000 45 f  x cp   Min( , arctg(1 4 ) for V  0 20 10000  75 f f ck   x k k c k  fc ; 0.55   (3.20)    ( f fc  fck 1 3 30 1.0 ck in MPa) (3.21) (3.18) In Eq. (3.4) F   fuk  u w v  u w  is evaluated considering the fibre orientation profile (FOP), the fibre pull-out constitutive law (FPCL) representative of each domain adopted for the FOP, and the corresponding number of fibres crossing the CDC. The    u w v  u w  means that F is evaluated for the variable fuk uv w (vertical movement of the two faces composing the CDC) that depends of u w (crack opening orthogonal to the CDC plane at shear failure conditions). bc hc Ac 1 1 Contribution to the shear capacity due to the flange in h A T/I cross section beam F c c 2 2 bw Fig. 3.1- Representation of the variables for the simulation of the contribution of the flange of T or I cross section shape beam for its shear capacity. Fig. 3.2- Physical meaning of the variables of Eqs. (3.14) and (3.15) [18]. 10 J. Barros Ffuk [ w ( ) ] uv wu / F z/2  u  z/2 z d w z/sin u  = w u z/2 CDC uv z/2   u  u V a) Rd,f Nf fibres of several b) orientations P P w fuk,11.25º ( w ) uv fuk,33.75º ( ) uv   i i z/2 z/2   i i + + z/2 z/2 22.5º 45º 22.5º 22.5º 22.5º 45º   u u   11.25º  33.75º i i N =C(11.25º) N N =C(33.75º) N f, f  f, f  i i Fibres in the interval Fibres in the interval [22.5º-45º[ c) [0º-22.5º[ d) P P w fuk,56.25º ( w ) fuk,78.75º ( ) uv uv   i i z/2 z/2   i + i z/2 z/2 90° 67.5º 67.5º 45º  45º  67.5º u 90° 67.5º u   56.25º  78.75º i i N =C(56.25º) N N =C(78.75º) N f, f  f, f  i i Fibres in the interval Fibres in the interval e) [45º-67.5º[ f) [67.5º-90º] Fig. 3.3 –Schematic representation of the proposed approach for the contribution of fibres bridging the CDC: a) relevant variables and concept of Ffuk[ wuv( wu)]; b) to f) example where the interval of fibre orientation domain was decomposed in four equal intervals of 25 of amplitude - contribution of fibre reinforcement with orientation in the: b) full interval ([0-90]), c) [0-22.5[, d) [22.5-45[, e) [45-67.5[, and f) [67.5-90]. Recent developments on the design of FRC structures 11 3.2.2 –Fibre orientation profile (FOP) A sec N  V   (3.26) The contribution of fibre reinforcement crossing the f f Af CDC can be determined by: n   where Af, Vf and   are the cross sectional area of a F       fuk  u w v  u w  fu P k,  u w v  u w  i fibre, the fibre volume percentage, and the fibre i 1  orientation factor, respectively. (3.22) In Eq. (3.26) Asec is the area of CDC (Fig. 3.3a): where n is the number of intervals in the fibre orientation range [0-90] adopted for the evaluation of z  se A c w b (3.27) sin the fibre orientation profile, and f P uk,  u w   is the i force supported by the percentage of fibres with an while C  i  is the ratio of number of fibres crossing inclination  , obtained for a crack opening i the CDC that lie in the range     2 to the total representative of the shear failure condition, w i i u (Fig. 3.3), where  is the angle between the direction of the number of fibres crossing the crack. A detailed i description of this approach is available in [25], fibres representative of the ith fibre orientation interval therefore in the present work only the relevant concepts and the orthogonal to the crack plane (Fig. 3.3b-f). and equations are presented, namely: Fig. 3.3 illustrates conceptually the proposed approach. The figure shows the domain of fibre orientation C     i  f  i  RE F   (3.28) decomposed in four equal intervals of 22.5 ( n   = 4;    = 22.5). The where f  i  is the frequency of fibres within f P uk,  u w   is evaluated in the i middle of each interval by considering the number of     2 i i , and RE F    accounts for the error that fibres with orientation in this interval, therefore Eq. (3.22) becomes: results from adopting discrete ranges of   i, compared with a continuous distribution function: F  fuk  uv w  u w  P  uv w  u w  fuk ,11.25    for       P    (3.29) RE F    1.29 0.38 0.75 uv w  u w   fuk ,33.75 1 for   0.75   (3.23)  P  uv w  u w  fuk ,56.25 which depends of the fibre orientation factor,   . In the  P  present model,   , is evaluated according to an uv w  u w  fuk ,78.75 enhanced strategy of the approach proposed in 29] is adopted in order to take into account the fibre where  f P uk,  u w v  u w    ( i = 11.25, 33.75, 56.25 i orientation during the cracking process up to shear and 78.75) are the forces supported by the percentage failure stage, as well as the wall effect due to the of fibres within inclination intervals [0-22.5[, [22.5- element boundaries on fibre orientation, as detailed in [24,25]. 45[, [45-67.5[ and [67.5-90], respectively, at wu.  The force  The evaluation of f  i  is as follow: f P uk,  u w v  u w    is determined from: i FPCL      f P uk,  u w v  u w  P    u w v  u w  N   f , f    F  , ,    F     1, , i i m m i m  m i i i (3.24) (3.30) FPCL where P F  , ,  i m m      u w v  u w  is the resisting pull-out where  is the cumulative i force for the crack opening at w distribution of the standardized Gaussian law at u for a fibre at an inclination      i  i i 1   2 , with: i, described in the following section, and N f , is the number of fibres crossing the CDC within i   arccos ( )180  m  (3.31) the range of orientations     2 i i :     90 1 m    (3.32) N  f , C  i  N   (3.25) i f 12 J. Barros 3.2.3 Fibre pullout constitutive law (FPCL)         , for 0 u i i u u, i (3.34) The evaluation of the pull-out force N f , for fibres i orientated at  , for a crack opening displacement max max           i 2 for 2 (3.35) u u u (COD) w, FPCL P  w  , is obtained according to the i According to the UVEM, FPCL P  is given by: u w   unified variable engagement model (UVEM) proposed i in [26, 27], while for the evaluation of crack width at shear failure ( wu) at the mid-depth ( z/2), the MCFT is FPCL P     u w v  u w  used.  u k , i d f bu, i b L    f , o i (3.36) According to [30], a fibre at N  f , , of orientation , i i is activated when the COD (vertical direction) equals where the crack width required for engagement:    uv w e w v, i  1      3 u, i    (3.33)    e w v, d tan i f  0 ... for w L max uv bf , o 3.5  2    u    k  L  w  L u, i   bf , o uv cru, i  where  u, i is the angle between the direction of 2  bf L , o uv w  loading ( V) and fibre orientation, as shown in Fig. 3.4,  ... for   e w v, i uv w bf L , o l  while max  is its maximum value, both cases at shear  f u failure conditions (represented by the subscript u). In (3.37) this figure  represents the fibre orientation of the ith i with (Fig. 3.4): interval (towards the orthogonal to the CDC plane, taken as positive in the clockwise direction),  is the orientation of loading towards the normal to the CDC w u w  (3.38) plane (due to the almost vertical movement of the crack uv cos  u  opening process of the CDC, Fig. 3.4, it is assumed  =), and w and s are the crack opening and sliding The fibre embedment length L is a critical length displacements, respectively. cru, i beyond which the force in the fibre, due to bond, is such For a pull-out failure mechanism, when a crack opens, at the fibre fractures, rather than slips [30]: on one side the fibre remains embedded in the matrix and on the other it slips. The average bonded length of d  f fu fibre crossing the failure plane ( L  bf,o), on the short c L ru, i  (3.39) embedment side, is l 2 f/4. bu, i From the geometry described in Fig. 3.4: In this equation  bu, i is the average fibre bond strength and includes the relevant fibre reinforcement Lf1 wu  i Represents Lf2 L =l /4 z/2 N Fibres s f,  u i bf,o w wuv u b CDC su z/2 L  bf,u  u = u   u u  u,i Flexural conventional reinforcement V Fig. 3.4 – Kinematics of fibre pull-out according to the UVEM. Recent developments on the design of FRC structures 13 Table 3.1: Values of kb (adapted from [26, 27]). Matrix type Fibre type HE HE-HS S C, FE and S-HS Mortar 0.67 0.75 0.3 0.5 Concrete 0.8 1.0 0.4 0.6 Table 3.2: Interval of values of the database for the model parameters. Value Model parameter Minimum Maximum Beam’s geometry b (mm) 50 1000 w d (mm) 112.79 1440 Concrete properties f (MPa), cylinders 19.6 205.0 cm dg (mm) 5 25 f (MPa) 1.18 40.89 1 R m f (MPa) 0.82 41.20 R 2 m f (MPa) 0.62 35.74 R 3 m f (MPa) 0.49 29.44 R 4 m Steel fibres V (%) f 0.25 2.0 l (mm) f 13 60 d (mm) f 0.16 1.12  (MPa) fu 966 3000 Passive longitudinal reinforcement A (mm2) 0* 3694 l  (%) 0* 4.35 l E (MPa) 200000 l  (‰) 2.0 2.78 lym Prestressed reinforcement A (mm2) p 0** 2520  (%) p 0** 6.23 E (MPa) p 200000  (‰) 7.85 9.59 pym mechanisms (e.g. hooked ends, if provided) and the   snubbing effect [31-33], and   fu is the effective u, i       (3.41) bu, k f f 1 cos( ) i b cm tensile strength of the fibre:  2     where f    cm is the average value of the concrete fu fu (3.40) max 2 compressive strength, f = 4.5 MPa is the maximum u frictional resistance of the fibre due to the snubbing effect, and kb is given in Table 3.1. where  fu is the uniaxial tensile strength of the fibre. From test results on hooked end and straight steel fibres by [26, 27, 31-33] proposed: 14 J. Barros 3.2.4 Coupling the modified compression field 6) Calculate R V d, f from Eq. (3.3). theory with the FOP and FPCL To evaluate the crack opening at the half of the effective 7) Calculate R V d, f from Eq. (3.4), with Ffuk( wu) shear depth (z/2) at shear failure stage, wu, (a value normal to the CDC plane), the MCFT is used. The obtained by Eq. (3.22) in combination with the MCFT is based on the following iterative procedure: FOP and FPCL models described in Sections 3.2.2 and 3.2.3. 1) Assume an initial value for  x (denoted as 8) Calculate kf according to Eq. (3.6).  x, i ). 9) Calculate VRd,F according to Eq. (3.2), and adding the VRd,s from Eq. (3.5) if beam 2) Calculate kv by Eq. (3.13), by considering Eqs. includes steel stirrups. (3.14) to (3.17), 10) Calculate VRd according to Eq. (3.1). Check 3) Evaluation of  according to Eq. (3.18), VRd does not exceed web crushing limit, V 4) Calculate of the crack width at z/2, orthogonal to Rd,max, calculated from Eqs. (3.19) to (3.21). the CDC, wu: 11) Determine the new estimate of the mid-depth    zk  longitudinal strain ( ) for current iteration,    x    u w  x  1000 dg 0.2 1000 0.125 mm 1300    x, i 1  , according to Eq. (3.14), by adopting: (3.42)  E V d R V d , M   Ed R V d  a deq  and and its component in the vertical direction, wuv (direction of crack opening at shear failure condition the applied prestressed force for NEd . of this type of beams, Fig. 3.4), according to Eq. (3.38). 12) If     x, i 1    x, i  lyk tol , the solution is 5) Calculate k converged, else return to step 2 with p from Eq. (3.12). Fig. 3.5 – Test to model comparisons for shear strength: a) ISM; b) MC2010_EEN; c) MC2010_MCFT Recent developments on the design of FRC structures 15    6     response of FRC elements reinforced flexurally with x, i x, i 1  . ( 1 10 tol ) and repeat conventional bars, which is designated by R/FRC until converged. members. The model has predicted with good accuracy the relationship between the bending moment vs crack At the conclusion of the iterative procedure the shear width. This predictive performance was better than the strength on the member VRd is determined, together with ones obtained by applying the recommendations of each of the sub-components VRd,F (consisting of R V d , c RILEM TC 162-TDF and fib Model Code 2010. and R V ) and V d , f Rd,s. The capacity of the member is The second part of the paper was devoted to the determined as the lesser of its shear and flexural presentation of model for predicting the shear capacity strength. of R/SFRC beams. A database comprising 122 SFRC beams was assembled for evaluating the performance of 3.3. MODEL ASSESSMENT AND VALIDATION the ISM. The predictive performance of the ISM was also compared with that of two approaches available in To evaluate performance of the model an already the fib Model Code 2010 (MC2010_EEN that uses the available database [34] was expanded; additional tests concept f for considering the contribution of fibre Ftu included prestressed concrete members and beams reinforcement, and the MC2010_MCFT, based on the reinforced with crimped (C), and flat end (FH) fibres, MCFT). For evaluating and comparing the performance as well as high-strength (HS) fibres. A large database in of each model, the average test to model prediction ratio this regards was also recently published [35], which ( λ=V includes many of the beams considered in this work for test/Vmodel) and its coefficient of variation (CoV) were determined. The average and CoV values for the the assessment of the predictive performance of the proposed model are 1.12 and 16.6%, respectively, while ISM. After having eliminated the tests of R/SFRC for the MC2010_EEN model and MC2010_MCFT beams of the flexural capacity (evaluated according the model the averages and CoVs were 1.32 and 23.4% and recommendation of MC2010) less than the maximum 1.32 and 24.2%, respectively. actuating bending at the registered experimental ultimate shear load, i.e. yield initiation of the flexural reinforcement has already occurred, the database was composed of 122 R/SFRC beams from 21 experimental research programs. Thirty seven beams have I- and T- 5 – ACKNOWLEDGES section shapes, with the remaining beams of rectangular cross section. None of the R/SFRC beams have The author aims to acknowledge the support provided conventional shear reinforcement (stirrups). Twenty by FCT through the research project ICoSyTec - three are prestressed and six have hybrid fibre Innovative construction system for a new generation of reinforcement (passive and prestress). high performance buildings, with reference: POCI-01- 0145-FEDER-027990. Table 3.2 shows the intervals of values (minimum and maximum) of the database for the model parameters, demonstrating to cover a large spectrum of R/SFRC beams possible to find in real applications. In the REFERENCES analysis undertaken nine equal intervals of 10 were 1. Belletti, B.; Meda, C.A.; Plizzari, G., “Design used ( n   = 9). aspects on steel fiber-reinforced concrete pavements”, Journal of Materials in Civil The results of the analysis of the ISM applied to the Engineering, 20(9), 599-607, 2008. database are shown in Fig. 3.5. The performance of the ISM is also compared with that of two approaches set 2. Yang, J.M.; Shin, H.O.; Yoo, D.Y., “Benefits of out in the Model Code 2010, one where the contribution using amorphous metallic fibers in concrete of fibres is obtained through the value of the ultimate pavement for longterm performance”, Archives of residual tensile strength of FRC ( f ), herein Civil and Mechanical Engineering, 17(4), 2017. Ftu designated as MC2010_EEN, and the other based on the 3. Tiberti, G., Minelli, F., Plizzari, G. (2014). MCFT approach, named by MC2010_MCFT. “Reinforcement optimization of fiber reinforced concrete linings for conventional tunnels”, In all the analysis performed unit values were used for Composites Part B: Engineering, Vol. 58, March the safety factors, and average values were adopted for 2014. the material properties. The higher safety and smaller 4. Colombo, M.; Martinelli, P.; di Prisco, M., “On the dispersion of the predictions obtained with the blast resistance of high performance tunnel developed ISM is visible. segments”, Materials and Structures, 49 (1-2), pp. 117-131, 2016. 5. Craig, R., “Malmo’s Construction Starts”, 4 – CONCLUSIONS Tunnelling & Trenchless Construction, 12-14, 2006. The first part of this paper was dedicated to the description of a model to predict the moment-rotation 16 J. Barros 6. Barros, J.A.O.; Taheri, M.; Salehian, H., “A model 19. Vandewalle, et al., RILEM TC 162-TDF: Test and to simulate the moment-rotation and crack width of design methods for steel fibre reinforced concrete, FRC members reinforced with longitudinal bars”, σ-ε design method - Final Recommendation. Engineering Structures, 100, 43-56, October 2015. Materials and Structures, 36,. 560-567, 2003. 7. Mazaheripour, H.; Barros, J.A.O.; Soltanzadeh, 20. Barros, J.A.O.; Taheri, M., Salehian, H., “A model F.; Sena-Cruz, J.M., “Deflection and cracking to predict the crack width of FRC members behavior of SFRSCC beams reinforced with hybrid reinforced with longitudinal bars”, ACI SP-319 prestressed GFRP and steel reinforcements”, Technical Publication, Symposium Volume on the Engineering Structures journal, 125, 546-565, Reduction of Crack Width with Fiber, Editors: October 2016. Corina-Maria Aldea and Mahmut Ekenel, ACI, 8. Barros, J.A.O.; Taheri, M.; Salehian, H., Mendes, ISBN-13: 978-1-945487-68-2, SP-319-2 chapter, P.J.D., “A design model for fibre reinforced 2017. concrete beams pre-stressed with steel and FRP 21. EN 206-1, Concrete - Part 1: Specification, bars”, Composite Structures Journal, 94(8), 2494- performance, production and conformity. p. 69, 2512, 2012. 2000. 9. Taheri, M.; Barros, J.A.O.; Salehian, H.R., “A 22. Salehian, H., “Evaluation of the Performance of design model for strain-softening and strain- Steel Fibre Reinforced Self-Compacting Concrete hardening fiber reinforced elements reinforced in Elevated Slab Systems - from the Material to the longitudinally with steel and FRP bars”, Structure”, PhD thesis, University of Minho. p. Composites - part B Journal, 42 1630-1640, 2011. 308, 2015. 10. Soranakom C., Multi scale modeling of fibre and 23. ASTM A370, Standard Test Methods and fabric reinforced cement based composites, PhD Definitions for Mechanical Testing of Steel thesis, Arizona State University, 2008. Products. 2014. 11. Soranakom C, Mobasher B. Correlation of tensile 24. Barros, J.A.O.; Foster, S., “An integrated and flexural response of strain softening and strain approach for predicting the shear capacity of fibre hardening cement composites. Cement & Concrete reinforced concrete beams”, Engineering Composites 2008; 30: 465-477. Structures Journal, 174, 346-357, 2018. 12. Ortiz Navas, F., J. Navarro-Gregori, G. Leiva 25. Oliveira, F.L., “Design-oriented constitutive Herdocia, P. Serna, and E. Cuenca, An model for steel fiber reinforced concrete”, PhD experimental study on the shear behaviour of dissertation. Department of Project and reinforced concrete beams with macro-synthetic Construction Engineering, Polytechnic University fibres. Construction and Building Materials, of Catalonia, Catalonia, Spain; 2010. 2018.169: p. 888-899. 26. Ng, T.S.; Htut, T.N.S.; Foster, S.J., “Fracture of 13. Soltanzadeh, F.; Behbahani, A.E.; Barros, J.A.O.; steel fibre reinforced concrete – the unified Mazaheripour, H., “Effect of fiber dosage and variable engagement model”, UNICIV Report R- prestress level on shear behavior of hybrid GFRP- 460, The University of New South Wales, UNSW steel reinforced concrete I shape beams without Sydney, Australia; 2012. stirrups”, Composites Part B Journal, 102, 57-77, 27. Ng, T.S.; Foster, S.J.; Htet, M.L.; Htut, T.N.S., October 2016. “Mixed mode fracture behaviour of steel fibre 14. Soetens, T. “Design models for the shear strength reinforced concrete”, Materials and Structures, of prestressed precast steel fibre reinforced 47, 67–76, 2014. concrete girders”, PhD dissertation, Gent 28. Bentz, E.C.; Vecchio, F.J.; Collins, M.P., University, Belguim; 2015. “Simplified modified compression field theory for 15. Foster, S.J., “The application of steel-fibres as calculating shear strength of reinforced concrete concrete reinforcement in Australia: from material elements”, ACI Structural Journal, 103,614–624, to structure. Materials and Structures”, 42(9): 2006. 1209-1220, 2009. 29. Krenchel, H., “Fibre spacing and specific fibre 16. Meda. A.; Minelli. F.; Plizzari, G.P.; Riva, P., surface”, In: Neville A, editor. Fibre reinforced “Shear behaviour of steel fibre reinforced concrete cement and concrete, UK: The Construction Press, beams”, Materials and Structures Journal, 38, 69-79, 1975. 343-353, 2005. 30. Htut, T.N.S., “Fracture processes in steel fibre 17. Casanova, P.; Rossi, P.; Schaller, I., “Can steel reinforced concrete”, PhD dissertation. School of fibres replace transverse reinforcement in Civil and Environmental Engineering, The reinforced concrete beams?”, ACI Material University of New South Wales, UNSW Sydney, Journal, 94, 341-354, 2000. Australia, 2010. 18. fib Model Code 2010. 2011: CEB and FIP - Final 31. Lee, G.G.; Foster, S.J., “Behaviour of steel fibre Draft. reinforced mortar in shear I: Direct shear testing”, UNICIV Report No. R-444. The University of New South Wales, UNSW Sydney, Australia, 2006a. Recent developments on the design of FRC structures 17 32. Lee, G.G.; Foster, S.J., “Behaviour of steel fibre 34. Foster, S.J.; Agarwal, A.; Amin, A. “Design of reinforced mortar in shear II: Gamma ray SFRC beams for shear using inverse analysis for imaging”, UNICIV Report No. R-445. The determination of residual tensile strength”, University of New South Wales, UNSW Sydney, Structural Concrete, 19, 129–140. 2018. Australia, 2006b. 35. Cuenca, E.; Conforti, A.; Minelli, F.; Plizzari, 33. Lee, G.G.; Foster, S.J., “Behaviour of steel fibre G.A.; Gregori, J.N.; Serna, P., “A material- reinforced mortar in shear III: Variable performance-based database for FRC and RC engagement model II”, UNICIV Report No. R-448. elements under shear loading”, Materials and The University of New South Wales, UNSW Sydney, Structures, 51(11), 1130-1137 2018 Australia, 2007. FRC Structures in the next EC2: advances and open questions MAB konstrukcije v naslednjem EC2 (Eurocode 2): napredki in odprta vprašanja Marco di Prisco Politecnico di Milano, Department of Civil and Environmental Engineering, Italy Abstract After several decades of research work and some years of pioneer applications, Fiber Reinforced Concrete (FRC) is nowadays a material ready for the world community, also considering that design rules are already available in several countries and a first draft of the Annex L to Eurocode 2 has been already submitted to the Project Team for a first writing. The Annex L is mainly based on the two chapters introduced in the Model Code and is aimed at considering only Steel Fibre Reinforced Concrete (SFRC). SFRC can be a suitable solution, especially for statically indeterminate structures, where stress redistribution occurs. In addition to the structural bearing capacity, SFRC is particularly useful for better controlling crack opening in service conditions, which has a particular influence on structural durability, especially in aggressive environments. Furthermore, structural robustness is nowadays a major concern among structural engineer: also in this perspective, SFRC could improve structural behavior since it provides to the cementitious material a specific toughness both in compression and in tension, i.e. in all the regions of the structural element. In the present paper, the main advances and the open questions are introduced and briefly discussed, profiting of the applied research and the design experience already carried out. Povzetek Po več desetletjih raziskovalnega dela in nekaj let pionirskih aplikacij je mikroarmirani beton (MAB) danes material, pripravljen za svetovno skupnost, ob upoštevanju, da so pravila projektiranja že na voljo v več državah in prvi osnutek Priloge L k Eurocode 2 je bil že predložen projektni skupini za prvo pisanje. Priloga L večinoma temelji na dveh poglavjih, ki sta bili uvedeni v Model Code. Namenjena je samo mikroarmiranemu betonu z jeklenimi vlakni (MAB- JV). MAB-JV je lahko primerna rešitev, zlasti za statično nedoločene konstrukcije, kjer pride do prerazporeditve napetosti. Poleg nosilnosti konstrukcije je MAB-JV še posebej uporaben za boljše nadzorovanje odpiranja razpok v pogojih uporabe, kar še posebej vpliva na trajnost konstrukcije, zlasti v agresivnih okoljih. Poleg tega je stabilnost konstrukcije danes glavna skrb projektanta: tudi s tega vidika bi lahko MAB-JV izboljšal obnašanje konstrukcije, saj daje cementnemu materialu specifično žilavost tako pri tlaku kot pri nategu, to je v celotnem konstrukcijskem elementu. V pričujočem članku se predstavlja in na kratko razpravlja o glavnih napredkih in odprtih vprašanjih, izkoriščanju že uporabljenih aplikativnih raziskav in projektantskih izkušenj. Keywords: Conceptual design, ductility, SFRC beams, elevated slabs, D-regions Ključne besede: idejna zasnova, duktilnost, nosilci iz MAB-JV, dvignjene plošče, D-razporeditve 2012, Banthia 2016) and around twenty years of pioneer 1. INTRODUCTION applications, Steel Fiber Reinforced Concrete (SFRC) After several decades of research work (ACI, 1996; is becoming in several countries an interesting option to Rossi and Chanvillard, 2000; di Prisco et. al, 2004; conventional R/C material (Bull. 79). Reinhardt and Naaman, 2007; Gettu, 2008; Barros, 26. slovenski kolokvij o betonih – Projektiranje mikroarmiranih betonskih konstrukcij in njihove aplikacije, Ljubljana, 16.5.2019 20 M. di Prisco In fact, after a long time where concrete was specified is able to better take into account fibre pull-out prescribing the cement content, we passed to the contribution. Last but not least, structural robustness is compressive strength classes; nowadays, after many nowadays a major concern among structural engineers; years of fibre content prescriptions, the designer can also in this perspective, FRC could enhance structural simply, long last, assign a performance class added to behaviour since it provides structural resistance, both in the compressive strength, that is a toughness measure in compression and in tension, in the whole volume of the bending. SFRC does not consist only in the addition of structural element. steel fibres to concrete, but it is a composite, whose properties must be specified by engineers and Some recent applications, proposed in Italy to show a controlled at the construction site. successful use of FRC in Civil Engineering, are used to highlight the recent advances and the open questions in The material performance is determined with EN 14651 EC2: the construction of several types of elevated slabs standard test. The peculiar property of FRC is the in a new industrial building, in a private residential residual post-cracking strength, directly correlated to house in Como region and in existing industrial the toughness measure, which makes FRC very buildings in Piacenza pre-Alps; new precast roof promising in elements subjected to diffused stresses, elements made of FRC and HPFRC for industrial where its enhanced residual post-cracking strength can buildings; post-tensioned foundation beams on piles, better resist tensile stresses diffused in the structural 750 m long, for a bridge-crane in Piacenza; a SFRC element. After cracking, depending on the properties of partially-precast retaining wall to secure a bank of the the concrete matrix and of the fibres (type, material, Idroscalo basin in Milan and a retaining wall to secure content), FRC can have a hardening behavior or a a slope in the foothills of Como-Lake region; a HPFRC softening behavior (either in bending or in uniaxial footbridge at south of Oslo; a composite prefabricated tension); being the latter significantly different than tunnel segment to improve fire and blast protection in Reinforced Concrete (RC), FRC can be a suitable tunnel linings. solution for statically indeterminate structures, where stress redistribution occurs. For this reason, MC 2010 According to the Model Code 2010, FRC represents a (2012) introduced special ductility requirements for new opportunity to simplify and make more efficient FRC structures that can be satisfied when the structure the reinforcement of concrete structures. In the all cases has a high degree of redundancy. The Annex L modifies discussed, a cost reduction of at least 15% of steel partially this approach to guarantee also at local level reinforcement is achieved with FRC elements when the ductility of the mechanical behaviour, with few compared to conventional R/C structures: it comes from exceptions; otherwise, some rebars should be a reduction of labour time for placing the reinforcement, introduced along lines where stresses tend to from structure maintenance due to an enhancing of local concentrate. toughness and durability caused by the reduction of the crack opening, an improvement of fire resistance due to Another significant aspect of FRC concerns the fibre the good performance of steel fibres at high orientation. Although a 3D distribution of fibres in the temperatures and a significant increase in robustness for structure is generally the desired solution, there are statically indeterminate structures. particular elements, as thin-walled ones, where fibres tend to orient (depending on their length with respect to general conclusion about this comparison can argue the element thickness) along the main element plane. that, due to the isotropic randomly distributed fibre These elements can take advantage from fibre reinforcement, fibres can act in any direction giving a orientation, since they may be aligned to the main significant contribution both to positive and negative structural stresses. In order to better evaluate the bending reinforcement as well as to punching and shear material properties, special “structural specimens”, that in any point (that significantly enhance robustness). better represent the real structure, may be adopted as This means that fibres are really able to contribute along suggested by Model Code (MC 2010, 2012): this effect any cracked plane in a three dimensional reference and, is taken into account by the same coefficient K in statically indeterminate structures, they appear very introduced in the Model Code, but some suggestions on efficient in terms of resistance and robustness when the minimum value as well as on special cases is compared to bars which provide only a significant suggested. The Model Code introduced also another contribution in one direction. significant coefficient (KRd) that takes into account the observed alignment of the structural response to the average strength values rather than to the characteristic ones: Eurocode modifies partially the formal approach by suggesting different design values according to the specific resistant mechanism evaluated. In addition to the structural bearing capacity, FRC is particularly useful to better control crack opening in serviceability conditions, which has a particular influence on structural durability, especially in aggressive environments (Vasanelli et al. 2013). Annex L introduces a new computation of the crack width that FRC Structures in the next EC2: advances and open questions 21 Partially precast slabs Foundation beams and slabs Retaining walls 22 M. di Prisco REFERENCES Concrete Structures – Proc. EURO-C 2014, Vol. 1, 2014, pp. 503-512, St. Anton am Arlberg; Austria. 