Salt crystallization laboratory test with a complex brine

Author(s): Beatriz Menéndez
Paper category: Proceedings
Book title: Proceedings of the International RILEM Conference
Materials, Systems and Structures in Civil Engineering 2016 segment on
Historical Masonry
Editor(s): Inge Rörig-Dalgaard and Ioannis Ioannou
ISBN: 978-2-35158-178-0
e-ISBN: 978-2-35158-179-7
Publisher: RILEM Publications SARL
Publication year: 2016
Pages: 266-266
Total Pages: 1
Language : English

Abstract: It is well known that in buildings and monuments salts are one of the most important weathering
factors. When analysing weathering products present in monuments a mixture of several
different salts are always found. The most common salts are chlorides, sulphates and nitrates of
sodium, calcium, potassium, magnesium, etc. Several authors tested complex brine
crystallization processes under different environmental conditions or performed crystallization
tests on laboratory stone samples using also a mixture of salts. In both cases they found that the
results are different from those obtained with single salt compositions (see review in [1]).
We realised non-standard salt crystallization ageing tests using single salt solutions (NaCl,
Na2SO4) at 6% wt and a mixture of them at 12% wt (6% NaCl and 6% Na2SO4). These one
week cycles consisted of an immersion phase, followed by a two days drying, and four
spraying/drying one day cycles. Drying temperature was 50°C. The salt crystallization test has
been modified to simulate more realistic and less aggressive conditions. 7 Cycles have been
done. Samples have been weighted after every wetting and drying period and have been
photographed after every drying period.
As salt weathering can be also a consequence of crystallization/deliquescence cycles, after the
crystallization cycles, samples have been subjected to 14 relative humidity cycles at 50°C, one
week at low RH (5%) and one week at high RH (90%). Once again the behaviour of samples
containing several salts is different from that of samples containing one unique salt.
In order to investigate the effect of stone microstructure on weathering process three different
building limestones, with quite a similar mineralogical composition but with quite different
pore systems, have been used. The selected stones are Lutetian, Caen and Vernon stones. A
description of these stones can be found in [1].
ECOS RUNSALT model has been used to model the salt volume evolution as a function of
environmental conditions during experiments. The main conclusions are:
x Complex salt brines produce less damage than single salt solutions.
x Caen limestone is the most affected by salt weathering which can be explained by the
smallest size of its pores.
x Changes in relative humidity can be as dangerous as crystallization cycles by salt
supply.
x Salt volume variations cannot explain the damage induced in samples by salts.

Online publication : 2016
Publication type : full_text
Public price (Euros) : 0.00