Improved suction technique for the characterization of construction materials

The suction technique is a method from soil science that is used for the study of moisture storage capacity in porous construction materials at high relative humidity levels (above approximately 93 %). The samples to be studied are placed in a pressurized container (an extractor) on a water saturated ceramic disk or membrane.

The pressure corresponding to a certain relative humidity level is established and moisture is expelled from the samples until moisture equilibrium is reached. This paper presents two adjustments to this method and their applicability. The first adjustment is a new procedure for determining the equilibrium moisture content of samples during the experiment.

The method (referred to as the balance method) is to simply keep track of all water entering and leaving the system and use these data to estimate the moisture content of the samples. The advantage of this approach is that the experiment does not need to be stopped and restarted for each relative humidity level tested.

The main disadvantage of the method is that the estimation of the moisture content in the samples depends on a correct estimation of the moisture content of the ceramic disk. The second adjustment is the development of a pressure regulation system that keeps the pressure constant (±0.015 bar) within an extractor for weeks.