The purpose of this study is to make clear the law governing flow of water forced to seep into concrete under pressure. Further, based on the results of the study, fundamental data on materials for watertight concrete, selection of mixture proportions, and cross-sectional design of watertight concrete members are furnished. Noting that the ratio of seepage water forced into concrete differs depending on the degree of water pressure and varies between approximately 1.0 and nearly 2.0 times in volume, flow of water in concrete is divided into Darcy seepage flow in case of low water pressure and osmotic diffusion flow under high water pressure. Next, analytical studies are made of these flows, and equations of seepage coefficients are indicated for Darcy seepage flows and a diffusion coefficient calculation formula for osmotic diffusion flows. It is proposed that watertightness of concrete be evaluated by the former in case of water pressure less than about 0.15 MPa and by the latter in case of higher water pressure. Based on the results, the effects of using various chemical admixtures are evaluated by seepage and diffusion coefficients. Further, a method of checking watertight concrete member thickness is tentatively proposed as a part of studies on safety at the serviceablility limit state.