1. ACI Committee 544 (1996), Design considerations for steel Fiber Reinforced Concrete, ACI 544.4R- 10. di Prisco, G., Plizzari, G., Vandewalle, L. (2009), 88, American Concrete Institute, ACI Farmington Fibre reinforced concrete: new design Hills. perspectives, Materials & Structures, 42(9), 1261- 1281. 2. Barros J. (ed.), Fibre Reinforced Concrete: challenges and opportunities, Proc. of the 8th Int. 11. Dinh, H.H., Parra-Montesinos, G.J., and Wight, J. Symp. Bagneux, France, RILEM Publications (2010), “Shear Behaviour of Steel Fibre- S.A.R.L., PRO88., 2012. Reinforced Concrete Beams without Stirrup Reinforcement”, ACI Structural Journal, V. 107, 3. Fib Bull. 79, Fibre-reinforced concrete: from No. 5, pp. 597-606. design to structural applications. FRC 2014: ACI- fib International Workshop Proceedings - ACI SP- 12. fib Bulletin 65 (2012), “Model Code 2010 - Final 310, 480 pages, ISBN 978-2-88394-119-9, May draft”, Volume 1, 350 pages, ISBN 978-2-88394- 2016. 105-2. 4. Conforti, A., Minelli, F., and Plizzari G.A. (2013), 13. fib Bulletin 66 (2012), “Model Code 2010 - Final "Wide-shallow beams with and without steel fibres: draft”, Volume 2, 370 pages, ISBN 978-2-88394- a peculiar behaviour in shear and flexure", 106-9. Composites Part B: Engineering, V. 51, pp. 282- 14. Gettu R. (ed.) (2008), Fibre Reinforced Concrete: 290, design and applications, BEFIB 2008, Bagneux, http://dx.doi.org/10.1016/j.compositesb.2013.03.0 France, RILEM Publications S.A.R.L., PRO60. 33. 15. Hedebratt, J., Silfwerbrand, J. (2013), Full-scale 5. Cuenca, E., and Serna, P. (2013), "Shear behavior test of a pile supported steel fibre concrete slab. of prestressed precast beams made of self- 16. Maya, L.F., Fernández Ruiz, M., Muttoni, A., compacting Fiber Reinforced Concrete", Foster, S. (2012), Punching shear strength of steel Construction and Building Materials, V. 45, pp. fibre reinforced concrete slabs, Engineering 145-156, Structures, Vol.40, pp. 83-94. http://dx.doi.org/10.1016/j.conbuildmat.2013.03.0 96. 17. Minelli, F., Conforti, A., Cuenca, E., and Plizzari, G.A. (2014), “Are steel fibres able to mitigate or 6. Cuenca, E., and Serna, P. (2013), "Failure modes eliminate size effect in shear?”, Materials and and shear design of prestressed hollow core slabs Structures, V. 47, No. 3, pp. 459-473, doi: made of Fiber-Reinforced Concrete," Composites 10.1617/s11527-013-0072-y. Part B: Engineering, Vol. 45, No. 1, ISSN 1359- 8368, pp. 952-964. 18. Reinhardt H.W., Naaman A.E. (eds) (2007), High Performance Fibre Reinforced Cement Composites 7. di Prisco M., Felicetti R., Plizzari G. (eds) (2004), (HPFRCC5), Rilem Publication S.A.R.L., PRO53. Fibre Reinforced Concrete, BEFIB 2004, Bagneux, France, RILEM Publications S.A.R.L., PRO39. 19. Vasanelli, E., Micelli, F., Aiello, M.A., Plizzari, G. (2013), Long term behavior of FRC flexural beams 8. di Prisco, M., Colombo, M., Dozio, D. (2013), Fibre‐reinforced concrete in fib Model Code 2010: under sustained load, Engineering structures, Vol. 56, pp. 1858, 1867. principles, models and test validation, Structural Concrete 14 (4), 342-361. 9. di Prisco, M., Martinelli, P. (2014), A numerical approach for the evaluation of the structural redistribution coefficient KRd, Comp. Modelling of Fibre Concrete – Tests, Design and Applications Betoni z vlakni – preskusi, projektiranje in aplikacije Johan L. Silfwerbrand KTH Royal Institute of Technology, Stockholm, Sweden Abstract Fibre concrete was invented during the second half of the 19th century in USA, but it was not before the 1950s that it received any practical use. Today, fibre concrete is used for rock strengthening, industrial floors, overlays, and small-size precast concrete products. The use of fibre concrete in typical load-carrying structures, e.g., beams and elevated slabs, has, however, been limited. The major reasons are limited experience and lack of codes. In recent years, several structural tests on fibre concrete beams and slabs have been carried out in several countries. The outcome has been mainly promising and some countries have also developed guidelines. The next version of Eurocode 2 is likely to contain an appendix on structural fibre concrete. Steel fibres is the traditional alternative but there are several alternatives, e.g., synthetic (mainly polypropylene), carbon, glass, hemp, and basalt. They have different advantages and disadvantages. In recent years, the use of basalt fibres has increased. Compared with steel fibres, basalt fibres have two advantages; (i) they have similar density as concrete implying less segregation risk and (ii) they do not corrode. This paper covers some Swedish experiences with fibre concrete structures by summarizing some tests, design specifications, and applications. Povzetek V ZDA je bil v drugi polovici 19. stoletja izumljen beton z vlakni, toda pred letom 1950 ni bilo praktične uporabe. Danes se beton z vlakni uporablja za utrjevanje kamnin, industrijske tlake, prekrivne površine in gotove betonske izdelke manjših dimenzij. Uporaba betona z vlakni v značilnih nosilnih konstrukcijah, na primer: nosilci in dvignjene plošče, pa je bila omejena. Glavna razloga sta omejene izkušnje in pomanjkanje standardov. V zadnjih letih je bilo v več državah izvedenih več konstrukcijskih preizkusov na nosilcih in ploščah iz betona z vlakni. Rezultat je bil večinoma obetaven in nekatere države so razvile tudi smernice. Naslednja različica Eurocode 2 bo verjetno vsebovala prilogo o betonskih konstrukcijah z vlakni. Jeklena vlakna so tradicionalna alternativa, vendar obstaja več alternativ, na primer: sintetična (predvsem polipropilenska), ogljikova, steklena, konopljina in bazaltna. Imajo različne prednosti in slabosti. V zadnjih letih se je povečala uporaba bazaltnih vlaken. V primerjavi z jeklenimi vlakni imajo bazaltna vlakna dve prednosti; (i) imajo podobno gostoto kot beton, kar pomeni manjše tveganje segregacije in (ii) ne korodirajo. Ta članek obravnava nekatere švedske izkušnje z betonskimi konstrukcijami z vlakni, s povzetkom nekaterih preskusov, specifikacij za projektiranje in aplikacij. Keywords: Fibre concrete, Industrial concrete floors, Standards, Steel fibre concrete, Basalt fibre concrete, Tests Ključne besede: beton z vlakni, industrijski betonski tlaki, standardi, beton z jeklenimi vlakni, beton z bazaltnimi vlakni, preskusi e.g., improved ductility and corrosion resistance and 1 INTRODUCTION substantial reduction of laborious reinforcement work. Despite its extensive and long-term use in specific 1.1 General areas, e.g., underground shotcrete structures and Fibre concrete, or more specifically, steel fibre concrete industrial floors, it has not conquered the general (SFC) has both technical and economic advantages, market of concrete structures. One reason is that the 26. slovenski kolokvij o betonih – Projektiranje mikroarmiranih betonskih konstrukcij in njihove aplikacije, Ljubljana, 16.5.2019 24 J. Silfwerbrand major international and national concrete codes have energy consumption ability of concrete shelters. In not covered SFC structures. This is presently going to Sweden, steel fibre concrete has been used in 50 years change since both national standards and international especially in two applications; shotcrete for rock standards are available. The aim of this paper is to strengthening and industrial floors. Recommendations summarize some Swedish tests on steel and basalt fibre have been developed in both these areas (Holmgren, concrete followed by a brief summary of the Swedish 1992; Swedish Concrete Association, 1997 & 2008). design guide and some application fields. The focus of this paper is on cast fibre concrete. Fibre shotcrete has 1.3 Fibre materials a long tradition in Sweden, both in research and The predominant fibre material is steel but other fibre practice. However, the interested reader is materials, e.g., synthetic (polymers), glass, carbon, recommended to other literature sources, e.g., basalt, and hemp, are also or have been in use to various Holmgren (2010). degree. 1.2 Brief history The second most frequent fibre is the synthetic fibre. It Already in 1874 the American A. Berard obtained a exists in two types; (i) macro fibres and (ii) micro fibres. patent for steel fibre concrete. Steel fibre concrete was Macro synthetic fibres have similar sizes as steel fibres and are also used to improve the concrete’s post further developed after the 2nd World War in order to - make concrete airfield pavements more resistant against cracking behaviour in tension and flexure. Research on bombs than ordinary reinforced concrete pavements. synthetic fibre concrete has shown that a volume Steel fibre concrete has also been used to improve the content equal to twice the steel fibre volume content is Figure 1. Full-scale tests on elevated fibre concrete slab on columns. From Hedebratt (2012). Figure 2. Slab geometry, load point (LP) numbers and reinforcing (left). ARH = 80 kg/m3 fibres + bars, BRH = solely 80 kg/m3 fibres, AFS = 40 kg/m3 fibres + bars. BRS = solely 40 kg/m3 fibres. Elevation of the test slab (right). From Hedebratt & Silfwerbrand (2015). Fibre Concrete – Tests, Design, and Applications 25 needed for equivalent structural performance Silfwerbrand, 2012; Hedebratt & Silfwerbrand, 2015). (Døssland, 2008). The tests were subjected to an elevated slab constructed for private home. The slab was designed as a half scale Micro synthetic fibres (polypropylene fibres) have been model of a pile supported industrial floor slab (Figure shown to have an excellent ability to prevent explosive 1). spalling in moist and dense concrete structures (e.g., tunnels) exposed to fire temperature (Jansson, 2013). The slab is supported by 25 reinforced concrete columns on a 3x3 m rectangular grid and sandwich wall Basalt fibres have recently shown up as a realistic panels on three of the four perimeter edges (Figure 2). alternative, see Section 2.2. The thickness of the slab is 130 mm, resulting in a span/depth ratio of just over 23 to 1. 2 SWEDISH TESTS ON FIBRE CONCRETE One-half of the test slab, from Grid 4 to 6, was STRUCTURES reinforced only with steel fibres. The other half was reinforced with a combination of steel fibres and 2.1 Tests on elevated slabs reinforcing bars. The bars were designed to carry In 2007-2009, unique load tests were carried out near section moments from a uniformly distributed load of the town of Västerås, Sweden, about 100 km from 10 kN/m2 in the ultimate limit state. Top and bottom Stockholm (Hedebratt, 2012; Hedebratt & layers each comprised three 12 mm diameter bars Figure 3. Construction of the roof structure and upper level sandwich walls took place during the long-term period. From Hedebratt & Silfwerbrand (2015). Figure 4. Deflection as a function of time identified by loading test number. Notation includes load number, load point (LP) number, and short-time loading (if any). Tests in slab regions not previously loaded during short-time tests (a); and tets in slab regions that were loaded during the short-time tests (b). From Hedebratt & Silfwerbrand (2015). 26 J. Silfwerbrand spaced at 100 mm. Bars were placed along column lines increased slab capacity by 10 to 40%. Although there as indicated in Figure 2. was large scatter in the physical properties of the delivered SFC, the slab test results indicated that SFC In the test program, selected panels of the slab were can be used with verifiable results in structural subjected to short-term and long-term loadings applications. Detailed test results for the short-term comprising concentrated loads applied at the panel testing program are presented in Hedebratt (2012) and midpoints. Corner panels were not loaded during the Hedebratt & Silfwerbrand (2012). long-term tests. In the second phase, four of the previously loaded slab The slab was constructed using fibre dosages of 40 or panels and an additional four panels were subjected to 80 kg/m3 (Figure 2) with the objective of obtaining a long-term point loads of about 50 or 75 kN. Loading residual strength factor R 10,30 ranging from 60 to more mechanisms (Figure 3) were installed on the slab-on- than 100%. We estimated the strain hardening/softening ground and pulled downward on the elevated slab using properties (here defined as R 10,30 > 100%) of the a 30 mm diameter all-thread rod, a lever arm, and a concrete based on our experience with similar mixtures, concrete block that had been cast on site. These tests information obtained in the research literature, and were started in May 2008 and continued until May extrapolation of the fibre supplier’s unofficial tabulated 2009. values of flexural toughness and R 10,30 (the latter are provided for guidance but are not guaranteed by the After nearly one year of loading at 50 to 75% of the supplier). initial cracking load, the data show that the rate of change in the deflection appears to be approaching zero The test building was constructed between November (Figure 4). This is also indicated by beam tests 2007 and February 2008. The slab-on-ground was according to Tan & Saha (2005), where only 7% completed on November 13. After walls and columns deflection growth occurred in about ten years of were constructed, the elevated slab was cast on sustained loading. February 18, 2008. The slab was water-cured for one week, the forms were stripped at 15 days, and the first 2.2 Tests on basalt fibre concrete specimens short-term load test was conducted on March 18. Thereafter, two to three individual tests were conducted 2.2.1 The basalt fibre per testing day. The short-term load tests ended on May 31, 2008. The basalt fibre is relatively new in concrete applications despite that it has its origin in the 1920s in The short term tests showed that structural capacity and USA. It is used in various fields, e.g., fire-proof textiles crack arresting performance increased with fibre for the automobile and aircraft industries. dosage. Also, the tests showed that the addition of conventional reinforcing bars along the column lines Figure 5 – Two types of basalt fibres. To the left chopped fibres (here denoted type C). To the right, bar- shaped fibres (often called Minibars, here denoted type M). Photo: A M Mohaghegh. Fibre Concrete – Tests, Design, and Applications 27 The basalt fibre is produced of crushed and washed Ålesund and KTH in Stockholm participated in the basalt that is taken from carefully selected rock supervision. quarries. The basalt melts at 1500°C. Extremely thin, continuous basalt fibres – filament – are extruded The project was mainly experimental and it consisted of through very thin nuzzles. From the filament, thicker four test series in order to study flexural moment, shear, basalt fibres are produced. The basalt material is punching shear, and fire. The various parts are encapsulated within a matrix consisting of a thermoset summarized in the following subsections. vinyl ester resin or another similar resin. 2.2.3 Concrete mix design In concrete mixes, basalt fibres with similar geometrical The background to the project was efforts to develop dimensions as straight steel fibres without hooked ends concrete structures that are resistant in the very harsh are usually used (Figure 5, right). The anchorage to the marine environment at the Norwegian west coast. surrounding concrete is provided by a rough, irregular Therefore, a concrete with low permeability and high surface. In these investigations, a basalt fibre with durability constituted the basis. In the latter test series, diameter = 0.65 mm and length = 43 or 55 mm. The the selected concrete mix consisted of 495 kg cement fibre is a small, slender bar, the product name is Minibar and 63 kg silica per cubic meter and a w/b = 0.33. In the (here denoted M type). first test series, slightly less cement and silica were used Also another basalt fibre can be used in concrete. It is resulting in a w/b = 0.40. The fibre content varied chopped from the melt. The fibres of this type (here between 0 and 2 volume percent or between 0 and 42 denoted C type) used in current investigation had the kg/m3. Maximum aggregate size was in all test series length = 13 mm (Figure 5, left). d max = 16 mm. As stated above, the basalt fibre cannot corrode. 2.2.4 Flexural moment capacity Another advantage is that it has almost the same density as the surrounding concrete mix. It means that it is less The ground for assessment when designing fibre prone to segregation. In concrete with a segregation concrete structures is the flexural concrete strength that risk, the heavy steel fibre may sink whereas the light is determined through flexural testing of beam polypropylene fibre may flow to the surface. specimens. Here, the method recommended by EN 14651 was used. Figure 6 shows the result from the tests on eight basalt fibre concrete beam specimens 2.2.2 Norwegian-Swedish research project where the so called residual flexural strength (the The technical universities KTH in Stockholm (Sweden) residual strength after cracking and at a given and NTNU in Ålesund (Norway) have carried out a PhD displacement) has been plotted versus the fibre content. project on basalt fibre concrete. The project was carried We may observe that the values increase approximately out between 2013 and 2018. The PhD student and later linearly with increasing fibre content. This is similar to the graduated doctor was Mr Ali Mohammadi the relationship that lot of researchers have found for Mohaghegh and he carried out all tests in Ålesund but steel fibre concrete beams. was registered as a PhD student at KTH. Both NTNU in Figure 6 – Residual flexural strength as a function of fibre content. 28 J. Silfwerbrand 2.2.5 Shear capacity about very small and thin so-called micro fibres and it According to Eurocode 2, the designer usually needs to has been shown that an amount as small as 1 to 1 kg/m3 insert a certain amount of shear reinforcement (= is sufficient to prevent fire spalling. The reason for this minimum reinforcement) in order to handle the shear success is not fully clear but the fact is that the polypropylene fibres are melting at 165°C and the most force in the concrete beam. The shear reinforcement usually consists of vertical stirrups but the installation frequent hypothesis is that the melting fibres open up of these units is more laborious and time-consuming channels that enable the vapour, that otherwise would than installing the horizontal flexural reinforcement. spall the concrete, to release. Many research papers have shown that a combination As mentioned above, the basalt fibre does not solely of conventional reinforcement for flexural moment and consist of rock basalt but also of a matrix of thermoset steel fibres for shear force results in a very good shear vinyl ester resin. Vinyl ester starts to degenerate at its capacity. glass transfer temperature about 120°C and the The shear test series consisted of seven concrete beam degeneration of the matrix continues at temperatures with the measures L×b×h = 1200×100×200 mm3. All around 350-450°C. The hypothesis was that the basalt beams were reinforced with four basalt fibre bars with fibres should improve the fire spalling resistance, partly diameter = 8.9 mm and mean tensile strength = 1095 due to a process similar to that of the polypropylene MPa. The basalt fibre content varied between 0 and 2 fibres, partly due to their possibility to bridge the cracks volume percent. At the tests, a substantial enhancement that arise during the spalling process. of the load-carrying capacity or shear capacity was The fire tests were carried out in the oven in RISE fire measured; 30% at 1 volume percent and 50% at 2 laboratory in Borås in the west of Sweden. Three volume percent. concrete specimens with the dimensions 500×600×200 The project also contained a test series on small circular mm3 were exposed to the so-called standard test fire curve with a maximum temperature of 900°C. One concrete slabs to study the punching shear capacity, see Mohaghegh et al. (2018b). Here, the results only specimen without basalt fibres was used as a reference, showed a slight improvement for specimens containing the second specimen contained 0.5 volume percent basalt fibres. The somewhat disappointing result can be fibres of type C and the third one contained 0.5 volume explained by the selection of the small specimens that percent fibres of type M. All specimens spalled and no in turn was a result of a very limited budget. The significant difference could be observed (Figure 7). specimen geometry did not allow the most beneficial The average spalling depth was 73, 73, and 62 mm, crack orientation to develop. respectively. One reason to the observed spalling could be the very low w/b (= 0.34). On one hand, it may be stated that the basalt fibres did not make any 2.2.6 Fire spalling improvement in this case. On the other hand, it could be There is a risk of explosive fire spalling in dense concluded that the basalt fibre did not cause any concrete in a moist environment. There are several impairment. More research would be beneficial on examples from tunnel fires that have resulted in spalling concrete mixes with slightly higher w/b, i.e., between of the surface layer of the concrete lining. One example 0.4 and 0.45. These values would be more is the Euro tunnel between Great Britain and France. representative for modern concrete tunnels. Research and experience show that there is a very good precaution: polypropylene fibres. Here, we are talking Figure 7 – Test specimens after fire testing. Left = reference concrete. Centre = concrete with 0.5 % fibres of type C. Right = concrete with 0.5 % fibres of type M. Photo: A M Mohaghegh. Fibre Concrete – Tests, Design, and Applications 29 3 DESIGN 2013 and in spring 2014, the printed version was completed, SS 812310:2014 (2014). One reason for the limited use of fibre concrete (FC) in load-carrying structures is that the major international The Standard applies to the design of buildings and and national concrete codes do not cover FC structures. other civil engineering works with steel or synthetic In Sweden, the Swedish Concrete Association (SCA) fibres. The Standard does not cover glass, carbon, basalt developed its first recommendations for SFC in 1995 or any other type of fibres. It is intended to be used in (SCA, 1997). In 2008, SCA published conjunction with Eurocode 2. This section describes the recommendations on industrial concrete floors (SCA, most important items in the standard and discusses how 2008). They cover both plain, conventionally reinforced it can be used in order to simplify the design and and SFR concrete floors and both slabs-on-grade, pile- production of fibre concrete structures with maintained supported slabs, and overlays. Pile-supported slabs are safety level. generally regarded as a load-carrying structure and since the Swedish code for concrete structures does not Fibre concrete is characterized through its flexural cover SFC solutions without conventional strength. The Standard bases the design on flexural reinforcement (“SFC only”) have not been possible to strength values determined through tests on the design. The new SCA recommendations have tried to European notched fibre concrete beam that has a height fill this gap and have consequently developed to span ratio = 150/550 and is tested in three point guidelines for pile-supported slabs of SFC only. The bending according to SS-EN 14651 (2007) at 28 days guidelines also present straight-forward methods to (Figure 8, left). Flexural strength classes R1, R2, R3, and design SFC floors and overlays for crack control. R4 are defined from the characteristic values (lower 5% Together, the two SCA reports will facilitate the proper fractile) of the residual flexural tensile strength. For all design and probably increase the future use of SFC four classes, six levels of the strength are given (1.0, structures. 2.0, …6.0 MPa). That means a total of 24 classes. In order to develop guidelines for designing load- The design of fibre concrete members is based on pure carrying fibre concrete structures, the Swedish tensile strength. In order to obtain design values, the Standards Institute (SIS) established a Committee in characteristic residual flexural tensile strength must be 2007. The original object was to develop an addition to (1) transferred to a characteristic residual tensile the Swedish structural concrete handbook BBK 04 strength and (2) transferred to a design residual tensile (Swedish National Board of Housing, Building & strength (Figure 8, right). Planning, 2004). In 2009, Eurocode 2 (SS-EN 1992-1- The second transformation contains two new factors, 1, 2005) was introduced in Sweden. The object of the the fibre factor taking the fibre orientation into account Committee was then changed to develop an addition to (more unilateral distribution gives higher values) and a Eurocode 2. A draft version was completed in summer factor considering the degree of static determination. F 52 1= 05 h sp 1 Notch = h 25 250 250 b = 150 l = 550 F L F R,1 F R,2 F R,3 F R,4 0,5 1,5 2,5 3,5 CMOD (mm) Figure 8. The design values for tensile strength is based on flexural tests on according to SS-EN 14651 (left) and transformations in several steps (right). 30 J. Silfwerbrand Statically indeterminate structures provide possible which is a shortcoming in certain cases as, e.g., drainage stress redistribution reducing the failure probability. structures. Otherwise the experiences are good. This beneficial condition is considered by setting a value > 1 for this factor. A theoretical background is The spraying technique also makes it easier to produce given in Silfwerbrand (2017). thin walled structures like shells and domes, where fibre reinforcement also gives large advantages, Figure 10. The overall conclusion is that the new Swedish Standard will remove an obstacle that has restrained the 4.2 Precast concrete elements use of fibre concrete in structural beams and elevated Reinforcing with fibres allows for the use of thinner slabs. However, full use of FC in applications where it sections than when bar reinforcement is used because is suitable and economic will hardly be the case before no concrete cover is needed. The fibre reinforced the introduction of next version of Eurocode 2 that elements are also less sensitive to damages since there probably will contain an appendix devoted to FC are fibres everywhere. A very good example is a vault structures. door with both fibres and bars. The fibres make it more difficult to crack the door into pieces with hydraulic 4 APPLICATIONS tools. Some examples are given in Figure 11 below. 