The potential of Bacillus pseudofirmus as healing agent of biological self-healing concrete in North Europe region

Abstract

Concrete is the most widely used building material in the world. However, cracks inevitably open up in concrete structures. Microbiologically induced calcite precipitation (MICP) can be used to fill cracks arising in concrete. For the formation of biological self-healing concrete specific alkaliphilic spore-forming bacteria, which can survive extreme pH values and harsh conditions in concrete matrix, and mineral precursor compounds such as calcium lactate are needed. In this study, the viability of Bacillus pseudofirmus in sub-zero temperatures and in a concrete matrix containing several types of cement with different metal ion concentrations was investigated. An expanded clay (EC) was used as a carrier for two-component self-healing agent consisting of Bacillus pseudofirmus spores and calcium lactate. After 72 days of incubation of EC particles at temperatures below 0 °C (-20 °C), the number of viable spores remained almost constant (~10^7 CFU/g of EC) compared to control specimens stored at the room temperature. That indicates that B. pseudofirmus has a potential to be used in biological self-healing concrete for the Northern Europe region with high number of freeze-thaw cycles. The concrete mix was obtained by mixing EC, cement, sand and water. Out of four cement types commonly used in Lithuania, the best survival rate was obtained in a concrete mix using white CEM I cement. The number of viable B. pseudofirmus spores after three days of concrete curing varied from 2.34 × 103 to 6.59 × 10^4 CFU/g of concrete [1]. These results demonstrate that additional coating of EC aggregates is needed to improve the viability of bacteria in the concrete.