Bacterial and Microcapsule-Based Self-Healing Concrete for Megaprojects: Advanced Multiphysics Formulation and Engineering Feasibility

Cracking is the dominant serviceability and durability pathway in reinforced concrete because it accelerates the ingress of water, chlorides, sulfates, carbon dioxide, and other aggressive species toward the cement matrix and steel reinforcement. Self-healing concrete (SHC) seeks to convert this passive material into an autonomous repair system. This paper examines two technologically mature autonomous routes: bacterial microbially induced calcium-carbonate precipitation (MICP) and microcapsule-based delivery of mineral or polymeric healing agents. The study develops a coupled chemo–hydro–mechanical framework in which crack opening, fluid transport, bacterial metabolism, carbonate speciation, mineral precipitation, capsule rupture, agent diffusion, and damage recovery are represented by governing equations. A reaction–diffusion–precipitation model is proposed for bacterial healing, while a fracture-triggered release model is formulated for microcapsules. The resulting crack-closure efficiency is linked to permeability, stiffness recovery, corrosion-risk reduction, and life-cycle cost. The analysis indicates that bacterial systems are attractive where crack widths are small, moisture is intermittently available, and long service lives justify biological protection and nutrient design. Microcapsules provide faster and more controllable release but introduce finite healing inventory, interface defects, and possible strength penalties. For megaprojects, the rational strategy is not indiscriminate replacement of conventional concrete, but a reliability-based hybrid deployment in exposure-critical zones, supported by probabilistic quality control, digital monitoring, and life-cycle costing. The equations presented are a research-grade constitutive framework rather than a universal calibration; site-specific parameters must be identified through fracture, permeability, durability, and long-term viability testing.