Surface modification of recycled tire rubber to enhance mechanical properties of rubberized cement mortar
The incorporation of recycled tire rubber in cement composite has shown potential as an environmentally sustainable approach to managing the increasing volumes of scrap tires. Due to the excellent shock absorbance and flexibility properties of rubber, the inclusion of discarded tire rubber in portland cement concrete has advantages like an increase in flexibility, toughness, and impact resistance. However, the inclusion of recycled tire rubber results in a significant decrease in compressive strength. This research explores using a new rubber chemical treatment process to modify the surface of discarded rubber. This new process is a two-step chemical treatment that entails halogenation of the rubber followed by amine functionalization. The effect of using rubber treated with this chemical treatment process in mortar was investigated. The results showed that the beneficial effects of adding rubber on impact resistance remained, and the adverse effects on strength were partially overcome when treated rubber was used. Specifically, it was seen that mortars containing treated rubber had higher compressive strength than mortars containing untreated rubber. This increase was attributed to the chemical surface treatment increasing the hydrophilicity of the rubber through the introduction of favorable functional bonds on the surface of the rubber with cement composite. Additionally, no adverse effect was observed on the early hydration kinetics of mortars containing treated rubber. Overall, the two-step chemical treatment showed promising results for the valorization of scrap rubber tires for use in cement-based composites. Furthermore, this study makes significant contributions to the current state of the art in several key areas. It shows that rubber hydrophilicity is a significant factor impacting the strength of Portland cement composites containing crumb rubber and highlights the potential for underestimation of the hydrophilicity of rubber when measured with deionized water. Additionally, the study sheds light on the efficacy of using halogenation and amine functionalization processes for the treatment of crumb rubber and provides valuable insights on which bond functionalization groups to target for the use of treated rubber in cement composites. The study also brings forth a new understanding of the behavior of concrete containing crumb rubber and indicates that there is an optimum treated rubber content at which further increases do not result in increasing impact resistance. Thus, design concrete at this optimum content to maximize compressive strength and impact resistance of concrete containing treated rubber.