Regulation of structure formation of pressed composites based on the modified gypsum binder

The main disadvantage of gypsum and gypsum concrete products molded by casting, vibrating, rolling, and pressing methods is low water resistance, which manifests itself in a significant decrease of strength at humidification. The authors have shown the possibility of increasing the strength and water resistance of pressed gypsum products by modifying their structure with an additional crystallization framework of sparingly soluble calcium hydrogen phosphate dihydrate. The purpose of the research is to obtain an adjustment equation that makes it possible to determine the rational dosages of modifying additives depending on the values of the specified strength and water resistance of pressed gypsum composites, as well as to assign the optimal duration of mixing the semi-dry molding mixture until the sealing pressure is applied to it. Using mathematical experimental planning methods, there was investigated the effect of the mixing time of the molding mixture and the dosages of the modifying additives on the basic physical and mechanical properties of pressed gypsum composites compacted at a pressure of 40 MPa. Ammonium dihydrogen phosphate and carbonate-containing sludge from the chemical water treatment of thermal power plant were used as modifiers. It has been revealed that in the proposed technology, along with the dosages of modifying additives, the physical and mechanical properties of the material are significantly affected by the duration of mixing the molding mixture, during which chemical interaction occurs between its components, which increases the strength and water resistance of gypsum modified pressed composites. Experimental and statistical models of the most important technical characteristics of the proposed material have been developed, depending on the main prescription and technological factors, which make it possible to determine the conditions for obtaining pressed gypsum products with specified properties. An adjustment equation has been obtained that makes it possible to establish rational dosages of modifying additives and the optimal mixing time of the molding mixture at a given value of the softening coefficient.