Durability and sustainability of self-healing concrete

By incorporating self-healing agents in concrete, cracks can be healed autonomously upon occurrence. As a result, a significant extension in service life can be achieved and environmental burdens related to maintenance and repair can be avoided to a large extent. This development is of high value for steel reinforced concrete infrastructures subject to carbonation- and/or chloride-induced corrosion. For self-healing concrete with macro-encapsulated polyurethane, chloride profiles and electron probe microanalysis indicated that this mechanism was efficient to reduce the chloride penetration. Electrochemical measurements on reinforced concrete specimens subjected to cyclic exposure with a NaCl solution indicated that autonomous crack healing could significantly reduce the corrosion propagation. Cracked specimens without integrated self-healing mechanism, showed active corrosion after 10 weeks of exposure and after 26 weeks clear pitting damage was observed on the rebars. On the other hand, if cracks were healed with low viscosity polyurethane, the rebars showed no or very limited signs of corrosion. While self-healing by encapsulated polyurethane is complete after one day, bacteria-based products take several weeks to heal a 300 μm crack. In this case, bacterial granules containing denitrifying cultures have the benefit to release nitrite as an intermediate metabolic product which can protect the reinforcement during the crack healing process. The experimental self-healing efficiency obtained for each system could then be implemented in a probabilistic prediction model that estimates the time to chloride- or carbonation-induced steel depassivation in comparison with what would be expected for ordinary cracked concrete. A significantly reduced maintenance and repair frequency was demonstrated for the polymer-based self-healing concrete. A subsequent life cycle assessment showed a substantial environmental benefit which can mainly be attributed to the service life extension possible with self-healing concrete which easily overcomes environmental burdens inherent to the polymers. A cradle-togate LCA study was also carried out for fibre reinforced Engineered Cementitious Composite (ECC) with Superabsorbent Polymers (SAP) to stimulate self-healing. The environmental impacts of the SAPs, mainly due to expected high energy use during the drying step, could not be neglected, but remained limited to 4-52% of the environmental impact of the cement in the self-healing ECC mix.