Hydrophobization of concrete and aerated concrete by impregnation with calcium polysulfide

Introduction. A method for protecting concrete and aerated concrete by treatment with a calcium polysulfide-based solution is considered. The solution penetrates into the pores of the materials and, after drying, forms a water-repellent nanoscale layer, protecting the material from water penetration. This ultra-thin layer is formed as a result of the destruction of calcium polysulfide molecules while drying the impregnating solution and gives the material hydrophobic properties. The paper presents research results of the properties and composition of the forming protective layer and its effect on water penetration into the materials. Materials and methods. In the article authors present data on water penetration into the studied concrete and aerated concrete samples, the size and composition of the hydrophobic agent using laser and X-ray diffraction, ultraviolet spectroscopy, as well as using visual research methods, including electron microscopy. Results. It has been revealed that the hydrophobic surface is formed from a mixture of sulfur and calcium carbonate. It is shown that concrete and aerated concrete impregnated with a calcium polysulfide-based solution acquires pronounced water-repellent properties, expressed in contact angles corresponding to superhydrophobic surfaces. The presence of sulfur was established by ultraviolet spectroscopy, and force microscopy showed the formation of nanocomposite particles from sulfur and calcium compounds. X-ray phase analysis showed that the protective layer deposited on the surface of the materials consists of sulfur nanoparticles (65%), as well as nanoparticles of calcium compounds – vaterite (21%) and calcite (13%). Surface treatment of concrete with a sprayer leads to a decrease in water absorption from 5.4% to 3.1%, and in the case of treatment by immersion to a value of 1.5%, while the use of preliminary vacuuming before immersion of the samples allows achieving a water absorption parameter of 0.9%. It is shown that impregnation with preliminary vacuuming leads to water absorption values of less than 1%, which indicates the practical water impermeability of samples of full-scale products (concrete curbs and pipes). Discussion. It is noted that during surface treatment of aerated concrete with a sprayer, a chemically resistant superhydrophobic layer in the form of a nanocomposite is being formed, which penetrates to a depth of 3–3.5 cm, reliably protecting the material from water and chemical penetration. Surface treatment is effective in cases where objects (facades, above-ground structural elements, etc.) are exposed to water in the form of rain. Treatment of concrete products by immersion and immersion treatment with vacuuming can be carried out in harsh cases of constant water exposure (underground utilities, tunnels, manholes). Conclusions. The limitation of water penetration, and in some cases the absence of water in the pores of building materials impregnated with calcium polysulfide, indicate the preservation of substance, since water is a carrier of substances that destroy concrete and aerated concrete. Accordingly, there is no destructive effect from freezing of water in the pores of such materials as a result of the formation of a nano-sized coating of sulfur particles. Comparison of the results for aerated concrete shows that it acquires superhydrophobic properties, which indicates its excellent modification and expands the possibilities of its use. The data observed for concrete products indicate that after treatment with a calcium polysulfide-based solution, they can be used under conditions of long-term and constant exposure to water.