W. ¯YCIÑSKI et al.: STUDY OF THE WORKABILITY AND MECHANICAL PROPERTIES ... 479–483 STUDY OF THE WORKABILITY AND MECHANICAL PROPERTIES OF CONCRETE WITH ADDED GROUND CORNCOBS [TUDIJA IZVEDLJIVOSTI IN MEHANSKIH LASTNOSTI BETONA Z DODATKOM ZDROBLJENIH KORUZNIH STOR@EV Wojciech ¯yciñski, Marcin Ma³ek * , Mateusz Jackowski, Waldemar £asica, Mariusz Owczarek Military University of Technology, Faculty of Civil Engineering and Geodesy, 2 gen. Sylwestra Kaliskiego, 00-908 Warsaw, Poland Prejem rokopisa – received: 2019-07-27; sprejem za objavo – accepted for publication: 2020-03-23 doi:10.17222/mit.2019.182 This work reports on how Portland cement was modified by adding ground corncobs to its matrix. The main purpose of this study was to observe direct influence of the addition on the concrete mechanical properties. The recipe for the modified concrete included three amounts of ground corncobs: 3 w/%, 5 w/%, 10 w/%. Fresh concrete mix was tested for air content and pH value. Samples of concrete were characterized with the compressive strength, tensile splitting strength and bending strength after 28 d of curing. The porosity and thermal properties of the concrete were also measured. Summarized results were compared with the reference samples. Physical characteristics and thermal parameters of the concrete were determined. This study proved that ground corncobs decrease the final mechanical properties of the studied concrete. Keywords: concrete, corncob, mechanical strength, modification V prispevku avtorji predstavljajo rezultate modifikacije betona na osnovi portlandskega cementa z dodatkom zdrobljenih koruznih stor`ev v matrico. Glavni namen pri~ujo~e {tudije je bil ugotoviti neposreden vpliv izbranega dodatka na mehanske lastnosti betona. Pripravljeni beton je vseboval tri razli~ne vsebnosti dodatka zdrobljenih koruznih stor`ev in sicer: (3, 5 in 10) w/%. Sve`im me{anicam betona so dolo~ili vsebnost zraka in njihovo bazi~nost oz. alkalnost (pH). Po 28-dneh su{enja izdelanih vzorcev betona so dolo~ili njihovo tla~no, natezno-cepilno in upogibno trdnost. Prav tako so izmerili njihovo poroznost in termi~ne lastnosti. Rezultate so primerjali z referen~nim vzorcem betona. S {tudijo so dokazali, da dodatek zdrobljenih stor`ev v matrico betona poslab{a kon~ne mehanske lastnosti preiskovanega betona. Klju~ne besede: beton, koruzni stor`i, mehanska trdnost, modifikacija 1 INTRODUCTION Millions of tons of waste are produced worldwide each year, and most of them are not recyclable. In addition, waste recycling consumes energy and causes pollution. Waste collection and disposal are harmful to the environment. The use of waste in the production of concrete is an appropriate method to achieve two goals: waste elimination and change of the concrete properties. Around 20–30 % of agricultural production becomes waste. 1–4 Using the waste from agricultural products has attracted the attention of scientists who wish to bring it back into the economic cycle. The most popular agricul- tural waste includes rice husk and corncob. 5–8 An addition of corncob as a substitute for a light aggregate significantly changes the properties of a fresh concrete mix, such as the flow or porosity, and also affects the strength properties of concrete by lowering them in part. Some researchers indicate that this additive can improve the insulation properties of concrete. 9–11 The main results obtained are presented and dis- cussed, showing that the proposed corncob concrete may have the material properties required for mortar or in- sulation concrete. 12–15 If the amount of the addition is large, not just a small fraction like in most research cases, the additive causes an increase in the insulation; such concrete could be used, e.g., in cold rooms because its density decreases while the thermal conductivity and porosity increase. 