Abstract
Construction waste is a global issue, with billions of tons being generated due to the demolition and renovation of old structures. Recycling and reusing surplus waste material is imperative, and recycled concrete aggregate (RCA) has emerged as a promising “earthen” material for geotechnical engineering applications, such as backfill, ballast, or foundation soil. The cement mortar coating and the complex composition of the RCA particles are hypothesized to result in unique interparticle contact behaviors; thus leading to the crushable nature and distinctive mechanical properties of RCA on the macro-scale. The current study examines a representative fraction (1.18–2.36 mm) of RCA particles from Nanjing, China (NJ) and Sydney, Australia (SYD), with a particular focus on particle strength and interparticle contact behavior. The characterization of the particles includes their composition, microstructure, and micro-indentation hardness, which influence their strength and interparticle contact behaviors. The study found that the overall strength of the RCA particles was significantly lower than that of typical quartz sands, and the particles were highly deformable. Notably, a ductile type of failure under compression was observed in 6% and 14% of the RCA particles from NJ and SYD, respectively, which is uncommon in other granular materials. The interparticle normal contact stiffness of RCA particles was comparable with highly decomposed tuff granules, placing it in the lower range of geomaterials. The removal of the surface cement mortar coating was found to increase the contact stiffness and surface microhardness markedly. Additionally, multi-cycles of normal loading enhanced the Young's modulus of the contact. These results provide useful insights into the mechanisms of the stiffness and strength of RCA, and can serve as valuable reference for improving mechanical properties of RCA in future applications.
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