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The effect of environmental conditions on sodium chloride damage: A step in the development of an effective weathering test

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Author: Lubelli, B. · Hees, R.P.J. van · Groot, C.J.W.P.
Type:article
Date:2006
Institution: TNO Bouw en Ondergrond
Source:Studies in Conservation, 1, 51, 41-56
Identifier: 280133
Keywords: Architecture Materials · Chemical analysis · Mechanical properties · Microscopic examination · Mineralogy · Sodium chloride · Weathering · X ray diffraction analysis · Laboratory weathering test · Mercury intrusion porosimetry · Environmental impact

Abstract

Laboratory weathering tests are important in the field of restoration as they provide a means of estimating, in a relatively short time, the longer-term performance of conservation materials when applied in practice. Accelerated tests to simulate the damage caused to porous materials by soluble salts such as sodium sulphate are well known and highly effective. However, when using sodium chloride the existing test methods are not particularly successful. Research on case studies has shown that the environmental conditions play an important role in determining the occurrence of the decay. Therefore understanding the effect of the environmental conditions on the damage constitutes a first step in the development of an effective weathering test for sodium chloride. The research described in this paper studies the effect of environmental conditions on the decay due to sodium chloride with the ultimate aim of defining an effective laboratory test. The experiments have been performed on two plasters with very dffierent physical, mechanical and mineralogical properties. Different techniques of analysis have been used: mercury intrusion porosimetry, optical polarized microscopy, environmental scanning electron microscopy, chemical analyses and X-ray diffraction. The results obtained highlighted which of the test conditions under evaluation were the most effective. Using this information, a new procedure for an effective accelerated salt weathering test using sodium chloride is proposed.