Press- Formed Composites with Alternate Wetting and Drying Resistance Based on Modified Gypsum Binder

Abstract

Water resistance of natural and artificial building materials is usually estimated by the softening coefficient. However, in the course of operation, materials, for example, for building enclosing structures, are rarely subjected to complete dewatering or water saturation. Therefore, one of the most important criteria for the durability of such products is their resistance to atmospheric influences (alternate wetting and drying resistance). In the present work, the possibility of increasing the alternate wetting and drying resistance of press-formed composites based on a modified gypsum binder is studied. We have developed a complex modifier of the gypsum binder and the structure of the resulting pressed composites, consisting of carbonate-containing slime of chemical water purification of thermoelectric power station and monoammonium phosphate. We studied the effect of the modifier on changes in the compressive strength of pressed composites in the dried and water-saturated state, softening and atmospheric durability coefficients, as well as linear deformations of control samples after a set number of cycles of alternating wetting and drying. We found that press-formed composites based on a modified gypsum binder are highly resistant to alternating wetting and drying. The complex modifier provides the formation of a more solid and monolithic structure of fine-crystalline calcium sulfate dihydrate, additionally reinforced with a hardly soluble phosphate-carbonate framework. The proposed method of modifying the gypsum binder prevents loosening of the structure of the press-formed stone-like material made from it under alternating stresses, reduces linear deformations and, as a result, slows down its fatigue failure. The technical characteristics of the obtained materials are sufficient for their use, in particular, in building enclosing structures.