UDK 625.821.5:691.332.2:57.012.3 ISSN 1580-2949
Original scientific article/Izvirni znanstveni ~lanek Mater. Tehnol.
A. WALIITAGI et al.: PERFORMANCE EVALUATION AND MICROSTRUCTURAL ASSESSMENT OF ECO-FRIENDLY ...
917–926
PERFORMANCE EVALUATION AND MICROSTRUCTURAL
ASSESSMENT OF ECO-FRIENDLY CONCRETE WITH
MICRONIZED BIOMASS SILICA AND STEATITE POWDER
OVREDNOTENJE LASTNOSTI IN OCENA MIKROSTRUKTURE OKOLJU
PRIJAZNEGA BETONA Z DODATKOMA IZ MIKRONIZIRANE SILIKATNE
BIOMASE IN STEATITNEGA PRAHU
Asha Waliitagi1*, A. K. Dasarathy1, Vijaya Sarathy Rathanasalam2
1Department of Civil Engineering, Faculty of Engineering and Technology, Jain (Deemed-to-be University), Bengaluru 562112, India
2Department of Civil Engineering, Atria Institute of Technology, Bengaluru 560024, India
Prejem rokopisa – received: 2025-09-23; sprejem za objavo – accepted for publication: 2025-10-14
doi:10.17222/mit.2025.1553
Cement is the most widely used binder in concrete around the globe. Natural assets are utilised as raw materials to make the es-
sential components used in the production of concrete. This process requires an enormous quantity of energy and emits green-
house gases, especially carbon dioxide (CO2), which contribute to global warming and have an adverse effect on the environ-
ment. These hazardous emissions produced by the cement industry can be minimized by employing alternate approaches, such
as partially replacing cement with supplementary cementitious materials (SCMs). Many research investigations examined the ef-
fectiveness and performance of pozzolanic substances as an alternative to cement. In the present study, cement is partly replaced
with different SCMs, such as micronized biomass silica (MBS) and steatite powder (SP). Various proportions of MBS – (3, 6, 9
and 12) % – were used. Furthermore, a consistent SP content of 5–10 % was utilised. Fresh, mechanical and microstructural fea-
tures of concrete were studied after the inclusion of SP and MBS. The incorporation of 6 % MBS and 5 % SP generated an ex-
cellent compressive strength of 41 MPa, which was 17 % higher than that of ordinary concrete. Similarly, the split tensile and
flexural strengths were 3.66 MPa and 4.5 MPa, respectively. It was observed that introducing these elements to cement en-
hanced its mechanical and microstructural properties. Thus, the optimal combination determined included 5 % SP and 6 %
MBS. According to the scanning electron microscopy (SEM) study, the structure of the concrete matrix was improved by seal-
ing the micropores and interfacial transition zone (ITZ) with the calcium silicate hydrate (CSH) and magnesium silicate hydrate
(MSH) gels, resulting in a denser microstructure. These components demonstrated their ability to substitute cement without im-
pairing the performance of concrete. Overall, MBS and SP are excellent supplementary cementitious materials. Thus, the results
of this research have practical significance for potential application of these components in the production of sustainable con-
crete.
