Water vapour storage capacity of masonry renovation plasters contaminated with chlorides

Abstract

The effect of sodium chloride presence on the water vapour storage capacity was studied for six types of plasters designed for application in masonry restoration. Sorption isotherms were measured using a static climate chamber method. The researched materials were characterised by their bulk density, matrix density, and total open porosity. For the studied materials, measurement of chloride binding isotherms by an adsorption method was done in order to reveal their capacity to accumulate salts and relate the adsorbed water vapour to the amount of contained salt. The experimental sorption data measured for salt contaminated samples were analysed using relation expressing the dependence of the mass equilibrium moisture content (EMC) of plasters saturated with salt solution of given molality on relative humidity of the environment. For relative humidity up to 70 %, good agreement between measured and calculated data was obtained. For higher relative humidity, the water vapour adsorption capacity of studied materials was not fully exploited especially for lower chloride concentrations. The type of binder together with physical parameters of examined materials was found to have a decisive role in chloride binding. One of the tested materials can be possibly classified as WTA renovation plaster, considering its total open porosity, bulk density and high binding capacity for chlorides. On the other hand, one must take into account its hygroscopicity, especially in case of a higher salt contamination.