Effect of internal concrete corrosion on reinforced-concrete sleepers

The field studies of reinforced-concrete sleepers were carried out on direct current (DC) electrified railway sections that house the sleepers exposed to the most intensive corrosion damage. The statistical analysis of data made it possible to establish the propagation of the different types of damages. It was demonstrated that the defects that demand the replacement of individual sleepers on the railway track with new sleepers are mainly sleeper cracks and fractures including concrete crushing. The railway sleepers removed from the railway track have been investigated to discover the reasons for the crack formation. The sleepers were subjected to microscopic and electron-microscopic analysis including electron – probe microanalysis and molecular spectroscopic investigations and the obtained results showed that the crack network in the sleepers is spatial or 3D and it has the most branched pattern in its upper planes. The internal crack surfaces show signs of concrete corrosion caused by the interaction of cement alkali with chemically reactive fillers. The crack surfaces in the lower part of the sleepers show the presence of dealkalization products that is obviously the result of electromigration. It can be indicative of the contribution of leakage currents to the corrosion processes on the DC-electrified railway tracks. Hence, the primary reason for the defects in question, which resulted in the replacement of the sleepers, was the concrete corrosion caused by the interaction of the cement alkali with chemically reactive fillers facilitated by leakage currents.