IMPACT OF FREEZE-THAW CYCLES ON BACTERIAL VIABILITY IN CONCRETE

Abstract

Calcium carbonate precipitating bacteria can improve mechanical and physical properties of building materials. Most commonly, bacteria are used for the crack repair, production of self-healing concrete, or as a cementitious agent for low-strength materials. The favorable effect of bacterial metabolism can only be achieved if the sufficient number of cells remain viable in the structural material. Besides the limited amount of oxygen, extremely high pH level and mechanical pressure on cell walls, bacteria must survive the repetitive freezing and thawing in concrete-type materials. Freezing water may generate additional internal pressure damaging the bacterial cells and suppressing the bacterial activity. In present study, the viability two of bacteria strains (Bacillus pseudofirmus and Bacillus cohnii), was studied under repeated freezing and thawing conditions. It was shown that concrete-embedded bacteria may survive fluctuations of low temperatures and freeze-thaw cycles, compromising approximately 50% of viable spores. This survivability may only be achieved if bacterial spores are protected from the concrete environment itself, for example, spores could be injected to the expanded clay particles and coated with the styrene-acrylate emulsion. These findings confirm that Bacillus pseudofirmus and Bacillus cohnii bacteria could be used in cold climatic regions, retaining viable bacteria spores within the concrete.