Determination of the dependence of ettringite phase stability in nanomodified cement systems under the influence of various factors

The object of research is the stabilization of the ettringite phase in cement systems containing gypsum-alumina cement and nanoparticles. One of the most problematic areas is the instability of the ettringite phase, which affects the durability and mechanical characteristics of materials. The main problems are insufficient consideration of transitions between macro-, micro- and nanolevels when forming the structure of the hardening system. Multicomponent mixtures cannot be calculated using existing models, since a significant number of initial parameters and characteristics are not taken into account. The transition of systems from one level to another is not taken into account, namely the transition of systems from macro- to micro- and to nanolevel. The study used nanomodification of cement systems based on gypsum-alumina cement by introducing synthesized composites (carbon nanoparticles) into the hardening matrix. The influence of the raw material mixture components on the correction of the factors of instability of the ettringite phase, the processes of structure formation was studied, which allows in the future to eliminate these shortcomings and control the structure formation at different levels of the hardening matrix system. The optimal amount of calcium sulfate for the formation of ettringite was obtained – 30–40 % of the composition mass. This is due to the fact that the proposed composition of GC-40/G – 70/30 % has a significant amount of calcium hydroaluminates in the hydration process, the compressive and bending strengths are, respectively, 14 and 10 MPa. In particular, a dispersed medium resistant to delamination is formed, the water release of which is stabilized within 3 hours. Obtaining such values is ensured due to the fact that ettringite is formed in the early stages of hardening and provides an increase in the strength of the stone at a high speed. Compared with similar known gypsum-alumina cements, this provides advantages in the formation of high-basic ettringite. The results obtained are recommended for use in the construction of tunnels, restoration of hydraulic structures and transport infrastructure.