Assessment of the mechanical performance of crumb rubber concrete

Crumb rubber concrete (CRC) has some known shortcomings in mechanical performance compared to conventional concrete, particularly with respect to compressive strength. Many previous researchers have tried to overcome the material deficiencies using different methods; however, the results have often been contradictory and highly variable. In this research, three methods to improve and then assess the mechanical performance of CRC have been examined namely, rubber pre-treatment using sodium hydroxide (NaOH) solution, using silica fume additives, and increasing concrete cement content. The effect of the rubber pre-treatment time (0-2 h), silica fume content (0-15%), and cement content (300-400 kg/m3) on CRC slump, short and long term compressive strength, and tensile strength were measured for fifteen concrete mixes prepared with 0% and 20% rubber content. Six 100 × 200 mm cylinders were prepared from each mix for evaluating the compressive strength at 7 and 28 days. Four additional 100 × 200 mm cylinders were prepared from two mixes for evaluating the compressive strength at 56 and 84 days. In addition, two 150 × 300 mm cylinders for each mix were prepared and tested to determine the indirect tensile strength at 28 days. The results showed that 0.5 h of rubber pre-treatment using NaOH solution, 0% of silica fume replacing cement by weight, and 350 kg/m3 cement content were the best alternatives in this assessment range to enhance the CRC performance.