16–18 2 EXPERIMENTAL PART The subject of the research was the addition of ground corncobs (Figure 1), the waste from agricultural products, to the concrete matrix. The addition of this organic additive was designed for investigating the effect of ground corncobs on the final mechanical and phy- sico-chemical properties of concrete. Four mixtures were made, all based on CEM I. The first was the reference concrete mix, not including any addition of corncobs. The rest of them had 3 w/%, 5 w/% and 10 w/% additions. From the mixtures, one sample was used, at a time, for the tensile and bending tests and Materiali in tehnologije / Materials and technology 54 (2020) 4, 479–483 479 UDK 67.017:666.974:664.784.8 ISSN 1580-2949 Original scientific article/Izvirni znanstveni ~lanek MTAEC9, 54(4)479(2020) *Corresponding author's e-mail: marcin.malek@wat.edu.pl (Ma³ek Marcin) two for the compression test. All samples were cured in water for 28 d. A deflocculant based on polycarboxylates reducing the amount of water and improving the workability of the concrete mix was used for the tests. Its amount was 1 % in the first three mixtures and 1.5 % in the fourth one. Due to the very difficult workability, it was ne- cessary to add more liquefier and it was decided to increase its quantity by 50 % in comparison to the other samples. The additive had no direct effect on the increase or decrease in the strength of the samples. All the re- search parameters were in line with European Standard EN 206-1:2011. 3 RESULTS AND DISCUSSION First, the fresh concrete mixture was tested. A slump test was done. In the reference mixture, a decrease by 20 mm was achieved, which classifies it as the S1 class. In the cases of adding corncob to the concrete, the mixtures did not exhibit any decrease. The air content in the mix- tures was also checked. The reference mixture exhibited a value of 2 w/%. Moreover, with the increasing amount of corncob, the mixture had (3, 4 and 4.6) w/% of air (Table 1). Table 1: Density and porosity of the mixtures Bulk density 0 /(kg/dm 3 ) Tightness ratios /% Porosity ratio p /% Ref. mix 2.59 92.4 7.6 Mix1(3w/%) 2.52 89.9 10.1 Mix2(5w/%) 2.50 89.4 10.6 Mix 3 (10 w/%) 2.40 85.7 14.3 The obtained results showed a decrease in the com- pression strength to 22.5 MPa, noted for 10 w/% of ground corncobs after 28 d of curing (Figure 2). The lowest decrease of the compression strength was ob- served for 5 w/% corncobs and its maximum was 33.8 MPa on the same day of measuring. All the samples exhibit a decrease due to the addition. The consequences of this process included a formation of large air voids and decomposition of the concrete. The pH was checked and a slight decrease from 13.0 to 12.7 % was found (for3%and5%ofcorncob) and 12.6 % for the 10 % of corn cob (Table 2). Table 2: PH values of the mixtures Ref. mix Mix 1 (3 w/%) Mix 2 (5 w/%) Mix 3 (10 w/%) pH 12.98 12.70 12.77 12.63 Figure 3 shows the results of the bending-strength distribution of the prepared samples. The largest strength was observed for the lowest addition, the amount of 3 w/%. Other samples exhibited very similar characteris- tics of the bending strength. Figure 4 shows the Brazil- ian tensile strength (BTS), but under different conditions as the splitting strength shows the same results as the W. ¯YCIÑSKI et al.: STUDY OF THE WORKABILITY AND MECHANICAL PROPERTIES ... 480 Materiali in tehnologije / Materials and technology 54 (2020) 4, 479–483 Figure 1: Ground corncobs Figure 3: Average bending force distribution Figure 2: Compressive-strength distribution, MPa bending measurements. The addition of corncobs signifi- cantly affected the loss of strength. Figure 5 shows the cross-section of the reference mix. Typical fragments of the concrete such as the aggregate and cement-matrix zones are visible. The addi- tion of ground corncob can be seen in Figures 6–8 as white and yellow points comparable to small aggregates. They definitely stand out against the background of the dark matrix and thicker aggregate. There was no evi- dence that