A focus on Ca2+ supply in microbial induced carbonate precipitation and its effect on recycled aggregate

Calcium ions play a crucial role in microbial-induced calcium carbonate precipitation (MICP), and the effects of calcium concentrations on the properties of recycled aggregate and recycled aggregate concrete were studied. The reinforcement mechanism of MICP technology on recycled aggregate was further analyzed by low-field nuclear magnetic resonance, X-ray diffraction and scanning electron microscope. The results show that the reinforcement effect of recycled aggregate increases first and then decreases with the increase of calcium concentration in the solution. Too high calcium concentration will inhibit the activity of bacteria and reduce the effect of modification. The formation of biological calcium carbonate in the inner pores greatly improves the microhardness of O-ITZ, and calcium carbonate formed on the surface of recycled aggregate is benefit for N-ITZ in recycled concrete. The dense surface layer and optimization of internal pore structure in recycled aggregates improve the strength and reduce the water absorption of the recycled concrete.