An overview on the efficiency of different pretreatment techniques for recycled concrete aggregate

The inferior quality of recycled concrete aggregate (RCA) caused by the adhered mortar (AM) can be principally enhanced through either removing or strengthening the AM. This paper reviews the effect of various pretreatment methods (removal, polymer impregnation, pozzolanic slurry immersion, accelerated carbonation curing and bio-deposition) on the inherent defects of RCA, and compares their modification efficiency based on statistical analyses of results in published papers. The pretreatment methods can significantly reduce the mercury intrusion porosity (an average of 41.3% drop) and water absorption (an average of 24.5% drop) of RCA and concurrently augment the mechanical properties considerably. The modification efficiency of removal methods is mainly governed by treatment approaches and parameters. The improved efficiency of polymer impregnation and pozzolanic slurry immersion is primarily determined by the quality of integument and cladding related to the type of treated materials and pretreatment parameters. The carbonation and bio-deposition efficiency of RCA is closely related to aggregate characteristic/the type of microorganism and pretreatment conditions. Overall, paraffin soaking, presoak-accelerated carbonation and combined removal of AM are the most efficient methods to improve the performance of RCA. A better understanding of the characteristics of the treated RCA can provide a theoretical base for future research and applications of RCA in construction industry.