Name
Julie Desarnaud
Title of research project / research interests
Crystallization dynamics and salt weathering of materials
Affiliation(s)
University of Amsterdam (Netherlands) and
UR Navier / IFFSTAR/ Ecole Centrale des Ponts et Chaussées (Paris, France)
Current position
Post-doctoral position
Supervisor(s)
Noushine Shahidzadeh-Bonn
Estimated date of completion
31st July 2011
Key words
Salt weathering, Stone degradation, kinetics of crystallization, conservation sciences
Previous education and/or work experience
- Ph.D. in environmental sciences with honors at the University Aix-Marseille III at CICRP Interregional Centre for Heritage Conservation and Restoration CINaM Centre of Nanosciences of Marseille (Marseille, France)- supervisors Pr. Alain Baronnet, CINaM-CNRS and Dr. Bromblet Philippe, CICRP Marseille
Thesis title: “Growth and dissolution of KCl crystal under load: Involvement in the knowledge on stone degradation by soluble salts”.
- Project Member Interregional Centre for Heritage Conservation and Restoration (conservation of F. Laurana altar piece in marble)
Abstract
Salt contaminated porous materials (such as stones or masonry materials) are often observed to deteriorate under environmental conditions due to crystallization of the salts. These can be naturally present in the stones, or get trapped inside the porous material for instance by imbibition with salt-containing precipitation. When environmental conditions such as humidity or exposure to rain or rising damp vary, salts in contact with water (liquid or vapor) can dissolve and cause damage to the material by re-crystallization upon drying.
In this study we investigated the impact of such re-crystallization dynamics of sodium sulfate on damage observed after repeated cycles of wetting/drying and humidification/drying. Combined macroscopic and microscopic-scale experiments show how the kinetics of crystallization can be related to damage for the sulfate when rewetting is done with liquid water. It leads to severe damage because of the only partial dissolution of anhydrous microcrystals in regions that are highly concentrated in salt. The remaining microcrystals act as seeds to form large amount of hydrated crystals creating grape-like structures that expand rapidly. We show that the growth velocity of the hydrated crystals in the form of clusters is more than an order of magnitude faster than for hydrated crystals that grow independently in the solution, giving rise to a crystallization pressure higher than the tensile strength of our sandstone
On the other hand, if sulfate-containing stones are slowly rewetted by bringing them in contact with saturated water vapour prior to drying, hardly any damage is observed on sandstone samples. The phenomenon is very slow, allowing the complete dissolution of anhydrous microcrystals, and the formation of independent hydrated crystals. The measured crystallization velocity leads to a crystallization pressure not sufficient to break the sandstone. During the following repeated cycles of humidification/drying only anhydrous crystals with a slow growth rate appear, the concentration is not sufficient to develop crystallization pressure higher than the tensile strength of our sandstone
The better understanding of the mechanisms involved in damaging developed here can significantly improve the methods used for preventing damage. For example, the use of water based poulticing methods for desalination on highly sodium sulfate contaminated stones is counter indicated since it requires rewetting of the stones. To the contrary, the control of the relative humidity, allows to choose the crystalline form (hydrated or not) of sulfate present in stones before desalination and thus should allow to avoid damage.
E-mail / Contact details
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