Low Adhesion due to Oxide Formation in the Presence of NaCl

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Low Adhesion due to Oxide Formation in the Presence of NaCl

Hardwick, C. / Lewis, R. / Olofsson, U.

This paper outlines work carried out to assess how adhesion may be influenced by contamination of the rail head with salt/grit from level crossings during winter months when they are applied to the road surfaces as a preventative method to stop ice formation. Twin-disc testing was carried out in which a mechanically formed oxide layer was produced on the disc specimens prior to assessing adhesion levels under realistic contact pressures and slips in the following conditions: dry, wet, dry salt, and two salt-water solutions. Under dry conditions adhesion levels differ little from reference tests without an oxide layer, however, the presence of an oxide layer under wet conditions can be seen to further reduce adhesion from a reference level (0.2) to below 0.1. When NaCl is entrained into the contact it increases adhesion levels above that seen under wet conditions in the presence of an oxide layer, however, the presence of NaCl is most likely to affect the generation of rail head oxides in the first place and in turn influence adhesion.