Stone recession in cultural heritage investigated by laboratory ageing tests

Carbonate rocks (limestones, marbles) are among the most commonly used building materials (both as dimension and ornamental stones), and are highly vulnerable to weathering, especially in polluted areas. One of the main issues in the evaluation of cultural heritage vulnerability is the quantification of the deterioration rate. With this goal in mind, and in the frame of the HYPERION Project, the water-driven recession of stone in cultural heritage was simulated and measured in the laboratory by exposing a set of carbonate rocks, historically exploited and used in northern Italy, to accelerated ageing tests by immersion in rainwaters with different compositions. The tests were run cyclically in an environmental test chamber, alternating wetting and drying phases; at fixed intervals, the recession of each sample was quantified by bulk weight-loss measurements and surface mapping at the confocal microscope. The relationship between the different mineralogy and texture of the stones and the rate and areal development of their recession was investigated, finding that, besides water pH, calcite grain size is the most important controlling decay factor. Correction coefficients were also calculated for obtaining more reliable recession estimations from recession equations known in the literature. The findings of this study can be exploited for predicting stone deterioration in cultural heritage constrained by the relevant environmental context and the expected future climate change.