4.1 Shotcrete For shotcrete in tunnels, fibre reinforcement has become nearly the only type of reinforcement that is 4.3 Industrial floors used (Figure 9), at least in Sweden where the rock The industrial floor is one of the major applications of quality to a large majority is very high. The fibre fibre concrete and especially steel fibre concrete. Most reinforced shotcrete used is normally strain softening, industrial concrete floors are regarded as a simple Figure 9. Tunnel lining of steel fibre reinforced shotcrete. Picture by courtesy of BESAB, Gothenburg, Sweden. Figure 10. Examples of thin-walled roof structures in fibre reinforced shotcrete. Fibre Concrete – Tests, Design, and Applications 31 structure (Figure 12). Traditionally, the industrial pile heads. The areas between has been relying solely concrete floor has been produced as a slab-on-grade on the fibre concrete. which is not regarded as a load-carrying structure. However, during the ongoing urbanization industrial Such floors span 4.0 to 6.0 m, comprise slabs that are buildings, distributions centres, and shopping malls, generally 180 to 300 mm thick, and are designed for that all include large concrete floors placed close to or loads ranging from 10 to 30 kN/m2 in the ultimate limit on the ground level, have been placed outside the cities, state (SCA, 2008). often in rural areas and often in areas with rather soft In Sweden, there has been a competition between two subgrade, e.g., silt and clay. If high mechanical loads different design strategies; one Swedish based on are anticipated, the floor is often strengthened by a pile Swedish praxis expressed in Swedish handbooks, grid, e.g., a pile-supported slab. The question is if the recommendations, and standards, and one based on pile-supported slab is a load-carrying structure or not. continental experience. The difference has been Industrial floor slabs constructed in Sweden typically quantified and highlighted in a paper written co-written by representatives of the both strategies (Destrée & comprise concrete with a water-cementitious material ratio w/ cm of 0.55 to 0.58. The concrete strength class Silfwerbrand, 2012). The Swedish traditional design normally ranges from C30/37 to C32/40. The concrete leads to thicker SFC floors with adherent higher safety is preferably of Consistency Class S3 to S4 per SS-EN against cracking and other damages. This finding does 206:2013 (2015). That is, it has a slump of 80 to 210 not state that the safety using the continental strategy is mm, although higher slumps are sometimes used. too low. Beneficial effects, e.g., arch action and membrane effects, are not taken into account in any of Traditionally, pile supported industrial floor slabs have the two methods and may provide the sufficient safety been reinforced with two layers of welded wire margin. However, in all cases, the importance of reinforcing or distributed deformed bars, with the top meticulous operations in structural design, detailing, and bottom layers anchored outside and inside the concrete mix design, concrete delivery, concrete moment inflection points, respectively. The production, casting, curing, loading, operation, and reinforcement has been installed in bands crossing the maintenance cannot be overestimated. Beam elements. Pipes Tunnel elements. Vault door. Figure 11. Examples of fibre reinforced precast concrete elements. 32 J. Silfwerbrand 4.4 Overlays or in the substrate. This condition could be secured Overlays – bonded or unbonded – are often used in through introducing a specific interlayer between the bridge deck repair (Figure 13), as a part of the two layers. pavement system (Figure 14) or as a part of the Bonded overlays are the most common case in bridge industrial floor. The idea with the bonded overlay is to deck repair. A thin bonded overlay may be cast in plain secure composite action between the existing layer concrete (i.e., without reinforcement), but steel fibre (substrate) and the overlay. If the bond is ensured, the concrete is quite often selected since this solution two layers act as a monolith. Unbonded overlays lack diminishes the risk of uncontrolled cracking. (There are, bond between the existing layer and the overlay, but of course, also solutions in conventional reinforced usually the absence of bond is intentional. The designer concrete.) may wish to minimize the stresses in either the overlay Figure 12. Example of an industrial concrete floor in a storage building. Photographer: J. Hedebratt. Figure 13. Gullmarsplan’s traffic interchange was repaired with a bonded SFC overlay in 1995 (Paulsson & Silfwerbrand, 1995). Fibre Concrete – Tests, Design, and Applications 33 Figure 14. Whitetopping. Steel fibre concrete overlay on an old asphalt road (Silfwerbrand, 1995). Both bonded overlays and unbonded overlays are used highest stresses and fibres will eliminate the need of in pavement design and pavement restoration. Concrete stirrups and its adherent laborious installation. pavements are often cast in two lifts, a thick bottom layer of ordinary concrete and a thin top layer of wear During the latest ten years, more research has been resistant concrete with high quality aggregates. Thin devoted to tests on larger SFC elements. In Norway, Døssland (2008) conducted tests on slabs both indoors concrete overlays can also be used to repair old asphalt pavements with extensive rutting. This solution is and outdoors. Field tests on elevated SFC slabs have called whitetopping and may contain a steel fibre been conducted in Luxemburg, Estonia, and Latvia concrete overlay (Figure 14). (Hedebratt, 2012). Personally, Hedebratt also conducted tests on elevated SFC slabs (Section 2.1). The overall conclusion is that SFC slabs have a 4.5 Beams and elevated slabs substantial load-carrying capacity. This has been an As stated above, the lack of standards and legal important prerequisite for the development of standards recommendations has prevented the use of fibre for load-carrying SFC structures. concrete in structural applications such as beams and elevated slabs. Industrial concrete floors, overlays, and 4.6 Marine structures minor precast concrete elements are hardly regarded as load-carrying structures making the facilitating the As stated above, the project on basalt fibre concrete design. However, the benefits of fibre concrete are (Section 2.2) was originally developed for the harsh several and ought to be taken into account also for environment at the Norwegian west coast and especially structural applications. Avoiding the manual work of for floating structures. The aim was to develop a basalt installing conventional reinforcement would improve fibre concrete meeting high demands on durability. the working environment and increase the productivity. Figure 15 shows an example of a floating structure that would be possible to make in basalt fibre concrete. The research in fibre concrete is vast and the allowable space is not sufficient to summarize it here. However, a large part of this research has been devoted to beams, most of them fairly small. We know that fibres substantially contribute to both flexural and shear strength. Tests on large beams and slabs are more scarce but here it may be stated that a combination of conventionally steel reinforcing bars for flexure and steel fibres for shear may be a very interesting solution where bars are localized to areas and section with the 34 J. Silfwerbrand 5 CONCLUDING REMARKS concrete properties that are similar to the ones steel fibres give. The fact that basalt fibres do not corrode Fibre concrete (FC) is a versatile alternative for many leads to an advantage in concrete structures in severely applications, e.g., shotcrete, precast elements, industrial aggressive environments like the one along the floors, and overlays. The lack of standards and Norwegian west coast. The project was carried out with recommendations have prevented the use of FC for a very limited budget leading to test series with a small beams and elevated slabs. Recent research has resulted number of small-size specimens. More tests with larger in new standards for FC for structural applications. In test specimens and preferably including parallel tests Sweden, a new standard was published in 2014. with steel fibre concrete would be desirable. However, As stated above, there are several alternatives to steel BSF is already used in Sweden, e.g., by a couple of fibres. The two most important ones for structural precast concrete producers. applications are synthetic fibres and basalt fibres. The Finally, it ought to be repeated that FC hardly may new Swedish standard is written in a material- replace RC in structural applications. Reinforcing steel independent way regarding fibres, but in order to use it is in many cases more economical since it can be for other materials than SFC, we need more test results localized to areas and sections subjected to the highest and experience. At KTH, a recent doctoral thesis stresses. However, combinations of steel fibres and (Mohaghegh, 2018), summarized in Section 2.2, shows reinforcing bars and meshes may provide an interesting that basalt fibre concrete has similar properties as SFC alternative; e.g., FC with additional reinforcing meshes regarding flexure, shear, and punching shear if the fibre above the pile heads in pile-supported slabs or dosages are the same. The basalt fibre has equal density reinforcing bars for flexure and fibres for shear. as concrete (making it easier to avoid segregation) and does not corrode. Generally, it is good to have many alternatives when we are making our material selection. Having lots of alternatives makes it easier to optimize load-carrying capacity, function, sustainability, and aesthetics. The above cited research project shows that basalt fibre concrete (BFC) constitutes an additional alternative. The test results indicate that the basalt fibres provide the Figure 15 – Floating fish factory in the North Sea. Photo: Ulstein Betong Marine Company. Fibre Concrete – Tests, Design, and Applications 35 REFERENCES of Concrete Structures, Dept. of Civil & Architectural Engineering, School of Architecture 1. ACI Committee 544, “Measurement of Properties & Built Environment, KTH Royal Institute of of Fiber Reinforced Concrete (ACI 544.2R-89 [Reapproved 2009]),” American Concrete Technology, Stockholm, Sweden. Institute, Farmington Hills, MI, 2009, 11 pp. 12. Mohaghegh A M, Silfwerbrand J & Årskog V (2017): ”Flexural Behaviour of Medium-Strength 2. BBK 2004 (2004): ”Handbook of Concrete Structures. Part 1 Design” (“Boverkets handbok and High-Performance Macro Basalt Fibre Concrete Aimed for Marine Applications”. Nordic om betongkonstruktioner. Band 1 Konstruktion”), Concrete Research, Vol. 57, No. 2/2017, p. 103- National Board of Housing, Building and 123. Planning, Karlskrona, Sweden, 271 pp. (In Swedish). 13. Mohaghegh A M, Silfwerbrand J, Årskog V & Jansson McNamee R (2017) ”Fire Spalling of 3. Destrée X & Silfwerbrand J (2012): “Steel Fibre High-Performance Basalt Fibre Concrete”. Reinforced Concrete in Free Suspended Slabs: Case Study of the Swedbank Arena in Stockholm”. Nordic Concrete Research, Vol. 57, No. 2/2017, p. Proceedings, fib Symposium on “Concrete 89-102. Structures for Sustainable Community”, 14. Mohaghegh A M, Silfwerbrand J & Årskog V Stockholm, Sweden, June 11-14, 2012, p. 97-100. (2018a): ”Shear Behaviour of High-Performance Basalt Fiber Concrete – Part I: Laboratory Shear 4. Døssland Å L (2008): “Fibre Reinforcement in Tests on Beams with Macrofibers without Bars”. Load-carrying Concrete Structures. Laboratory Structural Concrete, Vol. 19, No. 1, p. 246-254. and Field Investigations Compared with Theory and Finite Element Analysis”. Doctoral Thesis 15. Mohaghegh A M, Silfwerbrand J & Årskog V 2008:50, Norwegian University of Science and (2018b): ”Shear Behaviour of High-Performance Technology, Faculty of Engineering Science and Basalt Fiber Concrete – Part II: Laboratory Technology, Dept. of Structural Engineering, Punching Shear Tests on Small Slabs with Macro Trondheim, Norway, 254 pp. Fibers and Bars”. Structural Concrete, Vol. 19, No. 2, p. 331-339. 5. Hedebratt J (2012): “Industrial Fibre Concrete Floors – Experiences and Tests on Pile-Supported 16. Paulsson J & Silfwerbrand J (1995): "Förnyelse av Slabs”. Bulletin No. 113 (Doctoral Thesis), Div. of Gullmarsplans trafikplats - vidhäftande slitskikt av Structural Design & Bridges, Dept. of Civil & stålfiberbetong". Tidskriften Betong, No. 2, 1995, Architectural Engineering, School of Architecture p. 22-27. (In Swedish). & Built Environment, KTH Royal Institute of 17. Silfwerbrand J (1995): "Whitetoppings - Swedish Technology, Stockholm, Sweden. Field Tests 1993-1995". CBI Report No. 1:95, 6. Hedebratt J & Silfwerbrand J (2012): “Lessons Swedish Cement and Concrete Research Institute, Learned – Swedish Design and Construction of Stockholm, 77 pp. Industrial Concrete Floors”, Nordic Concrete 18. Silfwerbrand J (2017): “Safety Levels in Concrete Research, NCR, June 2012, p. 75-92. Slabs-on-Grade”. Proceedings, fib Symposium 7. Hedebratt J & Silfwerbrand J (2015): “Time- 2017, Maastricht, The Netherlands, June 12-14, Dependent Deflections of a Steel Fiber Concrete 2017, 8 pp. Slab.” Concrete International, Vol. 37, No. 7, July 19. SS-EN 14651 (2007): ”Test Method for Metallic 2015, p. 46-52. Fibre Concrete — Measuring the Flexural Tensile 8. Holmgren J (1992): ”Rock Strengthening with Strength (Limit of Proportionality (LOP), Shotcrete” (“Bergförstärkning med sprutbetong”), Residual)”. Swedish Standards Institute, Vattenfall Vattenkraft, Stockholm, Sweden, 74 pp. Stockholm, Sweden. (In Swedish). 20. SS-EN 1992-1-1 (2005): ”Eurocode 2: Design of 9. Holmgren J (2010): “Shotcrete Research and Concrete Structures – Part 1-1: General Rules and Practice in Sweden—Development over 35 Years”. Rules for Buildings”. Swedish Standards Institute, From: “Shotcrete: Elements of a System”, CRC Stockholm, Sweden, 225 pp. Press, London, 310 pp. Edited by E S Bernard. 21. SS-EN 206:2013 (2015): ”Concrete – 10. Jansson R (2013):“Fires Spalling of Concrete. Specification, Performance, Production and Theoretical and Experimental Studies”. Bulletin Conformity”. Swedish Standards Institute, No. 117 (Doctoral Thesis), Div. of Concrete Stockholm, Sweden, 15 pp. Structures, Dept. of Civil & Architectural 22. SS 812310:2014 (2014): ”Fibre Concrete – Design Engineering, School of Architecture & Built of Fibre Concrete Structures”. Swedish Standards Environment, KTH Royal Institute of Technology, Institute, Stockholm, Sweden, 38 pp. Stockholm, Sweden. 23. Swedish Concrete Association (1997): ”Steel Fibre 11. Mohaghegh A M (2018): “Structural Properties of Concrete – Recommendations for Design, High-Performance Macro Basalt Fibre Concrete; Construction and Testing” (”Stålfiberbetong – Flexure, Shear, Punching Shear and Fire rekommendationer för konstruktion, utförande och Spalling”. Bulletin No. 152 (Doctoral Thesis), Div. 36 J. Silfwerbrand provning”), Concrete Report No. 4, 2nd edition, 25. Tan K H & Saha M K (2005): “Ten-Year Study on Stockholm, Sweden, 135 pp. (In Swedish). Steel Fiber-Reinforced Concrete Beams Under Sustained Loads,” ACI Structural Journal, 24. Swedish Concrete Association (2008): “Industrial Floors – Recommendations for Design, Material American Concrete Institute, V 102, No. 3, May- Selection, Execution, Operation and Maintenance” June 2005, p. 472-480. (“Industrigolv – Rekommendationer för projektering, materialval, produktion, drift och underhåll”), Concrete Report No. 13, 1st Edition, Stockholm, Sweden, 296 pp. (In Swedish). Basalt fibers and basalt-carbon fibre reinforced polymers for reinforcement of concrete structures Bazaltna vlakna in polimeri ojačeni z bazalt- karbonskimi vlakni za armiranje betonskih konstrukcij Andrzej Garbacz Warsaw University of Technology Marta Kosior-Kazberuk Bialystok University of Technology Kostiantyn Protchenko, Marek Urbański, Maria Włodarczyk, Elżbieta Szmigiera Warsaw University of Technology, Poland Abstract The paper describes recent developments in the area of Fibre-Reinforced Polymers (FRP) reinforcement implemented in concrete structures. Durability, strength and stability are the main criteria when selecting FRP reinforcement. A major motive for the implementation of FRP lies in the unique characteristics of these materials and their constituents when they used to its considered design purpose. Extensive research on Hybrid FRP (HFRP) bars is being conducted at the Warsaw University of Technology in conjunction with an FRP manufacturing company under the programme of the National Centre for Research and Development in Poland. This research aims at investigating the mechanical and physical behaviour of HFRP bars, and the possibilities of using these types of reinforcement in structural systems for both flexural and compression members Povzetek Članek opisuje najnovejši razvoj armature iz polimerov ojačenih z vlakni (POV), ki se uporablja v betonskih konstrukcijah. Trajnost, trdnost in stabilnost so glavna merila pri izbiri armature iz POV. Glavni motiv za uporabo POV je v edinstvenih značilnostih teh materialov in njihovih sestavnih delov, ko so se uporabljali za načrtovani namen. Na Tehniški univerzi v Varšavi potekajo obsežne raziskave o palicah iz hibridnih POV (HPOV) v povezavi s proizvajalcem POV v okviru programa Nacionalnega centra za raziskave in razvoj na Poljskem. Namen raziskave je raziskati mehansko in fizikalno obnašanje palic iz HPOV ter možnosti uporabe teh vrst armiranja v konstrukcijskih sistemih za upogibne in tlačne elemente. Keywords: FRP reinforcement, basalt fibres, HFRP bars, FRP-RC members, Fire resistance of FRP, FRC Structures Ključne besede: armatura iz POV, bazaltna vlakna, palice iz HPOV, POV-AB elementi, požarna odpornost POV, MAB konstrukcije reinforcement, particularly in cases where de-icing salts 1. INTRODUCTION are used. The same problem of steel corrosion was The service life of reinforced concrete (RC) structures observed in marine structures where chlorides and is drastically affected by the corrosion of internal steel seawater are present [1]. 26. slovenski kolokvij o betonih – Projektiranje mikroarmiranih betonskih konstrukcij in njihove aplikacije, Ljubljana, 16.5.2019 38 A. Garbacz, M. Kosior-Kazberuk, K. Protchenko, M. Urbański, M. Włodarczyk, E. Szmigiera Therefore, routine maintenance is needed to counter this requires two distinct procedures, at the first the molten problem, however, the cost of repair, rehabilitation, rock is extruded through small nozzles to obtain strengthening of steel reinforced concrete structures, as continuous filaments of basalt fibre. The second is well as delaying and detouring traffic can be as high as whereby the fibres are bonded with the matrix during two times the original construction cost [2, 3]. moulding to produce ready products, BFRP bars. The advantage of fibre reinforced polymer (FRP) The basalt fibres are characterised as weak anisotropic composites lies in their high-strength, lightweight, materials with high tensile strength, improved chemical noncorrosive, nonconducting, and nonmagnetic resistance, extended operating temperature range, and properties. In addition, FRP manufacturing, using environmental friendliness. Moreover, basalt fibre has various cross-sectional shapes and material a good impact resistance, and a fire with less poisonous combinations, offers unique opportunities for the fumes [11, 12]. In addition, the basalt fibres do not need development of shapes and forms that would be difficult any other additives in the one-step producing process, or impossible with conventional steel materials [4]. The adding a distinct benefit in cost. widespread implementation of FRP as a reinforcement for reinforced concrete elements requires: a Therefore, these advantages make basalt fibre a comprehensive understanding of how each of these promising alternative to other types of fibres [13]. materials behaves alone as well as the behaviour of the BFRP composite is expected to provide benefits that are structural system as a whole. [5]. comparable or superior to other types of FRP while being significantly cost-effective [14-16]. Fibre Reinforced Concrete (FRC) has been widely used in different applications in constructions, such as The current situation on the market shows that using of geotechnical structures(dam, tunnels), roads (bridges, BFRP bars will be confined to applications where their pavements, railways objects), marine and industrial unique characteristics will be the most appropriate. structures (cooling towers, floors, overlays), etc., where Nevertheless, the data currently available on the the major concern is toughness and first-crack strength behaviour of BFRP-RC members are relatively scarce. in flexure. For engineering applications, the tension- North American design codes and guidelines such as weak nature of concrete is usually reduced by using CAN/CSA S806 (2012) [17], CAN/CSA S6 (2014) [18] different types of fibres. A recent development has been and ACI 440.1R (2015) [19] have been developed to the introduction of various types of non-metallic fibres, regulate the design conditions for structural elements which can provide a similar post-cracking performance reinforced with GFRP, CFRP and AFRP bars, but do [6-9]. not consider BFRP reinforcement.[20, 21]. Basalt fibre is an inorganic fibre that is assumed to be Therefore, BFRP bars are characterised as a new variety one of the most ecologically friendly type of fibres. of material whose properties are still have not been Basalt fibre is formed from basalt rock, which is a completely investigated and consequently this research ubiquitous natural resource covering nearly one-third of is aimed at investigating the mechanical and physical the earth’s surface, including much of the ocean floor behaviour of HFRP bars, and the possibilities to use [10]. The manufacture of basalt fibre involves the these types of reinforcement in structural systems for melting of the crushed and washed basalt rock at about both flexural and compression members. 1500 °C (2,730 °F). The manufacturing process Fig. 1: Fracture testing configuration and geometry of notched specimen. Basalt fibers and basalt-carbon fibre reinforced polymers for reinforcement of concrete structures 39 Table 1. Measured average values of concretes with various fibre contents Vf: compressive strength fcm and flexural strength fctm. Cement w/c Vf fcm fctm (kg/m3) (MPa) (MPa) CEM I 0.40 0.0 67.54 4.51 42.5 R 2.0 65.73 5.48 4.0 72.77 4.89 8.0 75.63 5.62 0.50 0.0 65.17 4.14 2.0 66.26 4.18 4.0 70.67 5.00 8.0 72.50 5.28 CEM II/A-V 42.5 R 0.40 0.0 52.28 5.03 2.0 55.78 5.10 4.0 58.26 5.64 8.0 60.19 5.89 0.50 0.0 51.09 4.84 2.0 54.52 4.65 4.0 54.87 4.89 8.0 58.88 5.55 The basalt fibres were added to concrete at three 2. FRACTURE TOUGHNESS OF CONCRETE contents, Vf of 2.0, 4.0 and 8.0 kg/m3, which gave WITH BASALT FIBRE volume fractions 0.075%; 0.15% and 0.31%, respectively. The fibres were added as a replacement for 2.1 Characteristics of the materials and specimens part of the coarse aggregate by volume. Comparatively, The aim of the investigation was to evaluate the effect the properties of concretes with no added fibres were of basalt fibre content on the toughness and post- also tested. The polycarboxylate polymer based super- cracking behaviour of concrete. The details of the plasticizer was used to minimize fibres clumping and experiment are presented in the work of M. Kosior- enhance fibre dispersion in concrete mix. The super- Kozberuk and J.Krassowska [22] plasticizer was applied in the amount of 1.0% of cement mass. Concrete mixtures were made with two cement types CEM I 42.5 R and CEM II/A-V 42.5 R (usually used in For each fibre-dosage combination notched beams of concrete pavements). The cement content in all size 100×100×400 mm were prepared for fracture mixtures tested was 320 kg/m3. The water to cement parameters determination. Every series was composed ratio was equal to 0.40 and 0.50, respectively. For the of four replicates. Moreover, the beams ( 100×100×400 aggregate, a mixture of sand (fraction 0-2 mm) and mm) for flexural strength were also cast and cubes natural aggregate with a maximum diameter of up to 16 ( 100×100×100 mm) for the compressive strength test mm was used. The basalt fibres with a diameter of 0.02 were cut from them. After demoulding all specimens mm and a length of 50 mm were characterized by a were cured in water at the temperature of 18 2oC until tensile strength of 1680 MPa, elastic modulus of 89 they were tested. GPa and density of 2600 kg/m3. 40 A. Garbacz, M. Kosior-Kazberuk, K. Protchenko, M. Urbański, M. Włodarczyk, E. Szmigiera The fracture performance of concretes with fibres and cyclic loading-unloading test procedure. Both the control concrete without reinforcement was tested parameters are related to the critical stress  c initiating in accordance with the recommendations of the RILEM the crack propagation and the effective length of the Fracture Mechanics Committee [19, 20]. The notched critical crack ac. The assessments for LEFM application beams of size 100×100×400 mm were used for a three- by Jenq and Shah were described in detail in [25]. point bending test corresponding to Mode I conditions. An initial saw-cut notch with a depth equal to 30 mm The fracture energy, GF, is defined as the area under the and width of 3 mm was located in the middle of the span load-deflection curve per unit fractured surface area. (Fig. 1). The elongated U-notches ( a The fracture energy of concretes tested in this 0/d = 0.30) were sawn under wet conditions one day before the test. Each experimental study, was evaluated using the procedure series was composed of four replicates. given by RILEM TC 50-FMT Recommendation [23], in which energy was calculated from load-deflection The fracture parameters considered were the critical curves obtained by performing a three-point bending stress intensity factor KIc and the critical tip opening test, dividing by the area of ligament, which is defined displacement CTODc. The critical stress intensity factor as the projection of the fracture zone on a plane KIc is defined as the stress intensity factor calculated at perpendicular to the beam axis. The scatter of the the critical effective crack tip, using the measured calculated values of GF results from the inevitable maximum load. The critical crack tip opening random length of the tail region of the P- curve and displacement CTODc is defined as the crack tip opening also from the uncertainty in extrapolating the curvès displacement calculated at the original notch tip of the descent toward zero. To reduce the impact of factors specimen, using the measured maximum load and the mentioned on the scatter of GF, the plot was turned critical effective crack length ac. The values of KIc and down when the load was approximately equal to 0.05 CTODc were determined using the procedure and Pmax (100 200 N). The area of the cross section of the equations given in RILEM TC 89-FMT specimen, which the total energy value was referred to, Recommendation [23], based on the fracture model was determined based on the width of the test specimen ( TPFM) elaborated by Jenq and Shah [24], assuming a b and the depth d excluding the notch ( a0 = 30 mm). a) b) Fig. 2: Load P- CMOD plots for concretes with different content of basalt fibres Vf for concretes with: a) w/c = 0.40 (CEM I 42,5 R) and b) w/c = 0.40 (CEM II/A-V 42,5 R). a) b) Fig. 3: Effect of fibre volume fraction Vf (%), cement type and w/c ratio on: a) fracture toughness KIc b) CTODc Basalt fibers and basalt-carbon fibre reinforced polymers for reinforcement of concrete structures 41 Table 2: Elastic GFel and plastic GFpl part of the fracture energy until crack propagation, GF– total fracture energy. Cement w/c Vf GF GFpl GFel (kg/m3) (Nm/m2) (Nm/m2) (Nm/m2) CEM I 0.40 0.0 147.8 9.0 52.0 42.5 R 2.0 159.8 16.0 53.0 4.0 190.3 27.0 78.0 8.0 210.4 33.6 88.0 0.50 0.0 128.0 7.0 39.0 2.0 154.6 15.0 54.0 4.0 185.7 24.0 71.0 8.0 200.2 30.0 84.0 CEM II/A-V 0.40 0.0 144.8 7.2 49.0 42.5 R 2.0 175.3 16.0 54.0 4.0 180.0 23.0 72.0 8.0 188.4 28.0 77.0 0.50 0.0 150.5 10.0 49.5 2.0 170.5 14.0 54.5 4.0 166.5 20.0 59.5 8.0 185.5 21.0 70.0 idea about the proportion of the elastic part of the 2.2 Results fracture energy, Table 2 illustrates the elastic GFel and The flexural strength of concrete was defined by the plastic GFpl part of energy until crack propagation load capacity at the first crack. The compressive related to the total measured energy GF. strength was determined according to EN 12390-3 [26] using cubes of size 100 mm (Tab.1). 