Recycled fine aggregate as a sustainable alternative to natural sand: Challenges, enhancement strategies, and performance evaluation

This study presents a systematic experimental investigation on the feasibility of using recycled fine aggregate (RFA) as a partial to full replacement of natural fine aggregate in structural concrete. Concrete mixtures were prepared with RFA replacement levels ranging from 0% to 100%, and their fresh, mechanical, and durability properties were evaluated. Compressive strength decreased by approximately 17.3% at 100% RFA replacement (from 38.19 MPa to 31.58 MPa), while split tensile strength showed a higher reduction of about 20.3% (from 3.16 MPa to 2.52 MPa). Compressive strength showed the least sensitivity to RFA incorporation, followed by flexural strength, while split tensile strength exhibited the highest sensitivity due to its dependence on interfacial transition zone quality. Statistical analysis confirmed strong linear correlations and significant relationships between RFA content and strength reduction. Durability performance assessed through water absorption increased by approximately 51% and sorptivity by about 38% at 40% RFA, while sharper increases were observed only at higher replacement levels (≥60%). Compressive, split tensile and flexural strength reduction below 7%, 12%, and 8% respectively, which remain within acceptable limits for structural-grade concrete. The combined results suggest that RFA can be effectively utilized as a sustainable alternative to natural sand at moderate replacement levels. The findings contribute to performance-based guidelines for RFA utilization and support its application in sustainable and circular concrete construction practices.