Properties and stress-strain curve of rubberized concrete cast with uncoated or pre-coated rubber with cement/waste materials

Replacement of fine aggregate with crumb rubber (CR) in concrete manufacturing has become necessary to reduce environmental problems resulting from the traditional disposal of waste tires and to produce environment-friendly concrete. The main problem resulting from incorporating CR into the concrete industry remains the reduction in the properties of concrete. Various methods have been employed to treat CR particles to enhance the overall performance of crumb rubber concrete (CRC). Nevertheless, most of the suggested treatment techniques exhibited little efficacy in improving the characteristics of CR particles, and certain chemical treatments pose risks and hazards to the environment. This work presents a novel method for pre-treating CR particles before their use in CRC. The methodology involves the utilization of several processing materials, including cement (C), supplemental cementitious materials (SCM) such as fly ash (FA), and waste materials such as marble powder (MP). Seventeen different mixtures in terms of rubber replacement ratios and rubber processing methods were prepared for the experiment. One mix served as the control without any addition of CR. Four mixtures were generated by substituting varying proportions (5%, 10%, 15%, and 20%) of sand with untreated CR, measured by weight. The remaining twelve mixes contain treated CR with C, FA, and MP. This study investigated the fresh and mechanical properties of CRC, as well as the overall behavior of the stress-strain curve, including yield, peak, ultimate strain, toughness, modulus of elasticity, and strain ductility. The findings indicated that pretreatment of CR with one of the proposed materials enhances the overall behavior of CRC, especially using FA, compared to untreated. The substitution of fine aggregate with 20% CR treated with FA significantly improved the overall properties of CRC. The compressive strength, splitting tensile strength, peak stress, modulus of elasticity, and toughness rose by 22%, 21.30%, 31.19%, 5.30%, and 37%, respectively, compared to using the same proportion of untreated rubber. Therefore, this type of treatment can be relied upon to improve the properties of CRC and give acceptable results.