Assessment of the Post-Thermal Performance of Concrete Modified with Treated and Untreated Crumb Rubber

Crumb rubber, obtained from discarded tires, presents a sustainable alternative in the construction industry, particularly in rubberized concrete. Treated crumb rubber offers improved mechanical performance; however, limited reports are available on its behavior at elevated temperatures. This study investigates the performance of rubberized concrete containing treated and untreated crumb rubber when exposed to elevated temperatures. The treatments employed are chemical (sodium hydroxide (NaOH)) and physical (cement coating) methods. M30-grade concrete was used as a control mix, and crumb rubber (CR) was added by replacing a portion of the fine aggregate. In order to mitigate the strength reduction, silica fume and polypropylene fibers were added. An optimal mix was determined using Taguchi’s L9 orthogonal array, by varying proportions of crumb rubber, silica fume (SF), and polypropylene (PP) fiber. The ideal mix contained 10% CR, 5% SF, and 0.2% PP fiber based on compressive strength. Specimens were cured for 28 days and exposed to temperatures of 200 °C, 400 °C, 600 °C, and 800 °C for 1 h. Mechanical properties such as compressive strength, split tensile strength, and modulus of elasticity were evaluated, along with an ultrasonic pulse velocity test. The results indicate that treated crumb rubber enhances bonding, improving the mechanical and thermal performance of rubberized concrete under high temperature.