Impact of trace elements in Portland cement on the bacterial viability in biological concrete

Abstract

The self-healing ability of biological concrete is closely related to the long-term viability of bacteria in the concrete matrix. However, the ability of bacteria to survive, grow and retain their metabolic activity in concrete is questionable. Our results show that the viability of Bacillus pseudofirmus bacteria in a white CEM-I cement is almost 100-fold higher compared to the other tested cement types. Analysis of different types of cement reveals that it contains metal oxides that may have antimicrobial activity. Those metal oxides are MgO; Al2O3; TiO2; Fe2O3; ZnO and CuO. The minimum inhibitory concentrations (MIC) of these metal oxides were further investigated. ZnO was found to be the most toxic metal oxide for all tested bacteria strains (B. pseudofirmus, B. cohnii and B. halodurans). Depending on the bacterial strain, the MIC values of ZnO varied from 12.5 μg/ml to 25 μg/ml. This metal oxide was not detected only in white CEM-I cement, resulting in higher bacterial viability. Common explanations for bacterial mortality are related to the high pH of the concrete and mechanical stress during cement hardening. This study has shown that the viability of bacteria is greatly influenced by the chemical composition of the cement used.