the additive caused more frequent crack for- mations, but it could have started them. During the test, it was determined how the thermal parameters changed during the drying of the samples in open air and in a dryer at 40 °C over a period of 18 h. The measurements were taken on two samples from each mixture, twice at the same sample site and the average values were calculated (Table 2). At the beginning of the preparation of the concrete mix, the effect of adding corncobs for consistency was noted. As the amount of the organic additive increased, the mixture became drier (the slump cone test). This is probably due to the high-water demand of ground corn- cob. W. ¯YCIÑSKI et al.: STUDY OF THE WORKABILITY AND MECHANICAL PROPERTIES ... Materiali in tehnologije / Materials and technology 54 (2020) 4, 479–483 481 Figure 6: Cross-section of the mix with 3 w/% ground corncob Figure 4: Average Brazilian tensile splitting (BTS) strength distribu- tion Figure 7: Cross-section of the mix with 5 w/% ground corncob Figure 5: Cross-section of the reference mix When the test of the compressive strength of concrete was carried, a much higher stress value was obtained than previously designed. Unfortunately, with the grow- ing amount of ground corncob, the compressive strength decreased. The corncob addition for testing the bending strength of concrete was the same. The results of the splitting tensile test were greater than the norm values, but the strength also decreased with the addition of ground corncob. The destruction of all the samples was considered to be correct. The density of individual mixtures was calculated and the porosity of concrete was determined. The density of concrete decreased along with the increase in the amount of added ground corncob. The increasing poro- sity of concrete caused by the gradual addition of ground corncobs had a significant impact on this parameter. The thermal tests of concrete showed that with a de- creased density of concrete, the thermal conduction coefficient decreased. The addition of ground corncobs had a positive effect on the reduction of the thermal conductivity of concrete. 5 CONCLUSIONS In conclusion, an addition of ground corncobs to concrete weakens the concrete in terms of strength. In contrast, it has a positive effect on the decrease in the thermal conductivity along with the increase in the amount of corncobs. This can have a positive effect on the insulation properties of concrete. The changes in the bending strength and the high amount of cellulose from ground corncobs have a positive effect in the case of an addition to any kind of mortar. Acknowledgment The financial support from the Research Statutory Program financed by the Military University of Technology, Faculty of Civil Engineering and Geodesy, called “Research of materials and construction elements of military infrastructure special objects”, No. 886/2019, is gratefully acknowledged. 6 REFERENCES 1 K. Lyons, G. Swann, C. Levett, Produced but never eaten: a visual guide to food waste, The Guardian, Wed 12 Aug, 2015 2 K. Bräutigam, J. Jörissen, C. Priefer, The extent of food waste gene- ration across EU-27: different calculation methods and the reliability of their results, European Commission, JRC Technical Reports, 2017, doi:10.1177/0734242X14545374 3 A. Abdullah, C. Lee, Effect of Treatments on Properties of Cement- Fiber Bricks Utilizing Rice Husk, Corncob and Coconut Coir, Procedia Engineering, 180 (2017), 1266–1273: doi:10.1016/j.proeng. 2017.04.288 4 R. Chmielewski, L. Kruszka, Cause and effect study of the structural failure of the historic complex of St. Anna’s Church in Warsaw, MATEC Web of Conferences, 284 (2019), doi:10.1051/mateconf/ 201928405002 5 R. Chmielewski, P. Muzolf, Selected problems of protection of his- toric buildings against the rainwater and the groundwater, MATEC Web of Conferences, 174 (2018), doi:10.1051/mateconf/ 2018174030012 6 J. Pinto, B. Vieira, G. Pereira, C. Jacinto, P. Vilela, A. Paiva, S. Pereira, V. Cunha, H. Varum, Corn cob lightweight concrete for W. ¯YCIÑSKI et al.: STUDY OF THE WORKABILITY AND MECHANICAL PROPERTIES ... 