Usability of sustainable materials on bacteria-based self-healing in cementitious systems

Damage and loss of strength resulting from deterioration in concrete structures are extremely expensive and time-consuming processes that require improvement. Therefore, special concrete demand to respond to crack formation with its self-healing action leads to microbial concrete research and development. In this study, the effects of bacterial utilization on both mechanical/physical properties of the recycled concrete aggregates (RCA) containing mortar mixtures and the crack-healing were investigated. Bacillus subtilis bacteria were cultivated on three different nutrient media, Tryptic Soy Broth, Modify Luria-Bertani, and urea-calcium phosphate, and then encapsulated in RCA with these nutrient media. Twenty-one different mortar mixtures were prepared by partially replacement of bacterial RCA with the limestone one. The compressive and flexural strengths as well as ultrasonic pulse velocity of mortar mixtures were determined. Also, physical properties of the mortar mixtures such water absorption, capillarity and total void ratio were obtained. It was observed that the physical and mechanical properties of the mortar mixtures containing less than 30% RCA are significantly healed by CaCO3 precipitated by bacteria. The results showed that that urea and Ca2+ in the nutrient media increase the CaCO3 precipitation efficiency of bacteria, but glucose in the media causes foaming in the mixtures and creates a hollow structure. The study also indicated that microorganisms had a positive role not only in the concrete strength increasing but also in facilitating the self-healing of cracks. It was observed that the cracks formed up to 0.3 mm in the bacterial mortar mixtures were mostly closed in 7 days.