Alkaliphilic Bacillus species show potential application in concrete crack repair by virtue of rapid spore production and germination then extracellular calcite formation

Aims: Characterisation of alkaliphilic Bacillus species for spore production and germination and calcite formation as a prelude to investigate their potential in micro-crack remediation in concrete.
Methods and Results: Conditions, extent and timing of endospore production was determined by dark field light microscopy; germination induction and kinetics was assessed by combining reduction in optical density with formation of refractile bodies by phase contrast microscopy. B. pseudofirmus was selected from several species as the most suitable isolate. Levels and timing of calcium carbonate precipitated in vitro by B. pseudofirmus was evaluated by atomic absorption spectroscopy and structural identity confirmed as calcite and aragonite by Raman spectroscopy and FITR. The isolate produced copious spores that germinated rapidly in the presence of germinants L-alanine, inosine and NaCl. Bacterial cells produced CaCO3 crystals in micro-cracks and the resulting occlusion markedly restricted water ingress.
Conclusions: By virtue of rapid spore production and germination, calcium carbonate formation in vitro and in situ, leading to sealing of micro-cracks, B. pseudofirmus shows clear potential for remediation of concrete on a commercial scale.
Significance and Impact of Study: Microbial sealing of micro-cracks should become a practicable and sustainable means of increasing concrete durability.