An experimental investigation into the salt-weathering susceptibility of building limestones

Abstract

Dimension and ornamental stones used for built heritage are frequently affected, under all climates, by intense weathering induced by the transport of saline solutions. Accordingly, researchers addressed the weathering mechanisms induced by salts (primarily Na2SO4), the stresses generated in the host material, and the durability of ornamental and dimension stones. This study investigates the behaviour of four sedimentary lithotypes, differing in texture and structure (Breccia Aurora, Rosso Verona, and fine- and coarse-grained Vicenza Stone) exposed to a selection of saline solutions, aiming at evaluating their susceptibility to weathering and the influence of petrographic features on durability. The chosen Na2SO4, MgSO4, Na2CO3, NaCl, and KNO3 solutions include the anions characterizing the major saline sources affecting built heritage: capillary rise, acid rain, atmospheric particulate deposition, bird or other animal scat, and de-icing salt contamination. The petrophysical properties of unweathered and salt-weathered samples were characterized by relative mass variation estimation, capillary rise, and hygroscopic absorption-based porosimetry. Scanning Electron Microscopy coupled with microprobe allowed studying the morphological changes triggered by weathering and analysing the chemical composition of the efflorescence crust. The whole of data, consistently with literature, allowed inferring pore type and distribution as the main intrinsic parameters controlling salt weathering susceptibility. Moreover, Na2SO4 and Na2CO3 proved to be the most harmful, probably due to their ability to crystallize in different hydration stages at room temperature. The comparative analysis of the induced weathering can help to choose suitable dimension stones for new buildings or restoration replacements.

Road Salt Damage to Historical Milestones Indicates Adaptation of Winter Roads to Future Climate Change May Damage Arctic Cultural Heritage

“…Sulphur dioxide deposition from acid rain has been particularly damaging to stone [29,32,33] and iron and steel [34,35], but emissions have dropped by 80% in Europe since the peak in 1980 [36][37][38]. Naturally occurring factors also cause damage, and airborne salt in sea winds causes structural failure in porous stone [39], and the propagation of cracks and flaking over freeze-thaw cycles [40]. Salt also corrodes metal and, consequently, corrosion is generally more prevalent in coastal areas [34].…”

Salt Weathering of Natural Stone: A Review of Comparative Laboratory Studies

“…Gaggero [19] Carbonate sedimentary rocks Magnesium sulphate, potassium nitrate, sodium carbonate, sodium chloride, sodium sulphate More intense effects (powdering and breakage) for sodium carbonate and sodium sulphate. Greater mass loss values for sodium carbonate than for sodium sulphate (around 16× times higher in one case) but with a wide interval, from less than 0.10% in both cases to around 34% for sodium sulphate and 100% for sodium carbonate.…”

The Crystallization Effect of Sodium Sulfate on Some Italian Marbles, Calcarenites and Sandstones

“…In laboratory studies, salt-induced decay is made by either partial immersion [31] or full immersion [21,[32][33][34] in the saturated solutions of one or more mixed salts, followed by oven or air drying. Soluble-salt crystals are then usually analyzed by several characterization techniques, such as visual inspection, X-ray-powder diffraction [35], optical [25], Raman [36] and scanning-electron microscopy [37], simultaneous thermogravimetry, and differential scanning calorimetry [38].…”