Use of micro-climatic monitoring to assess potential stone weathering on a monument: example of the Saint-Remi Basilica (Reims, France).

Temperature and humidity variations influence various weathering processes of historical building stones. The aim of this study is to define the possible micro-climates on a monument in order to identify the recurring stress events, allowing to assess the potential stone weathering. For this purpose, a sensor network was set up on the two towers of the Saint-Remi Basilica of Reims: fourteen i-Buttons recorded temperature and relative humidity for 2 years with a time step of 1 h or 2 min for short measurement campaigns. Two micro-climates were identified: the sunny micro-climate (areas oriented South and West) presenting higher temperatures and lower relative humidity than the shadowed micro-climate (areas oriented North, East, and other shadowed zones). On the micro-climates, three typical days (Sunny, Rainy, and Frost days) were determined and allowed to fragment 1 year in a succession of these days. Short temperature variations (1 C/min) due to cloud cover were also identified during the sunny days, thanks to the shorter time step of 2 min. The stress generated during the typical days could then be estimated. Depending on the repartition of typical days for each micro-climate, some weathering processes could be favored: concentration of stress near the surface on the sunny micro-climate, development of biological colonization, and harsher frost events for the shadowed micro-climate. Taking into account the properties of the main limestones present on the basilica, the weathering on-site could be explained.