Screening of native ureolytic bacteria for self-healing in cementitious materials

In recent years, microbial calcium carbonate has been recognised for its potential to self-heal cementitious material by mimicking the natural biological systems of healing wounds. Thus, the inevitable microcracks and concrete pores can be filled with microbial calcium carbonate to prevent any aggressive chemical flow or water and prolong the life span of the structure. Recently, numerous studies have reported on bio-concrete incorporating bacterial species such as B. sphaericus and B. pasteruii, although there are limited studies on the B. pseudomycoides species. In this study, new native ureolytic bacteria were isolated from soil samples collected in Universiti Teknologi Malaysia. The morphology, characteristics, and ureolytic production of the bacteria were investigated through biochemical tests. The bacterial enhancement efficiency of the concrete compressive strength was also examined. The results demonstrated that the bacteria are gram-positive with encouraging characteristics such as endospore formation, which is required for application in harsh environments such as concrete. The native bacteria also demonstrated high urease enzyme productivity. Furthermore, the applicability of the bacterial spores and vegetative cells-urea solution as a healing agent in concrete was demonstrated by increasing concrete compressive strength by 10% and 15% compared to the control sample with the optimum cell concentration of 2-107 cell/ml. This finding was attributed to the precipitation of calcium carbonate in the pore volume and confirmed by X-ray diffraction (XRD)