Experimentation of concrete properties of crumb rubber with SCMs: Mechanical, stiffness, NDT and micro-structural

The construction sector is grappling with an immense lack of natural sand that meets the requisite specifications for use in concrete. At the same time, the disposal of used rubber tires poses ecological, health, and aesthetic challenges due to the difficulty of recycling them. Utilizing industrial waste materials as alternative aggregates and binder components offers a promising solution that enhances environmental awareness, reduces adverse impacts, and promotes sustainable development in the construction industry. This study investigates the performance of M-40 grade concrete incorporating crumb rubber (CR) and binary blends of silica fume (SF) and rice husk ash (RHA). Crumb rubber, sourced from end-of-life tires, was used to replace 10 % and 20 % of natural sand by volume. Simultaneously, cement was partially replaced by binary combinations of SF and RHA in the range of 10–20 % and the fresh properties, mechanical strength, durability, and microstructural characteristics of the resulting crumb rubber concrete (CRC) are evaluated. Natural sand was replaced by CR alone (10–20 %), a reduction in compressive strength of up to 25.4 % was observed but however, this strength loss was significantly mitigated by incorporating binary blends of SF and RHA. Notably, the CRC mix containing 20 % CR, 20 % SF, and 10 % RHA demonstrated improved performance: a 37.5 % increase in compressive strength, a 25 % increase in split tensile strength, and a 42.5 % increase in flexural strength compared to the control mix. These enhancements are attributed to improved particle packing and the formation of additional hydration products from the blended pozzolanic materials, as confirmed by FESEM microstructural analysis. Moreover, this optimized CRC mix exhibited significantly higher static and dynamic moduli of elasticity—16.2 % and 65 % greater than the control mix, respectively—indicating increased stiffness. Non-destructive tests such as Ultrasonic Pulse Velocity (UPV), microhardness, and rebound hammer also showed markedly superior performance in the hardened CRC specimens. • Blended CRC with SCMs will bring sustainability in construction. • Blended CRC with SCMs improves mechanical concrete properties. • NDT parameters were boosted for blended CRC with SCMs. • Analytical Models of blended CRC with SCMs may support the quality control.