Mechanical, durability and drop weight impact performance of high-performance fibre reinforced rubberised mortar: effect of rubber size and content

This study investigates the mechanical, durability, and drop-weight impact performance of high-performance fibre-reinforced rubberised mortar, with emphasis on the influence of rubber particle size and replacement level. Fine dune sand was partially replaced with rubber in three size ranges: small (90 µm-1.18 mm), medium (150 µm-2.36 mm), and large (600 µm-2.36 mm), at replacement levels of 5%, 10%, and 15% by volume. Mechanical properties (compressive and flexural strength), durability indicators (water absorption, volume of permeable voids, ultrasonic pulse velocity, and electrical resistivity), and drop-weight impact resistance, as per ACI 544 specifications, were evaluated. Results showed that increasing rubber content reduced compressive strength, ultrasonic pulse velocity, and crack initiation resistance due to weaker interfacial bonding and increased porosity. However, medium-sized rubber retained better flexural strength. Durability performance remained acceptable at 5-10% replacement, with improved electrical resistivity, while 15% replacement increased voids and water absorption. Although impact resistance decreased with higher rubber content, post-crack energy absorption and ductility index increased, especially for large rubber particles. The LR-15% mix achieved the highest ductility index of 1.68, indicating enhanced post-crack deformability and energy dissipation capacity. The 5-10% larger particle sizes provide an optimal balance between strength retention, durability, and impact toughness.