Self-healing concrete in aggressive enironments

Although certain crack widths are allowed in reinforced concrete structures, without having immediate effects on the structural stability, they may impair the durability and service life of the structure in the long term. Cracks wider than 10 μm will result, for instance, in a faster penetration of chlorides into the crack and from there onwards into the concrete matrix. Fortunately, the autogenous healing ability of concrete may close cracks of up to 100 μm completely. The further hydration of binder particles, will be supplemented by the deposition of calcium carbonate crystals in case of wet/dry cycles. In case of marine infrastructures in tidal zones, the presence of magnesium sulfates may enhance the crack sealing by means of brucite precipitation. These processes will result in reduced chloride penetration rates. If the cracks are larger than 100 μm or the conditions are not favourable for autogenous healing, autonomous healing mechanisms can be incorporated. In this case, healing is obtained through encapsulated polymeric healing agents, superabsorbent polymers, microbial agents, expansive additives, etc. With encapsulated polyurethane based healing agents, a reduction of the chloride concentration by 75% or more was obtained in a zone with a 300 μm wide crack after chloride diffusion tests, relative to the case in which cracks were not healed. As a result, the service life of reinforced concrete elements in marine environments could be increased with a factor of about 10. Neutron radiography images obtained during a capillary sorption test indicated that release of encapsulated polyurethane in wet conditions was favourable for the polyurethane reaction. As an alternative to the autonomous healing with encapsulated polyurethane, also the incorporation of encapsulated water repellent agents and corrosion inhibitors, has proven to effectively delay reinforcement corrosion during electrochemical measurement campaigns. Accelerated corrosion tests on cracked, manually treated mortar samples, allowed to rapidly screen different agents for their efficiency.