Due to the intensive disposal of waste rubber, this study investigates the incorporation of recycled rubber, sourced from scrap tires, as a partial volumetric replacement for fine aggregate in concrete. The binder system consisted of 55% cement, 30% ground granulated blast furnace slag (GGBFS), and 15% silica fume by weight. All mixtures were designed with a constant water-to-binder ratio ( W/B ) of 0.35 . Recycled rubber was used to replace sand at volumetric levels of 0%, 10%, 20%, 30%, and 40%. The study evaluated the influence of recycled rubber content on key concrete properties, including dry unit weight, compressive strength, ultrasonic pulse velocity (UPV), water absorption (WA), drying shrinkage, and thermal conductivity (TC). Results indicated that increasing recycled rubber content reduced the dry unit weight, with a maximum reduction of 24% observed at 40% recycled rubber replacement, attributed to the lower density of rubber. Compressive strength increased with curing age but decreased as recycled rubber content rose, dropping from 67.3 MPa at 0% recycled rubber to 22.8 MPa at 40% after 28 days. Similarly, UPV values improved over time but declined with higher recycled rubber content. At 28 days, mixes with up to 20% rubber showed UPV values of 3695 − 4356 m/s (good quality), while higher contents yielded 3117 − 3463 m/s (acceptable quality). WA increased with recycled rubber content and decreased with age, increasing from 3.57% at 0% recycled rubber to 8.14% at 40% after 28 days. Moreover, an increase in rubber content resulted in higher drying shrinkage and lower thermal conductivity.
Trinh et al. (Sun,) studied this question.