3. BFRP REINFORCED BEAMS The fracture toughness, K Ic and the critical crack tip The first stage of this research project involved the opening displacement ( CTODc) were determined on the fabrication of several series of beams reinforced with basis of load P vs. CMOD curves obtained for the BFRP bars to test their flexural capacity. In order to concrete specimens subjected to cyclic loading- determine bending resistance, deflections and cracks, unloading (Fig.2) concrete beams reinforced with BFRP bars and The results of the critical stress intensity factor, K reference beams reinforced with steel bars of various Ic and the critical value of the crack tip opening displacement reinforcement ratios were subjected to flexural loading CTODc, derived from the P– CMOD relationships for in a four-point bending test. All specimens had different fibre content, were shown in Figure 3. rectangular cross-section with dimensions 140 mm wide and 260 mm high and were 3000 mm long. Every series The incorporation of the basalt fibre does not only contained a two samples. influence the post-peak behaviour of concrete beams but also the pre-peak part of both load-CMOD and load- (1 and 2 series) Top reinforcement (compression zone) deflection curves. The values of fracture energy given and shear reinforcement (stirrups) were kept constant in Table 2 were calculated according to load-deflection for all beams. Two BFRP bars with a diameter of 8 mm diagrams containing both the plastic and elastic part of were used as longitudinal top reinforcement for beams the fracture energy, up to the breaking load. To give an reinforced with FRP reinforcement and 4 mm BFRP 42 A. Garbacz, M. Kosior-Kazberuk, K. Protchenko, M. Urbański, M. Włodarczyk, E. Szmigiera Table 3: Specimen Details Mechanical Tensile Strength Elastic Modulus, Srain at reinforcement ratio fu E break εu Series Bottom reinforcement No. ρme = ρ( fu/ fck) MPa GPa % BFRP Steel BFRP Steel BFRP BFRP Steel BFRP 1 0,166 0,163 2Ø10 2Ø14 1020 49,4 2,06 2 0,250 0,244 3Ø10 3Ø14 200 3 0,326 0,322 2Ø14 2Ø20 943 42,8 2,36 stirrups, and two 10 mm steel bars for steel reference Deflections of beams with BFRP reinforcement were beams. The stirrups of reference beams were made of 6 significantly higher than the reference beam deflection, mm steel bars of class B500SP. The stirrup spacing was which can be caused by the much lower modulus of assumed as 100 mm and the mid part of the beam did BFRP bars compared to steel bars. However, in the final not have stirrups to simulate clear bending. The bottom phase of the loading, the difference in deflections was reinforcement (tensile zone) was changing depending decreased to 40%. on the series. Average width of cracks on the constant cross-section The average modulus of elasticity of BFRP bars with in beams with basalt reinforcement was 4 times higher the diameter of 10 mm was determined in the uniaxial than in the reference beams. tensile test and equals 49.4 GPa, average tensile strength 1019,83 MPa, and average strain at breaking The obtained results confirm the need to develop was defined as 2.4%. Hybrid FRP bars that are made by a material hybridization concept. This can reduce or eliminate (3 series) The average modulus of elasticity of BFRP excessive deflections in beams reinforced with FRP bars with the diameter of 14 mm was determined in the bars. uniaxial tensile test and equals 42,76 GPa, average tensile strength 942,98 MPa, and average strain at break 4. DEVELOPMENT OF HFRP BARS was defined as 2,36 %. The average concrete strength was f 4.1 Analytical and Numerical Considerations ck, cube = 43.82 MPa. Table 3 shows specimens characteristics and a detailed The HFRP bars were created by a physical substitution overview of the flexural testing of beams reinforced of part of the basalt fibres by carbon fibres and then with BFRP bars as is given in companion papers [27- embedded in a single epoxy resin during the pultrusion 29]. process. During the development, several parameters of proposed Hybrid Carbon/Basalt FRP (HFRP) bars were Loading was placed in a four-point system made of steel changed to investigate their performance, such as: the traverse, at one third and two thirds of the beam span. location of fibres, technological aspects, different Loading was performed in several cycles. During the volume fraction ratio of fibres. first cycle of loading, the beams were subjected to load equal to 10 kN and then the load was reduced to 5 kN. The carbon fibres are characterized by a strong In each following cycle loading was increased by 10 kN, anisotropy and were selected due to their strong and then reduced again to 5 kN, till the failure of the properties in the longitudinal direction. Low Strength structure. (LS) carbon fibres were chosen because their strain is approximately the same as for the basalt fibres. The It has been stated in this study that in contrast to the combination of basalt and LS carbon fibres and their bilinear stress-strain dependence for steel appropriate volume fractions can result in adjusting reinforcement, basalt reinforcement has a linear parameters of HFRP bars to desirable values. dependence until failure. The properties of FRP bars in the longitudinal direction The failure of beams with BFRP reinforcement did not can be calculated using the Rule of Mixtures (ROM) occur suddenly and this effect was a result of the (axial loading - Voigt model) as it comes from the transformation of the beam into a tie system since the literature. The transverse properties can be obtained flexural basalt reinforcement remained unbroken. with Halpin-Tsai and other semi-empirical models [30- 32]. However, these formulas do not consider bars Basalt fibers and basalt-carbon fibre reinforced polymers for reinforcement of concrete structures 43 Table 4. Results of Experimental Testing for BFRP and HFRP Bars HC/BFRP Ø8mm Maximum Tensile strength, Tensile strain Modulus of strength, Fu fu at rupture, εu elasticity, EL [kN] [MPa] [%] [GPa] Average 77,21 1277,92 1,73 73,89 Standard deviation σ 3,35 55,4 0,07 3,07 Variation 4,34% 4,34% 4,33% 4,15% BFRP Ø8mm Average 60,03 1103,3 2,52 43,87 Standard deviation σ 1,24 22,87 0,05 0,86 Variation 2,07% 2,07% 2,09% 1,95% configuration, i.e. location of fibres, so, it was agreed to More detailed description on HFRP development is prepare a numerical simulation for this purpose. provided in [33-35] The numerical simulation of tensile strength test for 4.2 Experimental Testing of HFRP Bars HFRP bars was performed in Finite Element Analysis FEA software ANSYS. Two different bar Two possible bar configurations were produced, but configurations were proposed, one where carbon fibres manufacturing companies faced some technological were substituting basalt fibres in the core region, the problems while placing carbon fibres in the near- other one with carbon fibres located in the near-surface surface layer. These issues include an increased region. heterogeneity in fibre distribution and local scorching of carbon fibres caused by temperature increases. The bars were modelled as cylindrical elements with a diameter of 8 mm and a length of 850 mm. A constant Therefore, it was decided to produce HFRP bars with a pressure of 500 MPa was applied on the side edges. One preferable distribution of carbon fibres in the core central point was fixed in the y and z directions. The region. The selected volume fractions of carbon-to- structure of the HFRP bars consisted of a core and basalt fibres were 1:4 (i.e. 16% of carbon fibres, 64% surface region, which were perfectly interconnected. of basalt fibres, 20% epoxy resin to ensure correct bonding). The results showed that bar configuration is less important than the volume fraction of fibres. The The tensile strength test was carried out in accordance difference between various bar configurations can be a with ACI 440.3R (2012) [36] standard for pultruded maximum of 2%, meanwhile, the volume fraction of all FRP bars. The average values of tensile strength (limit analysed combinations can influence the final stiffness stress), fu, modulus of elasticity, EL, and the limit strain, by 74.6%. Fig. 4. Destruction of 8 mm diameter HFRP bar. 44 A. Garbacz, M. Kosior-Kazberuk, K. Protchenko, M. Urbański, M. Włodarczyk, E. Szmigiera εu, for HFRP and BFRP bars were obtained and are 5. FIRE RESISTANCE OF FRP RC MEMBERS shown in the Table 4. Consequently, hybridization of constituents of hybrid The samples were destroyed by splitting and the FRP bars showed that properties of FRP bars are destruction mechanism of bars had a brittle character dependent on the properties of their constituents and the (Figure 4). relative proportions of the fibre, known as the fibre- volume ratio. The matrix can be seriously affected at BFRP and HFRP bars showed high tensile strength in elevated temperatures, therefore it is needed to examine the longitudinal direction. However, the mechanical the behaviour of bars subjected to fire exposure as well characteristics were lower than predicted by analytical as structures reinforced with these materials [40]. and numerical simulations by approximately 20%. Currently, the use of FRP reinforcement in RC structures is limited and only includes cases when fire In accordance with several studies [37-39] adding silica resistance aspects are not particularly meaningful. nanoparticles into the epoxy resin can improve the general performance of composite HFRP, chemical Therefore, it was agreed to analyse two possible cohesion between constituents, and fire resistance of situations, when beams were subjected to temperature bars etc. and then tested, and when beam were heated and loaded with a sustained load simultaneously. In the case of the For the experimental tests, it was decided to modify first type of testing, the required output was to analyse epoxy resin (a four-component 1300 System®), which the residual behaviour of FRP-RC beams and to find the was added during the pultrusion process. The silica level of reduction of the beam’s strength capacity. For nanoparticles were used as a concentrated sol of the second type of experiments, the task was to check nanosilica with a concentration of 25 to 30% by weight. for the duration of the period in which the structure can The structure of nano Hybrid FRP (nHFRP) is shown in withstand loading and elevated temperatures, reflecting the SEM image in the Figure 5. the conditions of a fire. However, the obtained results showed small reductions The reinforcement in the compression zone and shear in mechanical properties for bars with the diameter reinforcement (stirrups) were assumed to be consistent 8mm. The authors suggest that it can be related to the for all beams. The stirrups made of 6 mm diameter improper distribution of nanoparticles in epoxy resin for BFRP bars have a spacing assumed to be 100 mm. The such diameters, however for bars with bigger diameters, longitudinal top reinforcement is composed of two 8 the addition of nanosilica particles improved the overall mm diameter BFRP bars. For the tensile reinforcement strength properties for the nHFRP bars. (bottom zone) different reinforcement types and amounts were used. Either 2 bars with a diameter of 14 Fig. 5. nHFRP rod after cooling down to -20 °C. The figure shows a visible silica nanoparticles (Q) distribution. Bright points represent basalt fibres, darker area shows carbon fibres, space between nanoparticles and fibres is filled by epoxy resin. Basalt fibers and basalt-carbon fibre reinforced polymers for reinforcement of concrete structures 45 mm or 4 bars with a diameter of 8 mm of exposure until failure as it can be seen from force- BFRP/HFRP/nHFRP were used for the tensile deflection curves. reinforcement. As for the beams subjected to the simultaneous During the testing of residual behaviour of the beams, application of temperature and loading, the beams were all tested specimens were destroyed due to failure in the loaded by 50% of their ultimate load. The loading and tensile zone, unlike reference beams, where the heating were applied until the beams’ failure. Figure 6 destruction took place due to concrete crushing in shows the test Setup during the heating phase. compression zone. The overall strength capacity of the FRP reinforced beams was reduced by approximately Unlike the reference specimens, which were destroyed 42.4% after being subjected to fire exposure. due to concrete being crushed in the compression zone, the failure of beams subjected to heating and loading The highest strength capacity was obtained by beams occurred in different ways. Two beams reinforced with reinforced with HFRP bars. The beams` strength BFRP bars were destroyed due to failure of the capacity after applying elevated temperatures was reinforcement in the tension zone and four beams reduced by 40.34% and was equal to 50.71 kN. It is reinforced with hybrid FRP bars failed because of worth to mention that the post-fire behaviour of FRP- concrete crushing. RC beams was similar to beams not subjected to fire Fig. 6. Test Setup of Specimen, Beam Reinforced With 14 mm Two BFRP Bars, Being Heated and Loaded Fig. 7. HFRP Bars After the Matrix Evaporated in Specimen Reinforced with 14 mm HFRP Bars 46 A. Garbacz, M. Kosior-Kazberuk, K. Protchenko, M. Urbański, M. Włodarczyk, E. Szmigiera Table 5. The test results and specimens characteristics Nn – average Description Tensile strength/ experimental Elastic modulus ultimate force Type / #×Ø / stirrups spacing [MPa] [kN] Axially loaded HFRP/4×8/150 mm 1139/73.57103 905.50 HFRP/4×10/150 mm 1278/73.89103 972.20 HFRP/4×10/75 mm 1278/73.89103 980.60 BFRP/4×8/150 mm 1103/43.87103 906.00 BFRP/4×8/75 mm 1103/43.87103 1001.00 BFRP/4×10/75 mm 1153/48.18103 1001.50 Steel /4×10/150 mm 556/210103 999.00 Loaded with eccentricity e = 40 mm HFRP/4×10/75 mm 1278/73.89103 491.00 BFRP/4×10/75 mm 1153/48.18103 375.90 Steel/4×10/75 mm 556/210103 465.00 As it can be seen in Figure 7, after the hybrid FRP bars the ultimate force was reached; and after reaching the were uncovered by removing the clear cover, it showed limit point, the loading program was continued in order that the temperature caused a burning of the FRP bars. to obtain a full course of the static equilibrium path, This resulted in the evaporation of the matrix in the including the post-critical range. middle of the bars. A major part of the fibres stayed in the same place and continued to sustain the load. Figure 8a shows the destruction modes of axially loaded compressed members and Figure 8b describes the The highest temperature and the longest period of damage modes for elements loaded with eccentricity of heating was achieved by beams reinforced with BFRP e =40 mm. bars as opposed to beams reinforced with hybrid FRP bars in the same sets. The duration of the heating phase Table 5 shows the values of tensile strength of for the sample reinforced with four BFRP bars with the reinforcement and values of elasticity modules of diameter 8 mm was approximately 98 min.; deflections reinforcement and results of average experimental were 162 mm, and the temperature in the bars, measured ultimate force of tested columns. by thermocouples, was approximately 900 0C. The compression members with BFRP and HFRP reinforcement collapsed by the crushing of concrete 6. FRP RC COMPRESSION MEMBERS under an axial compression load. However, the destruction of the steel reinforced concrete elements The experimental process of testing compression took place due to reaching the capacity of steel bars of members involved the fabrication of samples with longitudinal reinforcement, which in consequence also dimensions 150x150 mm and a height of 750 mm caused the crushing of concrete. In the case of the reinforced with BFRP, HFRP bars and reference eccentrically loaded samples, the destruction occurred members reinforced with conventional steel in the shear mode due to concrete cutting. Steel reinforcement. reinforcement and FRP bars have significantly different The research project consisted of two series of mechanical properties represented by stiffness, experimental tests which differ in the setup of applied strength, plasticity or brittleness, and a symmetrical or loading, for the first series the loading was applying asymmetrical response in uniaxial tension or axially and for the second with the loading applied at a compression tests. The reported discrepancy in the big eccentricity. The load was gradually increasing until stress-strain relationships for the materials results in a Basalt fibers and basalt-carbon fibre reinforced polymers for reinforcement of concrete structures 47 different response from concrete members reinforced increase concrete resistance to initiation and by steel or FRP bars. More detailed description is propagation of cracks. provided in companion papers [41]. This work outlines the mechanical behaviour of FRP bars made with basalt fibres BFRP, carbon-basalt fibres 7. CONCLUSION HFRP and carbon-basalt fibres with modified epoxy The widespread application of FRP reinforcement can resin nHFRP. The possible application of the become possible after a comprehensive analysis of the aforementioned types of reinforcement was checked by mechanical and physical properties of these materials. applying them in flexural and compression members. In addition, it is quite important to examine the Additionally, the specimens were completely performance of FRP-RC members, particularly in reinforced with FRP reinforcement to eliminate the accidental situations, such as being exposed to fire or an influence of conventional steel reinforcement. aggressive chemical environment. Fire resistant aspects were examined for flexural The results of from measuring the toughness and the members, where they were tested by using a standard energy-absorption characteristics showed that basalt fire endurance test, i.e. the specimens where heated and fibre reinforced concrete specimens acquire a great loaded simultaneously. Moreover, the residual highly ductile behavior and energy absorption capacity, properties of the beams were checked by applying compared to ordinary concrete specimens. The addition elevated temperatures for some period of time and of basalt fibre in the tested amount of 2-8 kg/m3 has a allowing them to have a cooling phase, and finally significant influence on the fracture mechanics reloaded flexurally until failure. parameters of concrete, with relatively little impact on Based on experimental testing on the mechanical the compressive strength of concrete. The presence of behaviour of BFRP and hybrid FRP bars, it is possible fibres has improved the fracture mechanics parameters to conclude that their properties can become predictable such as KIc, CTODc, GF and recorded maximum values with the concept of material hybridization. of load. The analysis of the P-CMOD relationships Experimental testing of flexural and compression show that dispersed reinforcement can significantly members, and analyses related to fire resistance aspects change the nature of the behaviour of concrete elements suggest that the considered reinforcement can be a subjected to bending in both pre-cracking and post- promising alternative to steel bars, however, a cracking phases. The changes in fracture mechanics comprehensive investigation is still required. parameters and the modification of P-CMOD plots, recorded under loading, indicate that basalt fibres can a) b) Fig. 8. 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Czasopismo Inżynierii mechanics of concrete: Applications of fracture Lądowej, Środowiska i Architektury, JCEEA, mechanics to concrete, rock and other quasi-brittle materials. John Wiley & Sons, Inc., New York, 552, 63(1/1), 149–156, 2016. 1995. 13. W. M. Mingchao, Z. Zuoguang, L. Yubin, L. Min, and S. Zhijie, “Chemical Durabil 26. EN 12390-3. “Testing Hardened Concrete: ity and Mechanical Compressive strength of test specimens”, 2011 Properties of Alkali-Proof Basalt Fiber and Its Reinforced Epoxy Composites.” Journal of 27. M. Urbański and A. Łapko, “Effectiveness of Reinforced Plastics and Composites, 27 (4), 393– flexural basalt reinforcement application in RC 407., 2008. beam structures,” in Modern materials, Basalt fibers and basalt-carbon fibre reinforced polymers for reinforcement of concrete structures 49 installations and construction technologies, S. Fic, (ICPIC 2018) : Polymers for Resilient and Ed. 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In Materials and Processing in enhanced mechanical properties.” Polymer 49, Manufacturing, (162-194), JohnWiley & Sons, Inc., 3805–3815, 2008. ISBN 978-0470-05512-0, USA, 2008. 40. D.S. Ellis, H. Tabatabai, A. Nabizadeh, “Residual 32. Barbero, E. J. “Introduction to composite materials tensile strength and bond properties of GFRP bars design”. 2nd ed. Boca Raton, FL: CRC Press, after exposure to elevated temperatures”. Materials Taylor & Francis Group, 2011. 11, 346, 2018. 33. K. Protchenko, E.D. Szmigiera, M. Urbański & A. 41. M. Włodarczyk, D. Trofimczuk, “Prediction of Garbacz, “Development of Innovative HFRP Bars”. ultimate capacity of FRP reinforced concrete MATEC Web of Conferences, 196, 1-6, 2018. compression members. fib Symposium, Kraków http://doi.org/10.1051/matecconf/201819604087 (accepted) 2019 (Symposium w dniach 27- 34. A. Garbacz, E.D. Szmigiera, K. Protchenko, & M. 29/05/2019). Urbański, M. “On Mechanical Characteristics of HFRP Bars with Various Types of Hybridization”. In M. M. Reda Taha, U. Girum, & G. Moneeb, M. M. Reda Taha, U. Girum, & G. Moneeb (Eds.), International Congress on Polymers in Concrete Primena cementnih kompozita na bazi sintetičkih vlakana za prefabrikovane fasadne panele Application of synthetic fibre reinforced cement composites for prefabricated façade panels Tijana Vojnović Ćalić Coburg University of Applied Sciences and Arts, School of Design, Department of Architecture, Coburg, Germany Dragica Jevtić, Dimitrije Zakić Univerzitet u Beogradu, Građevinski fakultet, Beograd, Srbija Rezime Mikroarmirani cementni kompoziti su duže vreme u upotrebi u sastavu različitih fasadnih panela dostupnih na tržištu. To su uglavnom jednoslojne tanke vlaknasto-cementne ploče. U okviru ovog rada će biti prikazan fasadni panel sa podlogom od mikroarmiranog cementnog kompozita i dekorativnim licem od kamena. Specifičnost cementnih kompozita u ovom slučaju je to što sadrže i laki agregat u vidu drobljene opeke. Razmatraće se fizičko-mehanička svojstva primenjenih mikroarmiranih cementnih kompozita i pojedine karakteristike pomenutog fasadnog panela bitne za njegovu primenu. U skladu sa održivim pristupom u građevinskoj industriji, posebnu vrednost ovog panela predstavlja upotreba lokalnih i recikliranih materijala. Abstract Fibre reinforced cement composites are used in a longer period for production of various façade panels that are available on the market. These are mainly single-layer thin fiber-cement boards. The paper deals with façade panels composed of fibre reinforced cement composite substrate and a decorative face of stone. Specific for the cement composite in this case is that it contains light aggregate in the form of crushed brick particles. The physical-mechanical properties of the applied fibre reinforced cement composites and the particular properties of the aforementioned façade panel essential for its application are given. In accordance with the sustainable approach in the construction industry, the additional value of this research represents the application of local and recycled materials. Ključne besede: fasadni panel, mikroarmirani cementni kompoziti, fizičko-mehanička svojstva, primena Keywords: façade panel, fibre reinforced cement composites, physical-mechanical properties, application kompozita armiranog tkaninom od staklenih vlakana. 1. UVOD Lice ovog panela sačinjeno je od kamene obloge. Mikroarmirani cementni kompoziti nalaze sve širu U ovom radu se predlaže primena mikroarmiranog primenu kod različitih fasadnih panela, od kojih su cementnog kompozita u okviru višeslojnog fasadnog mnogi već prisutni na tržištu. To su, na primer, panela. Uvodi se novi fasadni element koji može naći vlaknasto-cementni paneli poznatih proizvođača Rieder ili Eternit. Takođe je zastupljen i višeslojni panel primenu u okviru provetravanog fasadnog sklopa. Kao firme sastavni materijali, razmatraju se podloga panela od Alsecco, koji se sastoji od lakoagregatnog cementnog 26. slovenski kolokvij o betonih – Projektiranje mikroarmiranih betonskih konstrukcij in njihove aplikacije, Ljubljana, 16.5.2019 52 T. Vojnović Ćalić, D. Jevtić, D. Zakić Tabela 1: Tehnički podaci za polipropilenska i polivinil-alkoholna vlakna [8],[9] Svojstva vlakana Sika Kuraray Sika Fibers Kuralon RMS702 Materijal polipropilen polivinil-alkohol Tip vlakna monofilamentna monofilamentna Oblik poprečnog preseka kružni bubrežasti Prečnik d (mm) 0,040 0,026 Dužina l (mm) 6 6 Faktor oblika l/d 150 230 Specifična masa γs (g/cm³) 0,91 1,30 Čvrstoća pri zatezanju fz (MPa) 360 1600 Modul elastičnosti E (GPa) 2,5 37,0 Izduženje pri lomu δ (%) 22 6 Preporučeno doziranje (kg/m³) 0,6-0,9 1,3-19,5 Otpornost u alkalnoj sredini otporna otporna lakoagregatnog mikroarmiranog maltera i usvaja dodatak polipropilenske mikroarmature malterima na obloga od kamenog mozaika. bazi drobljene opeke praktično ne utiče na svojstvo upijanja vode postepenim potapanjem [7]. Vodeći se trendom održivosti, evropska direktiva - The European Commission Waste Framework Directive, U radu je prikazan deo rezultata dobijen prilikom opisuje poželjnu hijerarhiju pri upravljanju otpadom: istraživanja za potrebe izrade doktorske disertacije [24]. prevenciju, ponovnu upotrebu, reciklažu, ponovno Radi se o rezultatima sopstvenih eksperimentalnih izdvajanje resursa poput energije i konačno, odlaganje istraživanja osnovnih fizičko-mehaničkih svojstava otpada [1]. U skladu sa tim, kao laki agregat u sastavu mikroarmiranih cementnih kompozita namenjenih za podloge predloženog panela usvojena je drobljena izradu fasadnih panela. opeka. Eksperimentalna istraživanja lakoagregatnih 2. MATERIJALI I METODE mikroarmiranih cementnih kompozita su relativno malobrojna. Istraživanja maltera zasnovanih na 2.1 Komponentni materijali agregatu od drobljene opeke armiranih U svrhu eksperimentalnih ispitivanja mikroarmiranih polipropilenskim vlakanima sa umerenim učešćem maltera korišćen je portland-kompozitni cement na bazi mikroarmature (~0,1% od ukupne zapremine) pokazuju cementnog klinkera sa dodatkom granulisane zgure i neznatne promene vrednosti čvrstoća pri pritisku u krečnjaka oznake PC 20M (S-L) 42.5R (CEM II/A-M (S- odnosu na kompozite bez vlakana. Pri većem doziranju L) 42.5R) proizvođača "Lafarge" iz Beočina, Srbija, vlakana od 0,5% i 1%, ova vrednost opada i za 25%. koji se odlikuje visokim ranim i krajnjim čvrstoćama. Čvrstoća pri savijanju raste sa umerenim učešćem Kao agregat je upotrebljen rečni pesak („Dunavac“) vlakana od 0,1% za 5%, a od 1% učešća čak i za 50% frakcije 0/2 i 0/4 i drobljena opeka frakcije 2/4, koja je [2], [3], [4]. S druge strane, ispitivanja potvrđuju porast izdrobljena za potrebe izvođenja eksperimentalnih vrednosti čvrstoće pri pritisku maltera (frakcija 0/8 mm) istraživanja u Laboratoriji za materijale Instituta za od 5-16% i čvrstoće pri savijanju od 4-25% u odnosu na materijale i konstrukcije Građevinskog fakulteta uzorke bez polipropilenske mikroarmature, a u Univerziteta u Beogradu. U svrhu mikroarmiranja zavisnosti od učešća sitne frakcije (0/4 mm) rečnog korišćena su dva tipa vlakana dužine 6 mm: agregata. Istraživanja ukazuju da dodatak vlakana polipropilenska vlakna niskog modula elastičnosti - unutar maltera sa agregatom od reciklirane opeke u Sika Fibers proizvođača Sika, i polivinil-alkoholna količinama od 1% mogu smanjiti deformacije vlakna višeg modula elastičnosti - Kuralon RMS702 skupljanja i do 17% [5], [6]. Takođe je primećeno da japanskog proizvođača Kuraray (tabela 1). Primena cementnih kompozita na bazi sintetičkih vlakana za prefabrikovane fasadne panele 53 Tabela 2: Sastav malterskih mešavina Oznaka serije E E1 E2 M1 M2 Komponenta (g) CEM II 42,5R(S-L) 450 450 450 450 450 Rečni pesak 0/4 1350 1350 1350 / / Rečni pesak 0/2 / / / 810 810 Drobljena opeka 2/4 / / / 270 270 Polipropilensla vlakna / 0,9 / 0,9 / Polivinil-alkoholna vlakna / / 1,5 / 1,5 Superplastifikator / 3,6 3,6 3,6 3,6 Lateks / 9 9 9 9 Voda 225 180 180 193 203 Svojstvo Vodocementni faktor mv /mc 0,5 0,4 0,4 0,43 0,45 Fluidnocementni faktor mf /mc 0,5 0,43 0,43 0,46 0,48 Agregatnocementni faktor ma/mc 3 3 3 2,4 2,4 Tabela 3: Rezultati ispitivanja svežeg maltera Oznaka serije E E1 E2 M1 M2 Svojstvo Konzistencija (mm) 120 130 110 110 110 Zapreminska masa γm,sv (kg/m³) 2201 2161 2275 2135 2110 U svrhu redukcije količine vode i bolje ugradljivosti svežeg maltera, primenjen je superplastifikator na bazi 2.2 Primenjene metode polikarboksilata Sika Viscocrete Techno 20 Malterske mešavine su spravljene mašinskim putem po proizvođača Sika. Predmetni malteri su takođe standardnom postupku, s produženim vremenom modifikovani tečnim polimernim lateksom Sika Latex mešanja do 5 minuta, odnosno do ravnomernog istog proizvođača. Ovaj dodatak u istom smislu (u dispergovanja vlakana. Ugrađene su u kalupe dimenzija funkciji plastifikatora) utiče na konzistenciju i 4x4x16 cm uz primenu postupka vibriranja. ugradljivost malterskih smeša, ali i na Prizmatične epruvete su 7 dana negovane pod vlažnom vodonepropustljivost, odnosno otpornost na mraz, i sargijom, a potom 21 dan na vazduhu u laboratorijskim redukciju napona skupljanja kod tankih elemenata. uslovima na temperaturi 20±2ºC. Vodeni rastvor lateksa je pripremljen sa zapreminskim Konzistencija svežeg maltera je utvrđena metodom udelom lateksa od 5%. Za spravljanje svih malterskih mešavina u okviru ovog eksperimentalnog istraživanja, rasprostiranja uz pomoć potresnog stola (prema SRPS korišćena je voda iz gradskog vodovoda. EN 1015-3 [10]). Nakon utvrđivanja čvrstoće pri savijanju, na delovima prizmi dobijenim prilikom loma, U vidu kamena primenjenog za lice fasadnog pilot vršeno je ispitivanje čvrstoće maltera pri pritisku elementa korišćen je lokalni kamen – granit "Šutica". (prema SRPS EN 1015-11 [11]). Određivanje skupljanja na prizmatičnim uzorcima je vršeno nabazi odredbi standarda SRPS B.C8.029 [12]. 