As objects for study samples of cement concrete exposed to biological growth-around have been used. A physical and mathematical model of diffusion processes in system "cement concrete-biofilm-liquid", taking into account the kinetics of the processes of growth, reproduction and death of microorganisms, has been developed. The model of mass transfer in an unlimited two-layer plate in the form of a system of partial differential equations of parabolic type with boundary conditions of the second kind at the boundary of concrete with liquid and the fourth kind at the boundary between concrete and biofilm is considered for the first time. The mathematical model takes into account the kinetics of the change in time of the thickness of the biofilm due to the birth and death of populations of microorganisms. The results of calculations of dimensionless concentrations of “free” calcium hydroxide by the thickness of a concrete structure and biofilm are presented. The results of the numerical experiment showing the influence of mass transfer criteria (Furier, Kirpichov) on the dynamics of corrosive destruction processes have been analyzed. With an increase in the mass transfer criteria of Kirpichov and Furier, large concentration gradients appear. It has been established that carrying out work on cleaning concrete and reinforced concrete underwater structures from biofouling once every 5 years, in conjunction with other scheduled preventive measures, will increase the time between repairs between 1.5 times. Practical recommendations were developed to monitor and increase the corrosion resistance of concrete and reinforced concrete structures in biologically active environments.