Multi-criteria optimization for sustainable concrete mix considering the synergistic effect of recycled steel fiber and LC3 concrete

This study comprehensively investigates the microstructure, mechanical performance, environmental impact, and cost of a novel high-strength fibrous LC3 concrete to determine the optimal mix for sustainable construction. Ten concrete mixes were designed: five were ordinary Portland cement (OPC)-based and five were limestone calcined clay cement (LC3) based. Four volume fractions of recycled tire steel fibers (RTSF) were considered for reinforcing the concrete. Ultrasonic pulse velocity, compressive strength, splitting tensile strength, 3-point flexural strength, flexural toughness, residual strength, and energy absorption were evaluated to assess the mechanical properties. In addition to cost analysis, the global warming potential (GWP) technique was employed to analyze the CO2 emissions of different mixes. The empirical relationships were developed to estimate the mechanical properties of OPC- and LC3-based concrete reinforced with RTSF. Additionally, LC3-based concrete reinforced with RTSF exhibited more favorable failure under uniaxial compression. Moreover, LC3-based concrete reinforced with RTSF showed comparable mechanical properties, flexural toughness, and flexural energy absorption to OPC-based concrete, while achieving lower costs and CO2 emissions. Scanning electron microscopy (SEM) observations combined with flexural post-peak performance revealed that the synergistic effect of RTSF and LC3 enhances the RTSF-paste matrix interface and improves the flexural post-peak behavior. Finally, based on multi-criteria ranking, the LC3 concrete reinforced with 0.9 % RTSF was identified as the optimal concrete mix.