Limestones durability study on salt crystallisation: An integrated approach

Limestones are often used as building stones in contemporary architecture. Salt weathering is one of the main threats affecting this lithology. In this study, two Portuguese limestones (Branco Real and Lioz Coral) were subjected to laboratory salt crystallisation cycles by reconsidering the normative EN 12370 (Determination of the resistance to crystallisation of salts). The proposed test method consisted of 2 h of immersion in a 14 % solution of sodium sulphate decahydrate followed by 22 h drying at 40◦C instead of 105 °C imposed by the normative. A series of physical/aesthetic parameters (e.g. CIE L*a*b* colour coordinates, roughness, weight variation), mineralogical and geochemical analysis (Optical microscopy, XRD and SEM) and mechanical properties (Leeb-D hardness, ultrasound P-wave velocity and uniaxial compressive strength) were evaluated before, and after salt crystallisation cycles. Results underline the importance of salt crystallisation action and its impact on stones durability, considering the stone fabric, porosity and structure. The appearance of efflorescences, colour changes, increase of roughness, weight gain or loss, decrease of hardness, changes in p-wave speed and uniaxial compressive strength were detected even at more realistic testing conditions with a lower drying temperature.