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Importance of Curing on Chloride-Induced Corrosion

The effect of a range of curing regimes on the resistance to chloride penetration of concretes has been studied. Concretes with two binder systems, namely normal portland cement (NPC) and a 30% fly ash blend (FA), were subject to 4 different curings. They include 1-day sealed, 7-day sealed, 7-day wet and a simulated steam curing. Subsequent to each curing regime, the samples of grade 40 concretes were air cured in standard laboratory conditions until the age of 28-days, before exposure to 15 cycles and 100 cycles of immersion in 3% sodium chloride solution and drying. Resistance to chloride ion penetration was evaluated by examining both the chloride profile and diffusion coefficient (calculated by Fick's second law). Thus the role of curing in governing the resistance of concrete to chloride ion penetration was established. NPC concrete was found to be more sensitive to the type of curing than the fly ash concrete. NPC concrete subjected to 1-day and 7-day sealed curing resulted in lower chloride penetration resistance than the 7-day wet curing. However, the fly ash concrete showed remarkable tolerance to the lack of moist curing, giving very similar performance in both 1-day and 7-day sealed curing as the 7-day wet curing. Steam curing resulted in poorer resistance to chloride penetration for both concretes. For each type of curing, the fly ash concretes gave significantly better resistance to chloride penetration than the NPC concrete (of similar grade). Effect of curing on sorptivity and volume of permeable voids of concretes of grades 20, 40 and 50 were also studied. Both sorptivity and volume of permeable voids were found to be influenced by the type of curing for both binders. Volume of permeable voids was found to show correlation to the long-term chloride penetration resistance of the concrete. No such correlation was found for sorptivity values.