To reduce water absorption of cement concretes resort to hydrophobization by introducing special additives in the manufacturing process of the product. In the study of liquid corrosion of hydrophobized cement concretes of the W4, W6 and W8 waterproofness grades in media of various degrees of aggressiveness, the terms for achieving a state close to the equilibrium concentration of calcium cations in the solution were established. Based on the experimental data on the liquid corrosion of cement concretes of various grades in terms of water resistance, the optimum amount of hydrophobizing calcium stearate additive was determined, which is sufficient to prevent corrosion damage in concrete, depending on the degree of aggressiveness of the medium. Tests of strength characteristics of hydrophobized cement concretes of the W4, W6 and W8 waterproof grades were carried out. It is established that when alkali and alkaline-earth stearates are introduced into concrete as hydrophobic additives, its strength is significantly increased compared to non-hydrophobized concrete samples. Some special cases of changes in the mass conductivity coefficient during colmatation of hydrophobized cement concretes of the W4, W6 and W8 waterproof grades are considered and graphically illustrated. Profiles of changes in the rate of colmatation and the thickness of the colmatant layer for cement concretes with and without hydrophobizing additives are presented. The profiles show that over time there is a weakening of the mass flow, which is obviously associated with an increase in the colmatant layer. The rate of colmatation is also reduced due to the fact that the layer of colmatant partially or completely clogged the pores and prevents further penetration of the aggressive medium deep into the concrete.

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Timely protection of underwater concrete and reinforced concrete objects from biofouling will significantly reduce the economic damage from the effects of corrosion damage, improve the reliability of structures operated in high humidity conditions, and reduce the likelihood of accidents. Despite the abundance of ways to protect against fouling, there are still no radical methods of struggle. It is expedient to find a solution to the problem of predicting the durability of concrete and reinforced concrete structures in biologically aggressive liquid media from the point of view of the theory of mass transfer. The model of mass transfer in an unlimited two-layer plate is considered for the first time in the form of a system of partial differential equations of parabolic type with boundary conditions of the second kind at the interface between concrete and liquid and the fourth kind at the interface between concrete and biofilm, which describes diffusion processes in the system of «cement concrete – biofilm – liquid». The proposed physical and mathematical model takes into account the properties of the solid and liquid phases, as well as the kinetics of growth, reproduction and death of microorganisms. The results of calculating dimensionless concentrations of «free» calcium hydroxide over the thickness of the concrete structure and biofilm are presented. The application of the obtained solutions will allow timely monitoring of the biocorrosion destruction of underwater structures and select effective protection methods.

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