Identifying the influence of nanomodifiers on the structure formation process regularities in the gypsum-alumina cement system

Gypsum alumina cement is resistant to magnesium solutions, seawater, and concentrated Na2SO4 and Mg2SO4 solutions, but it is less resistant to sodium chloride solutions. One of the ways to improve the gypsum alumina cement durability and enable its use in aggressive calcium chloride waters is to design a composition by incorporating modifiers. Thus, the composite is applicable for well-casing under conditions involving aggressive water exposure. However, such cements have their limitations: they are not suitable for processing at high temperatures in autoclaves. Up to now, the ettringite phase stability dependence on curing conditions and temperature has remained an unresolved issue. It has been theoretically proven and experimentally confirmed that the optimal calcium sulfate content in gypsum alumina cement and gypsum grade G-5 (GAC+G5) compositions, according to calculations, ranges from 28 % to 38 % of the mass of the alumina binder. That makes it possible to increase ettringite formation and obtain cement stone structure with predefined characteristics. As a result of modification with nano additives, the strength indicators of the composite materials have been improved: gypsum alumina cement GAC gypsum grade G-5:G (70:30) %+0.18 % nanotubes+0.4 % Sika – up to 70.2 MPa compared to 14.67 MPa in the reference composition. The scope of practical application includes the development of road surfaces and waterproofing materials, as well as hydraulic engineering. A condition for the practical implementation of results is the temperature range from –15 to 80 °С. Expected effects of application are shrinkage deformation reduction, improved crack resistance, increased strength, and enhanced durability of concrete articles under challenging operating conditions