Evaluating the crushing characteristics of recycled construction and demolition waste for use in road bases

With the increasing production of construction and demolition waste (CDW), the use of CDW as a road base has become a sustainable and eco-friendly disposal approach. The aggregate crushing value is an essential index in the construction of road bases and is defined as the mass percentage of fine particles after a confined compression test of recycled CDW. In this study, experiments and numerical simulations were conducted to evaluate the crushing characteristics of the CDW, consisting of three main components, i.e., gravel, brick, and mortar. From the single-particle crushing tests, the gravel was strongest, and the mortar was weakest. Multi-particle confined compression tests showed that the load-displacement curves of the recycled aggregates exhibited an increasing trend. The fluctuations during loading were attributed to the particle breakage. A three-dimensional discrete element method (DEM) with a laser scanning and reconstruction technique was proposed to model irregularshaped aggregate particles using a cluster of bonded particles. A comparison of the experimental and numerical results showed that the bond breakage ratio linearly increased with the aggregate crushing value, providing a quantitative linkage between the micro-scale numerical model and the macro-scale test. It was found that the volume proportion of the gravel significantly affected the mechanical behavior of the mixed aggregates, and 75% was the critical threshold of the gravel component. As gravel with a volume proportion from zero to 75% was added to the brick or mortar, the aggregate crushing value increased by only 10-15%. In the mixed aggregates with brick and gravel, more of the brick particles were crushed when gravel with a proportion of 50-75% was added due to inconsistent deformation and stress concentration. If the gravel proportion exceeded 75%, the aggregate crushing value was reduced by 30%. Based on the numerical and experimental investigations of the crushing characteristics of the recycled aggregates, a ternary diagram was proposed to design the proportion of the three components in recycled CDW for road bases.