Evaluating the salt content of salt-contaminated samples on the basis of their hygroscopic behaviour: Part II: experiments with nine common soluble salts

This article concerns experimental research carried out in order to test the applicability of the hygroscopic moisture content (HMC) method to determine the salt content in lime-mortar and ceramic brick samples contaminated with nine distinct soluble salts (NaCl, KCl, Na2SO4, K2SO4, NaNO3, KNO3, Na2CO3, K2CO3 and CaSO4.2H2O). It was verified that the nature of the base-materials does not influence the results. For the salts with RHeq below the RH of the testing environment, excellent linear correlations between HMC and salt content were obtained. However, in the case of Na2SO4, several non-equilibrium situations occurred, indicating that the HMC method should not be “blindly” applied to samples contaminated with this salt. It was also shown that the use of deep narrow receptacles may delay the dissolution process but also that, with shallow receptacles, it may be more difficult to reach stabilization of the masses of samples due to the inevitable fluctuation of the climatic parameters in the climatic chamber. A complementary HMC experiment on NaCl and on Na2SO4 corroborates the thesis that states that mirabilite can not normally be formed by direct hydration of thenardite.