Modelling the Influence of Hydrophobic Treatment on the Electrical Conductivity of Mortar and Brick

This study evaluates the suitability of electrical resistance-based moisture content measurements, which are known to guarantee reliable values for moisture contents of wood, when applied to selected mineral building materials with and without water-repellent treatment. For the testing specimens of cement – mortar and solid brick were produced – the water-repellent treatment for the mortar specimens was carried out both by internal hydrophobization and surface treatment, while the bricks were hydrophobized by surface treatment only. For the measurements of electrical resistance electrodes were inserted into the specimens. For this purpose a borehole was drilled and the measuring point at the tip of the electrodes was glued conductively into the material. The remaining outer part of the electrodes was sealed with electrically isolating glue in order to establish a conductive connection in the middle of the specimens only. After storage at different relative humidity, the electrical resistance of the specimens was recorded using data logging devices. Based on gravimetrically measured moisture contents resistance characteristics for each material were established. A satisfying accuracy resulting from the comparison between gravimetrically measured and mathematically calculated material moisture contents confirmed the suitability of electrical resistance based moisture content measurements for selected treated and untreated mineral materials.