Synergistic Effects of Crumb Rubber, Cement, Admixture, and Fiber Contents on Strength and Structural Performance of Rubberized Concrete

The widespread disposal of scrap tires has become a major environmental problem that necessitates finding an effective way of using recycled crumb rubber (CR) in concrete. Rubberized concrete, however, exhibits reduced mechanical strength compared to conventional concrete, which restricts its application in structures. This research adopted a mix design strategy based on the Taguchi method to overcome these drawbacks and improve the performance of rubberized concrete. A total of ten mixes, including one for normal concrete (NC) mix, were formulated by varying the CR content (10%, 20%, and 30% by weight of fine aggregate), cement content (400, 425, and 450 kg/m 3 ), admixture dosage (0.5%, 1%, and 1.5% by weight of cement), and polypropylene (PP) fiber content (0.2%, 0.25%, and 0.3% by weight of cement). The impact of these factors was assessed on concrete workability, density, mechanical properties, flexural performance of beams, and axial load capacity of columns. The use of CR reduced workability, density, and strength; however, the optimized mix combinations successfully alleviated these deficiencies. Based on the experimental results, four mix combinations were recommended, comprising different contents of CR, cement, admixture, and PP fiber. These combinations increased the slump by up to 7% and improved the compressive, split tensile, and flexural strengths of rubberized concrete by up to 16%, 15%, and 20%, respectively, compared with the NC. In addition, the bending strength of the beams and the axial load-carrying capacity of columns increased by up to 24% and 13%, respectively. Therefore, the test outcomes suggest that rubberized concrete can be modified from a non-structural material to a load-bearing structure with this strategic mix design.