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Study of the structure of cementitious composites under conditions of early-age compression is essential for development of measures to improve their response to mechanical and physical impact at the earliest stage of hardening. The article considers the influence of early-age compression on the structure of high-aluminate cement which has been studied using X-ray phase analysis. Concrete mixes with different water-cement ratio have been designated as targets for research. It has been established that the age of the cement to the moment of load application impacts on composition of formed hydrates, as well as on amorphousness of the structure of high-alumina cement stone. Compression at a very early age leads to an increase in the number of peaks related to hexagonal hydroaluminates and aluminum hydroxide. Load impact results in various recrystallization behaviors. Transformation of hexagonal hydroaluminates into cubical ones is proceeding faster with growth of water-cement ratio in the samples under compression. This is illustrated by an increase of a number of related peaks in X-ray patterns. Notation: C=CaO; A=Al2O3; H=H2O; S=SiO2; M=MgO.

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