Evaluation of Various Bacterial Self-healing Activities in Concrete

Concrete, a popular construction material, is prone to cracking, which affects its long-term strength and durability. An easier, eco-friendly, and economical approach to improve the durability of concrete is by applying ureolytic bacteria. Self-healing concrete is the concrete that fills the micro-cracks by producing calcite crystals when the bacteria come in contact with water and air. The study focuses on accessing the concrete healing mechanism using five different bacteria that contribute to the increase in compressive strength of the concrete. These five bacteria studied here are rarely used in concrete. The hardened properties of concrete with ureolytic bacteria were comparable with conventional concrete of grade M30. The present study aims to identify the potential ureolytic bacteria that can be effectively used in concrete. Microbially Induced Calcite Precipitation occurs when water encounters unhydrated calcium in the concrete, and calcium hydroxide, which serves as a catalyst, is produced with the aid of bacteria. The calcite formed filled up the voids and cracks formed in the concrete, enhancing its strength. In the presence of a calcium source, calcium carbonate can be precipitated through a biologically driven mineralization process. The ureolytic bacteria used in concrete in this study, with the exception of Proteus inconstans, showed good calcite formation. Concrete with Bacillus coagulans showed positive results for hardened property tests conducted after 7 and 28 days of curing. In addition, the densification of the concrete matrix was observed through microscopic analysis, such as X-ray Diffraction, Energy Dispersive Spectroscopy, and Scanning Electron Microscope. The calcite crystal formation was evident in the ureolytic bacterial concrete specimens, indicating self-healing activity in the concrete.