Initial corrosion presented by chloride threshold penetration of concrete up to 10 year-results under marine site

This research studied the initial corrosion of reinforced concrete presented by the chloride threshold penetration depth of concrete exposed to marine environment. The results of an on-going study of fly ash concrete exposed to a marine environment for up to 10 years were reported. Water-soluble chloride testing was conducted to measure the free chloride penetration in fly ash concretes that had been subjected to wet and dry cycles in a marine environment for 2, 3, 4, 5, 7, and 10 years. The free chloride penetration and chloride threshold levels obtained from this testing led to the determination of the chloride threshold penetration depth and time to initial corrosion of marine concrete. The study found that the chloride threshold penetration depth increased at a high rate during the first 5 years, after which the rate of increase declined. It seems that the water-to-binder (W/B) ratio has a greater effect on the reduction of the chloride threshold penetration depth in Portland cement concrete than in fly ash concretes. The use of fly ash at least 35% replacement in concrete with W/B ratio of 0.65 provides an initial corrosion resistance as good as the cement concrete with W/B ratio of 0.45. For concretes with the same cover depth and the same W/B ratio, a high content of fly ash (over 25% fly ash replacement) greatly prolongs the time to initial corrosion of the reinforcing steel in the concretes.

► Research evaluated the time to initial corrosion for any concrete cover depth.
► Findings can help predict the time to initial corrosion of concrete in marine site.
► Suitable concrete mix to be used in marine site is proposed based on 10 year-results.
► Effect of fly ash on the time to initial corrosion of reinforcing steel is proposed.