Synergistic effects of recycled rubber and polypropylene fibres in mortars: Experimental characterization and nonlinear predictive modeling

Abstract

This study examines the combined influence of recycled rubber aggregates (RRA) and polypropylene (PP) fibers on the mechanical and durability properties of mortar composites. Nine mortar mixtures were prepared with RRA contents of 0%, 10%, 20%, and 30% (by sand mass) and PP fiber volumes of 0%, 0.5%, and 1% (by binder mass). Results showed that increasing RRA content reduced compressive strength; however, the inclusion of PP fibers significantly mitigated this loss. Durability parameters such as dynamic modulus, porosity, ultrasonic pulse velocity, and capillary absorption were also measured. A nonlinear empirical model was developed to predict compressive strength based on RRA and PP content. The model was validated using two-way ANOVA and Leave-One-Out cross-validation, achieving excellent agreement with experimental results (R² > 0.98). Additionally, a simplified environmental analysis indicated potential CO₂ emission reductions through partial replacement of natural sand with RRA. Overall, the study demonstrates that rubberized and fiber-reinforced mortars can offer a sustainable alternative in construction, combining improved durability and environmental benefits without excessively compromising mechanical performance.