Salt-induced decay in calcareous stone monuments and buildings in a marine environment in SW France

Abstract

Salt weathering can be a hazard with significant cultural and economic implications. Salt-induced deterioration of architectural heritage is considered to be accelerated drastically in marine environments. This article investigates the weathering mechanisms and weathering forms in two calcareous stone types used in monuments and buildings on the SW coast of France. The mineralogical, chemical, textural and pore-system characteristics of freshly quarried and decayed stones from quarry, monuments and buildings were determined, and salts loading identified. The stones’ resistance against salt weathering was estimated by comparing calculated crystallisation pressures, which are function of the pore size distribution, with the tensile strengths measured by Auger [Alteration des roches sous influence marine; degradation des pierres en oeuvre et simulation acceleree en laboratoir. These Doctorat d'Etat es Siences. Universite de Poitiers, France (1987)]. Results show that Crazannes sparite and La Pallice micrite behave differently with respect to water and salt-spray absorption and local salt precipitation since their pore networks, which control hydric properties, are different. Therefore, diverse weathering patterns due to salt crystallisation pressures were identified in the stones as influenced largely by their pore size distribution: alveolar weathering and granular disintegration in the sparite vs. flaking and micro-fissuring in the micrite. These mechanisms operate in response to salt inputs from a variety of sources—mainly marine aerosols and atmospheric pollution—as corroborated by the so-called enrichment factors (EFs). Wind is believed to trigger alveolar weathering in the heterogeneous sparite. Short-term observations in La Pallice micrite show rapid salt-induced breakdown through ‘fatigue’ effects. Determining factors involved in stone deterioration is important in the design of proper interventions for protecting historic buildings.