Mechanical performance enhancement of crumb rubber concrete with basalt minibars

Crumb rubber concrete (CRC) offers environmental benefits through the recycling of waste tires, enhancing flexibility, durability, and impact resistance. However, its application is often limited by a reduction in mechanical strength. This study investigates the novel combination of crumb rubber (CR) aggregate and basalt minibars fiber (BMF) to mitigate these drawbacks and enhance the overall performance. An experimental program was conducted to evaluate the effect of rubber replacement ratios (5%, 10%, 15%, 20% by volume) and particle sizes (5 mm, No. 20) on the fresh and hardened properties of concrete. Test results indicated that a 5% substitution of fine aggregate with 5 mm crumb rubber particles increased the compressive strength by 13%. However, higher replacement levels generally reduced the compressive strength, with a maximum reduction of 49% observed for 20% of No. 20 particles. The incorporation of 1% BMF effectively compensated for these reductions, enhancing the compressive strength of CRC mixes by 4–10% and increasing the modulus of elasticity significantly across all replacement levels. Furthermore, BMF inclusion transformed the failure mode from brittle in conventional concrete to highly ductile in BMF-CRC, eliminating sudden specimen separation. The flexural strength of CRC with 5% 5 mm CR saw a 4% increase, and this was further boosted by 20% with BMF addition. The combined effect between crumb rubber and basalt minibars improved the overall mechanical performance, demonstrating the high potential of this sustainable composite for structural applications.