54 T. Vojnović Ćalić, D. Jevtić, D. Zakić Tabela 4: Rezultati ispitivanja očvrslog maltera Oznaka serije E E1 E2 M1 M2 Svojstvo Starost (dani) Zapreminska masa 7 2171 2139 2249 2101 2083 γm(kg/m³) 28 2138 2067 2156 2059 2065 Čvrstoća pri pritisku 7 44,8 48,4 59,1 49,4 49,5 fp (MPa) 28 61,0 60,8 73,0 67,4 66,5 Čvrstoća pri savijanju 7 6,8 7,2 8,0 7,2 6,8 fzs (MPa) 28 8,9 9,3 10,9 9,8 9,6 Skupljanje (mm/m) 28 0,541 0,520 0,593 0,614 0,666 Ispitivanje upijanja vode pod atmosferskim pritiskom je maltera za kamenu podlogu metodom pull-off je vršeno vršeno nakon 28 dana u vodi, u svemu prema u skladu sa standardom SRPS EN 1015-12 [15]. odredbama standarda SRPS B.B8.010 [13]. Otpornost Čvrstoća pilot panela pri savijanju je ispitivana prema prema mrazu je ispitivana u saglasnosti sa standardom prilagođenoj metodi u okviru Laboratorije za materijale SRPS U.M8.002 [14]. Opitna tela su nakon nege od 28 Instituta za materijale i konstrukcije Građevinskog dana podvrgnuta ciklusima naizmeničnog smrzavanja fakulteta Univerziteta u Beogradu, nanošenjem (4h), te odmrzavanja u vodi (4h). Nakon 25 ciklusa je ravnomernog opterećenja na površinu lica panela. vršeno ispitivanje čvrstoće pri savijanju i pritisku ovih Ispitivanje eflorescencije je vršeno prema američkom opitnih tela prema SRPS EN 1015-11 [11]. standardu ASTM C67-14 [16] koji je prvenstveno namenjen proizvodima od opeke. Dalja eksperimentalna istraživanja su obavljana na uzorcima specifičnih dimenzija čija će izrada detaljnije biti opisana u nastavku rada. Ispitivanje prianjanja Slika 1. Prizmatični uzorak sa drobljenom opekom: a) polutke nakon ispitivanja čvrstoće pri savijanju; b) površina loma Primena cementnih kompozita na bazi sintetičkih vlakana za prefabrikovane fasadne panele 55 3. SPROVEDENA EKSPERIMENTALNA 110-130 mm, odnosno kruta konzistencija svih serija ISPITIVANJA maltera (manje od 140 mm, prema SRPS EN 1015-6 [17]). Takođe je uočena neznatna razlika u vrednostima 3.1 Sastav cementnih kompozita zapremniske mase etalona E i preostalih ispitivanih malterskih mešavina sa različitim sastavom agregata i U okviru eksperimentalnih ispitivanja spravljeno je pet serija maltera, čiji se sastav razlikovao po vrsti i količini vlakana (videti tabelu 3). izabranih agregata i vlakana. Etalonska mešavina E predstavlja klasičnu maltersku mešavinu u masenoj 3.3 Svojstva mikroarmiranih cementnih kompozita razmeri cementa, agregata i vode m u očvrslom stanju c:ma:mv=1:3:0,5. Etalonske mešavine E1 i E2 su unapređene dodatkom U okviru tabele 4. prikazani su rezultati ispitivanja preporučene količine polipropilenskih (0,9 kg/m³; očvrslog maltera pet serija maltera starosti od 7 i 28 ~0,1%Vol), odnosno polivinil-alkoholnih (1,5 kg/m³; dana (slika 1). Na osnovu merenja, može se uočiti ~0,1%Vol) vlakana uz dodatak superplastifikatora i jedino jasan porast vrednosti skupljanja kod lateksa. U odnosu na prethodnu recepturu, pri prizmatičnih uzoraka pri zameni određene zapremine spravljanju mešavina M1 i M2, frakcija 2/4 rečnog peska agregatom od drobljene opeke kod uzoraka M1 i peska je zapreminski zamenjena lakim agregatom u M2. vidu drobljene opeke. Količine cementa (450 kg/m³), lateksa (9 kg/m³) i superplastifikatora (3,6 kg/m³) su U tabeli 5 su prikazani rezultati ispitivanja upijanja bile konstantne. Količina vode je dozirana zasebno za vode i otpornosti maltera pri dejstvu mraza. Na osnovu svaku seriju u svrhu postizanja krute konzistencije rezultata ispitivanja mogu se uočiti viši procenti sveže malterske mešavine (rasprostiranje manje od 140 upijanja kod maltera sa drobljenom opekom, mm, prema SRPS EN 1015-6 [17]). Recepture zahvaljujući upijanju samog agregata koji u ovom pojedinačnih serija su prikazane u tabeli 2. Sa slučaju iznosi 18% za 30 s i 21% za 24 h (tabela 5). primenom superplastifikatora i lateksa može se uočiti Otpornost pri dejstvu mraza predmetnih maltera trend umanjenja vodocementnog faktora mv /mc. Primenom agregata manje specifične mase, može se određena je iz odnosa računskih vrednosti čvrstoće uočiti i umanjenje agregatnocementnog faktora m uzoraka pri ekvivalentnoj starosti i laboratorijskog a/mc ispitivanja nakon 25 ciklusa smrzavanja/odmrzavanja. (tabela 2). Čvrstoće pri savijanju pri ekvivalentnoj starosti su određene na osnovu čvrstoća pri pritisku, odnosno 3.2 Svojstva mikroarmiranih cementnih kompozita aproksimacije njihovog odnosa preko izraza: u svežem stanju Ispitivanjem konzistencije malterskih mešavina metodom rasprostiranja, zabeleženo je rasprostiranje od f 2/3 zs = 0,566· fp (R2 = 0,85) a) b) Slika 2 . Ispitivanje uzoraka metodom Pull-off: a) isecanje cilindričnih zareza, b) testiranje uzoraka metodom pull-off 56 T. Vojnović Ćalić, D. Jevtić, D. Zakić Tabela 5: Rezultati ispitivanja upijanja nakon 28 dana i čvrstoće nakon 25 ciklusa mraza Oznaka serije E E1 E2 M1 M2 Svojstvo Upijanje vode u procentima mase (%) 8,23 6,75 6,83 8,54 9,01 Čvrstoća pri pritisku pri ekvivalentnoj starosti 64,2 67,0 76,6 70,6 69,7 fp,e (MPa) Čvrstoća pri pritisku nakon dejstva mraza fp,m 52,7 53,5 64,8 57,7 56,1 (MPa) Čvrstoća pri pritisku nakon opita mraza u 82,1 79,8 84,6 81,7 80,5 odnosu na etalon – Δfp (%) Čvrstoća pri savijanju pri ekvivalentnoj 9,1 9,3 10,2 9,7 9,6 starosti fzs,e (MPa) Čvrstoća pri savijanju nakon dejstva mraza 9,0 8,4 8,9 8,0 7,9 fzs,m (MPa) Čvrstoća pri savijanju nakon opita mraza u 99,1 89,9 87,1 82,5 82,3 odnosu na etalon - Δfs (%) Tabela 6: Rezultati ispitivanja prianjanja Oznaka serije M1 M2 Svojstvo Tip loma (%) 90a+10m 95a+5m Napon prianjanja fat (MPa) 4,19 3,27 Kao uslov otpornosti cementnih kompozita na dejstvo 10±1 mm. Nakon 28 dana mešovite nege, na svakoj mraza uglavnom se usvaja održanje čvrstoće pri pritisku ploči je urezano 5 cilindričnih zareza koji zalaze i u od 75% (SRPS U.M1.016 [18]). Nakon 25 ciklusa masu kamena (slika 2). Za ocenu adhezije smrzavanja i odmrzavanja, kod opitnih tela nije (prionljivosti), po standardu SRPS EN 1015-12 [15] su registrovan gubitak mase. Prilikom vizuelnog pregleda, dovoljna 3 uspešna ispitivanja uzoraka. nije primećeno ljuštenje, niti pojava prslina na površini Na površinu maltera je uz pomoć epoksi smole uzoraka. Na osnovu rezultata ispitivanja može se uočiti zalepljen metalni pečat. Nakon montiranja ispitne da su sve serije maltera zadržale čvrstoću pri pritisku i aparature, nanosi se normalna sila zatezanja i beleže se savijanju u procentu višem od 75%. sile loma uzoraka (slika 2). Rezultati ispitivanja prianjanja su prikazani u okviru tabele 6. 3.4 Ispitivanje prianjanja Ispitivanje prianjanja maltera za kamenu podlogu je Kao minimalni napon prianjanja preporučuje se vršeno u skladu sa standardom vrednost od 0,5 MPa, odnosno, da napon prianjanja pri SRPS EN 1015-12 [15]. Kao podloga za ispitivanje adhezionom lomu bude veći od čvrstoće pri zatezanju prianjanja su korišćene kamene ploče granita "Šutica" samog maltera [19]. U ovom slučaju pogodno je da dimenzija 30x30x4 cm koje su dobijene standardnim čvrstoće pri zatezanju komponentnih materijala budu rezanjem. Ispitivanja su vršena na dve vrste veće od iznosa adhezije, a takođe i ostvarenje lakoagregatnih maltera – serije M1 i M2. Kamene ploče mešovitog loma. su neposredno pre nanošenja maltera potapane u vodu, a zatim je suvišna voda uklonjena kako bi se malterska Prikazani rezultati ispitivanja ukazuju da napon mešavina nanela na površinski suvu podlogu u sloju od prianjanja kod svih uzoraka prelazi granicu od Primena cementnih kompozita na bazi sintetičkih vlakana za prefabrikovane fasadne panele 57 preporučenih 0,5 MPa. Uzorci pokazuju mešoviti tip površinski suve polažu u kalup sa licem na dole. Malter loma - sa dominantnim adhezionim tipom loma preko se nanosi preko pločica i ugrađuje u kalupe na vibro- dodirne površine dva materijala i propratnim lomom stolu. Mešovita nega od 28 dana se vrši po prethodno preko površine kamena. utvrđenom režimu. Lice od kamena je polirano, da bi preko tako obrađene površine uzorci kapilarno upijali 3.5 Ispitivanje eflorescencije vodu. Mogućnost pojave eflorescencije je ispitivana na Ispitivanje eflorescencije je vršeno prema američkom uzorcima dimenzija 10x60 cm. U sastav uzoraka ulaze standardu ASTM C67-14 [16] koji je namenjen granitne pločice dimenzija 10x10x1 cm i malterska proizvodima od opeke. Tri uzorka su postavljena na smeša sa polipropilenskim vlaknima M1. Uzorci su distancere i potopljena sa licem od kamena na dole u spravljeni u kalupima od blažujke unutrašnjih destilovanu vodu, tako da je svaki bio 15 mm pod dimenzija 10x60x3,5 cm. Kamene pločice su vodom. U vodu je uronjena cela kamena pločica i pripremljene potapanjem u vodu iz gradskog vodovoda. cementni malter u visini od 5 mm. Nakon 7 dana u vodi, Nakon ukljanjanja viška vode sa pločica, one se uzorci su sušeni u sušnici na temperaturi od 110-115 ºC a) b) Slika 3: Ispitivanje uzoraka na potencijalnu pojavu eflorescencije: a)i spitni uzorci, b) kapilarno upijanje vode preko finalno obrađenog – poliranog lica od kamena . Slika 4. Izrađen fasadni panel 58 T. Vojnović Ćalić, D. Jevtić, D. Zakić do konstantne mase (slika 3). Nakon ispitivanja uzoraka 4. ZAKLJUČAK vizuelno-makroskopskim pregledom, ustanovljeno je U radu su prikazani rezultati sopstvenih istraživanja da oni nisu pokazali znake eflorescencije. osnovnih fizičko-mehaničkih svojstava lakoagregatnih mikroarmiranih cementnih kompozita koji mogu ući u 3.6 Ispitivanje čvrstoće pri savijanju sastav predloženog fasadnog panela, kao i osnovne Nakon izvršenih ispitivanja serija cementnih karakteristike pomenutog pilot elementa. Na osnovu kompozita, pristupilo se planiranju i izradi fasadnog istraživanja maltera može se jasno uočiti porast pilot elementa. Ovaj element je projektovan kao vrednosti skupljanja usled sušenja i upijanja vode uzoraka sa agregatom od drobljene opeke u odnosu na dvoslojni sistem. Podloga je sačinjena od etalonske mešavine. I pored povećanog upijanja, može lakoagregatnog cementnog kompozita sa se zaključiti da su svi ispitani uzorci otporni na mraz. polipropilenskim vlaknima tipa M1, dok je lice sačinjeno od lokalnog kamena – granita "Šutica". Adhezija lakoagregatnih mikroarmiranih cementnih Obloga od kamenih pločica (10x10 cm) je projektovana kompozita za površinu od kamena je ocenjena kao debljine 1 cm, podloga od primenjenog maltera 2,5 cm, povoljna, sa vrednošću višom od 0,5 MPa i mešovitim a konačne dimenzije fasadnog pilot elementa su iznosile tipom loma. Nakon ispitivanja, pripremljeni uzorci nisu 60x60x3,5cm. Prianjanje dva sloja panela je pokazali znake eflorescencije. Ispitivanjem pilot ostvarivano polaganjem svežeg cementnog maltera fasadnog elementa dimenzija 60x60x3,5cm postignuto direktno na poleđinu kamenih pločica prilikom procesa je zbirno opterećenje od 5,13 kN. izrade. Postupak izrade je sledio isti tok kao kod izrade U skladu sa trendom održivosti, u okviru predloženog uzoraka za ispitivanje eflorescencije (slika 4). fasadnog panela korišćeni su reciklirani materijali u Što se tiče fasadnih ploča od kamena, kao minimalan vidu agregata od drobljene opeke i lokalni kamen – obim ispitivanja se pominju čvrstoća pri savijanju i sila granit "Šutica". Dalje se predlaže se da se fasadni loma na mestu veze sa potkonstrukcijom [20], [21], element primeni u okviru ventilisanog fasadnog sklopa. [22], [23]. Povlačeći paralelu sa predmetnim panelom, Tako bi se, cirkulacijom vazduha unutar provetrenog pristupilo se ispitivanju postepenim dodavanjem međuprostora, omogućavalo pasivno hlađenje fasadnog opterećenja na lice od kamena. Pri ispitivanju, fasadni zida tokom letnjeg perioda. U smislu životnog ciklusa pilot element je postavljen na linearne oslonce na materijala, ovi paneli se takođe mogu dalje reciklirati i međusobnom razmaku od 55 cm. Postignuta je zbirna ponovo upotrebiti u vidu agregata. sila od 5,13 kN, a naneto jednako podeljeno opterećenje nije dovelo do loma ispitivanog elementa (slika 5). a) b) Slika 5. Ispitivanje fasadnog pilot elementa: a) ispitna kompozicijai, b) tok ispitivanja Primena cementnih kompozita na bazi sintetičkih vlakana za prefabrikovane fasadne panele 59 ZAHVALNOST LITERATURA U radu je prikazan deo istraživanja koje je pomoglo 1. European Commission. Directive 2008/98/EC of Ministarstvo prosvete, nauke i tehnološkog razvoja the European Parliament and of the Council of 19 Republike Srbije u okviru tehnološkog projekta TR November 2008 on Waste and Repealing Certain 36017 pod nazivom: „Istraživanje mogućnosti primene Directives (Waste Framework Directive) (2008). otpadnih i recikliranih materijala u betonskim European Commission: Brussels, Belgium, pp. 3– kompozitima, sa ocenom uticaja na životnu sredinu, u 30. cilju promocije održivog građevinarstva u Srbiji“. 2. Corinaldesi, V., Giuggiolini, M., & Moriconi, G. (2002). Use of rubble from building demolition in mortars. Waste Management, 22, 893-899. 3. Radoičić, V. (1997). Beton na bazi reciklirane opeke armiran polipropilenskim vlaknima. Magistarska teza, Građevinski fakultet Univerziteta u Beogradu. 4. Vytlačilová, V. (2011). The fibre reinforced concrete with using recycled aggregates, International Journal of Systems Applications, Engineering & Development, 5(3), 359-366. 5. Jevtić, D., i Zakić, D. (2006). Mikroarmirani malteri i betoni – mogućnost poboljšanja fizičko- mehaničkih svojstava. Materijali i konstrukcije, 49(3/4), 35-44. 6. Jevtić, D., Zakić, D., i Harak, S. (2002). Ispitivanje različitih tipova maltera spravljenih na bazi opekarskog loma. Materijali i konstrukcije, 45, 60- 63. 7. Harak, S. (2001). Izbor građevinskog materijala za malter na bazi opekarskog loma na osnovu ispitivanja tržišta i uzoraka materijala. Diplomski rad, Građevinski fakultet Univerziteta u Beogradu. 8. Sika. http://srb.sika.com/ 9. Kuraray. http://www.kuraray.eu/en/ 10. SRPS EN 1015-3: Metode ispitivanja maltera za zidanje – Deo 3: Određivanje konzistencije svežeg maltera (pomoću potresnog stola) (2008). Institut za standardizaciju Srbije. 11. SRPS EN 1015-11: Metode ispitivanja maltera za zidanje – Deo 11: Određivanje čvrstoće pri savijanju i čvrstoće pri pritisku očvrslog maltera (2008). Institut za standardizaciju Srbije. 12. SRPS B.C8.029: Cement – Skupljanje cementnog maltera usled sušenja (1979). Institut za standardizaciju Srbije. 13. SRPS B.B8.010: Ispitivanje prirodnog kamena – Određivanje upijanja vode (1980). Institut za standardizaciju Srbije. 14. SRPS U.M8.002: Malteri za zidanje i malterisanje – metode ispitivanja (1997). Institut za standardizaciju Srbije. 15. SRPS EN 1015-12: Metode ispitivanja maltera za zidanje – Deo 12: Određivanje čvrstoće prianjanja očvrslih maltera za unutrašnja i spoljašnja oblaganja na podloge (2008). Institut za standardizaciju Srbije. 16. ASTM C67-14: Standard Test Methods for Sampling and Testing Brick and Structural Clay Tile (2009). ASTM International. 60 T. Vojnović Ćalić, D. Jevtić, D. Zakić 17. SRPS EN 1015-6: Metode ispitivanja maltera za Construction and Building Materials, 25, 3966- zidanje – Deo 6: Određivanje zapreminske mase 3971. svežeg maltera (2008). Institut za standardizaciju 22. Crnković, B., i Šarić, Lj. (2012). Građenje Srbije. prirodnim kamenom. Zagreb: UPI.2M PLUS. 18. SRPS U.M1.016: Beton – Ispitivanje otpornosti 23. Yu, J. Y. H., & Chan, S. L. (2001). Practice and betona prema dejstvu mraza (1992). Institut za testing of stone cladding in Hong Kong. standardizaciju Srbije. http://88.198.249.35/preview/2slqmYRsQTcNraJR 19. German Institute for Construction Engineering. vnLlRt2Kw9jhsPE_PvM81GpeswQ,/ Practice- (2008). General approval by the building and-testing-of-stone-cladding-in-Hong- inspectorate: Ventilated external wall cladding Kong.html?query=Granite-Cladding „Airtec Stone“. 24. Vojnović, T. (2015). Modeli tehnologije oblaganja 20. Lammert, B. T., & Hoigard, K. R. (2007). Material fasada kompozitnim panelima sa licem od kamena. strength considerations in dimension stone Doktorska disertacija, Arhitektonski fakultet anchorage design. Journal of ASTM Univerziteta u Beogradu.Infrastructure: Project International, 4(6), 40-57. description; March 2014 21. Pires, V., Amaral, P. M., Rosa, L. G., & Camposinhos, R. S. (2011). State flexural and anchorage considerations in cladding design. Effect of types and length of fibres in reinforcement concrete structures Vpliv vrst in dolžine vlaken v armirano betonskih konstrukcijah Naser Kabashi, Cene Krasniqi, Enes Krasniqi Department of Civil Engineering, University of Prishtina, Prishtina, Kosovo Hysni Morina Institute of Building Materials and Structures –IBMS, Prishtina, Kosovo Abstract Fibre-reinforced concrete (FRC) often referred as micro reinforcing concrete is defined as concrete containing relatively short and discontinuous fibres. Fibres used in FRC may differ in terms of origin (steel, carbon, glass, polypropylene etc.), length (micro-fibres, macro-fibres), shape (straight, hooked, fibrillated etc.) diameter etc. consequently resulting in concrete behavior. The addition of fibres, even at low fibre content, affects in post-cracking toughness and ductility of the concrete. Because of three dimensional dispersing, discrete nature and high mechanical properties, the main application is oriented in concrete elements to control plastic shrinkage cracking, improve fatigue strength, generally in structural parts where reinforcement is not statically required. Fibres improves also the tensile strength of concrete and therefore holds the potential for reducing or even eliminating the conventional bar reinforcement. Nevertheless the application for this tendency is still limited. Firstly there is no generally accepted design method and very complicated determination of post cracking behavior. Various abovementioned parameters tend to influence post cracking behavior and principally complicates to structure a general design method even though there are some design proposals, recommendation or standards. Nowadays fibres are commercially available and affordable. The tendency now is to define the improvement in tensile strength of concrete and if they will partially or fully replace the conventional steel bars in structural members. The experimental program of this study conclude results of 27 standard concrete beams with various fibres in term of origin, shape, length, diameter and fibre content. For comparative approach, reference specimens were cast without fibres. For polypropylene specimens, increasing the fiber ratio affects in pre-cracking behavior but the ratio taken for this experiment, didn’t archive the nominal fibre content in order to influence the post-cracking behavior. Specimens with steel fibres excluding the specimens with 0.25% volume, have enhanced post-cracking tensile behavior and improved crack control. Povzetek Z vlakni ojačeni beton, ki se pogosto imenuje mikroarmirni beton (MAB), je opredeljen kot beton, ki vsebuje razmeroma kratka in diskontinuirana vlakna. Vlakna, ki se uporabljajo v MAB, se lahko razlikujejo glede na poreklo (jeklo, ogljik, steklo, polipropilen itd.), dolžino (mikro vlakna, makro vlakna), obliko (ravne, kljukaste, fibrilirane itd.), premer itd. in posledično vplivajo na obnašanje betona. Dodana vlakna, tudi pri nizki vsebnosti, vplivajo na žilavost po razpokanju in duktilnost betona. Zaradi tridimenzionalne razporeditve in visokih mehanskih lastnosti je glavna aplikacija usmerjena v betonske elemente za nadzor razpok zaradi plastičnega krčenja, izboljšanje odpornosti na utrujenost, običajno v konstrukcijskih delih, kjer armatura ni statično potrebna. Vlakna izboljšajo tudi natezno trdnost betona in zato imajo potencial za zmanjšanje ali celo odpravo običajne armature. Kljub temu je uporaba te težnje še vedno omejena. Prvič, ni splošno sprejeta metoda projektiranja in zelo zapletena določitev obnašanja po razpokanju. Različni zgoraj navedeni parametri vplivajo na obnašanje po razpokanju in v glavnem zapletajo strukturo splošne metode projektiranja, čeprav obstajajo predlogi, priporočila ali standardi. Danes so vlakna na voljo na tržišču in cenovno dostopna. Zdaj je težnja, da se opredeli izboljšanje natezne trdnosti betona in ali bodo vlakna delno ali v celoti nadomestila konvencionalne jeklene palice v konstrukcijskih elementih. V eksperimentalnem programu te študije so bili ugotovljeni rezultati 27 standardnih betonskih nosilcev z različnimi vlakni glede na izvor, obliko, dolžino, premer in njihovo vsebnost. Zaradi primerjave so bili izdelani referenčni vzorci brez vlaken. Pri vzorcih s polipropilenskimi vlakni, povečanje vsebnosti vlaken vpliva na obnašanja pred razpokanjem, vendar vsebnost, 26. slovenski kolokvij o betonih – Projektiranje mikroarmiranih betonskih konstrukcij in njihove aplikacije, Ljubljana, 16.5.2019 62 N. Kabashi, C. Krasniqi, E. Krasniqi, H. Morina uporabljena za ta poskus, ni bila takšna, da bi vplivala na obnašanje po razpokanju. Vzorci z jeklenimi vlakni, razen vzorcev z 0,25-odstotnim volumnom, imajo izboljšano natezno obnašanje po razpokanju in boljšo kontrolo razpok. Keywords: Fibre-reinforced concrete, residual flexural strength, steel fibres, polypropylene fibres Ključne besede: mikroarmirani beton, rezidualna upogibna trdnost, jeklena vlakna, polipropilenska vlakna 1. INTRODUCTION 2. EXPERIMENTAL PROGRAM Concrete is characterised by brittle-failure, nearly The following part of papers describe the most complete loss of loading capacity, from beginning the important features of the experimental test. All the tests failure is initiated. This characteristic, which limits the described in this paper were performed following the applications of the material in many cases request to guidelines given by EN 14651:2005 and EN improve the behaviour parameters, can be overcome by 14845:2006. using the optimal amount different types of fibres with different characteristics (steel, glass, synthetic and 2.1. Materials natural). The using of fibres can be practiced in remedy In the present work three different types of fibres were weaknesses of concrete such as resistance, shrinkage, used: macro-synthetic fibres; micro synthetic fibres and cracking, ductility etc. a steel fibre. Figure 1 shows the fibres used and Table 1 Steel fibres remains the most used fibres followed by gives details on their geometry (length, lf, and diameter, polypropylene, glass and other fibres. Studies have df) and on their mechanical properties (elastic modulus, ′ shown that the addition of steel fibres and E, and tensile strength, 𝑓𝑡 ) polypropylene fibres in a concrete matrix improves all For each of type of fibres we apply three different the mechanical properties of concrete, especially tensile dosage , and in combinations we prepare the nine sets strength, impact strength, and toughness. The influence of prismatic samples for testing and one set of plain of polypropylene fibres with different proportioning concrete for comparison during the presentation the and fibre length improve the performance of results. Paralely we prepare the cubic samples (150 x mechanical characteristics. Different types of fibres 150 x 150)mm for verify the compressive strength. The used in two different lengths (12mm, 25 mm and 50-60 dosage of fibres is calculate in mass for cubic meter of mm) and different fibre proportions by weight in the concrete , considering the each type of fibres and also mixture design. The resulting material possesses higher dosage suggesting from the manufacturer. tensile strength, consolidated response and better ductility. 2.2. Test procedure This paper describes the results of an extensive The test procedure consist with guidelines given in EN experimental work performed at Laboratory of 14651: 2005 using the prismatic specimens with Materials and Structural Engineering of the University dimension 150x150 x 600 mm, testing in three point of Prishtina. In this test we used the same mix design in bending , presenteded in figure 2. The specimens are order to emphasise the influence of fibres. Several notched at mid span with hight of notch 25 mm. The concrete beams were casted using different types and specimens were cured in laboratory conditions and ratios of steel and macro-micro -polypropylene fibres prepared for testing after 28 days. Loading was where after curing in determined condition, specimens performed according to a deformation control. The were tested in a three-point bending scheme. method allows to measure force-displacement or force- CMOD (crack mouth opening displacement) relations. One transducer is installed to the specimen at mid-depth directly over supports to measure corresponding Fig 1: Macro fibres, steel fibres and micro fibres. Effect of types and length of fibres in reinforcement concrete structures 63 Table 1: Type , geometry and mechanical properties of fibres Series Reference Fiber type Length Tensile strength Modulus of elasticity E No. lf (mm) ft (Mpa) (Mpa) I SPPM1 Monofilament 12 600-700 3000-3500 polypropylene II SPPF1 Fibrillated 25 275-415 4100 4200 - polypropylene III SSF1 Steel 50-63 1000-1100 206000 Table 2: Fibre content in different set of samples Reference No. of Fiber type Amount Volume specimens of fibres kg/m3 % SPPM1 3 Monofilament 0.6 0.063 polypropylene SPPM2 3 Monofilament 0.7 0.074 polypropylene SPPM3 3 Monofilament 0.9 0.095 polypropylene SPPF1 3 Fibrillated 0.6 0.063 polypropylene SPPF2 3 Fibrillated 0.7 0.074 polypropylene SPPF3 3 Fibrillated 0.9 0.095 polypropylene SSF1 3 Steel 19.62 0.25 SSF2 3 Steel 39.25 0.5 SSF3 3 Steel 58.87 0.75 deflection. Another transducer mounted at the tip of the batches. This parameter is very important parameter and notch to measure the crack tip opening displacement comparison is always with plain concrete . During the (CTOD). During the flexure testing, the same rate of the casting process some properties of fresh concrete were CMOD is maintained during the process. All the tests meseaured: slump and density. The results are were ended when the specimens fails (PPM and PPF presented in table 3. The cementious content in beams) or CMOD exceeds 4mm. concrete mix was fixed at 370 kg/m3. The water- cementious ratio (W/C=0.52) and was kept constant in all mixes. All mixures including the control mixture 3. RESULTS OF THE EXPERIMENTAL were prepared with same ingredients. The control ANALYSES mixture –plain concrete contained no fibres. Fiber 3.1. Properties of the fresh concrete reinforced concrete (FRC) differ from each other (each set) from volume fraction Vf presented in Table 2.. To compare the mechanical properties using different Minor volume fraction Vf for samples with types of fibres, we take in considerations the stability polypropylene is done according to manufacturer and workability of fresh concrete matrix in different 64 N. Kabashi, C. Krasniqi, E. Krasniqi, H. Morina instruction and our intent to see effects of small amount Displacement) values were measured in each test. The of fibres. testing results present the increasing CMOD in the peak load (FL) with the increasing of volume of fibres Vf. In The preparing and maintenance the samples till testing specimens with minimum volume of fibres (PPM and are presented in fig.3. PPF) especially specimens with amount 0.6 kg/m3 ratio, in term of Load-CMOD response, just minimum 3.2. Flexural test and residual strength improvement. Testing procedure will lead to evaluate the relations: Load-CMOD (Load-Crack mouth opening For polypropylene specimens, increasing the fiber ratio affects in pre-cracking behavior but the ratio taken for Fig 2: Experimental setup for flexure test of notched specimens. Fig 3: Preparing, maintaining and examinating FRC specimens Comparison approach for PPM 12 Comparison approach for PPF 25 speciments speciments 40 40 30 30 m) m) 20 (µ (µ 20 10 OD OD 10 0 M M C 1 3 5 7 8,5 9 11 12,3 13 C 0 -10 1 3 5 7 8,5 10 12 12,5 13,5 -20 -10 Load (kN) Load (kN) F1 600 PP12 F2 700 PP12 F1 600 PPF25 F2 700 PPF25 F3 900 PP12 Control F3 900 PPF25 Control Fig 4: Effect of PPM 12 in relations Load-CMOD Effect of types and length of fibres in reinforcement concrete structures 65 Table 3: Properties of the fresh concrete measured during the casting of the different sets of specimens Reference No. of Fiber type Slump Density specimens kg/m3 mm SPPM1 3 Monofilament 60 2380 polypropylene SPPM2 3 Monofilament 65 2380 polypropylene SPPM3 3 Monofilament 63 2380 polypropylene SPPF1 3 Fibrillated 62 2380 polypropylene SPPF2 3 Fibrillated 60 2380 polypropylene SPPF3 3 Fibrillated 63 2380 polypropylene SSF1 3 Steel 57 2399 SSF2 3 Steel 60 2419 SSF3 3 Steel 61 2438 SPC 3 Plain concrete 60 2380 this experiment, didn’t archive the nominal fibre 3∙𝐹 𝑓𝑓 𝑙 ∙𝑙 𝑐𝑡,𝐿= (Mpa), (1) 2 content in order to influence the post-cracking behavior. 