Keywords: steatite powder, micronized biomass silica, interfacial transition zone
Cement je na svetu najbolj pogosto vezivo, ki se uporablja za izdelavo betona. Za proizvodnjo betona se poleg tega uporabljajo
{e druge dragocene naravne surovine. Proizvodnja cementa zahteva tudi ogromne koli~ine energije in proizvaja toplogredne
pline, predvsem CO2, ki prispeva k globalnemu segrevanju in tako ima negativni vpliv na okolje. Te nevarne izpuste
toplogrednih plinov, ki jih proizvaja industrija cementa, je mogo~e zmanj{ati z alternativnimi pristopi, kot je naprimer delna
zamenjava cementnega veziva z dodatnimi cementitnimi materiali (SCM; angl.: supplementary cementitious materials). Mnoge
znanstvene raziskave so bile namenjene ugotavljanju u~inkovitosti in sposobnosti pucolanske snovi (finozrnat vulkanski pepel)
kot alternativa cementu. Ime »pucolanski« materiali so dobili po mestu Pozzuoli v Italiji, kjer so ga prvi odkriti in uporabili
Rimljani. V tem ~lanku pa avtorji opisujejo raziskavo v kateri so cement delno nadomestili z razli~nimi dele`i SCM, kot sta
biomasa mikronizirane silike (MBS; angl.: micronized biomass silica) in steatitni prah (SP). Uporabili so razli~ne kombinacije
dele`ev MBS (3%, 6%, 9% in 12%) in SP (od 5% do 10%). Nato so analizirali mehanske in strukturne lastnosti izdelanega
betona v odvisnosti od vsebnosti izbranih dodatkov. Z dodatkom 6% MBS in 5% SP so dobili odli~en cement s tla~no trdnostjo
41MPa, kar je za 17 % vi{ja vrednost kot jo ima standardni beton. Podobno odli~ni sta bili tudi vrednosti za cepilno (3,66 MPa)
in upogibno trdnost (4,5 MPa). Tako so avtorji raziskave dobili potrditev, da vpeljava teh dveh dodatkov k cementu izbolj{a
mikrostrukturne in posledi~no mehanske lastnosti betona. Analize so pokazale, da je optimalna kombinacija dodatkov 5 % SP in
6 % MBS. Pregled in analiza strukture izdelanega betona pod vrsti~nim elektronskim mikroskopom (SEM) sta pokazali, da je
zaradi dodatkov pri{lo do zapiranja mikropor in medfazne prehodne cone (ITZ; angl.: interfacial transition zone) s
silikat-hidratnima geloma na osnovi Ca (CSH) in Mg (MSH). To je povzro~ilo nastanek gostej{e mikrostrukture. Ta dva dodatka
sta dokazala, da sta sposobna zamenjati del cementa, ne da bi pri tem pri{lo do poslab{anja lastnosti betona. Skratka, MBS in SP
sta odli~na dodatna cementna materiala.Zato imajo rezultati te raziskave prakti~en pomen za potencialno uporabo teh
komponent pri proizvodnji trajnostnega okolju prijaznega betona.
Klju~ne besede: steatitni prah,mikroniziranana silikatna biomasa, medfazna prehodna cona
*Corresponding author's e-mail:
waliitagiasha@gmail.com (Asha Waliitagi)
© 2025 The Author(s). Except when otherwise noted, articles in this jour-
nal are published under the terms and conditions of the Creative Com-
mons Attribution 4.0 International License (CC BY 4.0).
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1 INTRODUCTION as binder ingredients greatly decrease the cost and CO2
emissions while improving the concrete’s performance.18
Concrete is a composite material made from renew- There have been numerous studies on the effective-
able resources. It is employed around the world because ness of ordinary concrete that contains an agricultural
of its flexibility and economic benefits.1 A key ingredient byproduct such as RHA, but limited research has been
in the production of concrete is cement and its demand is done on concrete that incorporates MBS. Rice husk is
high due to rapid urban sprawl and infrastructural devel- burned under controlled conditions at 500–600 °C in a
opment.2 As cement is the primary binding component of rotating kiln to produce MBS. The husk is then crushed
concrete, the construction industry has increased its pro- in a jar mill for several hours to minimize the particle
duction.3 The manufacturing of cement causes consider- size. This process is called micronization; and since the
able energy consumption, resource depletion and global silica content is significantly higher than that of RHA,
climate change, as it emits significant amounts of CO2 as the product is referred to as micronized biomass sil-
well as other fluorinated gases.4 Around 7 % of CO2 is ica.19–22 MBS accounts for 20 % of the 590 million
produced annually by the fabrication of ordinary Port- tonnes of paddy produced globally. In addition, CSH gel
land cement; every metric tonne of Portland cement is formed as a result of silica’s interaction with hydration
clinker is proportional to around one metric tonne of products. This enhances the durability and strength of
CO2, which affects the atmosphere. This environmental concrete.23 The performance of the ready-mix geo-
contamination can be reduced by including a substitute polymer is enhanced when up to 20 % of MBS is re-
