Role of calcium sources in the strength and microstructure of microbial mortar

This study investigated the uniaxial compressive strength, splitting tensile strength and water absorption ratio of microbial mortars treated with three different calcium sources (CaCl2, Ca(CH3COO)(2) and Ca(NO3)(2)). The results showed that the uniaxial compressive and splitting tensile strengths of microbial mortars treated with Ca(CH3COO)(2) were about twice those of the microbial mortars treated with the other two calcium sources ('the others' hereafter). The results of mercury intrusion porosimetry analysis showed that the pore size distribution in the microbial mortar treated with Ca(CH3COO)(2) was much more uniform than that of the others. The mineralogical compositions and the microstructure morphology of the microbially induced calcium carbonate precipitation were analyzed in detail. Scanning electron microscopy and X-ray diffraction revealed that the calcium carbonate cemented in the microbial mortar treated with Ca(CH3COO)(2) were different from others. Besides the calcite and the vaterite crystals, aragonite crystals with an acicular mineral morphology were observed. Calcium acetate is a more appropriate calcium source than calcium chloride for the application of MICP technology in reinforced concrete structures because it avoids the corrosion of steel bars caused by chloride ion. (C) 2015 Elsevier Ltd. All rights reserved.