Experimental study on the products of coupling effect between microbial induced carbonate precipitation (MICP) and the pozzolanic effect of metakaolin

Abstract

In this paper, the performance of the products resulting from of coupling effect between microbial induced carbonate precipitation (MICP) and the pozzolanic effect of metakaolin in the same system is analyzed and discussed in depth. The inoculation parameters of the bacterial solution were optimized, and a method of increasing pH of medium step by step was used to acclimate the alkali tolerance adaptation of Sporosarcina pasteurii. Mixed slurries (MC-M) were prepared and cured for 30 days and 180 days using a ratio of metakaolin (MK) to calcium hydroxide (CH) of 1:1, the bacterial solution as mixing water and calcium acetate as the source of introduced calcium. The compressive strength of the specimens was compared and the properties of the products cured for 180d were analyzed based on test methods such as nanoindentation, SEM, XRD, and TG-DSC. The test results show that the macroscopic mechanical properties of the MC-M specimens were effectively improved and the discrete degree of the micromechanical property parameters was reduced. The particle size distribution of the products increased, within 0.9–12 μm. The decomposition temperature of calcium carbonate in the products decreased, and the water loss temperature of the hydrated products increased. CaCO₃ contains both aragonite and calcite phases, and the phase compositions of the hydrated products became more stable. This work demonstrates that MICP accelerates the depletion of CH in the pozzolanic reaction system and promotes the transformation of the hydration product phase composition. The pozzolanic effect reduces the particle size and degree of accumulation of calcite produced by MICP, resulting in a denser cured product. This phenomenon is referred to as the “coupling effect” of the two reactions and positively affects the mechanical properties, providing a new research idea on materials and methods for repairing concrete cracks.