Abstract: Microbial induced calcite precipitation (MICP) is a new soil improvement technology. As an important reactant in MICP reaction, calcium source has an important effect on the effect of microbial induced calcite precipitation. At present, the most widely used calcium source— calcium chloride (CaCl2), has the disadvantages of high cost and high environmental pollution. Therefore, this paper proposes to extract calcium source from limestone powder by adding acetic acid solution to limestone powder for microbial solidification of soil. The unconfined compressive strength test, scanning electron microscope observation of microstructure and calcium carbonate content test were carried out to verify the feasibility of using calcareous powder to extract calcium source for microbial induced calcite precipitation. The results show that: (1) It is feasible to extract calcium source from limestone powder for microbial solidification of soil. The strength and calcium carbonate content of sand column after solidifying is high and the structural integrity is high. (2) The mechanical properties of solidified sand columns treated by different calcium sources are different. The sand columns solidified by three kinds of calcium show typical brittle failure mode. But the unconfined compressive strength of sand columns solidified by calcium acetate is slightly higher than that of sand columns solidified by calcium source from limestone, and the unconfined compressive strength of sand columns solidified by calcium chloride is much lower than that of the first two. Sand columns solidified by calcium chloride are rougher and have more pores on the surface than the other two. They also have lower integrity after destruction. (3) The content of calcium carbonate in solidified sand columns treated by different calcium sources is different. Sand columns solidified by calcium acetate and calcium source from limestone have almost no difference, but sand columns solidified by calcium chloride have less calcium carbonate content. There is a positive correlation between calcium carbonate content and unconfined compressive strength of sand columns solidified by different calcium sources. (4) A large amount of calcium carbonate is precipitated between the surface and contact point of sand particles in the sand column solidified by calcium acetate and calcium source from limestone. Calcium carbonate crystal is mainly thin stacked calcite. Sand columns solidified by calcium chloride have less calcium carbonate precipitation than the first two, and calcium carbonate crystal is mainly hexagonal calcite. (5) Different calcium sources change the soildifying effect mainly by affecting the crystal appearance, crystal content, crystal distribution and cementation characteristics of microbial mineralization.

Key words: microbial induced calcite precipitation, MICP, limestone power, strength, calcium carbonate, microstructure