Monitoring of the absolute water content in porous materials based on embedded humidity sensors

Moisture transport monitoring may indicate the onset of deterioration in porous building materials prior to damage occurring. Most moisture measurement systems provide only qualitative values, require extensive calibration, or are destructive. Thus, non-destructive and calibration-free monitoring systems are required. Our approach of moisture monitoring is to embed sensors that measure the relative humidity. In our experiment, screed samples are monitored during the hydration and evaporation process. Every test sample is equipped with 10 embedded sensors which measure the relative humidity across the sample thickness. Based on Hillerborg's approach, the relative humidity is converted into the corresponding pore saturation. In our study, the free water is computed without knowledge of the sorption isotherm. The free water in the pore system is predicted and validated. The predicted weight decrease corresponds conclusively to gravimetrically measured weights. The embedded sensors yield the absolute liquid water content and enable an experimental, non-destructive monitoring of liquid water in porous materials.