Factors affecting measurement of hydraulic conductivity in low strength cementitious materials

The hydraulic conductivity (water permeability) is one of the most significant transport properties of concrete and measuring it is a key step in predicting the performance of concrete as a barrier to the movement of fluids and ions. The transport properties are critical for the performance of the cover layer in protecting embedded reinforcement as waste containments barriers (which are considered in this paper) and other applications such as dams. The measurements are difficult to interpret due to experimental effects of sample size and changes of flow with time and the chemistry of the fluid used. The intrinsic permeability to water and synthetic leachate was determined and the relationship between the eluted volume passing and permeability was established for mortar mixtures having compressive strengths ranging from 5 to 20 MPa. Two mortar mixtures containing portland cement and one without portland cement and incorporating cement kiln dust, lagoon ash, and Ferrosilicate slag were tested. The effects of the sample size were also investigated. The results indicate a decrease in hydraulic conductivity for lower strength mixtures and a slight increase in permeability coefficient for the higher strength mixtures with increasing permeating volumes. Increasing the testing specimen size also slightly increased the coefficient of permeability in lower strength mixtures and decreased the coefficient in higher strength mixtures. The permeability coefficient did not change significantly with pore solution pressure.