# Influence of Stray Current on Fastening System Components in Urban Railway Tracks
## 5 Discussion  
When the samples were dried, the current leaked through the fastening system into the lower part of the track structure, and stray current corrosion occurred on the elements that were in contact with the concrete--i.e., anchor bolts and steel plate in the ZG 3/2 fastening system. In the ZG 3/2 and PPE fastening systems, the rails are in direct contact with the clip and anchor bolts, and the stray current depends only on the electrical resistance of the concrete layer. Under the immersed condition, corrosion started at the locations where the current allowed the metal elements to enter the electrolyte. The components of the fastening system in which corrosion occurred under different conditions are listed in Table 8.  
\begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline \multirow{2}{*}{\begin{tabular}{c} **Fastening** \\ **System** \\ \end{tabular} } & \multirow{2}{*}{**Anchor Bolt**} & \multirow{2}{*}{\begin{tabular}{c} **Measured Diameter** \\ **of Anchor Bolt [mm]** \\ \end{tabular} } & \multicolumn{2}{c}{\begin{tabular}{c} **Thinning of** \\ **Cross Section** \\ \end{tabular} } & \multirow{2}{*}{**Corroded Surface**} & \multirow{2}{*}{\begin{tabular}{c} **Cracks in** \\ **Concrete** \\ \end{tabular} } & \multirow{2}{*}{\begin{tabular}{c} **Corrosion** \\ **Level** \\ \end{tabular} } \\ \cline{3-3} \cline{5-8}  & & 1 & 21.0 & 1 & 4.54 & 17,270 & 83 & Large & High \\ \cline{2-8}  & 2 & 21.0 & 1 & 4.54 & 16,221 & 78 & Large & High \\ \hline \multirow{2}{*}{\begin{tabular}{c} PPE \\ \end{tabular} } & 1 & 21.5 & 0.5 & 2.27 & 1601 & 79 & Medium & High \\ \cline{2-8}  & 2 & 21.5 & 0.5 & 2.27 & 17,028 & 84 & Medium & High \\ \hline \multirow{2}{*}{\
\begin{tabular}{c} DEPP \\ \end{tabular} } & 1 & 23.0 & 1 & 4.16 & 17,270 & 82 & Medium & High \\ \cline{2-8}  & 2 & 23.0 & 1 & 4.16 & 13,125 & 62 & Medium & High \\ \hline \multirow{2}{*}{
\begin{tabular}{c} Zagreb 21-CTT \\ \end{tabular} } & 1 & 21.5 & 0.5 & 2.27 & 15,543 & 75 & Small & Medium \\ \cline{2-8}  & 2 & 22.0 & 0 & 0 & 1375 & 7 & Small & Low \\ \hline \hline \end{tabular}
\end{table}
Table 7: Corrosion level classification for anchor bolts in all testing samples.  
Figure 15: Condition of the anchor bolts after testing was completed: (**a**) ZG 3/2, (**b**) PPE, (**c**) DEPP, and (**d**) Zagreb 21-CTT.  
Although all the samples were immersed in water to half the height of the rail neck and exposed to the same DC current, no uniform deterioration of the fasteners was observed. Thinning of the rail foot cross section was observed in all fastening systems, but the highest level of deterioration was observed for ZG 3/2 and PPE. No clip deterioration was observed in the ZG 3/2 fastening system; however, severe corrosion was observed on the steel rib with which the clip was in direct contact. The most severe clip deterioration was observed in the PPE and DEPP fastening systems, whereas in the Zagreb 21-CTT fastening system, clip deterioration was not as pronounced. The steel base plate corroded in all the tested samples. Owing to their larger dimensions, the corrosion of the plate was not as pronounced in the DEPP and Zagreb 21-CTT fastening systems. From the performed corrosion classification, it can be concluded that in the tested samples, when the samples were immersed in water up to the middle of the height of the rail neck, a high level of corrosion was observed in the following components:  
- ZG 3/2 fastening system: rail, steel ribs, anchor bolts,  
- PPE fastening system: rail, clip SKL-1 (1), steel plate, and anchor bolts.  
- DEPP fastening system: clip SKL-1 (2), anchor bolt,  
- Zagreb 21-CTT fastening system: only medium level of corrosion on the clip SKL-12 (2).  
This deterioration is a result of the current leaving the components of the fastening system and entering water or concrete.