Development of environment-friendly and ductile recycled aggregate concrete through synergetic use of hybrid fibers

The partial or full replacement of natural aggregates with recycled ones can lessen the harmful effects of concrete industry on the environment. Despite offering sustainability benefits, recycled aggregate concrete (RAC) is inherently brittle under tension similar to natural aggregate concrete (NAC). The present study aimed to enhance the ductility of plain RAC by using hybrid fibers. The effect of single and hybrid fibers was studied on the flexural behavior (flexural strength, flexural toughness, residual strength), splitting tensile strength, and compressive strength of RAC. Polypropylene fiber (PPF) and hooked steel fiber (HSF) and hybrid fiber combination (0.85% HSF + 0.15% PPF) were used in RAC and NAC at a 1% volume fraction of concrete. The results showed that RAC with 1% PPF performed poorly compared to the RAC with 1% HSF. RAC incorporating 1% HSF or hybrid HSF-PPF fibers showed overall better performance than plain NAC. A substantial increment in the tensile and flexural strength of RAC was observed with the incorporation singular HSF and hybrid HSF-PPF. Hybrid fibers have higher efficiency than singular HSF in both RAC and NAC. Residual strength, flexural strength, and flexural toughness of RAC with HSF and hybrid fibers were notably higher compared to the conventional plain NAC. The addition of 0.85% HSF + 0.15% PPF is beneficial to the imperviousness of concrete, and it reduced the water absorption capacity of RAC by 6.4%.