element instead of cement.5 Three quarters of the world’s placed with GGBS.24 All curing ages show the greatest
energy consumption and 40 % of its greenhouse gas strength metrics at 25 % blending, including nano-
emissions are due to the fabrication activity.6 For the de- biomass silica, polycarboxylate ether, and a bio-admix-
velopment of infrastructure, it is necessary to provide en-
ture.25 It was determined that the geopolymer concrete
vironmentally friendly and economically feasible con-
mix with 20 % MBS and the remaining proportion of
struction materials,7 limiting the emissions of greenhouse
gases while improving the infrastructure.8 For the GGBS as the binder exhibit the best performance in
long-term progress of the cement industry, while achiev- terms of strength and durability.26 According to the find-
ing sustainability goals and conserving earth’s resources, ings, the strength of concrete increases with MBS up to a
some important parameters must be considered such as certain level, after which it declines and is further
reducing the clinker-to-cement ratio, applying novel strengthened by fibres. The perfect blend for concrete is
technologies like carbon capture and using other supple- achieved with a 10 % MBS content and a 0.2 % fibre ad-
mentary cementitious compounds.9 dition.27 It was established that specimens containing
The process of making green concrete incorporates a 20 mL of bacteria and 8 % MBS give the most effective
variety of residues and byproducts which otherwise end results.28 The utilization of 10 % MBS combined with
up in landfills, but can be used as alternative cement- construction and demolition waste provided greater com-
itious elements.10 These can be developed from natural pressive, split-tensile, and flexural strength.29 After 28 d
pozzolans, dust, powders, ashes, natural minerals, indus- of curing, tests demonstrated that concrete containing
trial and agricultural byproducts such as fly ash (FA), 12 % MBS and 100 % recycled aggregate (RA) may re-
ground granulated blast furnace slag (GGBS), rice husk duce water permeability and increase compressive
ash (RHA), silica fume, metakaolin, marble powder, strength up to a certain level.30 It is feasible to replace ce-
glass powder, limestone powder, palm oil fuel ash, egg- ment with about 20 % MBS without affecting its perfor-
shell powder, volcanic pumice powder, ceramic waste mance, and a 10 % replacement results in good
powder (CWP), biomass fly ash, etc. SCMs have the po- strength.31 The identified ideal percentage is 12 % MBS,
tential to lower concrete’s carbon footprint.11,12 The in- which allows excellent concrete performance in terms of
clusion of SCMs in the materials composed of cement water permeability and compressive strength.32
influences its characteristics, notably its chemical reac- Steatite powder is a metamorphic material with a
tion, formation of strength, microstructure and durabil- high talc content, which gives it a great degree of versa-
ity.13 All these byproducts are utilised in different types tility and consists mainly of hydrated magnesium sili-
of concrete such as ultra-high-performance concrete, cate. SP is also known as soapstone.33 According to the
high strength concrete, mass concrete, self-compacting United Nations Framework Classification for Resources
concrete (SCC), geopolymer concrete (GPC), etc.14,15 as of 2010, steatite reserves and resources are estimated
The strength properties are enhanced by adding waste to be 269 million tonnes, of which a substantial amount
biomass ash and silica sand, substituting up to 10 % of (22 %) is available in Karnataka.34 SP is used in different
cement. Concrete with partial cement replacement could industries, producing paints, ceramics, pottery and poly-
be suitable for low-strength precast elements.16 A 15 % mers.35 Various researchers found that steatite powder
amount of textile effluent sludge in concrete can allow has a stable crystal structure and high chemical resis-
for the most effective fresh, mechanical, and non-de- tance; hence, it can be potentially employed as an SCM
structive outcomes.17 According to the results, the use of and used for special concrete, including self-compacting
ESP and agricultural waste from date palm trees acting concrete, geopolymer concrete and self-healing con-
918 Materiali in tehnologije / Materials and technology 59 (2025) 6, 917–926
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crete.36,37 Cement can be replaced by two materials, a longer hydration time.48 The above makes it apparent
namely FA and up to 30 % SP, which provide for a that there are numerous studies on MBS with different
higher strength compared to the reference concrete.38 supplementary cementitious substances and SP with
When the amount of ultrafine natural steatite powder other sustainable materials in the scientific literature.
