Abstract
The durability of building materials with respect to salt crystallization is commonly determined by accelerated weathering tests, carried out in the laboratory. An effective laboratory weathering test should assess the durability and, in the case of conservation of historic buildings, the compatibility of repair materials with those existing. Besides, the test should provide reliable results within a reasonable period of time, accelerating the deterioration process without however altering its mechanism. Despite several national and international standards, recommendations and guidelines, a commonly accepted testing protocol does not yet exist. Researchers often develop and apply their own procedure, a fact that complicates comparison between different studies. The RILEM Technical Committee 271 ASC has been set up with the scope of developing improved test procedures for the assessment of the behaviour of materials under the influence of salt crystallization, which should overcome the limitations of existing standards and recommendations. This paper constitutes one of the first results of the work of the Technical Committee. It critically reviews the literature on salt crystallization tests, identifies advantages and limitations of the several test protocols and provides new ideas for the development of improved salt crystallization procedures.
Highlights
Salt crystallization is a major cause of damage in porous building materials (e.g. [1,2,3])
In the case of sodium chloride, wet-dry cycles obtained by varying the relative humidity (RH) of the air around the equilibrium RH of the salt can produce several crystallization-dissolution cycles in a short period of time and lead to damage, provided that the salts have accumulated near the surface of the specimen and are, responsive to RH changes [50]
Some papers report on complex experiments, such as those carried out by Yu and Oguchi and Menendez and David who used different temperature and RH conditions, in order to investigate the aggressiveness of different forms of Na2SO4 [113] and CaSO4 [114] on the weathering
Summary
Salt crystallization is a major cause of damage in porous building materials (e.g. [1,2,3]). The European standard EN 12370 prescribes very aggressive weathering conditions (cycles of immersion in highly concentrated sodium sulphate solution followed by drying at 105 °C) [9, 10] This may result in damage patterns that are different from those known from practice for the material concerned (Fig. 1). None of the existing standards prescribes an accurate, reliable and quantitative method or technique for monitoring damage development during the test. Another limitation of current standards consists in the scarce validation of the results from the accelerated test through comparison with field data, e.g. in terms of damage type and severity [11]. Ideas are provided for the development of effective salt crystallization procedures
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