482 Materiali in tehnologije / Materials and technology 54 (2020) 4, 479–483 Figure 8: Cross-section of the mix with 10 w/% ground corncob Table 2: Thermal parameters of the samples Thermal conductivity /(W/mK) Thermal diffusivity a /(m 2 /s) Specific volumetric heat c /(J/m 3 K) Specific heat mass c p /(J/kgK) Density 0 /(kg/dm 3 ) Ref. 1.548 1.536 9.82 · 10 –7 8.76 · 10 –7 1.57 · 10 6 1.75 · 10 6 606 678 2.59 Mix1(3w/%) 1.442 1.427 8.99 · 10 –7 9.57 · 10 –7 1.60 · 10 6 1.49 · 10 6 635 593 2.52 Mix 2(5 w/%) 1.442 1.442 8.81 · 10 –7 8.48 · 10 –7 1.64 · 10 6 1.70 · 10 6 654 679 2.50 Mix 3(10 w/%) 1.301 1.177 8.65 · 10 –7 8.40 · 10 –7 1.50 · 10 6 1.40 · 10 6 627 584 2.40 non-structural applications, Construction and Building Materials, 34 (2012), 346–351, doi:10.1016/j.conbuildmat.2012.02.043 7 J. Faustino, E. Silva, J. Pinto, E. Soares, V. M. C. F. Cunha, S. Soares, Lightweight concrete masonry units based on processed granulate of corn cob as aggregate, Materiales de Construccion, 65 (2015), doi:10.3989/mc.2015.04514 8 S. Thakur, S. Saraswat, D. Jain, Use of Ash of Agricultural Waste as Partial Replacement of Cement in Concrete (Rice Husk Ash, Saw Dust Ash, Wheat Straw Ash), International Journal of Engineering Research and Management (IJERM), 01 (2014), 169–172, doi:10.3390/ma12071112 9 J. Prusty, S. Patro, S. Basarkar, Concrete using agro-waste as fine aggregate for sustainable built environment–areview ,International Journal of Sustainable Built Environment, 5 (2016), 312–333, doi:10.1016/j.ijsbe.2016.06.003 10 R. Chmielewski, A. Bak, Analysis of technical condition of foot- bridges over the railways in danger of collapse, MATEC Web of Conferences, 284 (2019), doi:10.1051/matecconf/201928401001 11 H. Arel, E. Aydin, Use of Industrial and Agricultural Wastes in Con- struction Concrete, ACI Materials Journal, 115 (2018), doi:10.14359/ 51700991 12 A. Dotun, O. Olalekan, A. Olugbenga, M. Emmanuel, Physical and Mechanical Properties Evaluation of Corncob and Sawdust Cement Bonded Ceiling Boards, International Journal of Engineering Research in Africa, (2019), 10.4028/www.scientific.net/JERA.42.65 13 N. Belie, J. J. Lenehan, C. R. Braam, B. Svennerstedt, M. Richard- son, B. Sonckf, Durability of Building Materials and Components in the Agricultural Environment, Part III: Concrete Structures, 76 (2000), 3–16, doi:10.1006/jaer.1999.0505 14 R. Kosturek, M. Wachowski, L. Œnie¿ek, M. Gloc, The Influence of the Post-Weld Heat Treatment on the Microstructure of Inconel 625/Carbon Steel Bimetal Joint Obtained by Explosive Welding, Metals, 9 (2019), 246, doi:10.20944/preprints201812.0252 15 A. Bak, R. Chmielewski, Analysis of repair works to remove the effect of structural failure after a gas explosion, MATEC Web of Conferences, 284 (2019), doi:10.1051/matecconf/201928402002 16 C. Grãdinaru, A. ªerbãnoiu, D. Babor, G. Sârbu, When Agricultural Waste Transforms into an Environmentally Friendly Material: The Case of Green Concrete as Alternative to Natural Resources De- pletion, Journal of Agricultural and Environmental Ethics, 32 (2019), 77–93, doi:10.1007/s10806-019-09768-1 17 M. Wachowski, L. Sniezek, I. Szachogluchowicz, R. Kosturek, T. Plociñski, Microstructure and fatigue life of Cp-Ti/316L bimetallic joints obtained by means of explosive welding, Bulletin of the Polish Academy of Sciences, Technical Sciences, 66 (2018), 925–933, doi:10.24425/bpas.2018.125940 18 A. Bak, R. Chmielewski, The influence of the fine fractions content in non-cohesive soils on their compactibility and the CBR value, Journal of Civil Engineering and Management, 25 (2019)4 , doi:10.3846/jcem.2019.9687 W. ¯YCIÑSKI et al.: STUDY OF THE WORKABILITY AND MECHANICAL PROPERTIES ... Materiali in tehnologije / Materials and technology 54 (2020) 4, 479–483 483