(UFNSP) is increased, the water requirement is also However, the research gap, or the grey area, is the mix-
higher and workability is reduced; however, the effective ture of MBS and SP, as there are no studies discussing
strength gain in concrete is achieved at the steatite opti- this combination. To ensure environmental sustainability,
mum dose of 15 %.39 Similarly, greater strength is ob- concrete should provide both strengths and benefits to
served with additions of 40 % GGBS and 10 % the ecology and economy. Therefore, the purpose of this
UFNSP.40 According to research, the addition of 15 % research is to evaluate the fresh, mechanical and
UFNSP results in peak strength and mechanical proper- microstructural characteristics of cement concrete that
ties remain high up to 20 % UFNSP due to its fine parti- contains MBS and SP. It is anticipated that the use of
cle size. In SCC and self-healing concrete, the inclusion MBS and SP will result in the creation of environmen-
of 15 % steatite powder achieves the optimum value.41 tally conscious infrastructures.
The incorporation of SP results in a rigid structure
and strengthens alkali-activated UFNSP-based geopoly-
mer mortar.42 Cement can be replaced with 15 % SP and 2 EXPERIMENTAL INVESTIGATION
polypropylene fibre, which produce good results.43 An
SEM study reveals that the mapping of silicate and mag- 2.1 Material
nesium shows uniform surface dispersion and the forma-
tion of magnesium silicate hydrate gels, which improve Ordinary Portland cement (OPC) of grade 53, which
the strength and durability and contribute to the develop- complies with IS 12269:2013, a cementitious compound
ment of denser forms.44 The amounts of pores in con- with a specific gravity 3.15, was used to make concrete
crete are reduced and the microstructure of geopolymer mixes. For the fine aggregate (FAG), crushed stone sand
concrete is improved using SP.45 The formation of CSH with a specific gravity of 2.65 was selected in accor-
and MSH is observed with SEM. When specimens are dance with IS 383:2016 and grading zone II standards.
treated with UFNSP, their microstructure density in- Furthermore, a coarse aggregate (CAG) having a specific
creases, leading to enhanced strength and decreased gaps gravity of 2.7 and a nominal diameter of 20 mm, that
in the concrete structure.46 A recent study showed that was easily accessible, was utilized. Potable water that
utilization of metasteatite, a thermally processed form of complied with IS: 456:2021 was employed in this experi-
steatite, results in the formation of magnesium sili- ment for the purpose of mixing and curing. Conplast
cate-rich compound and improved particle packing, lead- SP430, a chemical admixture, was added to maintain
ing to a dense and continuous microstructure. The 10 % workability. The SCM employed in the investigation in-
metasteatite improves the magnesium oxychloride ce- cluded MBS and SP. The grey MBS and white SP with
ment paste, exhibiting its effectiveness in enhancing re- specific gravities of 2.28 and 2.25 had been procured
silience to water.47 With 10–25 wt.% metasteatite, each from a local supplier. Figure 1 depicts the SP and MBS.
mixture shows a significant improvement in the strength Chemical characteristics of the MBS and SP are listed in
after 14 d and 28 d, along with a noticeable trend toward Table 1.
Figure 1: Steatite powder and micronized biomass silica
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Table 1: Chemical compositions of MBS and SP flow chart. In the cement, the amounts of SP were
Chemical composition MBS (%) SP (%) maintained at 5 % and 10 %, while the MBS proportions
SiO2 95.561 62.566 varied from 0 % to 12 % in an interval of 3 %. Among a
Al reference blend, four mixtures without SP, five mixtures
2O3 – 3.005
Fe2O3 0.164 2.51 with 5 % SP, and five mixtures with 10 % SP were pre-
CaO 0.797 1.42 pared, resulting in a total of 15 mix combinations. All
MgO – 30 mixes had a water-cement ratio of 0.43 and contained
K2O 1.982 – 1 % superplasticizer by weight of the cement. Precise
SO3 0.25 0.12 mix designs are listed in Table 2.
