Chloride Diffusion Models for Type V and Silica Fume Cement Concretes

One of several methods used to minimize reinforcement corrosion is the use of service-life prediction models to calculate mixture design and construction variables for the desired service life of a structure. Although several models are available for this purpose, very few incorporate the effect of environmental temperature on chloride diffusion. Moreover, most of the earlier studies were conducted under laboratory conditions and they are not based on actual field data. In the reported study, chloride diffusion in Type V and silica fume cement concretes was evaluated under laboratory and field conditions. Large-size concrete specimens were exposed in the tidal zone of a marine exposure site for 1, 2, 5, and 10 years while the laboratory specimens were exposed to a chloride solution maintained at 22, 35, 50, and 60[degrees]C (71.6, 95, 122, and 140[degrees]F) for 1 year. The coefficient of chloride diffusion ([D.sub.a]) for Type V cement concrete specimens placed in the field was noted to be much more than that of silica fume cement concrete specimens at all exposure periods. However, the [D.sub.a] for both Type V and silica fume cement concrete specimens decreased by 1.3 to 3 times with increasing period of exposure. The [D.sub.a] for the laboratory concrete specimens increased by 2.2 to 3.8 times as the exposure temperature was increased from 22 to 60[degrees]C (71.6 to 140[degrees]F). Furthermore, the [D.sub.a] for Type V cement concrete specimens was 2.9 to 5 times more than that of silica fume cement concrete specimens. Empirical models correlating the field and laboratory data were developed. These models could be useful for calculating the [D.sub.a] for field conditions from the laboratory data. Keywords: activation energy; coefficient of chloride diffusion; exposure temperature; field and laboratory exposure; silica fume; tidal zone; Type V cement.