The influence of blast furnace slag, fly ash and silica fume on corrosion of reinforced concrete in marine environment

Chloride penetration from sea water may cause corrosion of reinforcement in concrete structures. Adding reactive inorganic materials such as blast furnace slag, fly ash or silica fume to the cement matrix improves the resistance against chloride penetration as compared to Portland cement concrete. A relatively simple laboratory procedure was proposed to test concrete mixes for their expected service life in sea environment. The assumption is that chloride diffusion and cover depth determine the time-to-initiation of corrosion and electrical resistivity determines the corrosion rate and so the time-to-cracking. The sum is the total "service life". The proposed testing procedure was applied to five concrete mixes. They contained ordinary Portland cement; OPC + silica fume; OPC + fly ash + silica fume; blast furnace slag cement, all with gravel aggregate; opc and lightweight coarse aggregate. The predicted time-to-initiation and the time-to-cracking in marine splash zone were calculated from the test results. The calculated service lives range from 10 to 80 years, increasing in the order: OPC-lightweight aggregate < OPC-gravel < OPC + silica fume-gravel < OPC + fly ash + silica fume-gravel < blast furnace slag cement-gravel. The ranking and the numerical results are in general agreement with data from exposure research and with practical experience. The addition of blast furnace slag, fly ash and/or silica fume may significantly increase the resistance against chloride penetration and consequently the time-to-initiation of corrosion. Once corrosion has started, steel in concrete with additional cementing materials may have a decreased rate of corrosion. The proposed set of laboratory tests appears suitable for evaluating the effect on corrosion protection in marine environment of new and/or supposedly improved concrete compositions