Rheological, mechanical, environmental, and economic comparison of the use of industrial and recycled steel fibers in self-compacting concrete

Industrial steel fibers (ISFs) are the most widely-used fibers for the purpose of concrete reinforcement. The industrial production of these fibers is costly, and it contributes to Greenhouse gas emissions. The present study, therefor, aims to explore the ways in which these fibers can be replaced by recycled steel fibers (RSFs) made of scrap vehicle tires. To this end, the present study examined 13 mixtures containing different volume percentages (0%, 0.5%, 1%, 1.5%, and 2%) of ISFs, RSFs, and their combinations. The examinations included rheological properties of the fresh self-compacting concrete (J-ring, L-box, U-box, and V-funnel tests), mechanical properties of the hardened concrete (compressive, Brazilian tensile, and flexural strength tests), environmental characteristics (global warming potential (GWP)), and economic characteristics. Results showed that RSFs had a poorer performance than ISFs in terms of mechanical properties. The use of 2% ISFs increased the splitting tensile and flexural strengths by 114% and 82%, respectively, while the same amount of RSFs increased these parameters by 80% and 44%, respectively. On the other hand, RSFs showed better performance than ISFs in terms of rheological, environmental, and economic characteristics. Replacing ISFs with RSFs in mixtures containing 2% fibers could improve the rheological, environmental, and economic characteristics by 8%, 30%, and 65%, respectively. Finally, given the multi-criteria optimization results, RSFs were superior to ISFs in terms of rheological, mechanical, environmental, and economic characteristics.