TiO2 – 0.22 For the mixes, raw ingredients such as cement, MBS,
Cl 0.314 – SP, fine and coarse aggregates were weighed and
P2O5 0.805 – blended in dry conditions, then mixed with water and
superplasticizer. The workability of the new concrete
2.2 Mix proportions and methodology mixes was evaluated using a (100 × 200 × 300) mm
slump cone in compliance with IS 1199:2018 before the
In accordance with IS 10262:2019, the processes for specimens were cast in moulds. To assess the hardened,
obtaining the necessary components for standard con- the specimens were demoulded after 24 h, kept for cur-
crete were carried out. This study created an M30 con- ing in a curing tank, and then they were examined after
crete mix by substituting cement with supplementary 7 d and 28 d. To determine the compressive strength, a
binders MBS and SP. Figure 2 displays the methodology
Table 2: Mix proportions (kg/m3)
Mix ID Cement MBS SP FAG CAG Water Superplasticizer
M0S0 356.43 0 0 821.58 1109.62 153.264 3.56
M3S0 345.73 10.69 0 821.58 1109.62 153.264 3.56
M6S0 335.04 21.38 0 819.3 1106.54 153.264 3.56
M9S0 324.35 32.08 0 819.3 1106.54 153.264 3.56
M12S0 313.66 42.77 0 819.3 1106.54 153.264 3.56
M0S5 338.61 0 17.82 819.3 1106.54 153.264 3.56
M3S5 327.92 10.69 17.82 818.16 1105.002 153.264 3.56
M6S5 317.22 21.38 17.82 817.02 1103.46 153.264 3.56
M9S5 306.53 32.08 17.82 817.02 1103.46 153.264 3.56
M12S5 295.84 42.77 17.82 815.88 1101.92 153.264 3.56
M0S10 320.78 0 35.64 815.88 1101.92 153.264 3.56
M3S10 310.09 10.69 35.64 815.88 1101.92 153.264 3.56
M6S10 299.4 21.38 35.64 814.74 1100.38 153.264 3.56
M9S10 288.7 32.08 35.64 813.6 1098.84 153.264 3.56
M12S10 278.02 42.77 35.64 813.6 1098.84 153.264 3.56
Note: M = micronized biomass silica (MBS) and S = steatite powder (SP)
Figure 2: Methodology flow chart Figure 3: Testing of compressive strength and split tensile strength
920 Materiali in tehnologije / Materials and technology 59 (2025) 6, 917–926
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150 mm cube was constructed as per IS 516:2018. Simi-
larly, for the split tensile strength test, cylindrical speci-
mens measuring 150 mm in diameter and 300 mm in
height were utilized in accordance with IS 5816:2004.
Figure 3 shows the testing of compressive strength and
split tensile strength. The flexural strength test was con-
ducted using a beam with dimensions of (100 × 100 ×
500) mm as per IS 516:2018.
3 RESULTS AND DISCUSSION Figure 5: Compressive strength of concrete with various mix combi-
3.1 Fresh properties nations
Concrete’s fresh characteristics were examined using crease, the strength of the concrete mixture grows as
the slump cone test, as described in IS 1199:2018. Slump well up to a certain point. Similarly, when both MBS and
values for mixtures M3S5 and M3S10 were found to be SP mix combinations rise, the strength value also in-
78 mm and 75 mm, indicating a minor effect on work- creases to a certain level compared to the control con-
ability. Moderate workability was indicated for M6S5 crete. In comparison to all other mixtures, mix M6S5
and M6S10, when the slump values decreased to 75 mm provided an excellent strength of 41 MPa, which is 17 %
and 73 mm. Furthermore, M9S5, M12S5, M9S10, and higher than that of the control concrete. However, the
M12S10 showed a notable decrease in workability with strength of M12S10 is 12 % lower than that of ordinary
slump values of (70, 68, 69 and 65) mm, respectively. A concrete, with an exceptionally low strength of
medium slump was observed for the optimum mixture. 31.2 MPa. When cement is partially replaced with 5 %
The slump values for different mix compositions are dis- SP along with (3, 6, 9 and 12) % MBS, the compressive
played in Figure 4. The results show that when the MBS strength values are higher than that of ordinary concrete.
and SP content increased, the slump values gradually de- However, the results are less favourable when 10 % SP is
creased because the concrete mixture absorbed more wa- incorporated together with the same percentage of MBS.
