Effect of rubber surface pretreatment method on the rubberized precast concrete

Abstract Disposal of waste tires is one of the environmental problems that require urgent attention. Their durability and potential for leaching out toxic chemicals have been a problem associated with disposal. This led many researchers to conduct studies on its potential for reuse. Among them is its potential as alternative to natural aggregates in concrete. However, rubber normally negatively affects the mechanical properties of concrete due to its hydrophobic nature resulting to poor adhesion with cement. In this study, the researchers explored the effects of different pre-treatment methods of rubber from waste tires to improve its hydrophilicity, its workability when mixed Type I Portland cement, and the mechanical properties of the resulting “rubberized” concrete. The pretreatment methods considered included: 1) soaking rubber in polyvinyl alcohol at different concentrations (8%, 10% and 12%); 2) soaking rubber in a mixture of sodium hydroxide, potassium permanganate, and saturated sodium bisulfite solution; and 3) exposure to UVA/B/C radiation. The rubber pieces from waste tires were first shredded into 0.3-0.5mm pieces prior to pretreatment. Hydrophilicity was measured through the contact angle test using an Optical Theta Lite Tensiometer. Workability of the concrete mix was measured through slump test (ASTM C143). The results show that rubber soaked in PVA 10% yielded the lowest contact angle (better hydrophilicity) and the most similar workability with normal concrete. Several concrete specimens using the pretreated rubber aggregates were then produced and cured for 7 days and 28 days before subjecting to several tests to determine the compressive, tensile, and flexural strengths. Pretreatment by soaking in PVA yielded concrete with mechanical properties comparable and in some instances better than normal concrete.