2∙𝑏∙ℎ𝑠𝑝 Specimens with steel fibres excluding the specimens Where: b (150mm), hsp (125mm) and L (450mm) are with 0.25% volume, have enhanced post-cracking geometrical parameters of testing samples. tensile behavior and improved crack control. Since it is the post-cracking behavior that is affected, the In testing process the residual flexural tensile strengths characteristic residual tensile strength is the parameter fR,1, fR,2, fR,3 and fR,4 at the CMOD value of 0.025mm, governing the effects of fibres, presented in fig. 5. 0.05mm, 0.5mm and 3.5mm were computed using the following equations: The increase in the residual load carrying capacity with increasing CMOD indicates that the steel fibres are 3∙𝐹 𝑓 𝑅,𝑗 ∙𝑙 (Mpa), (2) effective in providing crack closing stresses with 𝑅,𝑗= 2∙𝑏∙ℎ2𝑠𝑝 increasing crack opening. The CTOD provides a qualitative measure of the crack opening when the load Residual tensile strengths fR,1 and fR,2 corresponds to recovery is initiated. Increasing the fiber volume specimens with polypropylene fibres and have minor content increases the resistance to crack openings. influence in post cracking behavior were in the meantime fR,3 can be used in the verification of the With reference to the curves experimentally recorded, serviceability limit states and fR,4 is applied in the the load at the limit of proportionality FL, the ultimate limit state analysis. corresponding strength f fct,L, and the residual flexural strengths f for different testing sets with results is presented in R,j were evaluated according to EN 14651 . Based on this recommendation, the load limit of Table 4. proportionality ( FL) is equivalent to the highest value of The strengths at the limit of proportionality reach the load recorded up to CMOD value of 0.05mm, and similar values, and it’s not affected by the increase of the strength corresponding to the limit of the fiber volume content, while the residual strengths proportionality (LOP) which can be calculated using the fR,1, fR,2, fR,3 and fR,4 increase about from (10 -23)% for following equations : specimens with steel fibers while for specimens with 66 N. Kabashi, C. Krasniqi, E. Krasniqi, H. Morina Table 4: Three point bending tests, tensile strength parameters F 𝑓 L 𝑓 fR,4 (Mpa) 𝑐𝑡,𝐿 (Mpa) fR,1 (Mpa) fR,2 (Mpa) fR,3 kN (Mpa) SPPM1 8.9 2.56 2.02 2.56 N/A N/A SPPM2 13.5 3.78 3.65 3.78 N/A N/A SPPM3 N/A N/A 3.53 N/A N/A N/A SPPF1 13.15 3.78 3.72 3.78 N/A N/A SPPF2 N/A N/A 3.47 N/A N/A N/A SPPF3 13.10 3.77 3.69 3.77 N/A N/A SSF1 13.60 3.91 3.80 3.92 N/A N/A SSF2 12.50 3.60 3.51 3.60 3.70 4.0 SSF3 13.40 3.86 3.96 4.06 4.11 5.21 *Note; N/A not achievable polypropylene fibers deviate while and residual 𝑃 𝑓 𝑙𝑓 ∙𝑙 𝑙𝑓 = (Mpa), (3) strengths f 𝑏∙(ℎ−𝑎 R,3 and fR,4 are unreachable. 0 )² The results of specimens with steel fibres (SFF2 and Where b (150 mm), h (150 mm), and l (450 mm) are SFF3) were analyzed using procedure given in UNI width, the height, and the span of the specimen, 11039-2 because they interfere in post-cracking respectively, and 𝑎0 (25mm) is the height of the notch. behavior. The first crack nominal strength represents Plf corresponds to the value of the load recorded for a the matrix behavior: crack tip opening displacement equal to CTOD0. The parameters feq(0-0.6) and feq(0.6-3) are the average nominal Fig 5: Effect of SSF in relations Load-CTOD. Effect of types and length of fibres in reinforcement concrete structures 67 Table 5: Corresponding strength values according UNI 11039-2 Plf (kN) flf (Mpa) feq(0-0.6) feq(0.6-3) SPC 12.21 3.51 SFF2 12.50 3.60 2.74 15.21 SFF3 13.40 3.86 3.22 18.17 *SPC-Usually plain Concrete stresses in the CTOD range between 0-0.6 mm and 0.6- fraction of fibres doesn’t influent the ductile behavior, 3 mm, respectively. These two parameters are the post- in contrary, a few parameters such as volume fraction, cracking equivalent strengths useful for the fiber length and modulus of elasticity tend to improve serviceability limit state and for the ultimate limit state brittle failure. Fibres on the fracture surface didn’t that can be computed using the following expressions: bridge the cracks and behave inactive like voids or errors in concrete matrix. 𝑙 𝑈 𝑓 1 𝑒𝑞(0−0.6)= ∙ (Mpa), (4) 𝑏∙(ℎ−𝑎0 )² 0.6 4. CONCLUSIONS 𝑙 𝑈 𝑓 1 𝑒𝑞(0−0.6)= ∙ (Mpa), (5) 𝑏∙(ℎ−𝑎0 )² 0.6 The present work investigate the flexural behaviourof notched beams made of concretes fibre-reinforced with where U1 and U2 can be evaluated: different types and amounts of fibres. 0.6 𝑈1= ∫ 𝑃(𝐶𝑇𝑂𝐷)𝑑 (𝐶𝑇𝑂𝐷) (6) 0  Fiber volume content plays a significant role while small amount of volume fraction tend to have no 3 𝑈2= ∫ 𝑃(𝐶𝑇𝑂𝐷)𝑑 (𝐶𝑇𝑂𝐷) (7) 0.6 influence in post-cracking behavior and very small fraction tend to have a negative impact. It can be seen that there is an increasing trend in the first crack strength with increasing fiber content alongside  Short, low modulus and small volume fraction of the values of feq(0-0.6) and feq(0.6-3) show clear fibres tend to improve the brittle failure of concrete. improvement on increasing the Vf from 0.5% to 0.75%.  The residual strengths increase about 10% and 23% In the case of plain concrete, a brittle failure occurred related to fibre volume content for specimens with by separating the elements into two parts. Adding small steel fibers while for specimens with Comparison approach for SSF2, Comparison approach for F1 600 SSF3 and plain concrete at low PPF25 and plain concrete stages of loading 6 0,15 4 2 0,1 ) ) 0 N m (k -2 (m ad 0,05 -4 Lo -6 CMOD 0 -8 1 3 5 7 8,5 10 12 12,8 -10 CTOD (µm) -0,05 Load (kN) Load increment F1 600 PPF25 F2 0.5 SSF F3 0.75 SSF Control Control Fig 6: Examples. 68 N. Kabashi, C. Krasniqi, E. Krasniqi, H. Morina polypropylene fibers deviate and the residual 4. Sahith Gali, Kolluru V. L. “Evaluation of crack strengths for ultimate limit state and service limit propagation and Post-cracking Hinge-type state are unreachable. Behavior in the Flexural Response of Steel Fiber Reinforced Concrete” , International Journal of  Data obtained from experimental work confirmed Concrete Structures and Materials, Vol.11, No.2, that the addition of steel fibres with corresponding pp.365-375, June 2017 aspect ration into concrete matrix, significantly 5. EN 14651, Test method for metallic fibre concrete- improves the post-peak behavior. Measuring the flexural tensile strength (limit of  At fiber volume content equal to 0.75% there is a proportionality (LOP), residual). European significant decrease in the crack depth for a given Committee for Standardization, B-1050 Brussels¸ crack tip opening displacement which improves the September 2007. post peak load resistance response in flexure. 6. N.Kabashi,Sh.Dermaku,C.Krasniqi.”The effects of polypropylene fibers on the energy-absorption SCOPE FOR FURTHER STUDY capabilities of reinforced concrete beams; The Ready Mix Concrete, Istanbul Octomber 20- Based on results of this study there are many scope for 22.2011; pp 542-549; ISBN:978-975-92122-7-8 further study, but below are listed only the basic points what is important to know further about used the 7. ACI 544.3.Indirect Method for Obtaining a Model different types of fibres in improvement the ductility, Stress-Strain Curve of Strain Softening FRCs;2007 focused on: 8. Miss Komal Bedi” Experimental Study For Flexure Strength On Polypropylene Fiber Reinforced  Improvement the post cracked stage in flexural Concrete”IOSR Journal of Mechanical and Civil load applied Engineering (IOSR-JMCE),2014  Experimental verifications the amount of different 9. F.A.Olutoge, V. Bhashya, G. Ramesh, B. type of fibres , not just orientated amount based on Hanumantharai, S. Sundar Kumar.” Evaluation of the manufacture specifications Residual Strength Properties of Steel Fiber Reinforced Concrete” Journal of Emerging Trends  Analyzing the analytical model of the behavior the in Engineering and Applied Sciences,2013 beams under loading process for different types of 10. EN 14845-1:2007. Test Methods for Fibres for loadings. Concrete-Part 1-Reference Concretes , 2007 11. Abbas H. Mohammed, Khattab Saleem Abdul- Razzaq, Raad D. Khalaf, Ali K. Hussein.” Suggesting Deflection Expressions for RC Beams” REFERENCES International Journal of Civil Engineering and 1. Ahmad, A. Di Prisco, M. Meyer, C. Plizzari, G.A. & Technology (IJCIET),2019 Shah, S.P. “ Fiber reinforced concrete: from theory to practice” , Bergamo, 24 12. N.Kabashi,Q.Kadir,C.Krasniqi.”Flexural Behavior - 25 September ,2004 of the Concrete Beams Reinforced with the GFRP 2. EN 14651:2005.”Test method for metallic fibres and Cracks analyses” Journal: Bulletin of the concrete-Measuring the flexural tensile strength Transilvania University of Brasov, (limit of pro-portinality)(LOP), residual Romania,CIBv,2017Commission, EUROPE 2020: 3. Soroushian,P.&Lee,C.D.” Distribution and A strategy for smart, sustainable and inclusive orientation of fibres in steel fiber reinforced growth, COM(2010)2020. concrete ”,ACI Materials Journal, 87(5),p.p. 262- 278 Krčenje mikroarmiranih betonov visoke trdnosti v zgodnjem obdobju Shrinkage of Fiber Reinforced High Strength Concrete at Early Ages Drago Saje in Jože Lopatič Univerza v Ljubljani, Fakulteta za gradbeništvo in geodezijo, Ljubljana Povzetek V članku je predstavljen in opisan fenomen krčenja mikroarmiranih betonov visoke trdnosti v zgodnjem obdobju, ki smo ga eksperimentalno preiskovali. Znaten del obravnavanega krčenja se odvije v obliki avtogenega krčenja. Različne vrste vlaken na zgodnji reološki pojav vplivajo s svojo togostjo, ki ovira proces krčenja. Vlaka vplivajo na avtogeno krčenje še s svojo sposobnostjo vpijanja vode in oddajanja le te v kompozit v času intenzivne hidratacije. V okviru eksperimentalnega programa smo v betone vgrajevali različne vrste mikroarmature: kratka in dolga jeklena vlakna, suha in predhodno namočena polipropilenska vlakna, predhodno namočena bazaltna vlakna ter predhodno namočena celulozna vlakna. Prostorninski delež vsebovanih vlaken v preiskovanih betonih znaša 0,75%, razen pri celuloznih vlaknih, kjer je znašal 0,33%. Zaradi primerjave krčenja mikroarmiranega betona s krčenjem betona brez mikroarmature smo merili tudi krčenje primerljivega betona enake sestave, ki ni vseboval mikroarmature. Ugotovili smo, da so imela največji vpliv na velikost avtogenega krčenja v zgodnjem obdobju predhodno namočena polipropilenska vlakna. Zmanjšanje krčenja lahko spremlja tudi zmanjšanje trdnosti betona, česar si ne želimo. Poleg krčenja smo zato merili tudi 28-dnevno tlačno trdnost vseh obravnavanih betonov. V splošnem vlakna zmanjšajo sposobnost vgrajevanja kompozita. Spremljali smo vgradljivost kompozita glede na vrsto vlaken. V naših raziskavah so se celulozna vlakna in suha polipropilenska vlakna, ki so se napila vode, izkazala kot večja motilca vgradljivosti. Abstract The article presents and describes the phenomenon of shrinkage of fiber-reinforced high-strength concrete at an early age. A significant part of the considered shrinkage takes place in the form of autogenous shrinkage. Different types of fibers affect the early rheological phenomenon with their stiffness, which impedes the process of shrinkage. The influence of fibers on autogenous shrinkage is also reflected in the ability of concrete to absorb water and transmit it to the composite during intense hydration. Within the experimental program, various types of fibres were installed in concrete: short and long steel fibers, dry and pre-soaked polypropylene fibers, pre-soaked basalt fibers, pre-soaked cellulose fibers. The volume content of the fibers contained in the tested concrete is 0.75%, except for cellulose fibers, where it amounted to 0.33%. In order to compare the shrinkage of fiber-reinforced concrete with the shrinkage of concrete without fibers, we also measured the shrinkage of comparable concrete of the same composition, but without fibers. We found that pre-soaked polypropylene fibers had the most significant influence on early autogenous shrinkage. Reduction in shrinkage can also be accompanied by a reduction in the strength of concrete, which we do not want. We measured the 28-day compressive strength of all treated concretes. In general, fibers reduce the workability. We monitored the workability of the composite with regard to the type of fibers. In our research, cellulose fibers and dry polypropylene fibers, which had been watered, proved to be a major impediment to workability. Ključne besede: beton visoke trdnosti, mikroarmirani beton, avtogeno krčenje Keywords: high strength concrete, fiber reinforced concrete, autogenous shrinkage elementov konstrukcije [1]. Geometrija vlaken 1. UVOD mikroarmature vpliva na adhezijski stik med vlakni in Vlaknasta mikroarmatura, ki jo dodamo betonu, ovira matrico in preko tega na učinkovitost dodanih vlaken širjenje razpok, in povečuje duktilnost kompozita, ne [2]. Mikroarmatura iz jeklenih ali drugih umetnih vlaken more pa nadomestiti statično potrebne armature vpliva na duktilnost, širino razpok in na reološke 26. slovenski kolokvij o betonih – Projektiranje mikroarmiranih betonskih konstrukcij in njihove aplikacije, Ljubljana, 16.5.2019 70 D. Saje, J. Lopatič lastnosti kompozita [3, 4]. N. Banthia in R. Gupta, ki sta izvajali od trenutka zabetoniranja preizkušancev, pri raziskovala vpliv geometrije polipropilenskih vlaken na čemer smo za začetek merjenja krčenja privzeli čas, ko razpokanost betona zaradi plastičnega krčenja je temperatura vzorca začela naraščati in so se pojavile ugotavljata, da je mikroarmatura iz polipropilenskih prve opazne deformacije preizkušancev. Laboratorijske vlaken zelo učinkovita za omejevanje razpokanosti raziskave krčenja mikroarmiranega betona visoke betona zaradi plastičnega krčenja. Trdita, da v splošnem trdnosti smo izvajali pri prostorninski vsebnosti vlaken polipropilenska mikroarmatura ugodno vpliva na 0,75%, razen pri celuloznih vlaknih, kjer jih je bilo zmanjšanje širine in števila razpok. Pri tem so tanjša 0,33%. vlakna bolj učinkovita od debelejših, in daljša prav tako bolj učinkovita od krajših [5]. 2 OSNOVNI PRINCIP KRČENJA BETONA V Betoni visoke trdnosti se v gradbeni praksi v zadnjem ZGODNJI STAROSTI času čedalje več uporabljajo ne le zaradi visoke trdnosti Po pričetku vezanja cementa se v betonu, odvisno od ampak tudi zaradi večje odpornosti na druge zunanje pogojev nege, pričnejo prostorninske spremembe v vplive. Zaradi zagotavljanja visoke trdnosti je pri obliki krčenja ali nabrekanja. V primeru, da je med betonih visoke trdnosti vodovezivno razmerje procesom hidratacije omogočen neprekinjen dostop razmeroma nizko, zato se ustrezna vgradljivost vode v vse pore cementne paste, se pojavi nabrekanje praviloma zagotavlja z dodajanjem betona. V nasprotnem primeru, ko je gibanje vode v superplastifikatorjev. cementno pasto preprečeno, se beton krči. Ker je v svežem betonu visoke trdnosti proste vode glede Krčenje betona sestoji iz kemičnega krčenja, avtogenega na količino cementa tako malo, da v celoti ne zadošča za krčenja, krčenja zaradi sušenja, plastičnega krčenja, proces hidratacije, se v kemijskem procesu porabi tudi temperaturnega krčenja in krčenja zaradi del vode iz finih por, kar v njih povzroči nastanek karbonatizacije. Avtogeno krčenje betona je posledica podtlakov oziroma nateznih sil, ki delujejo na stene por. samoizsuševanja v porah cementnega kamna, ko se Posledica tega je zmanjšanje prostornine relativno porablja voda v procesu hidratacije cementa. Kemično podajnega še ne otrdelega betona – fizikalni pojav, ki ga krčenje cementne paste je zmanjšanje volumna imenujemo avtogeno krčenje betona. Pri betonih visoke cementne paste, ki se pojavi zaradi kemičnega vezanja trdnosti, za razliko od betonov normalne trdnosti, vode v procesu hidratacije cementa. Pri kemijski reakciji avtogeno krčenje predstavlja znaten del celotnega cementa in vode v betonu se sprošča toplota, kar krčenja betona [6, 7]. Izhlapevanje vode skozi površino povzroči povišanje temperature betona in posledično betona pa dodatno k avtogenemu krčenju povzroča še deformiranje betona zaradi spremembe temperature. krčenje betona zaradi sušenja. Med procesom hidratacije se voda porablja za tvorbo V betonu se praviloma krči cementi gel, oziroma hidratacijskih produktov. Z napredovanjem procesa cementni kamen, medtem ko se zrna agregata iz večine hidratacije se povečuje prostornina por, ki so posledica uporabljenih kamenin praktično ne krčijo oziroma kemičnega krčenja cementne paste. Po Boylovem krčenje cementnega gela celo ovirajo. Iz tega razloga je zakonu je povečanje prostornine zaprtih por povezano z krčenje betona iz agregata, ki je iz kamenine večje zmanjševanjem tlaka zraka v porah. Zmanjševanje tlaka trdnosti manjše od krčenja betona iz agregata, ki je iz posredno vpliva na relativno vlažnost v porah. Ob kamenine manjše trdnosti [7]. Zaradi tega se v cementni vzpostavljanju termodinamičnega ravnovesja v porah pasti in kasneje cementnemu kamnu pojavijo natezne cementne paste izhlapeva najprej prosta kapilarna voda, napetosti, ki v mladem betonu hitro dosežejo natezno nato pa voda iz adsorpcijske ploskve stene pore. trdnost. Dodatne notranje napetosti v času hidratacije Tanjšanje adsorpcijske plasti vode na stenah por cementa pa povzroča tudi temperaturni gradient, ki je povzroča natezne napetosti v adsorpcijski ploskvi. posledica sproščanja hidratacijske toplote v procesu Natezne napetosti v adsorpcijski ploskvi povzročajo strjevanja betona. Posledica obeh omenjenih fizikalnih znatne deformacije, ki se jim struktura upira s svojo pojavov je nastanek zgodnjih razpok betona v času trenutno togostjo. V začetnem obdobju procesa vezanja cementa. strjevanja, ko je modul elastičnosti cementne paste še razmeroma nizek, lahko omenjene natezne napetosti Bayasi in Zeng, ki sta raziskovala vpliv vlaknaste povzročijo velike zunanje deformacije, ki jih imenujemo armature na tlačno trdnost mikroarmiranega betona avtogeno krčenje. običajne trdnosti sta ugotovila, da se tlačna trdnost betona v primeru mikroarmiranja s polipropilenskimi vlakni dolžine l = 1,27 cm pri prostorninski vsebnosti 3 PROGRAM EKSPERIMENTALNIH vlaken 0,1% poveča za 15%, pri prostorninski vsebnosti RAZISKAV vlaken 0,3% pa za 19%, pri vsebnosti vlaken 0,5% pa se Vpliv vrste vlaken na krčenje mikroarmiranega betona trdnost kompozita v primerjavi z betonom brez smo raziskovali pri vodovezivnem razmerju sveže mikroarmature zmanjša za 2,5% [8]. betonske mešanice 0,36. Meritve krčenja kompozita V okviru predstavljenih raziskav smo študirali vpliv smo izvajali na preizkušancih v obliki prizem z različnih vrst vlaken na zgodnje avtogeno krčenje z dimenzijami 10/10/40 cm, na preizkušancih v obliki vlakni mikroarmiranega betona visoke trdnosti. kock z robom 15 cm, pa smo informativno ugotavljali Elektronsko vodeno merjenje avtogenega krčenja smo 28-dnevno tlačno trdnost betona. Na treh prizmah iz vsake mešanice smo merili celotne specifične Krčenje mikroarmiranih betonov visoke trdnosti v zgodnjem obdobju 71 Preglednica 1: Lastnosti uporabljenih jeklenih vlaken Jeklena vlakna Dolžina Izmerjeni dimenziji prečnega prereza Nadomestni premer Natezna trdnost vlaken vlaken de [MPa] [mm] a [mm] b [mm] [mm] IRI 50/16 16 0,491 0,502 0,496 797 IRI 50/30 30 0,491 0,502 0,496 797 Preglednica 2: Lastnosti uporabljenih polipropilenskih vlaken Gostota vlaken Dolžina vlaken Nazivne dimenzije Natezna trdnost vlaken Elastični modul vlaken vlaken [g/cm3] [mm] [MPa] [MPa] [m] 0,91 12 35  250-600 340-500 8500-12500 Preglednica 3: Lastnosti uporabljenih bazaltnih vlaken Gostota vlaken Dolžina vlaken Nazivni premer Natezna trdnost vlaken Elastični modul vlaken vlaken [g/cm3] [mm] [MPa] [MPa] [m] 2,7 12 13 2800-4800 86000-90000 Preglednica 4: Lastnosti uporabljenih celuloznih vlaken Gostota vlaken [g/cm3] 1,1 deformacije mikroarmiranega betona visoke trdnosti, na Preizkušanci so bili mikroarmirani z jeklenimi, s vsaj treh kockah pa 28-dnevno tlačno trdnost. Vsi polipropilenskimi, z bazaltnimi ali s celuloznimi vlakni, preizkušanci za merjenje deformacij so bili ves čas ki so prikazana na slikah 1 do 4, njihove lastnosti pa so hranjeni v klimatski komori pri sobni temperaturi, podane v preglednicah 1 do 4. preizkušanci za določitev tlačne trdnosti pa v vodi. 3.1 Izdelava preizkušancev Preizkušanci mikroarmiranega betona so bili izdelani iz pranega drobljenega apnenčevega agregata z nazivnim največjim premerom zrn 16 mm z dodatkom kremenčeve mivke. Uporabljena sta bila cement CEM II / A-M 42,5 R in CEM I 52,5 R. Za zagotavljanje primerne vgradljivosti pri relativno nizkem vodovezivnem razmerju, je bil uporabljen superplastifikator naftalenskega tipa, ki je po kemijski sestavi sulfonirani naftalen - formaldehid kondenzat. 72 D. Saje, J. Lopatič Preglednica 5: Recepture in lastnosti svežega kompozita preiskovanih preizkušancev Mešanica M1 M2 M3 M4 M5 M6 M7 M8 Fini agregat 0-4 mm  1133 1133 1126 1126 1126 1126 1126 1133 kg/m3 Grobi agregat 4-16 mm  755 755 750 750 750 750 750 755 kg/m3 Količina veziva  400 400 400 400 400 400 400 400 kg/m3 Količina cementa  360 360 360 360 360 360 360 360 kg/m3 Vrsta cementa CEM II CEM I CEM II CEM II CEM II CEM II CEM I CEM I Količina mikrosilike  40 40 40 40 40 40 40 40 kg/m3 Vrsta vlaken - - IRI50/16 IRI50/30 PP PP BV CV Način vgradnje vlaken - - suha suha suha vlažna vlažna vlažna Prostorninski delež - - 0,75 0,75 0,75 0,75 0,75 0,33 vlaken % Vodovezivno razmerje 0,36 0,36 0,36 0,36 0,36 0,36 0,36 0,36 Količina superplastifikatorja 2,05 2,05 2,05 2,05 2,05 2,05 2,05 2,05 [% veziva] Posed cm 18 7,5 17 14,5 8,5 1,5 0,5 0 Razlez cm 55 33,5 43 46 41 38 39 24 Prostorninska masa  2436 2431 2450 2420 2383 2339 2376 2381 kg/m3 fcm,28 dni MPa 81,40 82,96 86,60 92,10 78,15 78,05 76,58 71,04 Izmerjena deformacija pri času 24 ur po -0,210 -0,293 -0,131 -0,139 -0,168 -0,051 -0,300 -0,197 zabetoniranju ‰ Avtogena deformacija pri času 24 ur po -0,216 -0,293 -0,144 -0,165 -0,179 -0,064 -0,301 -0,201 zabetoniranju ‰ Preizkušanci so bili izdelani iz osmih različnih mešanic mešanicah znašala po 400 kg/m3 kompozita, od tega je mikroarmiranega betona visoke trdnosti z vodovezivnim bilo 90% cementa (360 kg/m3) in 10% mikrosilike (40 razmerjem 0,36. Pri tem sta bila mešanici M1 in M2 brez kg/m3). Recepture in lastnosti svežih mešanic vlaken, mešanica M3 je vsebovala kratka jeklena vlakna mikroarmiranega betona so podane v preglednici 5. IRI50/16, M4 dolga jeklena vlakna IRI50/30, M5 suha polipropilenska (PP) vlakna, M6 predhodno navlažena polipropilenska vlakna, M7 predhodno navlažena bazaltna vlakna (BV) in M8 predhodno navlažena celulozna vlakna (CV). Skupna količina veziva je v vseh Krčenje mikroarmiranih betonov visoke trdnosti v zgodnjem obdobju 73 3.2 Priprava predhodno navlaženih vlaken Zaradi zmanjšanja trenja med preizkušancem in podlago V mešanici z oznako M6 smo uporabili polipropilenska oziroma kalupom smo pred vgradnjo betona na dno vlakna, v mešanici M7 bazaltna, v mešanici M8 pa kalupa vstavili teflonsko folijo (slika 6). celulozna vlakna, ki so bila predhodno 24 ur namočena Običajne jeklene kalupe za izdelavo betonskih prizem v vodi. S tehtanjem vlaken in pripravljene količine vode 10/10/40 cm smo za naše meritve priredili tako, da smo pred namakanjem vlaken in po namakanju vlaken smo na končnih stranicah jeklenih kalupov izvrtali luknji ugotovili vsebnost vode v predhodno namočenih skozi katere smo namestili bazne palice za merjenje vlaknih. Navlažena polipropilenska in celulozna vlakna krčenja. Te so bile nameščene tako, da je dolžina merske v cementni pasti služijo kot notranji rezervoar vode [9]. baze znašala 380 mm (slika 6). Temperaturo betona v Podatki o vsebnosti vode namočenih vlaken so razvidni sredini vzorca smo merili s pomočjo termo člena. Zajem iz preglednice 6. Zadržana voda v vlaknih ni upoštevana in obdelava rezultatov meritev specifičnih deformacij v vodovezivnem razmerju. betona sta bila avtomatizirana. 3.3 Izvedba laboratorijskih raziskav 4 REZULTATI EKSPERIMENTALNIH Krčenje preizkušancev smo spremljali neprekinjeno z RAZISKAV elektronsko vodenimi meritvami. Avtogeno krčenje betona smo določali na preizkušancih, ki so bili Rezultati meritev zgodnjega krčenja so v nadaljevanju zatesnjeni z nepropustno polietilensko folijo, ki podani v grafični obliki. Na ustreznih diagramih so preprečuje sušenje preizkušancev. Računalniško podprte podane celotne izmerjene specifične deformacije in meritve specifičnih deformacij zatesnjenih ocenjeno avtogeno krčenje. preizkušancev smo z uporabo elektronskih merilnih uric, izvajali v skladu z japonskim standardom [10] (sliki 5 in 6). Slika 1: Uporabljena jeklena vlakna Slika 2: Uporabljena polipropilenska vlakna Slika 3: Uporabljena bazaltna vlakna Slika 4: Uporabljena celulozna vlakna 74 D. Saje, J. Lopatič Preglednica 6: Vsebnost vode v navlaženih vlaknih Oznaka mešanice in Prostorninski delež vlaken (%) Masni delež vode v navlaženih vlaknih (%) vrsta vlaken M6, 0,75 74 polipropilenska M7, 0,75 31 bazaltna M8, 0,33 55 celulozna Izmerjene časovne spremembe dolžin preizkušancev sredini preizkušancev so bile merjene istočasno z vsebujejo časovne spremembe dolžin zaradi krčenja meritvami sprememb dolžin preizkušancev. Časovni betona in časovne spremembe dolžin zaradi časovnih potek deformacije krčenja preizkušanca je določen s sprememb temperature preizkušancev. Temperature v korekcijo izmerjenih časovnih potekov specifičnih Slika 5 : Spremljanje deformiranja betona v zgodnjem obdobju. Slika 6: Shematični prikaz instrumentacije preizkušanca. Krčenje mikroarmiranih betonov visoke trdnosti v zgodnjem obdobju 75 deformacij na račun temperaturnih raztezkov e ure po betoniranju, je bila upoštevana linearna preizkušancev zaradi časovnih sprememb temperature interpolacija med vrednostjo, ki velja za sveži in (enačba 1). Ker se je temperatura preizkušancev vrednostjo, ki velja za otrdeli beton. Na sliki 7 so kot spreminjala le v času intenzivnega vezanja cementa, to primer prikazane srednje vrednosti meritev temperature je v prvih 24-ih urah, pozneje pa je bila temperatura in celotnih specifičnih deformacij na treh preizkušancih preizkušancev približno enaka temperaturi okolja, je iz mešanice M2 v prvih 24-ih urah po zabetoniranju. vpliv spreminjanja temperature na dejansko časovno Časovni potek deformacij avtogenega krčenja betona spreminjanje dolžine preizkušancev potrebno upoštevati ( ca), ki je določen z upoštevanjem srednjih vrednosti le v prvih 24-ih urah. Časovno spreminjanje dolžine celotnih izmerjenih deformacij ( c) na treh vzorcih in preizkušancev zaradi spreminjanja temperature v času računsko določene temperaturne deformacije intenzivnega vezanja cementa, to je v prvih 24-ih urah, preizkušancev (( T)) zaradi povišane temperature, je za je bilo z upoštevanjem temperaturnega razteznostnega prvih 24 ur prav tako prikazan na sliki 7 s spodnjo koeficienta betona in izmerjenega časovnega krivuljo. spreminjanja temperature ocenjeno analitično. Pri tem je bila za temperaturni razteznostni koeficient svežega   ca= c+( T)= L/ L+T  T. (1) betona upoštevana vrednost  T,f = 1,4810-5, ki je bila določena s posebnimi meritvami [7], za tempe Pri tem so: raturni razteznostni koeficient otrdelega betona pa vrednost  T  L sprememba dolžine preizkušanca na merski bazi = 1,010-5, ki je bila privzeta iz splošne literature. Pri tem je bil beton kot svež upoštevan do časa, ko je začela L merska baza temperatura preizkušanca naraščati, kar približno predstavlja začetek vezan  ja cementa. Od 24-e ure dalje, T sprememba temperature ko se je temperatura preizkušancev ustalila, kar približno pomeni konec intenzivnega vezanja cementa, je bil beton, glede temperaturnega razteznostnega koeficienta, 4.1 Zgodnje avtogeno krčenje mikroarmiranega obravnavan kot otrdeli beton. Temperatura betona visoke trdnosti preizkušancev je bila v tem času konstantna in ni vplivala na časovno spreminjanje dolžine Na slikah 8, 9 in 10 so prikazani časovni poteki preizkušancev, zato je krčenje kompozita v tem času temperature in izmerjenih specifičnih deformacij betona enako izmerjeni spremembi dolžine preizkušancev. Za v prvih 24-ih urah, na slikah 11, 12 in 13 pa ob časovnih vmesne vrednosti temperaturnega razteznostnega potekih temperature še ocenjeni časovni poteki koeficienta v času intenzivnega strjevanja betona do 24- deformacij avtogenega krčenja. Pri tem je bilo avtogeno ε [‰] T [ºC] 0.3 30 M2 0.25 25 temperatura 0.2 20 0.15 15 0.1 10 0.05 5 t [ure] 0 0 0 6 12 18 24 30 -0.05 -5 -0.1 -10 -0.15 -15 -0.2 -20 izmerjene celotne specifične deformacije -0.25 -25 -0.3 -30 ocenjeno avtogeno krčenje -0.35 -35 -0.4 -40 Slika 7 : Časovni poteki srednjih vrednosti temperature, srednjih vrednosti izmerjenih celotnih specifičnih deformacij in ocenjenega avtogenega krčenja treh zatesnjenih preizkušancev iz mešanice M2 primerjalnega betona visoke trdnosti v prvih 24 urah po zamešanju. 