ter.27,37 The presence of finer MBS and SP particles could Based on the present work, the inclusions of 6 %
potentially explain this observation. The high specific ar- MBS and 5 % SP gave the optimum result. The main
eas of MBS and SP are one of the reasons for not achiev- cause for the strength improvement was the bonding be-
ing high workability, but the addition of superplasticizer tween the cement paste and aggregate. Due to fine parti-
helped them achieve the medium slump. Increased con- cles of MBS and SP, the cement binder became more ef-
tents of MBS and SP appear to contribute to the rigidity fective and concentrated. The CSH from MBS and the
of the mixtures.22 The cellular structure of MBS in- MSH gel from SP were generated during concrete
creases the absorption capacity of concrete, reducing the hydration. This minimised the weakest zone between the
amount of water available for workability.30,31
paste and aggregate called ITZ, and diminished the large
space in the matrix. The development of the concrete’s
3.2 Compressive strength strength highly improved due to this mechanism. It was
The strength of the cement concrete, which combines observed that as the formation of CSH and MSH gel
MBS and SP as the substitutes, was examined using a from pozzolanic action decreased, the filling of micro-
compression testing machine. The specimens that were pores and ITZ was reduced and the compressive strength
evaluated for compressive strength are represented in also decreased due to a higher level of inclusions of
Figure 5. Each strength result is the average of three MBS and SP. Based on the research, the ideal replace-
specimens that were tested after 7 d and 28 d. Once the ment percentage for MBS and GGBS was 20 % of the
cement replacement including only MBS continues to in- total weight, which also positively affected the compres-
sive strength of the material.23 Because of MBS, the
presence of more CSH gel and primary alumina silicate
gel helped the geopolymer reach a higher strength.26 It
was shown that the compressive strength increased with
up to 8 % of MBS and 20 mL of bacterial solution after
MBS was incorporated, partially replacing cement. MBS
performs as a pozzolanic material in the process of
hydration and as a filler increasing the density of micro-
systems.28 Similarly, the strength the RA concrete incor-
porating MBS was enhanced, indicating that long-term
strength improvements are facilitated by MBS.30 The in-
clusion of SP and other supplementary cementitious ma-
Figure 4: Slump values for different mix compositions terials like FA, GGBS and fibres leads to the formation
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of MSH and CSH gels, resulting in a significant im-
provement in the strength of concrete, SCC and
GPC37,39,43
3.3 Split Tensile strength
The split tensile strength of concrete with different
mix proportions cured for 7 and 28 days is illustrated in
Figure 6. Based on the studies, it was found that the split
tensile strength of the M3S5, M6S5, M9S5, and M12S5
concrete was (17, 23, 13 and 11) % higher compared to
the control concrete. Likewise, the split tensile strength Figure 7: Flexural strength of the concrete mixtures
of M3S10, M6S10, M9S10, and M12S10 was (12, 15, 11
and 9) % higher than that of the regular concrete. Excel- after 28 d. Meanwhile, the flexural strength declined
lent strength was achieved by the M6S5 combination, with an increase in the MBS & SP proportion. The
i.e., 3.66 MPa after 28 d, which was 23 % higher than strength was enhanced with the incorporation of MBS &
that of the reference concrete. The primary cause of this SP and the increased hydration effect. The packing ca-
strength increase was the fine MBS and SP particles. By pacity of concrete also increased. However, the spherical
reacting with cement hydrates during the pozzolanic re- particles of MBS caused inadequate bonding amongst
action, these substances created secondary CSH and other concrete ingredients, therefore the flexural strength
MSH gels in the mixture, strengthening the com- diminished above 8 % of MBS.28 When SP and poly-
positional bond, lowering the ITZ, minimising the propylene fibre were added to concrete, the flexural
microcracks, and improving the split tensile strength. strength increased by 31 % compared to ordinary con-
Nevertheless, as the proportion of MBS and SP in the crete.43 It was demonstrated that integrating MBS to the
mixture increased, these substances affected the work- concrete mix, combined with treated RA improved the
ability of concrete by reducing its water content and de- flexural strength.22
creasing its split tensile strength. The hydration mecha-
nism was improved due to the SiO2 concentration in the
MBS, which was above 80 %; thus, the strength in- 3.5 Microstructural studies
creased with 8 % MBS and 20 mL of bacterial replace-
ment.28 The results indicated that when 15 % SP and The microstructural investigation of the concrete was
