Surface treatment of recycled concrete aggregates through microbial carbonate precipitation

• Recycled concrete aggregates (RCA) were treated by microbial carbonate precipitation (MCP).
• MCP-treated RCA show increased weight and reduced water absorption.
• Rate, amount, and type of MCP can be modified by control of precipitation conditions.

Reuse of recycled concrete aggregates (RCA) in new concrete structures is limited due to their high water absorption and weak bonding to new matrix. These unfavorable properties are associated with the thin layer of old mortar attached to the surface of original aggregates. In this paper, a novel approach of RCA surface treatment by means of microbial carbonate precipitation (MCP) was studied. Factors influencing MCP on RCA were investigated. It was found that the amount of MCP peaks at pH = 9.5 and increases with higher temperature, bacteria concentration, or calcium concentration. Enhanced MCP on RCA can be achieved through proper control of culturing and precipitating conditions. Results show that surface modification of RCA through MCP is feasible evidenced by increasing weight and reducing water absorption of treated RCA.