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Predicting Efflorescence and Subflorescences of Salts

Published online by Cambridge University Press:  01 February 2011

Rosa Espinosa ,
Lutz Franke  and
Gernod Deckelmann
Rosa Espinosa
Affiliation:
espinosa.rosamaria@gmail.com, Princeton University, Dept. Civil & Env. Eng., Eng. Quad E-320, Princeton, NJ, 08544, United States, 609-258-5433
Lutz Franke
Affiliation:
lutz.franke@tuhh.de, Hamburg University of Technology, Institute of Building Materials, Physics and Chemistry of Buildings, Eissendorfer Strasse 42, Hamburg, 21071, Germany
Gernod Deckelmann
Affiliation:
deckelmann@tuhh.de, Hamburg University of Technology, Institute of Building Materials, Physics and Chemistry of Buildings, Eissendorfer Strasse 42, Hamburg, 21071, Germany
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Abstract

Crystallization of salts is a common cause of damage in porous building materials. Understanding of the crystallization mechanism of salts is important in order to prevent or avoid the problem. Subflorescence of salts (i.e., crystallization within the pores of the body) can induce scaling and cracking, while efflorescence (i.e., crystallization in a film of solution on the exterior surface of the body) does not generally affect the coherence and endurance of the building materials.

In this paper, we deal with the crystallization behavior of two salts, sodium sulfate and sodium chloride, in two bricks with different capillary porosity. The results reveal quite different crystallization behavior depending on salt and substrate.

The supersaturation of the solution is induced in our experiments by evaporation. Indeed, the main reason for the different behavior of these salts is the different ability for supersaturation. Thus, the sodium sulfate solution is prone to be much more supersaturated than sodium chloride. Furthermore, the solution transport, which depends on salt properties, material porosity, pore-clogging and climatic conditions, affects the position of the drying front and, with it, the crystallization front leading to the formation either of efflorescence or of subflorescence. A simulation of the experiments helps us to understand the effect of the influencing factors on the crystallization pattern. Therefore, considering both factors, supersaturation ratio and solution transport, it is possible to predict the different crystallization behavior observed in the experiments.

Keywords

nucleation & growthporositysimulation
Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 1047: Symposium Y – Materials Issues in Art and Archaeology VIII , 2007 , 1047-Y04-03
Copyright
Copyright © Materials Research Society 2008

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