76 D. Saje, J. Lopatič krčenje betona ocenjeno s pomočjo enačbe 1 z Na sliki 13 so prikazani poteki ocenjenega avtogenega upoštevanjem celotnih izmerjenih in ocenjenih krčenja preizkušancev iz mikroarmiranega betona temperaturnih deformacij preizkušancev. visoke trdnosti z vsebnostjo predhodno navlaženih bazaltnih vlaken M7 in z vsebnostjo predhodno Na sliki 8 so prikazane celotne izmerjene deformacije navlaženih celuloznih vlakni M8 ter primerjalnega preizkušancev mikroarmiranih s krajšimi jeklenimi betona brez vlaken M2. Iz prikazanih rezultatov je vlakni IRI 50/16, daljšimi jeklenimi vlakni IRI 50/30, razvidno, da so celulozna vlakna, glede zgodnjega suhimi polipropilenskimi vlakni in preizkušancev iz ocenjenega avtogenega krčenja betona bolj učinkovita primerjalnega betona brez vlaken v prvih 24-ih urah. kot bazaltna vlakna. Zgodnje ocenjeno avtogeno krčenje Sveže betonske mešanice M1, M3, M4, M5 in M6 si preizkušancev iz mešanice M7, ki vsebuje predhodno imele enako vodovezivno razmerje. Količina agregata v navlažena bazaltna vlakna, je celo za 3% večje, medtem betonskih mešanicah, ki so vsebovala vlakna, je bila ko je avtogeno krčenje preizkušancev z vsebnostjo zmanjšana za velikost prostornine dodanih vlaken. predhodno navlaženih celuloznih vlaken, pri starost Ocenjeno avtogeno krčenje kompozita M3, kompozita 24 ur, za približno 31% manjše od primerljivega betona brez vlaken. mikroarmiranega s kratkimi jeklenimi vlakni, je en dan po zabetoniranju, v primerjavi s primerljivim betonom Z vodo napolnjena celulozna vlakna v mešanici M8 v brez vlaken M1, manjše za približno 33%, ocenjeno cementni pasti delujejo kot notranji rezervoar vode. Na avtogeno krčenje betona M4, ki vsebuje dolga jeklene ta način je voda po cementni pasti razporejena bolj vlakna, pa za približno 23% (slika 11). enakomerno in jo je tudi več kot v primeru enake Slika 9 prikazuje časovno spreminjanje temperature mešanice brez dodanih navlaženih celuloznih vlaken. preizkušancev in časovne razvoje izmerjenih celotnih Posledica tega so manjše kapilarne sile v svežem mikroarmiranem betonu in s tem manjše ocenjeno deformacij mikroarmiranega betona visoke trdnosti s suhimi M5 in navlaženimi M6 polipropilenskimi vlakni avtogeno krčenje v prvih 24-ih urah po zabetoniranju. ter primerjalnega betona brez vlaken M1 v prvih 24-ih urah po zabetoniranju. Iz prikaza rezultatov ocene avtogenega krčenja (slika 12) je razvidno, da je ocenjeno avtogeno krčenje mikroarmiranega betona s suhimi polipropilenskimi vlakni za približno 17%, ocenjeno avtogeno krčenje kompozita z navlaženimi pa za 70% manjše glede na avtogeno krčenje primerjalnega betona brez vlaken M1. ε [‰] T [ºC] M1 0.3 30 M6 0.25 M5 25 M3 M4 0.2 20 temperatura 0.15 15 0.1 10 0.05 5 t [ure] 0 0 0 6 12 18 24 30 M6 -0.05 -5 -0.1 -10 M3 M4 -0.15 -15 M5 -0.2 M1 -20 izmerjene celotne -0.25 -25 specifične deformacije -0.3 -30 -0.35 -35 -0.4 -40 Slika 8 : Srednje vrednosti izmerjenih celotnih specifičnih deformacij in temperature preizkušancev iz mikroarmiranega betona visoke trdnosti in primerjalnega betona brez vlaken v prvih 24-ih urah po betoniranju Krčenje mikroarmiranih betonov visoke trdnosti v zgodnjem obdobju 77 ε [‰] T [ºC] M1 0.3 30 M6 0.25 M5 25 0.2 20 temperatura 0.15 15 0.1 10 0.05 5 t [ure] 0 0 0 6 12 18 24 30 M6 -0.05 -5 -0.1 -10 -0.15 -15 M5 -0.2 M1 -20 izmerjene celotne -0.25 -25 specifične deformacije -0.3 -30 -0.35 -35 -0.4 -40 Slika 9 : Srednje vrednosti izmerjenih celotnih specifičnih deformacij in temperature preizkušancev iz mikroarmiranega betona visoke trdnosti z dodanimi suhimi M5 ali predhodno navlaženimi M6 polipropilenskimi vlakni in primerjalnega betona brez vlaken M1 v prvih 24-ih urah po betoniranju ε [‰] T [ºC] 0.3 30 M2 0.25 25 M7 M8 0.2 20 0.15 15 0.1 10 temperatura 0.05 5 t [ure] 0 0 0 6 12 18 24 30 -0.05 -5 -0.1 -10 -0.15 -15 M8 -0.2 -20 -0.25 -25 M2 -0.3 -30 M7 izmerjene celotne -0.35 -35 specifične deformacije -0.4 -40 Slika 10 : Srednje vrednosti izmerjenih celotnih specifičnih deformacij in temperature preizkušancev iz kompozita visoke trdnosti z dodanimi predhodno navlaženimi bazaltnimi vlakni M7 in predhodno navlaženimi celuloznimi vlakni M8 in primerjalnega betona brez vlaken M2 v prvih 24-ih urah po betoniranju 78 D. Saje, J. Lopatič ε [‰] T [ºC] M1 0.3 30 M6 0.25 M5 25 M3 M4 0.2 20 temperatura 0.15 15 0.1 10 0.05 5 t [ure] 0 0 0 6 12 18 24 30 -0.05 M6 -5 -0.1 -10 M3 -0.15 -15 M4 M5 -0.2 M1 -20 -0.25 -25 ocenjeno avtogeno krčenje -0.3 -30 -0.35 -35 -0.4 -40 Slika 11 : Časovni razvoj ocenjenega avtogenega krčenja in temperature preizkušancev iz mikroarmiranega betona visoke trdnosti in primerjalnega betona brez vlaken v prvih 24-ih urah po betoniranju ε [‰] T [ºC] M1 0.3 30 M6 0.25 M5 25 0.2 20 temperatura 0.15 15 0.1 10 0.05 5 t [ure] 0 0 0 6 12 18 24 30 -0.05 M6 -5 -0.1 -10 -0.15 -15 M5 -0.2 M1 -20 -0.25 -25 ocenjeno avtogeno krčenje -0.3 -30 -0.35 -35 -0.4 -40 Slika 12 : Časovni razvoj ocenjenega avtogenega krčenja in temperature preizkušancev iz mikroarmiranega betona visoke trdnosti z dodanimi suhimi M5 ali predhodno navlaženimi M6 polipropilenskimi vlakni in primerjalnega betona brez vlaken M1 v prvih 24-ih urah po betoniranju Krčenje mikroarmiranih betonov visoke trdnosti v zgodnjem obdobju 79 4.2 Diskusija dobljenih eksperimentalnih rezultatov je razvilo le 30% zgodnjega ocenjenega avtogenega krčenja v V preiskovanih betonih visoke trdnosti z jeklenimi primerjavi z ocenjenim avtogenim krčenjem vlakni se je razvilo do 33% manjše krčenje v primerjavi primerljivega betona brez vlaken. Voda v predhodno s krčenjem primerljivega betona brez vlaken. navlaženih polipropilenskih vlaknih se zadržuje delno v Jeklena vlakna s kljukami na konceh omogočajo dober oprijem poroznih vlaknih in delno v tri-dimenzionalnih porah, ki z betonom in so, v primerjavi s strjujočim se cementnim so med posameznimi vlakni, v snopičih fibriliranih gelom, relativno toga. V zgodnjem obdobju znatno vlaken 12. vplivajo na krčenje kompozita, ker s svojo sprijemnostjo Učinek dodatne rezerve vode v kompozitu je opazen tudi med vlakni in cementnim gelom ter s svojo togostjo, v primeru vgradnje predhodno namočenih celuloznih ovirajo krčenje strjujočega se cementnega gela, ki se krči vlaken. Omenjeni kompozit je razvil za približno eno zaradi kapilarnih sil. tretjino manjše zgodnje avtogeno krčenje glede na Polipropilenska vlakna so manj toga kot jeklena, zato je krčenje primerljivega betona brez vlaken. tudi vpliv na velikost krčenja manjši. Bazaltna vlakna imajo majhno togost, po namočenju Pri vmešanju predhodno navlaženih vlaken v mešanico zadržijo relativno malo vode in je njihova sprijemnost s za beton visoke trdnosti se pojavita dva fizikalna učinka, cementnim gelom nizka. Predvidevamo, da bazaltna ki ugodno delujeta na zmanjšanje deformacij zaradi vlakna v preiskovanem kompozitu zato niso ublažila avtogenega krčenja betona: zgodnjega avtogenega krčenja le tega. 1. oviranje krčenja cementnega gela zaradi togosti Iz ocenjenih krivulj časovnega razvoja avtogenega vlaken in sprijemnosti le teh z matrico, ki je prisotno krčenja betona visoke trdnosti z vlakni, ki so prikazane tudi pri uporabi suhih vlaken, na slikah 11, 12 in 13, je v času med dvanajsto in štiriindvajseto uro opazno rahlo zmanjšanje avtogenega 2. pri uporabi navlaženih vlaken se pojavi še ugoden krčenja betona in sicer med časom, ko je v betonu učinek dodatne rezerve vode, ki je nakopičena v dosežena največja temperatura in časom, ko se vlaknih, ki na kakršenkoli način zadržijo vodo in jo temperatura betona izenači s temperaturo okolice. Ta postopoma oddajajo v strjujočo se matrico v času fizikalni pojav je posledica termodinamičnega hidratacije 11. ravnovesja v porah cementnega kamna. Ko začne temperatura v betonu padati, se beton krči, s čimer se Znatno se učinek fibriliranih polipropilenskih vlaken zmanjša tudi prostornina zaprtih por v cementnem lahko poveča, če ta pred vgradnjo, za 24 ur, namočimo kamnu. Zaradi zmanjšanja prostornine zaprte pore se po v vodo. V betonu visoke trdnosti z omenjenimi vlakni se zakonih termodinamike poveča relativna vlažnost v pori, ε [‰] T [ºC] 0.3 30 M2 0.25 25 M7 M8 0.2 20 0.15 15 0.1 10 temperatura 0.05 5 t [ure] 0 0 0 6 12 18 24 30 -0.05 -5 -0.1 -10 -0.15 -15 M8 -0.2 -20 -0.25 -25 M2 -0.3 -30 M7 -0.35 -35 ocenjeno avtogeno krčenje -0.4 -40 Slika 13 : Časovni razvoj ocenjenega avtogenega krčenja in temperature preizkušancev iz kompozita visoke trdnosti z dodanimi predhodno navlaženimi bazaltnimi vlakni M7 in predhodno navlaženimi celuloznimi vlakni M8 in primerjalnega betona brez vlaken M2 v prvih 24-ih urah po betoniranju 80 D. Saje, J. Lopatič kar zmanjša natezne sile, ki delujejo na stene pore to pa LITERATURA povzroči zmanjšanje avtogenega krčenja betona. Zaradi 1. Pfyl, T., Marti, P., Versuche an padca temperature zraka v zaprti pori, ob vzpostavitvi Stahlfaserverstärkten Stahlbetonelementen, ETH termodinamičnega ravnovesja, naraste relativna vlažnost zraka, kar povzroči še dodatno zmanjšanje Zürich, 2001. avtogenega krčenja kompozita [7]. 2. Institution of Civil Engineers, The technology of SFRC for practical applications, UK, Part 1, May 1974, pp 143-159. 5 ZAKLJUČKI 3. Balaguru, P. N., Shah, S. P., Fiber-Reinforced Na podlagi rezultatov opravljenih eksperimentalnih Cement Composites, McGraw-Hill, Inc., New York, raziskav zgodnjega avtogenega krčenja z jeklenimi, 1992. polipropilenskimi, bazaltnimi ali celuloznimi vlakni ojačenega betona visoke trdnosti in analize dobljenih 4. Bentur, A., Mindess, S., Fiber Reinforced rezultatov podajamo naslednje ugotovitve: Cementitious Composites, Taylor and Francis, London and New York, 2007. - Zmanjšanje zgodnjega avtogenega krčenja betonov 5. N. Banthia, R. Gupta, Influence of polypropylene visoke trdnosti z vlakni je močno odvisno od vrste fiber geometry on plastic shrinkage cracking in uporabljenih vlaken. concrete, Cement and Concrete Research, Vol. 36 - Vlakna v kompozitu vplivajo na velikost krčenja s No.7, 2006, pp 1263-1267. svojo togostjo in/ali s sposobnostjo zadržanja vode 6. Barr, B., EL-Baden, A., Shrinkage of normal and med mešanjem in oddajanja le te v kompozit med high strength fibre reinforced concrete, procesom hidratacije. Proceedings of the Institution of Civil Engineers, Structures & Buildings 156, 2003, 15-25. - Glede oviranja krčenja betona v prvem dnevu po zabetoniranju so se, izmed vseh uporabljenih 7. Saje, D., Tlačna trdnost in krčenje betonov visoke vlaken, izkazala kot najbolj učinkovita predhodno trdnosti, Doktorska disertacija, 2001. navlažena polipropilenska vlakna. Predvidevamo, 8. Bayasi, Z., Zeng, J., Properties of polypropylene da je manjše krčenje kompozita z vsebnostjo fiber reinforced concrete, ACI Material Journal. predhodno navlaženih polipropilenskih vlaken v Vol. 90(6), 1993, pp 605-610. primerjavi z betonom brez vlaken, posledica dveh 9. Saje, D., Bandelj, B., Lopatič, J., Saje, F., Notranja vplivov in sicer togosti vlaken in sprijemnosti le-teh nega betona, v: Lopatič, J. (ur.), Saje, F. (ur.), z matrico ter dodatne rezerve vode, ki je ujeta v Markelj, V. (ur.). Zbornik 30. zborovanja gradbenih vlaknih. konstruktorjev, 2008. Ljubljana: Slovensko društvo - Predhodno navlaženim polipropilenskim vlaknom gradbenih konstruktorjev. 2008, str. 245-252. glede ugodnega vpliva na velikost zgodnjega 10. JIS A 1129-1., Methods of test for length change of avtogenega krčenja kompozitov po vrstnem redu mortar and concrete, JIS Standards, Tokyo, 2001. sledijo krajša jeklena vlakna, dolžine l=16mm, 11. Saje, D., Reduction of the early autogenous predhodno navlažena celulozna vlakna, daljša shrinkage of high strength concrete. Advances in jeklena vlakna, dolžine l=30mm, suha Materials Science and Engineering, 2015, str. 1-8, polipropilenska vlakna in predhodno navlažena http://www.hindawi.com/journals/amse/2015/3106 bazaltna vlakna. 41/. - Pri prostorninskem deležu vlaken 0,75%, je 12. Saje, D., Bandelj, B., Šušteršič, J., Lopatič, J., Saje, vgradljivost kompozita, ne glede na vrsto F., Shrinkage of polypropylene fibre reinforced uporabljenih vlaken, opazno zmanjšana. high performance concrete. Journal of materials in civil engineering, ISSN 0899-1561, 2011, vol. 23, iss. 7, str. 941-952. Možnost uporabe mikroarmiranega betona za izdelavo zabojnika za NSRAO Possibility of using fibre reinforced concrete for the production of the LILW disposal container Jakob Šušteršič, Rok Ercegovič, IRMA Inštitut za raziskavo materialov in aplikacije, Ljubljana Franc Sinur, Boštjan Duhovnik IBE Ljubljana Aljoša Šajna ZAG Ljubljana Teja Török Resnik Pomgrad Murska Sobota Povzetek Zabojnik za odlaganje z nizko in srednje radioaktivnimi odpadki (NSRAO) je bil razvit z uporabo samo-zgoščevalnega betona (SCC), ki zagotavlja dolgotrajne mehanske lastnosti in izjemno nizko prepustnost za tekočine. V članku so predstavljeni rezultati dodatnih raziskav, ki dopolnjujejo oceno obnašanja SCC med uporabo. Glavni poudarek je na predstavitvi in razpravi o rezultatih MA-SCC-JV (mikroarmiranega samo-zgoščevalnega betona z jeklenimi vlakni) v svežem in strjenem stanju. Iz teh rezultatov je razvidno, da obstaja možnost nadaljnjega izboljšanja lastnosti SCC in s tem zabojnika. Abstract The disposal container with low and intermediate level radioactive waste (LILW) was developed using self- consolidating concrete (SCC), which provides long term mechanical properties and extremely low permeability for liquids. In the paper, some results of additional investigations are presented, which complement the assessment of the behavior of SCC during use. The main focus is the presentation and discussion of the results of SFR-SCC (steel fiber reinforced - self-consolidating concrete) tests in fresh and harden state. From these results it can be seen that there is a possibility of further improving the properties of the SCC and thus the container. Ključne besede: mikroarmirani samo-zgoščevalni beton z jeklenimi vlakni, samo-zgoščevalni beton, odlagalni zabojnik za NSRAO, posed-razlez, krčenje, cepile trdnosti Keywords: steel fiber reinforced self-consolidating concrete, self-consolidating concrete, disposal container with LILW, slump-flow, shrinkage, split strengths radioaktivnih odpadkov (NSRAO). Uporablja se za 1. UVOD izdelavo armiranobetonskih sten, dna in pokrova SCC je bil razvit v okviru razvojnega projekta za zabojnika. Poleg SCC sta bila razvita še naslednja dva izdelavo kontejnerja za odlaganje nizko in srednje kompozita: 26. slovenski kolokvij o betonih – Projektiranje mikroarmiranih betonskih konstrukcij in njihove aplikacije, Ljubljana, 16.5.2019 82 J. Šušteršič, R. Ercegovič, F. Sinur, B. Duhovnik, A. Šajna, T. Török Resnik 1. polnilna malta za zapolnitev prostora med 2. KRATKA INFORMACIJA O ODLAGALNEM vstavljenimi sodi z NSRAO in notranjo površino ZABOJNIKU IN LASTNOSTIH SCC zabojnika ter V razvojnem projektu zabojnika za odlaganje z oznako 2. tesnilna malta za zapiranje praznega prostora med N2d je sodelovala velika ekipa strokovnjakov IBE malto za polnjenje in notranjo površino pokrova in (odlagališče in projektant zabojnika), Pomgrad za tesnjenje stika med pokrovom in zgornjo (proizvajalec prototipov zabojnika), ZAG in IRMA površino sten. (sodelujoča inštituta v projektu). V okviru projekta so bile določene zahteve za lastnosti 2.1. Odlagalni zabojnik osnovnih materialov za pripravo kompozitov in za Betonski zabojnik, kot eden najpomembnejših lastnosti vseh treh kompozitov (SCC, polnilne in elementov inženirskega dela večstopenjskega sistema tesnilne malte). Te zahteve so določene v Programu za preprečevanj testiranja zabojnikov, meritev in preskusov [1]. Podane e prehoda radioaktivnih snovi iz so tudi v članku Sinurja in Duhovnika [2]. Za pridobitev odlagališča v okolje deluje kot: (a) biološki ščit v času Slovenskega tehničnega soglasja (STS) je bilo potrebno pred odložitvijo, (b) mehanska zaščita NSRAO med skladiščenjem in odlaganjem, (c) osnovni element razviti kompozite z lastnostmi, ki izpolnjujejo vse zahteve. Rezultati preskusov iz poročila Rezultati varnosti med izvajanjem transporta in internega transporta (premešč testiranja, meritev in preskusov zabojnikov [3] so anja) NSRAO v zabojniku, (d) pokazali, da so izpolnjene vse zahteve. Zabojniki s osnovni gabaritni kriterij v procesu priprave odpadkov takimi kompoziti so bili izdelani[4] in testirani v na odlaganje in (e) osrednji predmet ravnanja z NSRAO preskuševališču v proizvodnem obratu Pomgrad v na območju odlagalnega silosa. Lipovcih [5] Najpomembnejša in najbolj specifična zahteva za V tem članku so podane le kratke informacije o zabojnik je poleg odpornosti in stabilnosti proti vsem zabojniku in rezultatih preiskav SCC. V nadaljevanju so predvidenih obremenitev v fazi polnjenja in transporta predstavljeni rezultati preiskav nekaterih ključnih pred končno odložitvijo tudi trajnost v pričakovani značilnosti MA življenjski dobi 300 let. -SCC-JV, na podlagi katerih bi lahko ocenili možnost uporabe MA-SCC-JV za izdelavo Glede na znane okoljske razmere, katerim bodo zabojnika za odlaganje NSRAO. zabojniki izpostavljeni po odlaganju v silosu, bodo zabojniki izpostavljeni karbonatizaciji v prvi fazi (v obdobju 2020 - 2061), po polnjenju in zapiranju silosa ter opustitvi. črpanje vode od leta 2062 dalje, bo silos z zabojniki izpostavljen podzemni vodi. Zabojniki, pripravljeni za odlaganje, bodo prepeljani na odlagališče v skladu z določbami zahtev za prevoz nevarnega blaga po cesti (ADR) [6]. Določbe ADR [6] so bile uvedene v nacionalno zakonodajo z Zakonom o prevozu nevarnega blaga (ZPNB) [7]. Ta natančno določa, da je treba zabojnike za prevoz nevarnega blaga preskusiti z „drop testom“. Skupno bo odloženih 950 zabojnikov tipa N2d z največjo dovoljeno maso 40 t. Zabojniki se odlagajo v silos s pomočjo portalnega dvigala in posebnih ročajev. Prazna mesta med zabojniki in zabojniki ter steno silosa se zapolnijo z betonom 2.1.1 Geometrijske značilnosti zabojnika N2d Osnovna geometrija zabojnika je bila določena na osnovi vgradnje 4 TTC sodov. Zabojnik N2d je nadgradnja zabojnika N2b, ki se bistveno razlikuje le pri zasnovi pokrova in sidranja pokrova v armiranobetonski zabojnik. Specifične rešitve zabojnika so podane v nadaljevanju in so rezultat razvoja zabojnika s pridobitvijo Slovenskega tehničnega soglasja (STS): (1) Zunanje mere (širina = 1,95 m, dolžina = 1,95 m, višina = 3,30 m), (2) debelina spodnje plošče = 23 cm, (3) debelina stene na vrhu = 20 cm, (4) debelina stene na dnu = 23 Slika 1. 3D pogled zabojnika z armaturo [2]. cm, (5) debelina pokrova = 20 cm, (6) masa prazne Možnost uporabe mikroarmiranega betona za izdelavo zabojnika za NSRAO 83 Preglednica 1. Povprečni rezultati preskusov lastnosti svežega SCC. Lastnost (merjena po standardu) Povprečna vrednost Posed – razlez (SIST EN 12350-8:2010) 680/710 mm Gostota (SIST EN 12350-6:2009) 2393 kg/m3 Vsebnost zraka (SIST EN 12350-7:2009, Poglavje 5) 2,0 % w/c razmerje (SIST 1026:2016, Dodatek NC) 0,37 Preglednica 2. Povprečni rezultati preskusov lastnosti strjenega SCC. Lastnost (merjena po standardu) Povprečna vrednost Tlačna trdnost pri 28 dneh (SIST EN 12390-3:2009) 86,0 MPa Prodor vode pri 28 dneh (SIST EN 12390-8:2009) 3,0 mm Krčenje do 182 dni (DIN 4227-Part 1) 0,374 mm/m Odpornost proti zmrzovanju/tajanju/do 200 ciklov (SIST 1026:2016, 101,0 % Dodatek ND) Modul elastičnosti pri 28 dneh (DIN 1048) 42500 MPa Totalna poroznost (EN 1936: 2006) 10,85 % Vsebnost kloridov (SIST EN 206: 2013, Poglavje 5.2.8) 0,070 % posode s pokrovom = 14,92 t, (7) največja dovoljena Priraščanje tlačne trdnosti pri zgodnejši starosti SCC in masa polne posode = 40 t. polnilna malta do 28 dni, je veliko bolj intenzivno kot v primeru starosti nad 28 dni. Podobno priraščanje 2.2 Nekatere lastnosti SCC modula elastičnosti SCC je bilo ugotovljeno v daljšem časovnem obdobju. Da bi dosegli popolno polnjenje gosto armiranih elementov zabojnika (stene, dno in pokrov) (slika 1) [2], je bila v okviru razvojnega projekta razvita sestava 2.2.2. Merjenje avtogenega krčenja SCC. SCC. SCC se je v elemente vgrajeval z neprekinjenim Avtogeno krčenje je večje pri betonu visoke trdnosti ali vlivanjem skozi cev [4]. Pri pripravi sestave SCC so betonu z nižjim razmerjem v/c [8]. Avtogeno krčenje upoštevana pravila za SCC, ki so določena v SIST EN betona, imenovano tudi hidratacijsko krčenje, je 206: 2013. posledica samo-sušenja v porah cementnega kamna, ko se vode v porah porabi v procesu hidratacije cementa. V laboratoriju smo pripravili veliko število mešanic Tako se avtogeno krčenje pojavi takoj, ko se začne SCC, pri čemer smo spreminjali količine in razmerja postopek hidratacije cementa v betonu. Glede na vrsto posameznih komponent tako, da smo dobili mešanico, betonske mešanice se postopek krčenja začne približno ki je bila primerna za izbrano metodo vgrajevanja. 2 do 24 ur po mešanju. Ker se v tem času že vzpostavi Povprečni rezultati meritev svežega in strjenega SCC so nega in je beton vgrajen v opažih, se izhlapevanje vode podani v preglednicah 1 in 2. Rezultati so v mejah bistveno prepreči. V tem času pride do deformacij zahtevanih vrednosti [2, 3]. betona zaradi avtogenega krčenja in temperaturnih deformacij betona. Po končani negi se beton deformira 2.2.1. Priraščanje tlačne trdnosti SCC s časom - krči se zaradi izhlapevanja vode s površine betonskega Priraščanje tlačne trdnosti SCC, polnilne in tesnilne elementa. malte glede na čas je razvidno iz slike 2. 84 J. Šušteršič, R. Ercegovič, F. Sinur, B. Duhovnik, A. Šajna, T. Török Resnik Meritve avtogenega krčenja so bile izvedene v skladu z mikroarmiranega betona je bilo pri vseh preiskanih japonskim standardom JIS A 1129 v laboratoriju vsebnostih in vrstah uporabljenih vlaken manjše kot pri Fakultete za gradbeništvo in geodezijo v Ljubljani. Na primerljivem betonu brez vlaken. Ob koncu merilnega sliki 3 tanka črta prikazuje potek celotnega izmerjenega obdobja je bilo celotno krčenje preiskovanega zgodnjega krčenja SCC. To je povprečna vrednost mikroarmiranega betona glede na vsebnost in vrsto rezultatov meritev na treh prizmah z dimenzijami 10 × uporabljenih vlaken približno 17% do 29% manjše kot 10 × 40 cm. Razvoj temperature SCC kot funkcije časa pri primerljivem betonu brez vlaken. Razlike v je podan z rdečo črto (zgornji diagram). Potek ocenjene skupnem krčenju mikroarmiranega betona z različnimi avtogene deformacije SCC je predstavljen z debelo vsebnostmi in različnimi vrsta vlaken, so bile relativno linijo, ki se določi z odštetjem temperaturne majhne. 2) Za zmanjšanje zgodnjega avtogenega deformacije betona od celotnega izmerjenega krčenja. krčenja betona je uporaba jeklenih vlaken učinkovitejša Rezultati kažejo relativno majhno avtogeno krčenje kot uporaba suhih polipropilenskih vlaken. Pri uporabi SCC. Izmerjeno je tudi manjše krčenje SCC zaradi jeklenih vlaken z vsebnostjo 0,25 vol.% ali 0,50 vol.% sušenja. Povprečno krčenje SCC pri starosti 182 dni je so daljša vlakna učinkovitejša, medtem ko so v primeru 0,374 mm / m. vsebnosti 0,75 vol.% krajša vlakna učinkovitejša. (3) Za zmanjšanje skupnega avtogenega krčenja pri vsebnosti V enem od prejšnjih raziskovalnih projektov [9] so bili vlaken 0,25 vol.% so najbolj učinkovita daljša jeklena opravljeni laboratorijski preskusi krčenja vlakna, medtem ko so polipropilenska vlakna najmanj mikroarmiranega visoko zmogljivega betona z učinkovita. Pri vsebnosti vlaken 0,50 vol.% in 0,75 vsebnostjo 0,25 vol.%, 0,50 vol.% in 0,75 vol.% vol.% pa je relativno majhna razlika v učinkovitosti naslednjih vlaken: daljša (l = 32 mm, d = 0,5 mm) ali jeklenih in polipropilenskih vlaken pri zmanjšanju krajša (l = 16 mm, d = 0,5 mm) jeklena ali celotnega avtogenega krčenja. (4) Krčenje betona polipropilenska (l = 12 mm). zaradi sušenja je pri vseh preiskanih vsebnostih in vrstah uporabljenih vlaken bistveno manjše od Na podlagi razprav o rezultatih izvedene eksperimentalne raziskave o krčenju ustreznega krčenja zaradi sušenja primerljivega navadnega betona brez vlaken. visokozmogljivega betona, ki vsebuje polipropilenska ali krajša/daljša jeklena vlakna, je mogoče podati naslednje zaključke: (1) Skupno krčenje 120 y = 15,003ln(x) + 30,406 R² = 0,969 100 ]aP 80 M[ y = 10,562ln(x) + 39,528 t R² = 0,9223 os 60 trdn ačna 40 SCC tl y = 9,5176ln(x) + 13,854 R² = 0,9943 polnilna malta 20 tesnilna malta 0 0 10 20 30 40 50 60 70 80 90 100 110 starost kompozita [dni] Slika 2. Tlačna trdnost SCC, polnilne in tesnilne malte v odvisnosti od starosti kompozita. Možnost uporabe mikroarmiranega betona za izdelavo zabojnika za NSRAO 85 3. SFR-SCC znašali faktorji oblike (razmerje med dolžino in premerom vlakna) l/d = 32, 40 in 46. V nadaljevanju laboratorijskih preiskav so se pripravili in raziskali MA-SCC-JV (mikroarmirani samo- V tem članku so podane samo informacije in nekateri zgoščevalni betoni z jeklenimi vlakni). Dodane so bile rezultati raziskav MA-SCC-JV. Cilj je bil ugotoviti različne količine (0,25, 0,5, 0,75 in 1 vol.%) jeklenih možni potencial za nadaljnje izboljšanje obnašanja vlaken s sidri, enake dolžine 16 mm in različne debeline odlagalnega zabojnika med uporabo, zlasti z (premeri presekov) 0,50 , 0,40 in 0,35 mm. Tako so zagotavljanjem njegove dolge življenjske dobe.  [‰] T [ºC] 0,1 30,00 0,05 temperatura 25,00 t [ure] 0 20,00 0 24 48 72 96 120 144 168 192 ocenjene avtogene -0,05 15,00 deformacije -0,1 10,00 celotne izmerjene -0,15 deformacije 5,00 -0,2 0,00 -0,25 -5,00 -0,3 -10,00 Slika 3. Rezultati merjenja avtogenega krčenja SCC do 7 dni po mešanju. 760 750 ]m 740 l/d = 32 [mz 730 e l/d = 40 azlr 720 inčer 710 pvo 700 p l/d = 46 690 680 0,25 0,5 0,75 1 jeklena vlakna [vol.%] Slika 4. Povprečni razlez svežega MA-SCC-JV v odvisnosti od vsebnosti vlaken njihovega faktorja oblike. 86 J. Šušteršič, R. Ercegovič, F. Sinur, B. Duhovnik, A. Šajna, T. Török Resnik 3.1 Preiskave svežega MA-SCC-JV 3.2. Preiskave strjenega MA-SCC-JV Izvedeni so bili isti preskusi svežega MA-SCC-JV kot Glavni namen dodajanja vlaken betonu je povečanje za svež SCC. Preiskovalo se je, kako količina vlaken in njegove duktilnosti, žilavosti in odpornosti proti njihovi faktorji oblike vplivajo na obdelovalnost in širjenju razpok. Izvaja se več vrst preskusov. Ta članek vgradljivost MA-SCC-JV. V tem članku so podani le bo podal le nekaj rezultatov preskusa cepitve s klinom rezultati preskusa poseda/razlez. Meril se je povprečni (WST). razlez svežega MA-SCC-JV po standardu SIST EN 12350-8. Dobljeni rezultati so prikazani na sliki 4, v WST je preskusna metoda za izvajanje stabilnih odvisnosti od količine dodanih vlaken in njihovega preskusov mehanike loma na betonskih in betonu podobnih materialih. Predlagali so jo Brühwiler in faktorja oblike (l/d = 32, 40 in 46). Wittman [10] ter Linsbauer in Tschegg [11]. Metodo, ki Rezultati kažejo, da vlakna v količini do 0,75 vol.% ne sta jo predlagala zadnja avtorja [11], se je uporabila v vplivajo na obdelovalnost in vgradljivost svežega MA- teh in v prejšnjih [12-14] raziskavah, da bi dobili SCC-JV. Nekateri rezultati kažejo, da prisotnost vlaken diagrame obtežba - CMOD. Ekvivalentne trdnosti do celo izboljša obdelovalnost, kot da bi vlakna povečala izbrane širine razpok (CW = 0,1, 0,2, 0,3 in 0,4 mm) se notranjo "drsenje" sveže MA-SCC-JV mase in ne izračunajo z enačbo, pri kateri se uporabljajo parametri, ovirajo njene obdelovalnosti - pretočne sposobnosti, kot ki izhajajo iz diagrama obtežba - CMOD. se dogaja pri večji količini daljših vlaken. Obdelovalnost svežega MA-SCC-VL se rahlo zmanjša, Preskusi po metodi WST so bili izvedeni na kockah z če se doda 1 vol.% vlaken. Zmanjšanje obdelovalnosti dolžino roba 150 mm in z začetno globino zareza 50 je večje, če se uporabljajo vlakna z večjim faktorjem mm, pri starosti 28 dni. Princip preskusne metode je oblike. prikazan na sliki 5 [15]. Slika 5. Princip WST metode [15]. Možnost uporabe mikroarmiranega betona za izdelavo zabojnika za NSRAO 87 Preglednica 3. Povprečni rezultati trdnosti SCC in MA-SCC-JV dobljeni z WST f f f f f f FC ct 0,1 0,2 0,3 0,4 (MPa) (MPa) (MPa) (MPa) (MPa) (MPa) SCC 2,8 3,2 2,7 2,2 1,8 1,5 MA-SCC-JV z 1 vol.% vlaken z 4,9 5,7 4,5 4,9 4,9 4,8 l/d = 30 MA-SCC-JV z 1 vol.