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.

This paper describes the work on cement paste development and short-term leaching tests in Standard Canadian Shield Saline Solution (SCSSS) in the presence of bentonite at 150°C. It has been found that:

-supplementary cementing materials such as silica fume or fly ash could significantly improve the properties of sulphate resistant portland cement (SRPC), in particular, permeability to water and pore size distribution.

-the addition of bentonite suppressed the normal tendency of the pH of groundwater to increase rapidly in the presence of cement.

-the presence of bentonite increased the release of potassium ions from the cements.

-– SRPC blended with 20% silica fume resulted in a groundwater pH lower than that of SRPC, with and without bentonite. Moreover, its cumulative fraction of release of potassium was significantly lower than that of SRPC.