Meso-cracking characteristics of rubberized cement-stabilized aggregate by discrete element method

As a sustainable solution, embedding rubber inclusions in the semi-rigid pavement base course can ensure the consumption of a large amount of waste tire pollution and improve the mechanical properties of cement-treated base materials. The rubber modification has a potential effect on reducing the possibility of pavement reflective cracks caused by base cracking. This paper aims to investigate the meso-cracking characteristics of rubberized cement-stabilized aggregate (RCSA) mixtures and to quantitatively evaluate the influence of rubber inclusion content and particle size through numerical simulation. The rubber particle size of 0.6-4.75 mm was selected. The virtual RCSA samples were prepared by replacing similar-size aggregates with rubber particles based on the reference mixtures without rubber. Five volumetric replacement contents (20%, 40%, 60%, 80% and 100%) of three gradation ranges (0.6-1.18 mm, 1.18-2.36 mm, and 2.36-4.75 mm) were adopted. An indirect diametric tensile (IDT) simulation test was adopted to obtain the investigated performance of IDT strength, static stiffness, toughness and toughness index. The simulation results show that the incorporation of rubber inclusion has a negative effect on the IDT strength of the RCSA sample. However, material extensibility and post-peak toughness are improved and stiffness is reduced with increasing rubber replacement percentage. The optimal rubber content of the investigated mixtures should be controlled within 80% of the corresponding aggregate gradation volume, which is conducive to controlling the reduction of the overall strength and the play of the extensibility. The strength reduction and ductility improvement of modified concrete are positively correlated with the particle size of rubber inclusion. The modified RCSA mixture with a smaller rubber particle size could ensure a higher IDT strength and extensibility. For the investigated sample, the best comprehensive modification effect can be obtained using the finer rubber substitute with a particle size of 0.6-1.18 mm. The rubber inclusion acts similarly to a cavity defect, which will result in fracture preferring to occur adjacent to the rubber aggregate. Ignoring the adverse effect of strength, the practical implication of rubber incorporation is to improve the ductile behaviour of the RCSA mixture and reduce base cracking. The present numerical simulation methods have the potential to investigate the meso-cracking mechanism of RCSA. It also provides a theoretical guidance for the gradation design of rubberized mixtures.