Mechanical properties and crack resistance of crumb rubber modified cement-stabilized macadam

Abstract

With the development of the transportation industry in the past decades, the amount of waste tires annually has increased rapidly. In consideration of the successful application of rubberised concrete and recycling utilization of waste tire rubber, this study aimed to evaluate the potential effect of crumb rubber manufactured by waste tires on the mechanical properties and crack resistance of cement-stabilized macadam (CSM). Three different particle sizes of crumb rubber (40 mesh, 60 mesh, and 80 mesh) were incorporated into CSM with three different contents (substituting 1.0%, 1.5%, and 2.0% of fine aggregates by volume). Unconfined compressive strength test, splitting strength test, compressive resilient modulus test, dry shrinkage test and scanning electron microscopy (SEM) test were performed in this study. The results indicated that due to the elasticity of rubber particle, the compressive strength of CSM was decreased with the increase in rubber content. The incorporation of crumb rubber effectively reduced the resilient modulus of CSM. However, the adverse influence on the splitting strength was not obvious when a low volume of crumb rubber was incorporated. According to the results of dry shrinkage test, the incorporation of crumb rubber could significantly improve volume shrinkage resistance of CSM, thereby preventing against the formation and propagation of initial cracks. Moreover, the SEM images demonstrated that the cement hydration near rubber particles was hindered and led to the poor interfacial adhesion bond between cement mortar and crumb rubber. The small micro-cracks between cement matrix and rubber particle made space for the extension of dry shrinkage cracks, which revealed the improvement on the crack resistance of crumb rubber modified macadam.