The aim of this research is to investigate effects of stray current on concrete durability and its microstructural changes. The structural changes can be studied by changes in the permeability, volume of capillary pore, resistivity, electrical charge in Rapid Chloride Penetration (RCP) test, chloride diffusion and changes in Electrochemical Impedance Spectroscopy (EIS) spectra of concrete. They are related to concrete durability in environmental conditions and so can act as an effective agent in rebar corrosion. In this study, water saturated concrete samples with different mix design were exposed to 220 and 380 AC voltage and 50 DC voltage. Effects of applied voltages on concrete microstructure of concrete were investigated using several techniques including; resistivity, EIS, RCP, chloride diffusion, depth of chloride penetration and SEM. In addition, for validation of laboratory data, field tests were done on some concrete power poles which had been failed by leakage of high voltage power from surface of insulators in rainy conditions. ased on the results obtained, high voltage AC stray current can reduce concrete durability in a short time by increasing its capillary pore size, creating new network of pores, creating micro cracks and extensive concrete microstructural changes such as changes in volume and size of capillary pores. AC current in concrete can flow through two different paths including; solid paths and capacitor paths (capillary pore paths). At high voltage, in water saturated concrete, passing current through the pores is the main reason for generation of thermal and shrinkage stresses and mass transfer. These phenomena would reduce concrete durability. Compared with AC current, DC current can only pass through solid phase and not capacitor paths. Therefore, under DC stray current thermal stresses are less important and thus have less destructive effects compare with AC stray current in water saturated concrete. Reducing water to cement ratio and adding pozzolanic materials such as silica fume to concrete mix design would reduce the volume of capillary pores, increase concrete density, reduce permeability, reduce calcium hydroxide phase. The impedance of capacitor paths would also increase due to reducing the volume of capillary pores. Therefore, destructive effects of AC stray current on water saturated concrete would reduce. Also, with decreasing permeability, transfer of calcium hydroxide by diffusion mechanism due to DC stray current and thus its degradation effects would decrease. Furthermore, adding non-metallic fiber such as polypropylene (PP) to concrete mix design reduce the cracks propagation in concrete due to AC stray current. Keywords : Stray current, Concrete, Structure, Durability
