Experimental and predictive assessment of recycled rubber-modified lightweight mortars

This study examines lightweight cement mortars reinforced with Polyvinyl Alcohol (PVA) fibers to elucidate how introducing recycled rubber as a sand replacement influences microstructure-sensitive transport and load-bearing behavior. Using a standardized mix with a binary pozzolanic binder (Class F fly ash and silica fume), we assessed compressive and flexural strength, elastic modulus, stress–strain re-sponse, dry density, water absorption, and Ultrasonic Pulse Velocity (UPV). Increas-ing rubber fraction generally reduced strength and stiffness due to weaker interfacial bonding and elevated internal porosity; nevertheless, mortars with moderate rubber contents retained adequate strength while exhibiting enhanced plasticity/ductility, indicating potential for semi-structural use when properly optimized. An artificial neural network that ingests rubber content, dry density, water absorption, and UPV predicted 28-day compressive strength with high fidelity (R² = 0.94; MSE = 0.72MPa²; MAPE = 1.87%), with UPV emerging as the most influential predictor. The combined experimental and data-driven findings provide non-destructive, UPV-anchored guidance for designing PVA-reinforced lightweight rubberized mortars for sustainable construction.