Technique for measuring moisture storage capacity at high moisture levels

Knowledge of moisture storage capacity above the hygroscopic range is essential when calculating moisture, especially when different materials are to be connected. Generally, the storage capacity is represented by water retention curves, in which suction is plotted against the moisture content. In a number of laboratories in Europe and North America, the pressure plate and pressure membrane techniques are used to measure water retention curves. There are, however, various ways of carrying out such measurements. This paper compares two different methods of presaturating the specimens before testing, namely capillary and vacuum saturation. It also examines the effect of different beddings between the specimen and the ceramic plate. It is shown, as expected, that capillary and vacuum saturated specimens give differential results. Absorption tests clearly show that, for some materials, capillary saturation is a vague concept. For this reason, vacuum saturation is generally to be preferred. In the test with different beddings, no significant differences were found.