The hydraulic conductivity of three concretes with a high ratio of water to cementitious solids (w/cs) was measured using a test device in which confining and driving pressures are controlled separately (triaxial, or Hassler cell). Test variables included: confining pressure (c), driving pressure (d), ratio of these two pressures (c/d), and sample length. The objective was to determine the effect of these variables on measured permeability (K).

For these concretes, the driving pressure has a strong influence on K values, which generally are significantly higher at lower driving pressures. The c/d ratio controls K to a lesser extent, and not in a consistent direction. K increases as c/d increases for specimen lengths of 3X the maximum aggregate size or longer. For specimens the length of which is closer to the aggregate size, K values decrease with increasing c/d, making specimen length an important variable. Removal of entrapped air from the system and presaturation of the specimens also are important.