Microstructural characteristics and compression stress–strain behavior of recycled steel fiber‐reinforced recycled self‐compacting concrete

This study aims to manufacture sustainable and environmental‐friendly concrete incorporating multi‐waste, namely waste concrete, waste tires and industrial waste. Recycled steel fiber‐reinforced recycled self‐compacting concrete (RSF‐RSCC) incorporating various industrial by‐products was developed in this study. Natural coarse aggregate was replaced with recycled coarse aggregate at a replacement ratio of 75%, and RSFs recovered from waste tires were incorporated at volume fractions of 0.5%, 1.0%, and 1.5%. Supplementary cementitious materials (SCMs), including fly ash, ground‐granulated blast‐furnace slag, and silica fume, were used in combination to replace cement. The mechanical properties and stress–strain behavior of RSF‐RSCC were investigated via uniaxial monotonic compression tests. Microstructural analysis via scanning electron microscopy (SEM) was implemented to analyze the microstructural characteristics of RSF‐RSCC. Acoustic emission (AE) technique was used to monitor the damage evolution and failure mechanism of RSF‐RSCC. Test results indicate that the incorporation of RSFs and SCMs improves the mechanical properties of RSF‐RSCC, with peak stress increasing up to 45% and elastic modulus increasing up to 10.98%, compared with control mixture R75‐S0‐SF0. Fiber‐free RSCC exhibited brittle tensile failure, whereas RSF‐RSCC exhibited ductile failure mode associated with the pull‐out and sliding of RSFs. AE test results indicate that substantial fiber sliding and pull‐out occurred during the failure stage, which restrained the propagation of cracks and delayed the damage process. RSF‐RSCC mix with 1.0% RSF shows the most cumulative AE counts. AE parametric analysis indicates that the failure of RSF‐RSCC is predominately induced by the development of shear cracks, whereas the failure of RSCC is dominated by tensile cracks. SEM analyses provided complementary information on the internal continuity and microstructural characteristics of RSF‐RSCC. Finally, constitutive models for RSF‐RSCC under uniaxial monotonic compression were proposed, and the predictions show good agreement with the experimental results.