Novelty in bacteria source production and concrete binders in self-healing cementitious samples

Abstract

One of the challenges associated with creating bacterial-concrete systems capable of biomineralizing CaCO3 to fill cracks is the high pH environment of the hydrated cement paste. In this study two approaches to address this challenge were investigated: (i) the use of calcium sulfoaluminate (CSA) cement, which develops a naturally lower pH, and (ii) the use of non-axenic bacterial cultures, which may facilitate growth of bacterial strains more resilient to harsh alkaline conditions. Axenic B. subtilis and a non-axenic bacterial system from soil were produced and utilized in ordinary portland cement (OPC) and CSA samples. The mechanical properties, water absorption, calcium carbonate precipitation capability, and survivability of bacteria were investigated. The highest B. subtilis and soil bacteria viability was obtained through use of CSA cement and may enable greater later age crack healing potential than mixtures using OPC. Incorporation of axenic bacteria resulted in increased bacteria survivability in the mortar samples when compared to non-axenic bacteria mixes. However, in both cementitious systems, use of B. subtilis and soil bacteria led to similar improvements, suggesting that non-axenic cultures may be used in concrete effectively.