Effect evaluation of repairing cement-mortar microbeams by microbial induced carbonate precipitation.

The technique of microbially induced calcium carbonate precipitation (MICP) has a bright prospect in the repair of concrete structures with diseases, so the evaluation of the repair effect and its influencing factors are very important issues for civil engineers. In this paper, multi-phase mixed precipitate models are established by using the random particle generation and packing algorithm. Combined with the cohesive zone model, the deformation and failure behavior of notched cement-mortar microbeams before and after repair under three-point bending loading are numerically simulated. The recovery rate is proposed to characterize the repair effect of microbeam. The repair effect and the influences of the proportion of crystalline phases in the precipitate, particle size and notch location on it are evaluated. It is found that the recovery rate of peak load of microbeam decreases from 22.16 to 20.60% as the proportion of calcite increases from 0 to 1 for the combination case of calcite and vaterite in the particles of the precipitate. However, for the combination case of calcite and aragonite, as the proportion of calcite increases from 0 to 1, the recovery rate of peak load decreases from 35.01 to 20.77%. For only calcite grains as the particles of the precipitate, the recovery rate of peak load increases from 12.73 to 36.85% when the particle size increases from 2  to 3.4 μm. When the distance between the notch center and the microbeam midspan increases from 0 to 40 μm, the recovery rate of peak load increases from 20.44 to 77.26%. The effects of the proportion of crystalline phases, particle size and notch location on the repairing effect of microbeams can be explained from the population of matrix-particle interface and stress concentration degree in precipitate. Considering that the precipitate compositions can be regulated by the control of environmental and process parameters, the research in this paper is of great significance for the engineering application of MICP technique.