Effect of seawater on the self-healing of biomineralized recycled aggregate concrete

To study using seawater instead of freshwater to repair concrete cracks is worthwhile with microbial mineralization. This study used recycled concrete coarse aggregates (RCA) and brick coarse aggregates (BCA) as carriers to soak in Bacillus pasteurii solution with different saltwater salinity for modification. The modified aggregates were adopted to prepare concrete and experimentally investigate their compressive strength, crack repair, and microstructure. Test results show that the aggregates using saltwater of the same salinity as seawater present the best modification. After the modification the saturated surface dry weight of the two aggregates increases, and the water absorption decreases. The strength of modified aggregate concrete is higher than that of unmodified aggregate concrete, and the strength of modified RCA concrete is higher than that of modified BCA concrete. The 56-day compressive strength of saltwater mixing and curing modified aggregate concrete is interestingly found to be lower than the 28-day compressive strength. In addition, for the artificially cracked concrete previously cured 56 days in saltwater, after air curing at 1 day, the surface cracks started to be repaired by calcium carbonate, while after 91 days, the surface cracks were greatly repaired, the repairable crack width was up to 0.5 mm. Moreover, the particle inside the concrete may promote calcite precipitation with better stability compared to that at the concrete surface.