Using microbial carbonate precipitation to improve the properties of recycled aggregate

•Recycled aggregates (RAs) were modified with microbial carbonate precipitation (MCP).•Efficient precipitation method was proposed by inducing more MCPs on RAs’ surface.•Water absorption of RAs decreased by using proposed precipitation method.•Compressive strength of concrete enhanced with bio-modified RAs.•After bio-modification, microhardness of interfacial transition zone increased. This paper attempts to find an efficient precipitation method to modify recycled aggregates (RAs) with microbial carbonate precipitation and investigate the modification effect of RAs on the properties of the recycled aggregate concrete (RAC). Firstly, laboratory prepared concrete cubes were prepared as model RAs to compare the effectiveness of different precipitation methods, considering calcium-source addition methods and ways of rotation treatment. Based on the tested results, an efficient precipitation method was proposed. Secondly, the industrial sourced RAs were modified by the proposed precipitation method, and cast into concrete. The bio-modified RAC showed higher compressive strength because of the enhancement of the microhardness of the interfacial transition zones after modification.