Long term performance of chloride binding capacity in fly ash concrete in a marine environment

The capacity of binding chloride ions in fly ash concrete under marine exposure was studied. The free and total chloride contents in concrete were determined by water and acid-soluble methods, respectively. In order to study the effects of W/B ratios, exposure time, and fly ash contents on chloride binding capacity of concrete in a marine site, a class F fly ash was used as a partial replacement of Portland cement type I at 0%, 15%, 25%, 35%, and 50% by weight of binder. Water to binder ratios (W/B) were varied at 0.45, 0.55, and 0.65. Concrete cube specimens of 200 mm were cast and placed into the tidal zone of a marine environment in the Gulf of Thailand. Consequently, acid-soluble and water-soluble chlorides in the concrete were measured after the concrete was exposed to the tidal zone for 3, 4, 5, and 7 years. It was found that the percentage of chloride binding capacity compared to total chloride content increased with the increase of fly ash in the concrete. The percentage of chloride binding capacity significantly decreased within 3–4 years after the concrete was exposed to the marine environment, and then its value was almost constant. The research also showed that the W/B ratio does not noticeably affect the chloride binding capacity of concrete.