Improvement in properties of concrete with modified RCA by microbial induced carbonate precipitation

The mechanical and durability properties of recycled aggregate concrete (RAC) are generally inferior to conventional concrete due to the old mortar attached to the surface of original aggregate, which induces more complicated interfacial transition zones (ITZs) in the RAC. The microbial induced carbonate precipitation (MICP) modification is a novel and environmentally-friendly method to improve the ITZs and old mortar in RAC. In this study, the physical properties of recycled coarse aggregate (RCA) before and after the MICP modification were tested; then, the effects of the MICP modification on the mechanical and durability properties of the concrete with the RCA and the modified RCA were investigated. The SEM observation and ITZs microhardness test were conducted to reveal the micro mechanism of improvement due to the MICP modification. The results show that the modified RCA exhibits lower water absorption and apparent density; the concrete specimens with the modified RCA exhibits higher compressive strength, higher steel corrosion resistance, and less corrosion-induced cracks, which can be explained by the enhanced microhardness of ITZ between the old and new mortar.