Quality improvement of recycled aggregate

This chapter deals with the technologies needed to improve the quality of recycled concrete aggregate to conform to the specifications regulated by various countries around the world and to make the aggregate useful for utilization in the precast and structural concrete. Recycled concrete aggregate (RCA) have inferior qualities compared to natural aggregate attributed mainly to the porous residual attached mortar, which has low specific gravity, high water absorption and possible cracks in its interfacial transition zone (ITZ), developed during the crushing process. These impediments contribute the increase in water demand when concrete is freshly mixed in a mixer, higher shrinkage and creep, and poor microstructure, which results in lower compressive strength and low durability of recycled concrete. It is therefore crucial to improve the RCA quality such that the properties of improved aggregate become comparable with those of virgin aggregate. To separate the residual attached mortar several research studies have been carried out using different treatments such as (a) pulsed power (b) mechanical (c) thermo-mechanical (d) chemical and (e) a combination of the above (hybrid) treatments. In the case studies presented in this chapter, research was carried out at the Kumamoto University, Japan using Pulse Power treatment and at the Mataram University using thermal-mechanical-chemical treatment to improve the quality of recycled aggregate. Another case study presented represents research carried out at the Bialystok University, Poland using thermo-mechanical treatment. In addition, various processes that can effectively transform or utilize the removed mortar particles from above treatments, have also been discussed.