Penetration of Water and Chloride Dissolved in Water into Concrete under Hydraulic Pressure

Migration of dissolved ions into concrete by capillary absorption (convection) and by diffusion has been studied in great detail in recent years. These two processes are considered to be major mechanisms of chloride penetration into concrete in contact with seawater or with water containing deicing salt. In practice, however, there exist many reinforced concrete structures, such as harbor constructions, subsea tunnels or bridge pillars, which are in permanent or temporary contact with salt containing water under considerable hydrostatic pressure. Penetration of chloride into concrete under hydrostatic pressure has been investigated to the same extent so far. Chloride penetration into concrete under the influence of a hydrostatic pressure has been studied on five types of concrete. The influence of blended cements has been investigated in particular. The results indicate that a pressure less than 0.1 MPa has hardly any influence on chloride penetration. Once the water pressure overcomes 0.3 MPa, the water and chloride penetration depth as well as the chloride content at a given exposure time increase significantly. If fly ash and slag are added to Portland cement, the resistance with respect to water and chloride penetration increases. Longer moist curing reduces the rate of chloride penetration. If an aqueous salt solution penetrates into concrete under hydrostatic pressure, the dissolved chloride does not follow the penetrating water but it is accumulated in a surface near zone. The porous structure of concrete obviously acts like a molecular filter. The ratio between water and chloride penetration depths can be expressed by means of an exponential function. (A)