KINETICS OF CARBONIZATION OF THE PROTECTIVE LAYER OF CONCRETE OF REINFORCED CONCRETE POLES OF RAILWAY CONTACT NETWORK

Reinforced concrete conical centrifuged poles of the contact network are widespread on electrified railways. In addition to electrocorrosion of the underground part of the supports on electrified sections with direct current, the above-ground part of the supports is also damaged. The influence of carbonization of the protective layer of concrete, which causes the loss of concrete protective properties to steel reinforcement, on the durability of the supports has been studied. An analysis of the influence of design features and technological factors on the characteristics of the protective layer of concrete supports of the contact network has been performed, a thermodynamic analysis of the reaction of neutralization of cement hydration products by carbon dioxide, a theoretical analysis of the carbonization process and the kinetics of its front advancement, and an experimental study of the kinetics of carbonization have been performed. It has been established that centrifugation provides high density of concrete and very slow carbonization. However, due to structural and technological features, a significant number of operated supports have an insufficient thickness of the protective layer. As a result of thermodynamic analysis, it was established that the neutralization of concrete with carbon dioxide occurs through the dissolution of CO2 molecules, and the kinetics of the carbonation front advancement is determined by the diffusion of these molecules through the pore space of concrete. Equations of carbonation kinetics based on Fick's law are proposed. It is shown that the reactivity of concrete for carbonation is determined by the volume of pores accessible to water and, consequently, by the water absorption of concrete, a new equation is proposed for its determination. As a result of experimental studies of carbonation kinetics, the values of the effective diffusion coefficient of CO2 in the concrete of the supports were determined, and the kinetic dependences of the carbonation front advancement were obtained. As a result of statistical analysis, it was established that the most influential factor determining the durability of the supports of the contact network is the thickness of the protective layer. The minimum thickness of the protective layer is established, which is guaranteed to provide a standardized service life of the supports of 50 years.