Particle breakage behavior of recycled construction and demolition waste mixed aggregates during compaction and biaxial compression

The breakage behavior of construction and demolition waste (CDW) materials significantly impacts the mechanical performance of pavement base courses. In this study, a DEM model was employed to simulate the compaction and biaxial compression of recycled CDW base-course filler. The model was parameterized using compaction and sieving tests and morphology analysis, explicitly accounting for particle shape, gradation, and mix proportion. By integrating laboratory and numerical results, the mesoscopic breakage mechanisms and their evolution during compaction and post-compaction biaxial compression were systematically revealed. Results show that the mixing ratios of recycled concrete aggregate (RCA), recycled brick aggregate (RBA), and recycled mortar aggregate (RMA), as well as the particle size distributions of RCA and RBA, primarily determine the crushing behavior of the mixture. RBA and RMA are the main sources of breakage. Smaller RBA particles are more susceptible to pulverization, which increases the bond breakage ratio but reduces the volumetric breakage ratio. Higher RBA content and smaller RBA size further accelerate bond breakage during post-compaction biaxial compression. RCA serves as the skeleton, forming main force chains, while RBA and RMA form secondary chains that help redistribute and alleviate breakage of RCA. Optimizing RCA proportion and RBA size improves compactness and stability. When the mix ratio of RCA: RBA: RMA is 6:3:1 and RBA particle size is less than 9.5 mm, maximum dry density and optimal mechanical performance are achieved. These findings provide theoretical and practical support for mix ratio optimization and engineering application of recycled CDW pavement base fillers.