VOLUME STABILITY ASSESSMENT OF DISCARDED TIRE STEEL FIBER HIGH-STRENGTH SELF-COMPACTED CONCRETE

Abstract

The tire manufacturing sector occupies a significant portion of the global economy. The production of vehicle tires requires the utilization of different raw and processed materials. Steel fibers are one of these main ingredients. In this study, the effect of incorporating discarded tire steel fiber (DTSF) on high-strength self-compacting concrete (HS-SCC) was experimentally evaluated in terms of rheological, hardened, and mechanical properties. Additionally, the effect of these fibers on long-term behavior of HS-SCC including shrinkage and creep was examined. For this purpose, four HS-SCC mixes were prepared including one reference mix and other three mixes with three volume fractions of DTSF which were 0.3%, 0.6%, and 1% with the same water to binder ratio (w/b) which is 0.26. DTSF was incorporated into HS-SCC mixes as a hybrid form by using four lengths of 10, 20, 30, and 35 mm with 25% for each length. The rheological properties of HS-SCC were assessed by performing slump flow, T500, V-funnel, L-box, and sieve segregation tests. While, compressive strength, splitting tensile strength, flexural toughness, density, UPV, water absorption tests were conducted in order to investigate the effect of DTSF on mechanical and hardened properties of HS-SCC. The effect of these fibers on shrinkage behavior of HS-SCC was evaluated by implementing free shrinkage tests under controlled conditions, crack width overtime, and fractal dimensions (FD) by using Image J software. Finally, the effect of these fibers on creep behavior of HS-SCC was evaluated by performing compression creep test. Based on the results of this study, it was found that DTSF had a clear negative effect on rheological properties of HS-SCC. Slump flow diameters decreased with 1.3%, 2.89%, and 3.94%. Conversely T500 increased by 6.9%, 18.9%, and 37.2% for SF1, SF2, and SF3 as compared to SF0. The III viscosity of HS-SCC increased by adding DTSF, thus the time required to pass the V-funnel increased dramatically about 7%, 23%, and 31%. Moreover, the blocking ratio decreased by 6%, 12%, and 15%. While, the segregation indeces were found to be decreased by 9%, 17%, and 28%. A slight enhancement in the compressive strength was found by incorporating DTSF with 7%, 13%, and 10.5% for cubic specimens, whereas it increased by 3.2%, 9.7%, and 8.6% for cylindrical specimens. Moreover, the splitting tensile strength increased significantly with 17.8%, 27.9%, and 52.2% as compared to the reference mix. Then, the modulus of elasticity was found to be increased slightly by 1.7%, 4.6%, and 5.7%. Furthermore, the flexural toughness was found to be improved dramatically as DTSF volume fraction increased. The toughness index I20 increased by 944%, 1169%, and 1455%. Additionally, the density and the water absorption increased by adding DTSF, while UPV was found to be decreased. On the other hand, the free shrinkage strain was decreased significantly by 11%, 19%, and 36% as compared to the reference mix. Regarding the cracking tendency of HS-SCC mixes reinforced with DTSF, it was found that those fibers contributed in differing the initiation of cracks as well as reducing the crack width significantly about 43%, 68%, and 81% for the last day of testing. Fractal dimension values were to be increased by 5.627%, 8.86%, and 17.146%, respectively. Furthermore, the creep strain was found to be increased by 0.72%, 7.3%, and 15% for SF1, SF2, and SF3 as compared to SF0. Finally, DTSF proved its efficiency in enhancing mechanical properties, shrinkage, and creep behavior of HS-SCC which made it a good alternative of standard steel fiber, Moreover, SF3 was found to having the best performance among the four mixes.