Durability Based Service Life Estimation for Chloride Exposed Cracked and Self-Healed Concrete

Abstract

Chloride ingress in cracked concrete leads to rapid corrosion of embedded steel reinforcement and a decrease of the expected service life. Corrosion monitoring experiments showed that a 300 μm wide crack caused initiation of corrosion of a rebar (O 10 mm) with a concrete cover of 26 mm within three weeks of cyclic exposure to a 33 g/l NaCl solution. After a period of unstable corrosion activity during the first 20 weeks of exposure, corrosion propagated further at a relatively high rate (0.345 to 0.718 mm³/week). Application of a theoretical pitting model revealed that a reduction of about 50% of the rebar cross-section would occur after a period of 9 to 20 years of continuous cyclic exposure to chlorides. To avoid such rapid degradation, the use of self-healing concrete can be proposed. Introduction of macro-encapsulated polyurethane into the concrete matrix, will lead to the formation of a (partial) barrier against ingress of chlorides at the moment cracks appear. Corrosion monitoring experiments showed that the autonomous crack healing could not always prevent corrosion initiation, but caused an important reduction of the corrosion rate during the 44 weeks exposure period. The mean rate of volumetric loss of steel amounted to 0.042 mm³/week, about 15 times lower than for the untreated cracked samples. The rebars also showed no or very limited signs of corrosion after visual inspection. The simplified pitting model indicated that a 50% reduction in steel cross-section would take more than 5 times longer for samples with self-healing properties versus ordinary cracked samples.