Properties enhancement of recycled coarse aggregates by pre-coating/pre-soaking with zeolite powder/calcium hydroxide

Abstract The reuse of construction and demolition waste by recycling as aggregates can not only protect the environment, but also alleviate the shortage of natural resources. However, the application of recycled aggregates in practical engineering is limited due to their shortcomings, such as the higher crush value and water absorption, and the lower apparent density. In this study, four different treatments were designed to modify recycled coarse aggregates (RCAs) based on zeolite powder (ZP) and calcium hydroxide (CH), which were CH slurry pre-coating, CH solution pre-soaking, zeolite powder-cement (ZP-C) slurry pre-coating and ZP-C solution pre-soaking, respectively. Moreover, the macro-properties, micro-properties and nanomechanical properties of untreated and treated RCAs have been investigated, respectively. The results show that four treatments improve the properties of RCAs to some extent. Meanwhile, the width of cracks (Wc) of interfacial transition zone and cement matrix of treated RCAs also decreases according to the scanning electron microscope observation. Among the four treatments, the properties of RCAs pre-coated by ZP-C slurry present the most significant improvement, and the crush value and water absorption decrease by 30.4% and 19.8%, respectively, and the apparent density increases by 1.5%. In addition, there is the linear relationships between Wc and the crush value or the water absorption of RCAs. Furthermore, from the perspective of nanomechanical properties, the elastic modulus of cement matrix is the main factor affecting the marco-properties of RCAs.