How can concrete be engineered to self-heal minor cracks caused by environmental stress?

Concrete can be engineered to self-heal minor cracks through several innovative methods that address environmental stress damage. Autogenous healing utilizes the natural continuing hydration of unreacted cement particles when water enters cracks, forming calcium silicate hydrate to seal fractures. More advanced approaches incorporate engineered additives like shape-memory polymers that expand when activated by moisture to fill cracks. Microencapsulation techniques embed healing agents such as sodium silicate or epoxy resins within concrete; when cracks form, the capsules rupture and release these agents to polymerize and seal the void. Biological methods introduce bacterial spores (often Bacillus species) and nutrient calcium lactate into the concrete matrix. Upon crack formation and water ingress, the bacteria activate, metabolize nutrients, and precipitate calcite to effectively seal cracks. These self-healing mechanisms significantly enhance concrete's durability by autonomously repairing microcracks up to 0.8mm wide, reducing maintenance needs and extending structure lifespan while preventing corrosive elements from penetrating the reinforcement.