Mechanical and Ultrasonic Pulse Velocity Performance of 3D Printed Rubberised Cementitious Composites Reinforced with PVA Fibers (2025-08)¶

Crumb rubber and polyvinyl alcohol (PVA) fibres are increasingly used in cementitious composites to improve sustainability and mechanical properties. However, their combined effects, particularly within 3D concrete printing (3DCP), remain inadequately explored. This study investigates the synergistic impacts of crumb rubber (0 - 20 vol.% replacement of fly ash) combined with a fixed PVA fibre content (1.75 vol.% of binder) on the mechanical performance and ultrasonic pulse velocity (UPV) of cementitious composites. Incorporating PVA fibres notably reduced slump flow by approximately 20.1%. Mechanical tests revealed that crumb rubber decreased compressive strength by up to 45.1%, whereas flexural strength substantially increased (up to 213.3%) due to effective fibre bridging. Additionally, 3D printed specimens exhibited anisotropic mechanical behaviour, with a significant reduction (54%) in flexural strength perpendicular to the printing direction, underscoring the critical importance of interlayer bonding quality. Early-age UPV measurements displayed distinct dormant, acceleration, and deceleration phases, and demonstrated a strong inverse correlation with crumb rubber content (R2 up to 0.90). Regression models effectively correlating UPV with mechanical properties were developed.