Abstract

This paper investigates the structural performance and mix optimisation of prestressed concrete sleepers incorporating recycled concrete aggregate (RCA) and crumb rubber (CR). Nine mix proportions of full-scale sleepers were tested in four-point bending under three regimes including centre positive, rail-seat positive, and rail-seat negative. Load-deflection responses were processed to obtain ultimate load, initial stiffness, energy absorbed to peak, and deflection at peak. Quadratic response-surface models were fitted to RCA and CR contents and combined with a multi-response desirability approach to identify compromise-optimal mixtures balancing capacity, stiffness, toughness, and sustainability. Results show that increasing RCA causes modest, smooth reductions in strength and stiffness, with no abrupt thresholds up to 50 % replacement, while peak deflection remains largely unchanged and absorbed energy follows the strength trend. CR introduces a controlled strength-ductility trade-off, enhancing toughness and peak deflection at moderate penalties to capacity and stiffness. Optimisation highlights a practical corridor centred on 25 % RCA with 4 % CR across all regimes.