Physical features of the problems of liquid corrosion of reinforced concrete from the standpoint of the theory of heat and mass transfer

Abstract

The results of the study of non-isothermal mass-exchange processes occurring during liquid corrosion of iron-concrete are presented. The degree of development of this direction of research is shown: the classification of liquid corrosion of concrete is given, the effect of “free calcium hydroxide” on the stability of cement stone minerals is described, the relative change in the strength of concrete depending on the dimensionless concentration of calcium hydroxide is shown. For concrete and reinforced concrete structures subjected to liquid corrosion, the boundary value problem of non-isothermal mass transfer in the “cement concrete - liquid” system is formulated on the basis of a nonlinear differential equation of mass conductivity of a parabolic type with an arbitrary form of the initial concentration distribution function and combined boundary conditions of the first, second and third kind. A combined approach to solving the problem of non-isothermal unsteady mass transfer is proposed, based on the division of the life cycle of a building structure into “micro-processes”, followed by the separation of the thickness of the structure within the considered small time interval into concentration zones. Analytical solutions to the problem of unsteady mass transfer in the processes of liquid corrosion of concrete for each selected concentration zone have been obtained, allowing to calculate the concentrations of the target component in the solid phase, thereby predicting the dynamics and kinetics of destructive processes of cement concretes. Extensive numerical experiments have been carried out showing the effect of process parameters on the dynamics and kinetics of liquid corrosion of reinforced concrete.

Keywords

• liquid corrosion
• durability
• reinforced concrete
• unsteady mass transfer
• method of “micro-processes”
• dimensionless variables