Establishing Patterns in the Influence of Micro- and Nano-dispersed Mineral Additives on the Water Resistance of Construction Gypsum

This paper reports a study into the effect of mineral fillers such as ground granulated blast furnace slag, microsilica, and nano dispersed alumina on the structure formation and water resistance of gypsum. The theoretical models of gypsum stone structure with mineral fillers have been built and described, taking into consideration the sign of the surface charge of gypsum crystals and filler particles. In accordance with the developed models, the fillers enable the formation of a dense structure of gypsum stone as a compositional material with a large number of electro-heterogeneous contacts. With this structure, the gypsum dihydrate crystals are maximally protected from contact with water and dissolution. The electron microscopic study of the gypsum stone with mineral fillers has been carried out, which has confirmed that the rational ratio of gypsum to slag ensures the densest structure of the stone. The dependences of the strength of gypsum stone in the dry and water-saturated condition and a water resistance factor (softening) on the content of slag, micro-and nano dispersed filler, a water-hardened ratio, have been experimentally established. The introduction of a rational amount of microfiller with a negative surface charge (microsilica) has increased the water resistance ratio by 0.2‒0.4 amounting to a value of 1. The introduction of a rational amount of micro-filler with a positive surface charge (nano dispersed alumina) has improved the water resistance ratio by 0.8 amounting to a value of 0.9. The established mechanism that forms the gypsum stone structure with fillers would make it possible to develop the compositions for a mineral binder based on gypsum, which could be used under wet operational condition