% vlaken z 5,2 6,1 5,0 5,2 5,4 5,5 l/d = 40 Karakteristična diagrama obtežba - CMOD za SCC brez 30 in 40 so podane povprečne vrednosti teh trdnosti v vlaken in MA-SCC-JV z 1 vol.% jeklenih vlaken z l/d preglednici 3. = 30 sta podana na sliki 6. Povprečne končne trdnosti fct so prikazane na sliki 7, v Obstaja zelo velika razlika med površinami pod odvisnosti od faktorja oblike l/d (faktor oblike l/d = 0 diagrami, ki predstavljajo količino absorbirane energije ima SCC brez vlaken). SCC in MA-SCC-JV med preskusom. Iz teh diagramov se izračunajo naslednje trdnosti: končna trdnost f Povprečna trdnost pri prvi razpoki fFC in ekvivalentne ct, trdnosti do izbrane širine razpoke f trdnost pri prvi razpoki f CW so podane na sliki FC in ekvivalentne trdnosti do izbrane širine razpoke (CW = 0,1, 0,2, 0,3 in 0,4 mm). 8, v odvisnosti od širine razpoke (CW = 0, 0,1, 0,2, 0,3 Za SCC, MA-SCC-JV z 1 vol.% jeklenih vlaken z l/d = in 0,4 mm). Trdnost pri prvi razpoki fFC se določi v trenutku, ko nastane razpoka in je njena širina 0. 6 5 MA-SCC-JV z 1 vol.% jeklenih vlaken, l/d = 30 4 ] [kNa 3žbtebo2 SCC 1 0 0 0,5 1 1,5 2 2,5 3 3,5 4 CMOD [mm] Slika 6. Karakteristična diagrama obtežba – CMOD za SCC brez vlaken in MA-SCC-JV z 1 vol.% jeklenih vlaken z l/d = 30. 88 J. Šušteršič, R. Ercegovič, F. Sinur, B. Duhovnik, A. Šajna, T. Török Resnik Iz povprečnih rezultatov trdnosti (preglednica 3, sliki 7 in 8) je razvidno, da so te pri MA-SCC-JV precej višje kot pri SCC. Vlakna pomembno vplivajo na obnašanje betona po nastanku prve razpoke. Pri preskušanju SCC brez vlaken so se s povečevanjem širine razpoke zmanjševale ekvivalentne trdnosti – prišlo je do »mehčalnega« odziva (slika 8). Po drugi strani pa je pri preskušanju MA-SCC-JV prišlo »strjevalnega« odziva, ekvivalentne trdnosti so se povečevale s povečevanjem širine razpoke (slika 8). To še posebej velja, kadar so uporabljena vlakna z večjim faktorjem oblike (l/d = 40). 7 6 Pa] 5 [M f ct 4 st ond 3tra nč2n ko 1 0 0 30 40 faktor oblike l/d Slika 7. Povprečne končne trdnosti fct v odvisnosti od faktorja oblike l/d. 6 MA-SCC-JV z 1 vol.% vlaken z l/d = 40 , Pa] 5 f FC [M ki f CW MA-SCC-JV z 1 vol.% vlaken z l/d = 30 4 azpo sti ri o v n r d p i tr r e 3 p tnn ost e nd alv 2 tr SCC kvie 1 0 0 0,1 0,2 0,3 0,4 širina razpoke CW [mm] Slika 8. Povprečna trdnost pri prvi razpoki fFC in ekvivalentne trdnosti do izbrane širine razpoke fCW v odvisnosti od širine razpoke (CW = 0, 0,1, 0,2, 0,3 in 0,4 mm). Možnost uporabe mikroarmiranega betona za izdelavo zabojnika za NSRAO 89 3 ZAKLJUČEK LITERATURA SCC, katerega sestava je bila razvita v okviru 1. S Duhovnik, B., Kavnik, T., Šušteršič, J., Šajna. A. razvojnega projekta zabojnika za odlaganje NSRAO, (2017) Program testiranja zabojnikov, meritve in kaže lastnosti (v svežem stanju), ki zagotavljajo dobro preskusi, potrebni za certificiranje zabojnika, Št. obdelovalnost in zgoščenost v stenah, dnu in pokrovu NRVB-POM_Program, Murska Sobota, Pomgrad. zabojnika, kljub veliki količini armaturnih palic. 2. Sinur, F. & Duhovnik, B. (2018) Odlagalni Podobno obnašanje je bilo ugotovljeno v svežem MA- zabojnik za nizko- in srednjeradioaktivne odpadke. SCC-JV, kljub dodanim vlaknom. Nekateri rezultati Zbornik 25. Slo. kolok. o betonih (str. 53-60). kažejo, da prisotnost vlaken v količini do 0,75 vol.% Ljubljana, IRMA. celo izboljšajo obdelovalnost, kot če bi vlakna povečevala notranjo "drsenje" sveže mase MA-SCC-JV 3. Török Resnik, T, Šušteršič, J., Šajna, A., Kavnik, T., in ne ovirajo njegove obdelovalnosti - pretočnosti. Sinur, F. (2017) Rezultati testiranj zabojnikov, meritve in preskusi, potrebni za certificiranje Dobljeni rezultati meritev avtogenega krčenja in zabojnika, Št. NRVB-POM_Rezultati, Murska krčenja zaradi sušenja SCC kažejo, da ni tveganja za Sobota, Pomgrad. razpokanost, seveda, pod pogojem, da se izvede dobra 4. Török Resnik, T., Kavnik, T. (2018) Odlagalni nega vgrajenega SCC. Rezultati predhodnih zabojnik za odlaganje nizko in srednje eksperimentalnih raziskav o krčenju visoko radioaktivnih odpadkov (NSRAO): Izdelava zmogljivega mikroarmiranega betona pa kažejo, da je prototipov zabojnikov in testiranje padcev celotno krčenje mikroarmiranega betona manjše od zabojnikov, Zbornik 25. Slo. kolok. o betonih (str. primerljivega betona brez vlaken. Za zmanjšanje 61-68). Ljubljana, IRMA. zgodnjega avtogenega krčenja visoko zmogljivega mikroarmiranega betona je učinkovitejša uporaba 5. Bohinc,U., Robič, S., Šajna, A. (2018) Preskus kratkih jeklenih vlaken (dolžine 16 mm) z vsebnostjo padca AB zabojnika za odlagališče NSRAO in 0,75 vol.% kot uporaba daljših vlaken (dolžine 32 mm). vrednotenje poškodb, Zbornik 25. Slo. kolok. o betonih (str. 79-87). Ljubljana, IRMA. Ena od bistvenih ugotovitev raziskav je, da je bil 6. European Agreement concerning the International dobljen »strjevalni« odziv MA-SCC-JV z 1 vol.% Carriage of Dangerous Goods by Road (ADR); vlaken, medtem ko je bil dosežen »mehčalni« odziv, ko http://www.unece.org/trans/danger/publi/adr/adr2 se je preiskoval SCC brez vlaken. To še posebej velja, 017/17contentse0.htlm. kadar se uporabljajo vlakna z večjim faktorjem oblike. 7. Zakon o prevozu nevarnega blaga (ZPNB), Ur.l. Na podlagi dosedanjih rezultatov raziskav lahko UPB1 33/06, 41/09, 97/10. sklepamo, da obstaja možnost povečanja odpornosti 8. Saje, D. (2005) Krčenje betona visokih trdnosti v SCC proti širjenju razpok z dodajanjem določene prvih dneh po vgraditvi, Zbornik 12. Slo. kolok. o količine jeklenih vlaken, brez poslabšanja betonih (str. 41-48). Ljubljana, IRMA. obdelovalnosti in vgradljivosti SCC, ki bi se uporabljal za izdelavo zabojnika za odlaganje NSRAO. 9. Saje, D., Bandelj, B., Šušteršič, J., Lopatič, J., Saje F. ((2012) Autogenous and Drying Shrinkage of Fibre Reinforced High-Performance Concrete. Journal of advanced concrete technology, Feb. 2012, Vol. 10, No. 2, str. 59-73 10. Brühwiler E., Wittman F.H. (1988) The Wedge Splitting Test, a New Method of Performing Stable Fracture Mechanics Tests. Fracture and Damage of Concrete and Rock. Pergamon Press. 1988. Ed. H.P. Rossmanith. (str. 117 – 125). 11. Linsbauer H., Tschegg, E.K. (1986) ‘Die Bestimmung der Bruchenegie an Würfelproben’ (Fracture Energy Determination of Concrete with Cube-Shaped Specimens). Zement und Beton, 31 1, (str. 38 – 40). 12. Šušteršič J., Kolenc M., Zajc A., Riček F., Zajc P.M. (1999) High-Performance Fibre Reinforced Concrete for Mine Roadway Support Panels. Proceedings, Second CANMET/ACI International Conference Gramado, RS, Brazil,. SP-186. (str. 101 – 112). 13. Šušteršič, J., Ukrainczyk, V., Zajc, A., Šajna, A. (2001) Evaluation of Crack Opening Resistance of SFRC. Concrete Under Severe Conditions. Vol. 2. 90 J. Šušteršič, R. Ercegovič, F. Sinur, B. Duhovnik, A. Šajna, T. Török Resnik Vancouver.. Eds. N. Banthia, K. Sakai, O.E. Gjørv. held on 3-4 September 2003 at the University of (str. 1594 – 1601). Dundee, Scotland, UK. London: ˝Thomas Telford˝, 14. Šušteršič J., Zajc A., Leskovar I., Dobnikar V. str. 167-174. (2003) Improvement in the crack opening 15. Tschegg, E.K. ‘New Equipments for Fracture Tests resistance of FRC with low content of short fibres. on Concrete’; Materialprüfung 33 (1991) 11 - 12, Ed.: Dhir, Ravindra K. Role of concrete in München, 1991, str. 338 - 342. sustainable development : proceedings of the International Symposium dedicated to professor Surendra Shah, Northwestern University, USA Ocena trajnosti prednapetih železniških pragov iz mikroarmiranega betona Estimation of the durability of prestressed railway sleepers from fiber reinforced concrete Andrej Zajc, Jakob Šušteršič in David Polanec IRMA Inštitut za raziskavo materialov in aplikacije, Ljubljana Povzetek V članku se obravnava problematika trajnosti prednapetih železniških pragov iz mikroarmiranega betona (PŽP- MAB). Na kratko je opisan razvoj teh pragov do poskusne proizvodnje in vgradnje v poskusno polje, ki je v uporabi že 23 let. Z občasnimi pregledi se spremlja obnašanje PŽP-MAB med uporabo. Ugotavlja se, da do sedaj ni bilo opaziti razpok, še posebno na mestih nastopa največjih nateznih napetosti. Na nekaj PŽP-MAB pa so bile ugotovljene poškodbe na spodnjem delu zaradi abrazijskih in udarnih obremenitev, do te mere, da so morali biti odstranjeni s proge. Za ta problem obstaja rešitev, ki bi se morala upoštevati pri proizvodnji PŽP-MAB, v kolikor bi bila vzpostavljena ta proizvodnja. Abstract The paper deals with the problem of the durability of prestressed railway sleepers from fiber reinforced concrete (PRS-FRC). The development of these spleepers is briefly described up to experimental production and installation into the test field, which has been in use for 23 years. Periodic reviews monitor the behavior of the PRS-FRC during use. It is noted that until now no cracks have been observed, especially in the places where the greatest tensile stresses occur. On some PRS-FRC, damage to the lower part was detected due to abrasion and impact loads, to the extent that they had to be removed from the line. There is a solution for this problem, which should be taken into account in the production of the PRS-FRC, insofar as this production would be established. Ključne besede: prednapeti betonski železniški prag, mikroarmirani beton, jeklena vlakna, razpoke, odpornost proti abraziji, odpornost proti udaru Keywords: prestressed concrete railway sleeper, fiber reinforced concrete, steel fibers, cracks, abrasion resistance, impact resistance razvoju visokozmogljivega betonskega praga so 1. UVOD nakazale meritve in raziskave, ki so se izvajale na Razvoj novega betonskega železniškega praga v progovnih odsekih v Sloveniji, kjer so bili betonski sodelovanju s Salonit Anhovo je potekal v okviru železniški pragovi vgrajeni že nekaj let in niso vzdržali razvojno-raziskovalnega projekta, ki ga je financiralo eksploatacijskih obremenitev. Razpoke so se zelo Ministrstva za znanost in tehnologijo [1 - 4]. Potreba po pogosto pojavile na srednjem delu praga, zgoraj, kot je razvidno iz slike 1 [5]. 26. slovenski kolokvij o betonih – Projektiranje mikroarmiranih betonskih konstrukcij in njihove aplikacije, Ljubljana, 16.5.2019 92 A. Zajc, J. Šušteršič, D. Polanec Rezultati preskusov novo razvitega prednapetega Ker so mehanske lastnosti praga direktno povezane s železniškega praga iz mikroarmiranega betona (PŽP- sestavo betona, iz katerega je izdelan, je možno prirejati MAB) so pokazali, da ima bistveno izboljšane mehanske lastnosti PŽP-MAB potrebam. To pomeni, mehanske lastnosti v primerjavi s prednapetimi da bi se lahko za potrebe železnice izdelovalo več vrst betonskimi pragovi, ki so se uporabljali pri nas in drugih pragov v odvisnosti od zahtev na progah, v katere bi državah. železnica pragove vgradila. Poleg številnih preiskav karakteristik uporabljenih materialov so bile izvršene tudi preiskave samega 2.0 MAB – SESTAVA IN NEKATERE praga. Diagram v sliki 2 prikazuje obnašanje praga pri LASTNOSTI V STRJENEM STANJU tri točkovni upogibni preiskavi, kot je bila predvidena s takratnim veljavnim pravilnikom. 2.1 Sestava MAB Za izdelavo prototipnih pragov se je uporabljala sestava V trenutku pojava prve razpoke so preskušani PŽP- MAB, ki je bila določena v okviru obsežnih MAB prenesli koncentrirano obtežbo okoli 80 kN (po laboratorijskih preiskav, njena dokončna sestava pa se takrat veljavnem pravilniku je bila minimalna je določila med poskusno proizvodnjo, pri kateri so zahtevana koncentrirana obtežba v sredini pri pojavu posamezni parametri variirali med naslednjimi prve razpoke 38 kN) pri deformaciji praga približno 3 vrednostmi: mm. (a) (b) Slika 1(a), (b): Tipične razpoke na prednapetih betonskih pragih [5] Ocena trajnosti prednapetih železniških pragov iz mikroarmiranega betona 93 Preglednica 1: Povprečne vrednosti rezultatov preskusov lastnosti 90 dni starega MAB in betona brez vlaken lastnost MAB beton brez vlaken tlačna trdnost (MPa) 95,0 84,0 tlačna trdnost pri starosti 1 dan (MPa) 44,5 39,6 upogibna natezna trdnost (MPa) 8,7 7,5 udarna žilavost po Charpy-jevi metodi (kJ/m2) 18,4 10,9 odpornost proti obrusu po Böhmejevi metodi (cm3/50cm2) 11,9 14,3  cement = 300 – 340 kg/m3, povprečne vrednosti rezultatov preskusov lastnosti 90 dni starega MAB in betona brez vlaken.  (v/c)ef = 0,35 – 0,38,  jeklena vlakna (z dolžino 32 mm in premerom 0,5 2.3 Odpornost proti utrujanju mm) = 0,50 – 0,63 vol.%, Prizme dimenzij 10×10×40 cm so bile v več fazah preiskovane po naslednjem vrstnem redu: statični in  mineralni dodatek = 8,5 – 10,0 mas.% na vsebnost dinamični modul elastičnosti, upogibne karakteristike cementa, pri statični obremenitvi z risanjem delovnega diagrama  obtežba – upogib, iz katerega je bila, poleg drugih kemijski dodatek = 2,0 – 3,0 mas.% na vsebnost parametrov, določena obtežba pri prvi razpoki F cementa, b.  Nato so sledile preiskave odpornosti proti utrujanju z poroznost = 2,0 – 3,0 vol.%. naslednjimi parametri: Fmax = 0,7 – 0,9 × Fb, Fmin = 0,1 Uporabljal se je eruptivni agregat z D Fb, število ciklov N = 10.000, hitrost nanašanja obtežbe max = 16 mm. je znašala 1 cikel v sekundi. 2.2 Primerjava med nekaterimi lastnostmi Po utrujanju so se isti preskušanci preiskovali glede na strjenega MAB in betonom brez vlaken statični in dinamični modul elastičnosti ter upogibne Vpliv dodanih vlaken na mehanske lastnosti strjenega karakteristike, kot pred utrujanjem. Pri statičnem MAB je razviden iz preglednice 1, kjer so podane obremenjevanju prizme na upogib in pri utrujanju je Slika 2: Značilni diagram obtežba – upogib, dobljen s preskusom PŽP-MAB. 94 A. Zajc, J. Šušteršič, D. Polanec delovala točkovna obtežba na sredini medsebojne 4.0 VGRADNJA PŽP-MAB V POSKUSNO razdalje podpor l = 30 cm. POLJE Iz rezultatov je razvodno, da sta se po utrujanju statični Zaradi poligonalnega poteka kablov in oblike naležne in dinamični modul zmanjšala, pri večini preskušancev ploskve je bil razvit tudi nov stroj za proizvodnjo takih pa se je absorbirana energija po prvi razpoki povečala pragov, ki omogoča istočasno vibriranje betona, (slika 3). V trenutku nastanka prve razpoke se aktivirajo prednapenjanje vrvi in oblikovanje naležne ploskve. v betonu vgrajena vlakna, kar privede do povečanja Delovanje stroja je bilo preskušeno pri polindustrijski žilavosti in odpornosti MAB proti utrujanju. proizvodnji 1000 kosov pragov. V nadaljevanju projekta je sledila vgraditev pragov izdelanih v okviru polindustrijske proizvodnje v železniško progo in 3.0 STATIČNA ZASNOVA PŽP-MAB vzpostavljeno je bilo opazovanje z vstavljenimi Upoštevajoč možnosti in omejitve, ki jih nudita MAB merskimi celicami v nekatere pragove. in oblika praga je bila statična zasnova definirana na naslednji način: V sklopu remonta desnega tira na odseku Borovnica – Verd, na železniški progi Ljubljana – Sežana so bili v 1. kakovostne značilnosti MAB omogočajo uporabo letu 1996 poskusno vgrajeni PŽP-MAB in sicer v Km le štirih vrvi za prednapenjanje; 587+363/837, v krivini z R = 500 m. Preko pragov, ki so vgrajeni na medsebojni razdalji 60 cm, so položene 2. sledeč obliki praga, vrvi za prednapenjanje tirnice oblike UIC 60 s Pandrol pritrditvijo (slika 4). potekajo prostorsko poligonalno, razen v srednji tretjini praga, kjer so med seboj vzporedne in Gramozna greda je bila v celoti odstranjena ter zagotavljajo enak pozitivni in negativni moment v nadomeščena z novo iz tolčenca. Pod gramozno gredo trenutku nastanka prve razpoke; je vgrajena tamponska plast debeline 50 cm. Maksimalna hitrost vlakov na obravnavanem odseku 3. poligonalni potek vrvi v predelih praga pod znaša 80 km/h, kategorija proge pa je D3 (225 kN tirnicama zagotavlja poleg vzdolžne tudi prečno osnega pritiska ter 7,2 kN/m). tlačno napetost zaradi prednapenjanja in s tem zmanjšuje vpliv prečnih deformacij, kar je tudi sicer značilnost MAB (efekt velikega števila 5.0 PROGRAM MARITEV VGRAJENIH PŽP- drobnih stremen); MAB V POSKUSNO POLJE Z namenom opazovanja obnašanja poskusnih PŽP- 4. doseganje visokih začetnih tlačnih trdnosti MAB MAB v železniški progi so bili v 4 pragove med omogoča, ob upoštevanju manjših prečnih poskusno proizvodnjo vgrajeni merilni lističi deformacij MAB, uporabo večjih sil za meritev prednapenjanja, kar v kritičnem srednjem prerezu deformacij. Po 90 dneh starosti so bile izvedene zagotavlja višjo začetno tlačno napetost in s tem umeritvene preiskave, ki bi pri meritvah v eksploataciji omogočile definiranje dejansko nastopajočih večjo deformacijo v trenutku nastanka prve obremenitev v pragih skozi daljše obdobje uporabe. razpoke. Slika 3: Značilna delovna diagrama obtežba – upogib (F – ), dobljena pri tri točkovnem upogibnem preskusu, pred utrujanjem (1) in po utrujanju (2). Ocena trajnosti prednapetih železniških pragov iz mikroarmiranega betona 95 Nadalje je program opazovanja predvideval, da bi se Zaradi navedenega bi morale meritve potekati daljši lahko s temi meritvami ovrednotili vplivi obrabljanja čas, predvidoma najmanj 6 mesecev. Trajanje gramozne grede med dvema podbijanjima ter efekti opazovanja pa je v osnovi odvisno od: (1) kakovosti zmanjšanja obremenitev, ki naj bi se pokazali po dobljenih rezultatov, (2) stanja merilnih lističev, ki so izvedbi podbijanja. Poleg tega bi bile merljive tudi vgrajeni v pragih in (3) stanja električnih vodov, preko maksimalne obremenitve, ki lahko nastopijo v katerih se meritve izvajajo. eksploataciji ter njihova povprečna pogostost v odvisnosti od časovnega zamika med dvema Pri vsem tem pa je in bo obstajal osnovni pogoj – vzdrževalnima cikloma. zagotovljena morajo biti zadostna sredstva za izvedbo meritev in vrednotenje dobljenih rezultatov. Za izvedbo Slika 4: Pritrjene trnice oblike UIC 60 na PŽP-MAB s Pandrol pritrditvijo. Slika 5: Shema principa meritev dinamičnih deformacij PŽP-MAB [6]. 96 A. Zajc, J. Šušteršič, D. Polanec predmetnih meritev so bila pridobljena sredstva, ki so merilne lističe. Rezultati meritev so podani v poročilu omogočala izvedbo le uvodnih meritev. [6], v obliki diagramov. Shematičen prikaz izvajanja meritev je razviden iz slike 5. 6.0 MERJENJE DINAMIČNIH DEFORMACIJ V slikah 6 do 8 so podani diagrami, ki prikazujejo PŽP-MAB specifične deformacije (ɛ) v odvisnosti od časa (t) med Meritve je zasnoval in izvedel Laboratorij za tehnično prehodom različnih vrst kompozicij vlakov (dveh fiziko Fakultete za strojništvo Ljubljana. Uvodne tovornih – A v sliki 6 in B v sliki 7 ter enega potniškega meritve deformacij med prehodom vlaka so se izvedle v sliki 8). V vsaki od teh slik je podana skica praga na enem od štirih PŽP-MAB, ki so imeli vgrajene z označenimi mesti merilnih lističev: (poz. 1) na Slika 6: Specifične deformacije PŽP-MAB pri prehodu tovornega vlaka A [6]. Slika 7: Specifične deformacije PŽP-MAB pri prehodu tovornega vlaka B [6]. Ocena trajnosti prednapetih železniških pragov iz mikroarmiranega betona 97 spodnjem delu praga, pod tirnico, (poz. 2) na spodnjem informacij dobilo z dolgotrajnimi meritvami, najmanj 6 deli praga, na sredini in (poz. 3) na zgornjem delu praga, mesecev, na osnovi katerih bi se dalo sklepati o na sredini. obnašanju vgrajenih PŽP-MAB med uporabo. Kot je razvidno iz vseh treh slik (6 do 8), so največje specifične deformacije dobljene v natezni coni, na 7.0 VIZUALNA OPAZOVANJA OBNAŠANJA zgornjem delu praga, na sredini (poz. 3). V odvisnosti VGRAJENIH PŽP-MAB od vrste vlaka in mase lokomotive ter vagonov so prav Vizualna opazovanja obnašanja vgrajenih PŽP-MAB tako lahko velike natezne specifične deformacije na potekajo ves čas od vgradnje pa do danes, to je v spodnjem delu praga, pod tirnico (poz. 1). Relativno obdobju njihove uporabe 23 let. majhne pa so specifične deformacije v tlačni coni, na spodnjem delu praga, na sredini (poz. 2). Dobljene Po treh letih uporabe vgrajenih PŽP-MAB so Slovenske specifične deformacije so bile pričakovane. Kot je bilo železnice, Sekcija za vzdrževanje prog Postojna že podano v programu meritev, bi se dosti več pripravile poročilo o stanju desnega tira Borovnica – Slika 8: Specifične deformacije PŽP-MAB pri prehodu potniškega vlaka [6]. Slika 9: Grajeni PŽP-MAB po 9 letni uporabi. Posneto v smeri Postojna, v obratni smeri vožnje vlakov 98 A. Zajc, J. Šušteršič, D. Polanec Verd na odseku z PŽP-MAB [7]. V tem poročilu je MAB ugotovljene nobene poškodbe in razpoke (slika podano naslednje mnenje: »Pri dosedanjem spremljanju 9). stanja tira z merilnim vozom ter vizualnimi pregledi V letošnjem letu, to je po 23 letni uporabi je IRMA ugotavljamo, da je stanje tira na obravnavanem odseku izvedel ponovni detajlni pregled vgrajenih PŽP z mikroarmiranimi betonskimi pragi dobro, tako v -MAB pogledu stabilnosti kakor tudi v pogledu smerne in (slika 10). višinske ureditve tira. V medtirju, t.j. na notranji strani Pri pregledu posameznih vgrajenih PŽP-MAB prav krivine, je opaziti bel gramoz od brušenja zaradi tako ni bilo opaziti poškodb. Posebna pozornost je bila vibracij pri prevozu vlakov. Pri vizualnih pregledih posvečena pregledu zgornjega dela pragov, na sredini, vgrajenih mikroarmiranih betonskih pragov nismo kjer bi se lahko pojavile razpoke. Ta predpostavka opazili kakršnikoli nepravilnosti ali poškodb oz. izhaja iz rezultatov meritev PŽP-MAB (slike 6 – 8) in razpok.« ugotovljenih razpok na enih od prvih vgrajenih Po 9 letni uporabi je bil izvršen detajlni pregled s strani prednapetih betonskih pragih pri nas (slika 1(a), (b)). IRMA. Pri tem pregledu pav tako niso bile na PŽP- Slika 10: Vgrajeni PŽP-MAB po 23 letni uporabi. Posneto v smeri Postojna, v obratni smeri vožnje vlakov. Slika 11: Vgrajeni PŽP-MAB po 23 letni uporabi brez razpok na zgornjem delu, na sredini. Ocena trajnosti prednapetih železniških pragov iz mikroarmiranega betona 99 Takih razpok na PŽP-MAB po 23 letni uporabi ni bilo To pomeni, da so se vlakna pri vgrajevanju (med opaziti (slika 11). vibriranjem) neenakomerno razporedila po celotni masi svežega betona. Vlakna so med vibriranjem tonila v Na površini pragov je bilo opaziti jeklena vlakna, ki svežem betonu tako, da je na zgornjem delu opaženega rjavijo (slika 11). Korozijski produkti tankega vlakna praga (spodnjem delu vgrajenega praga) (slika 16) (0,5 mm) pa niso taki, da bi razdirali betonsko matrico prisotna relativno najmanjša količina vlaken. (slika 12). Zaradi manjše količine vlaken na spodnjem delu PŽP- Že predhodne raziskave [8] so pokazale, da jeklena MAB se je zmanjšala odpornost MAB proti obrusu po vlakna samo na površini ali blizu površine elementov iz Böhmejevi metodi. Iz preglednice 1 je razvidno, da MAB rjavijo in povzročajo površinsko barvanje z rjavo dodana predvidena količina vlaken povečuje odpornost barvo zaradi nastajanja rje, ki ne vpliva na trdnost in MAB proti obrusu, oziroma količina obrušenega MAB žilavost MAB, vendar vliva na videz površine elementa. je manjša od količine obrušenega betona brez vlaken. Z zmanjševanjem količine vlaken se odpornost MAB Pri nadaljnjem pregledu je bilo na nekaj mestih opaziti zamenjavo PŽP proti obrusu zmanjšuje. -MAB z lesenimi pragovi (slika 13). Na odstranjenih PŽP Iz preglednice 1 je prav tako razvidno, da je udarna -MAB je razvidno, da je prišlo na spodnjem delu do abrazijskih in mehanskih poškodb žilavost MAB s predvideno količino vlaken precej večja (slika 14). Na nekaterih seže poškodba do kabla (slika v primerjavi z betonom brez vlaken. Z zmanjševanjem 15). Iz te fotografije je možno tudi videti, da je v betonu količine vlaken se tudi zmanjšuje udarna žilavost MAB, prisotnih zelo malo število jeklenih vlaken, kar je zaradi česar prihaja med podbijanjem do dodatnih poškodb spodnjega dela PŽP opaziti tudi na spodnjih delih vseh ostalih odstranjenih -MAB. PŽP-MAB. Slika 12: Jekleno vlakno z dolžino 30 mm in premerom 0,5 mm na površini praga. Slika 13: Zamenjava na spodnjem delu abrazijsko in mehansko poškodovanih PŽP-MAB z lesenimi pragovi. 100 A. Zajc, J. Šušteršič, D. Polanec 8.0 MOŽNOSTI NADALJNJEGA RAZVOJA IN proizvodnji, to je enakomerna porazdelitev vlaken po UPORABE PŽP-MAB celotnem volumnu praga. Na ta način se bo izboljšala, V kolikor bi obstajala možnost vgradnje PŽP ne samo odpornost proti obrabi in proti udarnim -MAB v obremenitvam spodnjega dela PŽP določene -MAB, ampak tudi progovne odseke v Sloveniji, bi bilo potrebno učinkovitost dodanih jeklenih vlaken. Pri tem bo pri pripravi novih PŽP-MAB upoštevati in popraviti potrebno upoštevati ugotovitve raziskav, kjer je v pomanjkljivost, ki se je pokazale pri poskusni Slika 14: Na spodnjem delu abrazijsko in mehansko poškodovani PŽP-MAB.. Slika 15: Poškodbe spodnjega dela PŽP-MAB do kabla. Ocena trajnosti prednapetih železniških pragov iz mikroarmiranega betona 101 zaključkih podana ugotovitev, da se na osnovi dobljenih vibracij kompozitov z granulirano gumo in z različnimi rezultatov laboratorijskih preiskav in matematičnega modificiranimi sestavami [10, 11] izkazujejo, da bi se modela sklepa, da učinkovitost dodanih jeklenih vlaken lahko ti kompoziti uporabljali za zgoraj opisan namen. v MAB ni odvisna samo od njihovih dimenzij in količin, ampak tudi od kakovosti cementne paste, pri čemer ima 9.0 ZAKLJUČEK pomemben vpliv tudi njena poroznost [9]. Na osnovi občasnih pregledov vgrajenih PŽP-MAB v Še vedno pa ostaja globalno vprašanje o smiselnosti poskusno polje se lahko zaključi, da v obdobju 23 letne uporabe betonskih železniških pragov, vgrajenih na uporabe ni prišlo do nastanka razpok, predvsem na gredo iz apnenčevega agregata, kar je slučaj na trasah mestih največjih nateznih napetosti, to je na sredini slovenskih železnic. Betonski pragovi bi se morali praga, zgoraj. Zaradi neenakomerne porazdelitve vgrajevati na gredo iz eruptivnega agregata, ki pa je v jeklenih vlaken po volumnu praga je prišlo na nekaterih Sloveniji na razpolago v zelo omejenih količinah. Zato PŽP-MAB do poškodb na spodnjem delu tako, da so obstaja in bo obstajala samo ena možnost, da se morali biti odstranjeni s proge. Poškodbe so nastale betonski pragovi še veno vgrajujejo na gredo iz zaradi abrazijskih in udarnih obremenitev. V zadnjih apnenčevega agregata. Pri tem pa je potrebno, da se na 20. letih so pridobljena nova znanja, na osnovi katerih spodnjo (naležno) površino praga pritrdi plast gume. Ta obstaja možnost rešitve tega problema. Ostaja pa še guma mora biti sposobna dušiti vibracije, ki nastopijo vedno osnovni problem uporabe betonskih železniških med prehodom vlaka preko teh pragov. Na ta način bi pragov, vgrajenih na gredo iz apnenčevega agregata. Ta se zmanjšala intenzivnost drobljenja apnenčevih zrn, ne problem bi se dal delno rešit z izdelavo sloja spodnje, samo zgornjega, ampak tudi spodnjega ustroja grede. naležne površine praga z določeno debelino iz Obstaja pa tudi možnost, da se spodnji del praga, v materiala, ki ima sposobnost absorbiranja vibracij. določeni debelini izdela iz betonskega kompozita z granulirano gumo. Številni rezultati preskusa dušenja Slika 16: Princip izdelave PŽP-MAB. 102 A. Zajc, J. Šušteršič, D. Polanec LITERATURA 8. Šušteršič J., Zajc A., Leskovar I., Ercegovič, R. Study of corrosion resistance of steel fibres in 1. Zajc A. et al Razvoj mikroarmiranega betonskega železniškega praga. RR projekt, M SFRC. V: OH, B. H. (ur.). Concrete under severe inistrstvo za conditions: environment and loading : proceedings znanost in tehnologijo – 42-0820-93. IRMA. 1993. of the Fourth International Conference on 2. Korla J., Zajc A., Šušteršič J. Prenapeti betonski Concrete under Severe Conditions, CONSEC ʼ04, prag iz mikroarmiranega betona. Zbornik gradiv in Seoul, Korea, June 27-30, 2004. Volume 2. Seoul: referatov. Slovenski kolokvij o betonih. Seoul National University, Korea Concrete Mikroarmirane malte in betoni. Ljubljana 1994. Institute. 2004. IRMA . str. 31 – 36. 9. Šušteršič J., Korla J., Zajc, A. Učinkovitost jeklenih 3. Šušteršič J. Vorgespannte Eisenbahnschwellen vlaken v mikroarmiranih betonih in brizganih aus Stahlfaserbeton. Zem. Beton (Vienna), vol. 37. betonih. Zbornik referatov, 10. mednarodni 1995. simpozij o gradnji predorov in podzemnih 4. Šušteršič J. Vorgespannte Eisenbahnschwellen prostorov, 16-18 november 2011, Ljubljana: aus Stahlfaserbeton. Bau im Spiegel. jesen 1996. Naravoslovnotehniška fakulteta, 2011, str. 205- str. 9. 211. 5. Leskovar I., Zajc A. Poročilo o preiskavah 10. Šušteršič J. Sposobnost dušenja vibracij betonov z materialno – tehničnega stanja prednapetih granulirano gumo. Doseganje posebnih lastnosti železniških pragov na progi Borovnica – Preserje. betonov z uporabo odpadnih materialov : zbornik Opr. št. 585-90/5013-Če. ZRMK, Inštitut za gradiv in referatov. Ljubljana: IRMA, Inštitut za materiale. 29.05.1990. raziskavo materialov in aplikacije. 2012, str. 31- 40. 6. Susič E., Mužič P, Grabec I. Poročilo o merjenju dinamičnih deformacij železniških pragov. 11. Šušteršič J. Ability of mechanical vibration Univerza v Ljubljani, Fakulteta za strojništvo, damping of fiber reinforced polymer and latex- Laboratorij za tehniško fiziko. Ljubljana, april modified concrete with granulated rubber. 1996. 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