Architectural heritage and climate change: performance prediction of exposed natural building stone to rainfall through a combination of laboratory leaching tests and X-ray computed tomography

Natural stone has been over the centuries among the most common and prominent materials used in construction. The natural and irreversible process of ageing results in a progressive deterioration of the original properties, whose level and rate are determined by the interaction of environmental factors and the stone’s intrinsic features. Water represents one of the most important causes of decay for historic buildings; atmospheric precipitation is responsible for the surface recession of carbonate stones, especially in areas where the presence of pollution induces a decrease in the rainwater pH. In connection to the climate change issue, recession rate in high-rainfall regions of Europe is expected to increase, due to the rise in carbon dioxide atmospheric concentration. However, not only the mineral composition, but also the structural properties are important factors influencing the performance. Experimental testing carried under laboratory conditions shows the existence of correlation between the stone’s microstructure and its degradation caused by wet deposition. This indicates the need for a specific and targeted evaluation of the individual case to inform decision-making about conservation and selection of stone for necessary material replacement. The aim of this work is the performance evaluation of different calcareous sedimentary stones presenting a range of compositional and structural properties when exposed to surrogate rainfall, through a unique combination of chemical and morphological analyses with multivariate data treatment. The presented preliminary test revealed good discrimination between individual responses to the action of surrogate rainwater, highlighting the necessity to further investigate the relationship between the weathering process and the chemical and physical properties of the stone.