Quantifying the relative contributions of particle crushing and ITZ damage to the strength of cement-stabilized pervious recycled aggregate base materials: Laboratory testing and refined DEM simulation

Driven by the sponge city initiative and zero net carbon emission strategy, recycled brick and mortar aggregates from building demolition wastes (BDWs) have emerged as partial or full substitutes for increasingly depleted natural aggregates to construct cement-stabilized pervious recycled aggregate base materials (CPRABMs). These recycled aggregates feature lower particle crush strength, greater variability, and lower durability, thus jeopardizing the long-term stability of CPRABMs. This study aimed to reveal the micromechanical mechanisms that influence the macroscopic compressive strength of CPRABMs by focusing on damage to the interfacial transition zone (ITZ) and the behavior of particle crushing. First, single-particle crushing experiments were conducted on various types of aggregates in the laboratory, along with unconfined compression tests on CPRABM specimens, to ascertain the statistical distribution characteristics of the single-particle strength and modulus, as well as the crack propagation patterns throughout the experiments. A refined discrete element method (DEM) model was subsequently constructed to simultaneously account for particle crushing and ITZ damage, quantifying the contribution rate of each component within the material to the overall strength of the specimens. The results show that the single-particle crush strength and modulus exhibit significant size effects, with their magnitudes decreasing in the order of natural gravel, recycled mortar, and recycled brick aggregates. The macroscopic compressive strength of CPRABMs is strongly controlled by the ITZ strength, but the controlling role is weakened by the increasing degree of crushing of recycled aggregates. The aggregates within the grain size range of 4.759.50 mm experienced the most profound particle crushing, thus necessitating a reduction in their proportion and/or replacement by natural aggregates. The maximum content of recycled aggregates is recommended to not exceed 50 %. The findings could provide theoretical basis and technical guidance for the design optimization of CPRABMs.