A comparative study of strength and durability characteristics of concrete and mortar admixture by bacterial calcite precipitation: A review

Frequently used concrete is the second most used material after water worldwide, but it is vulnerable to cracks, leading to decreased durability and service life. Self-healing techniques, including natural processes, polymers, carbonated steel slag, S.C.M.s, biological/chemical, bacteria direct/liquid, and immobilization/encapsulation, have been studied. The most recent technique is Microbially Induced Calcium Carbonate Precipitation (MICCP), which uses ureolytic bacteria of the bacillus family to heal or fill cavities, fissures, and cracks by precipitating CaCO3. Researchers aim to enhance self-healing efficiency in mortar and concrete by non-pathogenic bacteria, such as B. Megaterium, Subtilis, Aerius, Sphericus, Cereus, Pseudoforms, Shewanella, and Sporosarcina pasteurii. Previous studies found that 105 cells/ml was the most effective concentration for concrete, while mortar specimens interacted better with bacteria at various cell concentrations. Bacterial concrete at 105 cells/ml exhibited improved microstructure interaction and densification due to the formation of “C.S.H.” gel and a depletion in C.H. bond with confined pore space. Consolidated bacteria produced a copious volume of minerals that could fill the cracks in the concrete, as observed in SEM and EDS studies. XRD analysis confirmed the increase in calcite composition at the bacteria's concentration level of 105 cells/ml in cement concrete specimens. Bacterial concrete at this concentration level has the potential for sustained and strong concrete properties.