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The analysis of relaxation processes in water activated by thermal or ultraviolet radiation has been carried out. The activation of the mixing water leads to an earlier hardening of the cement. At the same time, activated water loses its properties with a relaxation time, which is equal to the activity time of melt water, which is explained by the common reasons for the origin of the increased reaction properties of activated water and melt water. These properties are due to the fact that activation increases the content of free water molecules. In the normal state, some of the water molecules enter the voids of fractal-clathrate structures. During thermal or radiation activation processes, characterized by certain relaxation times, these structures are destroyed, and free water molecules are released. But after the termination of activation, relaxation processes take place to restore thermodynamically equilibrium fractal-clathrate structures, and part of the free water is again captured by these structures. Therefore, the reactivity of water after the termination of activation decreases.

The analysis of the influence of ultraviolet irradiation of building sand, which is a filler in a concrete mixture, on the dependence of the strength of concrete on the content of filler is carried out. With an increase in the content of sand due to the hydrophilicity of the surface of its particles in the mixture, the amount of free water required for the hydration of cement and the formation of cement stone decreases. Along with a decrease in the content of binder cement, this factor is an additional reason for a decrease in the strength of concrete with an increase in the content of sand. Ultraviolet irradiation leads to dehydration of the surface of the sand particles and the appearance of hydrophobic centers. As the hydrophobicity of the sand in the concrete mix increases, the content of free water available for cement hydration increases, and the strength of the cement stone increases. The change in the hydrophobicity of the surface of sand particles depending on the time of irradiation is non-monotonic. Therefore, there is an optimal UV activation mode that provides the greatest increase in concrete strength.