Healing Mechanisms in Concrete: A Pathway to Durable and Sustainable Infrastructure

Concrete, the world's most consumed construction material, is inherently susceptible to cracking, which compromises its durability and structural integrity, leading to significant economic and environmental costs from maintenance. This research comprehensively investigates and optimizes advanced self-healing concrete technologies as a sustainable solution. The study systematically compares autogenous (mineral-enhanced) and autonomic (bacterial and capsule-based) healing mechanisms. Experimental mixes were designed incorporating Magnesium Oxide (MgO), bentonite, hydrogel-encapsulated Bacillus subtilis, and polyurethane-filled microcapsules. Performance was rigorously evaluated through mechanical strength recovery, crack closure quantification, water permeability tests, and microstructural analysis (SEM-EDS, XRD) over a 56-day healing period under varied curing regimes. The results demonstrate that autonomic systems significantly outperform autogenous mechanisms. The bacterial mix with Bacillus subtilis encapsulated in hydrogels achieved the highest overall performance, with 93.3% crack closure, 94.4% compressive strength recovery, and an 89% reduction in gas permeability for cracks up to 0.45 mm. Response Surface Methodology (RSM) optimization identified an optimal bacterial agent concentration of 4.0%. Capsule-based systems excelled at sealing wider cracks (0.5 mm), while autogenous mixes were effective for narrower cracks (