Using the Karsten tube to estimate water transport parameters of porous building materials

Over the last decades the Karsten tube has been used as a versatile testing device to measure the water absorption of porous walls. It is non-destructive and it can give reproducible results when used accurately. A major drawback however is the lack of a physical interpretation of the results. This paper uses analytical models and a numerical simulation in 3D to allow a more fundamental and general interpretation of the test results. A relatively simple model for a soil infiltrometer test was proven to give a good fit to experimental field data and to lab test results. 3D numerical simulations, performed with Delphin 5 software, provide extra insight about the correctness of the model assumptions of a sharp front process and a simplified shape of the wetting front. A supplementary measurement of the increase of the diameter of the wetted zone during the test allows a straightforward calculation of the capillary saturated moisture content and the sorptivity of the material. Moreover an analytical relation is presented between the results of the Karsten test as described in the old standards and the sorptivity.