Improving microbially induced calcium carbonate precipitation effects by nacre extractions

In microbially induced calcium carbonate precipitation (MICP) process, it is the precipitated calcium carbonate that cements loose sand particles together to improve their mechanical properties. Seashell nacre composed of calcium carbonate is a natural product, which is worth researching for its remarkable hardness, strength and toughness. However, there has been no study that bridges this natural nacre mineralisation with MICP. Therefore, a precedent herein is established to modify the MICP process by way of the water-soluble matrix (WSM) extracted from nacre, where WSM contributes to the great mechanical properties of nacre. This study examines the effects of WSM with different concentrations on urease activity of bacteria and strength as well as the microstructure of bio-cemented sand samples. The results show that a small number of WSM (50 mg/l) can improve the average strength of bio-cemented sand samples by 1·5 times. This is because 50 mg/l WSM can significantly improve the urease activity. Thus, more calcium carbonate crystals are precipitated, and the higher unconfined compressive strength of bio-cemented sand samples is achieved. The microstructures are investigated by x-ray diffraction and scanning electron microscopy. Overall, this study is an unprecedented exploration imitating nacre that hopefully paves way for future studies.