# Influence of Stray Current on Fastening System Components in Urban Railway Tracks
## 4 Results
### Visual Inspection and Corrosion Classification on Fastening System Components  
During and after the experiment, the samples were visually inspected and the detrimental effects of stray currents on the rail and fastening system were determined. Before the samples were immersed in water, only surface corrosion was observed; however, after the testing was completed, severe localized damage to the rail foot and fastening system components was observed in all samples. Furthermore, because the corrosion products have a significantly larger volume, their deposits at the contact of the anchor bolts with the concrete cause cracks in the concrete base and leveling layer. The conditions of all the samples after testing are shown in Figure 11.  
Figure 11: Conditions of all samples after testing was completed: (**a**) ZG 3/2, (**b**) PPE, (**c**) DEPP, (**d**) Zagreb 21-CTT. Figure 10: (**a**) Vulcanized steel plate for the Zagreb 21-CTT fastening system with the rail pad. (**a**) Cross section of the Zagreb 21-CTT fastening system in contact with the steel plate and anchor bolt CTT. (**b**) Current circuit during the measurement of the electrical resistance of the rail pad. When the ZG 3/2 fastening system was dry, and the water level was at the top of the concrete base, no local corrosion was observed in the elements of the rail or fastening system. Under these conditions, current flows from the rail through the rail clip and steel rib to the steel plate and anchor bolts. From the bolts and plate, the current flowed into the concrete base and leveling layer, such that corrosion occurred only at the point of contact of the steel plate with the leveling layer and at the point of contact of the anchor bolts with the concrete base. Under immersed conditions, current flows from the rail, steel rib, and steel plate directly into the water, causing corrosion and deterioration of the components of the fastening system. In the PPE fastening system, under dry conditions, despite the insulation pads used under the rail, clip, and steel plate, current can leak directly into the concrete and return to the negative terminal at the laboratory power supply because of the direct contact between the rail, clip, and anchor bolt. When dry, only the anchor bolts are in contact with the concrete; therefore, they corrode. When the water level reaches half the height of the rail neck, the current from all the elements flows into the water and causes corrosion. Under dry conditions, in the DEPP and Zagreb 21-CTT fastening systems, corrosion can also occur only at the anchor bolt, i.e., at the part of the bolt that is in contact with the electrolyte; however, because the anchor bolts in these fastening systems are partly insulated, the corrosion rate will be lower than that on the ZG 3/2 and PPE fastening systems. Visual inspection revealed that the current did not flow uniformly from the metal elements into the water when the samples were immersed. Discharge points occurred on the metal surface where localized material loss was observed. In addition to the corrosion of rails and fastening systems, cracks were observed in the leveling layers and concrete bases. These cracks resulted from the deposition of corrosion products at the contact between the bolt and the concrete. The cracks were classified based on a visual inspection (Figure 11) and were divided into three groups: large, medium, and small. The ZG 3/2 fastening system exhibits cracks across the entire width of the concrete base (Figure 11a). The maximum measured width of the crack was 4.5 mm, which is considered large. In the PPE and DEPP fastening systems (Figure 11b,c), cracks were observed in the leveling layer and in the concrete base near the anchor bolts, which are referred to as medium cracks. The maximum crack widths for the DEPP- and PPE-fastening systems were 2 mm, and the maximum crack width for the PPE fastening system is 1.8 mm. The width of the largest crack detected in the concrete block using the Zagreb 21-CTT fastening system was 0.8 mm (Figure 11d).