Experimental evaluation of the synergistic effect of calcium precursor dosage and bacterial strain interactions on the biogenic healing potential of self-healing cement mortar

Abstract

This study investigates the microbially induced calcium carbonate precipitation (MICP) in repair mortar, focusing on the impact of calcium precursor dosage and bacterial strain selection. C<inf>6</inf>H<inf>10</inf>CaO<inf>6</inf>·xH<inf>2</inf>O and (CH<inf>3</inf>COO)<inf>2</inf>Ca·xH<inf>2</inf>O were used as calcium precursors at dosages of 0.1, 0.25, and 0.4 M with Bacillus subtilis VEB4, Priestia megaterium TSB16, and Halobacillus halophilus MCC2188 microbes. Quantitative assessment of precipitate and optimization of precursor dosages were conducted before making mortar cube specimens of size 70.6 × 70.6 × 70.6 mm with bacterial spores and nutrients immobilized in Modified Expanded Perlite. Cracked cube specimens underwent automated wet-dry cycles of 12 h daily for 60 days to induce healing. Comparative analysis of biomortar specimens showed P. megaterium as the most effective in compressive strength recovery (up to 89.33%) and crack healing with a maximum healed crack width of 0.64 mm, followed by B. subtilis with significant CSR improvements. H. halophilus, less efficient in non-saline conditions, healed cracks up to 0.48 mm. Calcium lactate was considered the better calcium source choice for B. subtilis and P. megaterium strains, whereas calcium acetate improved MICP by H. halophilus. Microstructural analysis of healed precipitates collected from cracked cubes identified distinct morphology of MICP and the presence of polymorphs viz, calcite, aragonite, and vaterite. Tailored selection and dosage of calcium precursors for each strain significantly enhanced MICP and improved the quality of healing products in cracks, advancing the understanding of self-healing construction biomaterials. © 2024 Informa UK Limited, trading as Taylor & Francis Group.