Novel Method for Measuring Permeability of Concrete

Princeton University, Princeton NJ

Investigators

Abstract

0070092 The goal of this work is to develop a novel technique for measuring low liquid permeabilities in heterogeneous materials, particularly including high-performance concrete. In contrast to conventional methods, the new method does not require high pressure apparatus and it yields results in a few hours, rather than days or weeks moreover, it is easiest to perform on samples of low permeability, which are the most difficult to measure by other methods. The principle of the new method is that the thermal expansion kinetics of a saturated porous body involves flow of the pore liquid, so the permeability can be determined by measuring the dilatation during a thermal cycle. When a saturated porous material is heated, the pore liquid expands much more that the solid phase, so the liquid tends to flow out of the pores. Our objective is to design and build a dilatometer to perform the measurement on cylinders of the kind typically used for strength measurements. The resulting permeability values will be compared to those obtained by conventional methods. Test will be performed on cement, mortar, and concrete to explore the range of measurable permeabilities. A numerical analysis of the experiment will be performed to explore the limits of the analytical calculation, which involves some simplifying assumptions However, the low permeability of the body prevents the liquid from escaping as fast as it expands, so is forced to expand within the pores, stretching the porous body like a spring. If the body is heated and then held at a constant temperature, the initial expansion is caused in part by the liquid; during the isothermal hold, the liquid drains from the pores and the body contracts to the dimension determined by the thermal expansion coefficient of the solid. The magnitude of the dilatation contributed by the liquid can be calculated, so fitting the measured expansion to the theory provides the permeability as a parameter.