Properties of hydrophobised lightweight mortars with expanded cork

The article evaluates the efficiency of surface hydrophobisation based on organosilicon compounds. The subject of the study involved expanded cork mortars produced from Quercus Suber oak. Surface hydrophobisation was carried out by means of: a solution of methyl-silicone resin with high VOC content, aqueous emulsion from methyl-silicone resin in potassium hydroxide and low-molecular alkyl-alkoxy-silane in an organic solvent. The basic mechanical and physical parameters were investigated in this paper. The following parameters were studied: compression strength, tensile strength, density, open and total porosity, absorbability, water vapour diffusion capacity, vapour-permeability, capillary water absorption coefficient, frost resistance, resistance to sodium sulphate corrosion, surface free energy (SFE), thermal conductivity coefficient. The contact zone, micro-structure, and decomposition of polysiloxane gel in the mortars were presented on the basis of a scanning electron microscope (SEM) research. The mortar characterized by the greatest porosity exhibits the highest absorptivity. The mortar with sand is the tightest; its absorptivity is almost three times lower than the one of a mortar without sand. The mortar C2S with sand has the highest resistance. All considered samples exhibited good resistance to salt crystallization after 15 cycles. The mortars subjected to hydrophobisation showed virtually no damages following the frost resistance test, whereas the mortar samples with 20% cork and lime content were badly damaged and suffered a 14% weight loss. The contact angle and SFE determine the wetting and adhesion properties of mortars. The latter can be modified by means of cork and sand additions.