Experimental study on salt crystallization in plasters subjected to simulate groundwater capillary rise

Plasters belong to a group of cementitious materials which by nature have a capillary-porous structure. It causes many unfavorable phenomena, such as excessive dampness of the material in effect of capillary rise of pore water or crystallization of salts on material surfaces. Salt weathering is one of the main damaging factors that affects the durability of plasters or renders. The objective of the research was to compare the resistance to salinity and efflorescence of common plastering mortars and renovation plasters. Experience shows that some ready-made systemic mortars for the general use display such properties and plasters or renders made of them subjected to salinity do not deteriorate. Conventional mortars were also additionally modified by air-entraining plasticizing admixtures (APA). The research studies consisted in carrying out salinity tests in simulated conditions, which imitated a fragment of wall subjected to capillary water adsorption from subsoil. For comparison, the samples were also subjected to a reference test using demineralized water to capture the source of salinity. For the experiment, traditional plasters and systemic plasters were applied on the substrates from aerated concrete blocks used for construction of walls. Following both tests, the content of sulphates in individual plasters was determined. The aim of the research was to compare the effects of salinity in individual plasters and to determine the relationship between the degree of salinity and physical properties. The analyzed physical properties included: bulk density, water absorption, porosity and pore-size distribution. The pore structure distribution was determined by mercury intrusion porosimetry (MIP) in the initial state and after the salinity test under simulated conditions. Also selected comparative observations with a scanning electron microscope (SEM) were made. The highest correlation was obtained between salinity increments and total porosity. Comparing the effects of salinity in individual plasters, it was observed that they are different in terms of the degree of salinity and efflorescence. Based on the relationship between the salinity degree and physical features, it was found that the features of some common systemic plaster are similar to those of renovation plaster, and thus they have the ability to accumulate salt. The obtained results are of cognitive importance in relation to traditional plasters and their properties, in particular their resistance to salinity and durability issues of wall plasters in buildings.