ABSTRACT
Disadvantages of conventional surface treatments have drawn the attention to alternative formulations for the improvement of the durability of concrete. Promising results of an innovative biotechnology based on microbial mineral precipitation have lead to research concerning the use of bacteria in concrete; This paper reports the effects of bacterial CaCO3 precipitation on parameters affecting the transport processes and durability of concrete and mortar. Pure cultures of ureolytic bacteria were compared for their effectiveness in relation to conventional surface treatments, such as water repellents and coatings. Microbial calcite precipitation was visualized by SEM. The results indicated the presence of a newly formed layer on the surface of the mortar specimens, consisting mainly of calcite. Bacterial deposition of a layer of calcite on the surface of the specimens resulted in a decrease of capillary water uptake and permeability towards gas. The results obtained with cultures of the species Bacillus sphaericus were comparable to conventional surface treatments.
