# Influence of Stray Current on Fastening System Components in Urban Railway Tracks
## 3 Materials and Methods
### Methodology  
The samples were placed in plastic tubes and treated with a DC current from a laboratory power supply. Each sample was connected to a separate DC source. A voltage of 26 V was applied to the samples, and the current value depended on their electrical resistance. The rail was connected to the positive terminal of the power supply, and the circuit was closed using a steel rib built into the concrete (Figure 6a). In this circuit, current flows into the rail and fastening system and through the electrolyte (in these cases, concrete or water) back to the negative terminal of the power supply.  
The experiment was performed in three different states of the samples:  
* The samples are dry (Figure 7a),
* Water on the top of the concrete base (Figure 7b)
* In the immersed condition: the water level was half the height of the neck of the rail (Figure 7c).  
Figure 5: Fastening system Zagreb 21-CTT: (**a**) cross section and (**b**) sample for testing.  
Different water levels simulate different conditions that can occur on tram tracks. In tracks embedded in lanes shared by road vehicles, the drying process is very slow; therefore, the concrete base is wet for most of the year. These conditions were simulated using the water level at the top of the concrete base. If track drainage is inadequate, water will remain in the track, resulting in direct contact between the rail and the fastening system with the electrolyte. These conditions were simulated by immersing the samples in water to half the height of the neck of the rail. Before immersing the samples in water, the electrical conductivity of water was measured using an SI Analytics Lab 945 conductometer. The electrical conductivity of water was 0.0775 S/m. The electrical conductivity of water affects the electrical resistance of the entire sample. Therefore, it is important that the conductivity of water be the same in all samples. Notably, the electrical resistance of the water retained in the track structure depends on the substances dissolved in the water, mainly salt. This experiment can also be performed using water containing dissolved salts to accelerate the corrosion process. However, because the aim of this study was to determine the influence of stray currents on rails and fasteners, the experiment was carried out with tap water with a defined electrical conductivity.  
The experiment lasted 191 days, during which, for 92 days, the water level was at half the height of the rail neck, and for 74 days, the water level was on the concrete base.  
During testing, the current and voltage were measured, and the samples were periodically visually inspected. The current was recorded using a multimeter GWInstek GDM9061, and the voltage was measured for all the components of the fastening systems. Measurements were taken at the beginning of the test, when the samples were dry, when the water level was at the top of the concrete base (case I), in the immersed condition (case II), and after the test was finished and the water level was lowered by the top of the concrete base (case III). The voltage was measured between the analyzed elements (rail, clip, anchor bolt, steel plate, T-bolt, and steel rib) and the negative terminal of the current source. Before starting the measurements, the resistance of the testing equipment was measured to exclude its influence on the measurement results.  
Because the accumulation of corrosion products under immersion conditions increased the electrical resistance, the water in the tubs was changed every week to maintain a constant current.