Microbially Induced Calcite Precipitation (MICP)-Based Bio-Mediated Self-Repairing Concrete Incorporating Bacillus subtilis: Mechanical Performance and Chemical Durability Enhancement

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The use of concrete as the primary building material for infrastructure is widespread. The structural components of concrete tend to crack due to a variety of factors. These cracks allow harmful substances such as water, chlorides, sulfates, and carbon dioxide to enter the concrete and cause it to deteriorate. The maintenance and repair of cracked concrete increases the cost and ecological impact of constructing and operating these infrastructures. One way to manage this problem is to create Self-Repairing Concrete using biological materials. Several types of bio-based self-healing agents have been developed, and many have been verified in concrete. One such approach is called Microbially Induced Calcite Precipitation (MICP). This technique uses certain bacteria, such as Bacillus subtilis, that can survive within the concrete in a dormant state. Once the concrete is placed and water is introduced, these dormant bacteria become active. The bacteria secreted calcium carbonate fills the fissures in the concrete. The primary goal of this research was to use Bacillus subtilis to create bacterial concrete that heals itself. M25-grade concrete as per Indian Standards was used to prepare three types of concretes. The control concretes contained 0 cells/mL (M0). Bacterial concrete contained 10⁵ cells/mL (B1) and 10⁶ cells/mL (B2). The properties that were tested included workability, strength of compressive, split-tensile, and flexure, along with durability in alkaline-acidic environments. The results obtained indicate that the use of bacteria significantly improves the mechanical properties of concrete and durability. All of the bacterial concretes exhibited increased tensile, flexural and compressive strength. The B2 mix (10⁶ cells/mL) exhibited the highest 28-day compressive strength. The durability tests indicated that bacterial concrete resists chemical deterioration better than conventional concrete. This study confirms that bacterial Self-Repairing Concrete is a sustainable substitute to usual concrete repair. The ability of bacterial concretes to autonomously seal microcracks and increase the durability of the concrete indicates that such concretes have great potential to be utilized in constructing long-lasting and low-maintenance infrastructures.

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