Mathematical Model of Mass Transfer Processes in Biological Corrosion of Cement Concretes

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.