Iefimenko A. Increasing the water resistance of gypsum materials by polyfractional mineral additives

The dissertation is devoted to the development of theoretical and experimental foundations for increasing the water resistance of gypsum by polyfractional mineral additives. The electro-surface properties of gypsum and mineral additives have been determined. It was found that different faces of gypsum dehydrate crystals have surface charges of different signs: longitudinal - positive, end - negative, particles of slag and micro silica have a negative surface charge, and Nano dispersed alumina – positive. Taking this into account, the regularities of the formation of electro heterogeneous contacts between gypsum-dehydrate crystals between themselves and with particles of mineral additives were established. Optical-microscopic and electron-microscopic studies have been carried out, models of the structure of artificial gypsum stone with mineral additives have been developed, which will ensure its maximum water resistance. It is shown that the maximum water resistance will be provided by the structure of the composite material with a matrix of densely packed crystals of gypsum dehydrate with the maximum number of electro heterogeneous contacts between crystals and particles of mineral additives. Such contacts maximally protect crystals of gyp-sum dehydrate from dissolution and wedging action of water. A thermodynamic analysis of the possibility of chemical interaction of gypsum with mineral additives has been carried out; it is shown that gypsum and mineral additives generally do not chemically interact, except for the case of the presence of free lime in the slag, when calcium hydro-sulfa-aluminate of mono-sulfate form can be formed. The dependences of physical and mechanical properties, water resistance index, moisture deformations of artificial gypsum stone on the content of a mineral additive of one fraction (slag) and two different fractions (slag and Nano dispersed alumina or micro silica) have been experimentally investigated. The obtained dependences confirmed the idea of the influence of the composition and structure of artificial gypsum stone as a composite material with electro heterogeneous contacts between crystals and particles in it on water resistance. Compositions of a gypsum binder with poly-fractional mineral additives, providing a water-resistance index of up to 1, and materials based on them, as well as a technology for their manufacture, have been developed. Experimental industrial implementation and implementation in the educational process have been completed.