Use of Fiber Optic and Electrical Resistance Sensors for Monitoring Moisture Movement in Building Stones Subjected to Simulated Climatic Conditions

Moisture is critical to the weathering of stone buildings and almost all weathering processes in building stones are influenced by the presence of moisture--especially the cyclic process of repeated ingress and egress of moisture that promotes their decay. Therefore, monitoring the moisture distribution in building stones is essential in understanding the material behaviour and degradation mechanisms associated with stone decay. In this study two real-time monitoring systems, viz. fiber optic sensor probe for relative humidity and electrical resistance sensors are compared by placing them, together with commercially available thermistors and humidity probe, at different depths in a limestone block in order to characterise patterns of moisture and temperature changes with depth from the exposure surface. This surface was then exposed to simulated wetting by a water spray, short-term cycles of heating and cooling beneath an infrared lamp to mimic solar radiation, and an intermittent air flow across the surface of the block. The experiment was conducted within an environmental chamber that kept ambient air temperature at 20°C. Results indicate that variations in external environmental factors, such as wind and intermittent heating cycles, can significantly affect the temperature and moisture variations in building stones.