Repair mechanism of induced calcium carbonate on microcracks of cement mortar under carrier protection

Abstract:

Microbial-induced calcium carbonate precipitation can effectively fill and repair the inevitable hydration cracks during the cement slurry consolidation process， enhancing the mechanical strength and impermeability of cement stone， thereby reducing many induced well cementing quality issues. This paper focuses on Bacillus subtilis with good mineralization properties， investigating the mechanics and impermeability performance of cement stone under different process formulations and curing conditions， after activation and expansion cultivation of bacterial strains and their addition to cement slurries in various ways. The results indicate that environmental temperature， pH， and calcium source concentration are the main factors affecting the mineralization ability of the bacteria. The alkaline environment of the cement slurry （pH：11~13） has a significant inhibitory effect on bacterial activity， with a maximum reduction in mineralization ability of 15.1%. Porous and adsorbent shale ceramic sand carriers can effectively mitigate the influence of alkaline environment on bacterial activity. Compared to direct addition， the addition of carrier+bacteria can respectively increase the compressive strength， flexural strength， and impermeability pressure of cement stone by 11.5%，14.8%，and 33.3%. When the adsorption rate of the bacteria solution increases from 0% to 35%， the compressive strength， flexural strength， and impermeability pressure of microbial cement stone increase by 10.8%， 47.0%， and 25.0% respectively. Therefore， the microbial cement slurry studied can effectively improve the mechanical and impermeability properties of cement stone， providing valuable guidance and reference for enhancing well cementing quality and promoting the application of microbial cement slurries.

Key words:microcracks of cement hydration;microbial remediation;carrier protection;mechanical properties;impermeability performance;cement strength;bacillus subtilis