10 % FA were incorporated into a special type of con- carried out using SEM. In this research, SEM images
crete, like SCC, the tensile strength increased by up to 19 were generated to find optimal mix combinations such as
%.39 In a similar way, adding 0.5 % of polypropylene M6S5. Figure 8 depicts a SEM visualization of the
fibres and 15 % of the steatite powder to cement resulted M6S5 mixture. The formation of a thick gel-like struc-
in a maximum strength value of 3.9 MPa after 28 d.43
ture can be observed in the images. During the hydration
process in the mixture, silica and alumina react with
3.4 Flexural strength Ca(OH)2 and Mg(OH)2 and generate essential hydration
The flexural strength of the concrete mixtures is products like ettringite, CSH and MSH gels. These prod-
shown in Figure 7. According to the research, the flex- ucts enhance the strength. Ettringite is a substance cre-
ural strengths of the M3S5, M6S5, M9S5, and M12S5 ated when tricalcium aluminate (C3A) interacts with gyp-
concrete were (6, 9, 5 and 4) % higher than that of ordi- sum to form needle-like structures that enhance early
nary concrete. It should be noted that 6 % MBS and 5 % strength. When MBS and SP are incorporated into con-
SP provided the best results, with a strength of 4.5 MPa crete, their unique qualities, especially their large surface
areas and small particles, improve the pozzolanic activ-
ity. The image depicts a dense, compact matrix with
small apparent pore spaces, suggesting reduced porosity,
improved mechanical interlocking and adequate particle
packing, which are advantageous for the strength in-
crease. A strong physical connection between the binder
and reactive silica or magnesium-based phases is indi-
cated by the rough and uneven surface appearance. The
image shows a relatively crack-free matrix, implying a
better stress distribution and reduced risk of crack propa-
gation. The fine particle size of MBS and SP allows
them to act as microfillers, enhancing particle packing
Figure 6: Split tensile strength of concrete with different mix propor- and the cohesion of the microstructure with embedded
tions hydration products, while minimizing permeability.
922 Materiali in tehnologije / Materials and technology 59 (2025) 6, 917–926
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Figure 8: SEM image of M6S5 mix combination
Figure 9: SEM-EDS image of M6S5 mix combination
The concrete with an 8 % MBS inclusion has a erate amounts of Al2O3 and Fe2O3 suggest potential for-
dense, solid surface whose ITZ is difficult to identify, as mation of secondary hydration products such as C-A-H
demonstrated by the SEM analysis. MBS makes it possi- and C-F-H, contributing to the matrix densification. The
ble to fill in the ITZ, which results in dense concrete.32 presence of MgO from steatite could lead to the forma-
Strength and durability are improved due to the develop- tion of the MSH gel, adding additional binding capacity.
ment of CSH gel and MSH, as evidenced by the com- Minor oxides such as K2O, Na2O, and SO3 may influence
plete filling of the microcracks and a substantially denser the setting behaviour and early-age strength. According
morphology of the SCC utilizing SP and FA.39,44 to the analysis, CaO and SiO2 are the main oxides in the
Another study found that using up to 15 % UFNSP modified concrete matrix and are necessary for the de-
would improve the strength and create a denser velopment of CSH gels that are strong.
microstructural bond.46 Steatite (primarily magnesium Enhancing structural connectivity and densification,
silicate) may contribute to the formation of MSH, which the addition of MgO and Al2O3 permits the creation of
also adds strength and enhances durability. Therefore, it additional gel phases, such as MSH and C-A-H. This is
is noticeable from the microstructural analysis that the supported by the SEM micrograph, which displays a
combined use of MBS and SP significantly enhanced the dense microstructure with well-distributed hydration
strength and pore structure. The SEM–EDS study was products and decreased porosity. These microstructural
carried out on M6S5, the ideal mixture of blended con- changes contribute to the significant improvement in me-
crete, as illustrated in Figure 9, to acquire a complete chanical features. The amounts of CSH in the mixes are
understanding of the concrete specimen’s chemical struc- impacted by pozzolanic processes over time. A drop in
ture. The EDX spectrum reveals high contents of SiO2 the atomic calcium-to-silicon (Ca/Si) ratio indicated that
and CaO, indicating strong potential for CSH gel forma- the majority of the cements reacted with portlandite
tion, the key contributor to the concrete’s strength. Mod- (CH).49 The denser structures were often developed when
Materiali in tehnologije / Materials and technology 59 (2025) 6, 917–926 923
A. WALIITAGI et al.: PERFORMANCE EVALUATION AND MICROSTRUCTURAL ASSESSMENT OF ECO-FRIENDLY ...
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