Technical Papers

Comparison of Permeability of Cementitious Materials Obtained via Poromechanical and Conventional Experiments

Abstract

Permeability testing of concrete is useful to predict moisture transport within the pore network. Conventional permeability tests based on steady-state linear flow-through take too long to get a reliable result and therefore are not frequently used. Development of poromechanical techniques has reduced the permeability testing time significantly. Systematic comparisons of the permeability of cement pastes and mortars obtained by a poromechanical method and a flow-through method were done in this study. The hollow dynamic pressurization (HDP) test was the poromechanical technique used, and the radial flow-through (RFT) test was the flow-through test utilized. Cement paste showed virtually identical results between the HDP and RFT permeability results. However, mortar and concrete, showed a significant difference between the HDP and RFT permeability results. It is hypothesized that the two methods measure effectively different transport properties in the same material. The RFT captures the effect of microstructure on the flux of fluid across or through the cross section of a material, whereas the HDP captures the effect of microstructure on flux of fluid into the smallest pore network of the material. Thus, the RFT is primarily influenced by the largest pores that provide a short-circuit through the cross section (e.g., the pores in the interfacial transition zone), whereas the HDP is primarily influenced by the smaller pores that must be pressurized in order to induce poromechanical coupling. In materials like cement paste that have a large number of rather uniform, well-distributed pores, transport rates through and into the pore network are essentially equivalent because no short-circuits through the cross section exist.