Self-Healing Efficiency of Cementitous Mortar Using Different Bacteria Protection Methods and Mineral Precursors

Abstract

Concrete cracking provides a path for water and other detrimental agents into structures leading to accelerated deterioration. To address this issue, several bacterial self-healing technologies have been implemented. Even though bacterial concrete has been thoroughly studied, a consensus regarding which protection method and mineral precursor would optimize the self-healing abilities of the material have not been determined. In this investigation, Bacillus pseudofirmus bacteria was encapsulated along with yeast extract and three mineral precursors (i.e., magnesium acetate, calcium lactate, and sodium lactate) using three protection methods (i.e., hydrogel beads, vacuum impregnation into porous aggregates, and electrostatic attachment with cellulose nanocrystals). Compressive and flexural strength tests were performed to characterize the mechanical properties of the materials. Moreover, cracked beam specimens were subjected to wet/dry cycles for 28 days to allow for self-healing. During healing, the crack closure was monitored, and by day 28, the flexural strength recovery was determined. Finally, scanning electron microscopy (SEM) along with x-ray energy dispersive spectroscopy (EDS) was performed to characterize the healing products. Experimental results showed that the addition of calcium lactate enhanced the compressive strength regardless of the encapsulation method. Furthermore, the flexural strength and the flexural strength recovery were not affected by the protection mechanism. In terms of self-healing efficiency, the hydrogel beads were the best-performing protection technology among the three analyzed. Furthermore, the SEM-EDS analysis revealed a high presence of calcium-rich particles (i.e., calcite) as the main healing product of this investigation