Denitrification-based MICP for cementation of soil: treatment process and mechanical performance

Microbially induced calcium carbonate precipitation (MICP) is a novel and potentially sustainable bio-mediated soil stabilization technology for geotechnical engineering applications, which can be promoted by many processes, including denitrification and urea hydrolysis. Compared to urea hydrolysis-based MICP, no ammonium is produced in denitrification-based MICP, but the amount of precipitation induced by the conventionally adopted methods (semi-stagnant column and continuous flow) reported in the early studies is small. This paper presented a large-volume circulation method to induce calcium carbonate precipitation into the sands via denitrification. The sands were treated with denitrification to different levels, and a series of consolidated drained (CD) triaxial tests were conducted after the treated sands were fully saturated to investigate the mechanical response. The results show that the peak drained strength and dilatancy are all improved by the denitrification-based MICP for samples treated. The cohesion and peak strength effective friction angle can be improved by 22 kPa and 3° with 4.48% calcium carbonate contents for denitrification-based MICP. However, the critical state line of soil cannot be shifted. The resulting calcium carbonate precipitation amount and rate can be as high as 4.61% by weight and 0.129% per day. The precipitation rate is increased by at least 5 times compared to the conventional adopted methods for denitrification-based MICP. In addition to CaCO 3 precipitation, biofilms were also produced during denitrification. The high conversion ratio and precipitation-substrates ratio also indicate the high efficiency of this method.