-The most important task at the present stage of the formation of modern society is the intensive development of the national economy on the basis of the latest achievements of science and technology. The building materials industry in the Russian Federation is one of the most energy-intensive industries. In this regard, reducing energy costs and environmental pressure on nature through the introduction of alternative energy sources in production is relevant for the state. Previously, it was proved that plasma-chemical modification contributes to the increase of water resistance, acid resistance, alkali resistance, microhardness of the fused (glazed) face layer, and also allows one to expand the possibilities of obtaining various types of decor. However, plasma-chemical modification leads to significant thermal shock, dehydration of hydrosilicates in cement stone and its softening, which reduces the operational parameters of the protective and decorative coating on concrete products, in particular, adhesion strength and frost resistance. Using a plasma jet will significantly intensify the formation of vitreous protective and decorative coating with increased technical and operational performance, and the use of various industrial waste and color salts will provide an opportunity to significantly expand the base for obtaining a variety of types of decor on the face of the concrete. In connection with the foregoing, the development of an effective technology for the production of protective decorative coatings on concrete products is a relevant area of research. The purpose of the work is the development of protective and decorative coatings on products made of concrete using recycled materials and coloring metal salts. The macro and microstructure of the protective and decorative coating and the surface layer treated with a plasma jet, the microhardness of the fused layer of fine-grained concrete after plasma-chemical modification are given in the article. The regularities of the formation of the structure of protective and decorative coatings on concrete with the use of coloring salts are substantiated.

Plasma chemical modification (PCM) improves chemical resistance of a glazed decorative coating and expands opportunities for designing various types of the decoration of concrete. However, PCM exposes the material to a significant thermal shock that leads to dehydration of hydrosilicates in the cement matrix followed by loss of strength of the concrete coating. This results in a reduction in the service characteristics of the concrete protective and decorative layer such as adhesion strength and freeze-thaw resistance and shortens the coating durability. Therefore, the improvement of the PCM method is a hot topic of the study and it is one of the most effective and modern technologies, which will result in enhancement of serviceability of concrete with the glazed decorative coating. This study investigated the effect of incorporation of calcium aluminate cement as a silicon-based intermediate layer between the glazed decorative layer and the concrete surface. The study demonstrated that the calcium aluminate cement intermediate layer after plasma chemical modification was dehydrated. Based on mineral composition and structural analysis, the dehydrated layer was visually divided into three zones: the upper dense layer; an intermediate layer with micro cracks; and the bottom dense layer. The microstructure of the dehydrated zone is represented by small non-developed microcracks less than 50 μm. Magnesium spinel was the main crystal phase in a calcium aluminate cement matrix. The dense dehydrated zone had a shell-like fracture, which is typical for spinel with imperfect cleavage. This study developed a glazed decorative coating and a protective calcium aluminate cement-based intermediate layer with the adhesion strength of 4.1 MPa and freeze-thaw resistance of more than 50 cycles that exceed service characteristics of concrete with the coatings using other materials.