Analytische Chemie
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Subfloors are layered structures, consisting largely of porous building materials, such as screed. They are often suffering damage from tap water leakage, which is a typical problem in buildings, and which has largely contributed to repair costs of almost 3 billion Euro in 2018 alone in Germany. In this context, especially mould plays a role, which is both destroying the structure and posing severe health risks.
To determine the damaging effects of moisture, it is necessary to know the respective processes occurring in building materials, especially to quantify the amount of moisture and its progress in the material. In this study, humidity sensors are used to derive the material moisture experimentally.
Capacitive sensors recording the relative humidity are embedded into the screed and in the insulation materials such as expanded polystyrene, extruded polystyrene, perlite and glass wool. For the application in screed, the sensors need to be shielded against the aggressive alkaline materials. To ensure an appropriate exchange with the environment, a permeable membrane is requested. Different membrane materials have been investigated regarding their robustness and their permeability.
In the first experimental setup, two humidity sensor arrays with seven individual sensors are embedded in homogeneous screed samples. The measured corresponding relative humidity of the screed is converted to the material moisture based on the approach of Hillerborg. In a second experimental setup, a layered structure of a complete subfloor is built in a box of 0.8 m times 0.8 m. The humidity sensors are positioned in the different insulation materials of various thicknesses. By adding water, leakage damage is simulated and its progress and effect is investigated experimentally.
The investigations point at the question if the observed moisture is able to generate damage such as mould. The moisture and corresponding humidity values are discussed. It will be shown that this low-cost hygrometric approach can be used easily for moisture monitoring of screed and insulation materials as well
Damages in infrastructure due to moisture amount to billions of Euros every year. For a more predictive structural health monitoring in civil engineering, the detection and monitoring of hazardous moisture in steel reinforced concrete constructions is of high interest. The sensors have to be wireless, elsewise they weaken the concrete cover of the rebars. The lifetime of such constructions is normally decades, thus the sensors have to be battery-free and fully passive. Considering these requirements, passive RFID-based sensors are developed. Communication and energy supply are realized wireless via the electromagnetic field of a RFID transmitter. The passive RFID based sensors are embedded into the concrete to enable the monitoring of moisture transport in porous materials. Results of the hydration process are shown.