The role of saline solution properties on porous limestone salt weathering by magnesium and sodium sulfates |
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Authors: | E Ruiz-Agudo F Mees P Jacobs C Rodriguez-Navarro |
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Institution: | (1) Departamento de Mineralogía y Petrología, Universidad de Granada, Fuentenueva s/n, 18002 Granada, Spain;(2) Department of Geology and Soil Science, Ghent University, Krijgslaan 281 S8, 9000 Ghent, Belgium |
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Abstract: | Saline solution properties, viscosity in particular, are shown to be critical in salt weathering associated with sodium and
magnesium sulfate crystallization in porous limestone. The crystallization of sodium and magnesium sulfate within a porous
limestone has been studied at a macro- and microscale using different techniques, including mercury intrusion porosimetry,
environmental scanning microscopy and X-ray computed tomography. Such analysis enabled the visualization of the crystallization
process in situ, and at high magnification, yielding critical information as to where and how salts crystallize. Sodium sulfate
decahydrate (mirabilite) tends to crystallize in large pores as euhedral micron-sized crystals formed at low supersaturation
near to the surface of the stone. In contrast, magnesium sulfate heptahydrate (epsomite) tends to precipitate as anhedral
wax-like aggregates formed at high supersaturation and distributed homogeneously throughout the stone pore system filling
large and small pores. While the former crystallization behavior resulted in scale formation, the latter led to crack development
throughout the bulk stone. Ultimately, the contrasting weathering behavior of the two sulfates is explained by considering
differences in flow dynamics of solutions within porous materials that are mainly connected with the higher viscosity of magnesium
sulfate saturated solution (7.27 cP) when compared with sodium sulfate saturated solution (1.83 cP). On the basis of such
results, new ways to tackle salt weathering, particularly in the field of cultural heritage conservation, are discussed. |
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Keywords: | Stone decay Sodium sulfate Magnesium sulfate Salt weathering ESEM |
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