Effects of W/B ratios and fly ash finenesses on chloride diffusion coefficient of concrete in marine environment

The objectives of this investigation were to study the effect of W/B ratios and fly ash finenesses on chloride diffusion coefficient (D_c) of concrete under marine environment. Original and classified fly ashes were 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 as 0.45, 0.55, and 0.65. Concrete cube specimens of 200 mm were cast and removed from the molds after casting 1 day and then cured in fresh water for 27 days. After that, the specimens were placed to the tidal zone of marine environment in the Gulf of Thailand. Subsequently, the specimens were tested for chloride penetration profile after being exposed to the tidal zone for 2, 3, 4, and 5 years. The regression analysis of investigated data was carried out and Fick’s second law of diffusion was applied to calculate the chloride diffusion coefficient (D_c) and chloride concentration at concrete surface (C_o) based on one-dimensional analysis. The results showed that D_c of all concrete mixtures decreased with an exposure time and the decrease of W/B ratio resulted in the decrease of D_c. When the W/B ratio of concrete was reduced, the decrease of D_c in cement concrete was higher than that of the fly ash concrete. The use of fly ash with high fineness clearly reduced the rate of chloride ingress into concrete. In addition, fly ash with high fineness has more effective on reducing of D_c in concrete with higher W/B ratio than that with lower W/B ratio.