Mechanical properties, microstructural features, and acoustic behaviour of recycled aggregate concrete reinforced with plastic and polypropylene hybrid fibers for sustainable construction

The increasing demolition of aged infrastructure has significantly raised the generation of recycled aggregates, posing sustainability challenges in construction waste management. Integrating recycled aggregates into concrete production is a potential solution, although they typically exhibit inferior mechanical performance compared to natural aggregates. To overcome this, hybrid fiber reinforcement has gained research interest for improving Recycled Aggregate Concrete (RAC) characteristics. This study examines the performance of RAC reinforced with a combination of plastic and polypropylene fibers used in macro and micro forms respectively to improve resistance against cracking and enhance structural integrity. The concrete was prepared with a 50% replacement of natural aggregates by recycled aggregates, and fiber contents were varied (0.5%, 1%, and 2%). For hybridization, combinations of plastic and polypropylene fibers were tested at three dosage levels: (0.5% PF + 0.5% PP), (0.75% PF + 0.25% PP), and (1.5% PF + 0.5% PP). The impact of fiber type and dosage on mechanical strength, failure patterns, stress strain response, and acoustic emission behavior was investigated. Results showed that the hybrid mix RAC50-PF0.75-PP0.25 yielded superior strength values, achieving 48.56 MPa in compressive strength, 5.19 MPa in splitting tensile strength, and 5.75 MPa in flexural strength, representing improvements of approximately 7%, 5.5%, and 4% respectively over the plain RAC mix.