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In this study, a new bio-deposition approach was used to improve the properties of recycled concrete aggregate (RCA). The new bio-deposition approach is based on bacterially induced CaCO3 precipitation through respiration, which differs from the traditional bio-deposition treatment that produces CaCO3 by urea hydrolysis. The experimental investigation was conducted in two parts. First, the physical properties including water absorption, crushing value, and density of the bio-deposition-treated RCA were determined. Then, the workability, compressive strength, and water absorption of mortars prepared with treated RCA were determined. It was found that the bio-deposition-treated RCA had a higher density and lower crushing value and water absorption compared with untreated RCA. In case of mortar, not only the workability, but also the compressive strength improved and the water absorption decreased. Moreover, the effect of bio-deposition treatment on the RCA surface and interfacial transition zone was observed by SEM.

This study aims to clarify the role of bio-deposition in improving the properties of recycled concrete aggregate (RCA) to enhance its reusability. Two bio-deposition treatments were investigated (immersion and spraying). The physical properties, pore structure, and micro-morphology of the RCA were investigated both before and after treatment, and the compressive and flexural strength of mortars prepared with treated and untreated RCA were also analysed. In addition, the micro-mechanical properties of the hydration products of bio-calcium carbonate were determined. The results showed that the water absorption, porosity, and crushing values of treated RCAs were lower than those of untreated RCAs. The compressive and flexural strength of mortars made with untreated RCAs were lower than those of mortars with treated RCAs. The results show that bio-calcium carbonate and its hydration products have a positive effect on the interfacial transition zone of the mortars, thereby reducing crack widths and improving the micro-mechanical properties.