Wide use of calcium sulfate-based materials and structures in construction requires an increase in their durability, which is determined by the degree of water resistance of gypsum products. The purpose of this study was to increase the water resistance of the gypsum matrix by activating fluorohydrite with sodium phosphate and studying its practical application to strengthen the road foundation. This study revealed that the structure of the fluorohydrite matrix activated with so-dium phosphate is built by column-like (batch) crystals of lamellar two–water gypsum formed during hydration of β-CaSO4 and providing a dense structure of the entire composition. The limited access of water to the intercrystalline space of the fluorohydrite-based binder matrix is due to the formation of a honeycomb-like package of crystals with strong intercrystalline contact. It has been established that fluorohydrite can be used as a binder instead of Portland cement for soil stabilization. Microstructure analysis of the soil composition showed the interaction of the gypsum matrix with loam minerals with calcium hydrosulfoaluminate crystals (ettringite 3CaO·Al2O3·3CaSO4·32H2O) formation, making the composition denser and providing it with increased water resistance. It is shown that the use of sodium phosphate-activated fluorohydrite leads to a significant increase in the water resistance of the gypsum matrix, which can be used for practical purposes to strengthen the road foundation. Moreover, the use of industrial anhydrite improves the environmental situation in landfills due to the utilization of fluorohydrite byproduct in the production of hydrofluoric acid.
Yakovlev et al. (Mon,) studied this question.