Pressed Composites Based on Gypsum and Magnesia Binders Modified with Secondary Resources

Abstract

The results of the studies aimed at increasing the water resistance of the pressed building materials based on gypsum and magnesia binders due to their modification with active dispersed fillers from secondary resources are presented. The gypsum binder modification was carried out by the joint introduction of carbonate-containing sludge from it into the chemical treatment of thermal power plants and monoammonium phosphate, and of magnesia cement - silica fume and finely ground burnt mines. Physical and mechanical characteristics of the materials’ control samples were determined according to the standards and generally accepted methods. The increase in water resistance of the pressed modified composites was evaluated by changing the softening coefficient. It is shown that when using gypsum binders, an increase in the water resistance of products based on them can be achieved by changing the structure formation of the pressed material and the formation on the elements’ surface of its fine-crystalline structure of the sparingly soluble calcium phosphates’ screening protective films. The increase in water resistance of pressed products made of modified magnesia binders is explained by the appearance of insoluble hydro silicates, hydro aluminates and hydro aluminosilicates of magnesium, in the structure of the hardened artificial stone as well as the formation of a complex combined structure containing coagulation, condensation and crystallization phases. The technical characteristics of the materials obtained are sufficient for their use, in particular, in the building envelope. The possibility of replacing a significant amount of binders with secondary resources has been identified. This allows not only to increase the water resistance of the pressed products on the basis of the proposed modified binders, but also to reduce their cost, as well as free up the land allocated for dumps.