Keywords: adhesion, sanding, conductive, materials.

Sufficient adhesion in a wheel-rail contact is one of the key requirements for safe and efficient railway operations. Low adhesion conditions significantly increase the risk of braking issues leading to extended braking distances, passing signals at danger, reduced acceleration rate, and damage to the wheels and rails. Sanding remains one of the most common methods to overcome low adhesion conditions. However, over application of electrically insulating sand may interfere with railway track circuits of some signalling systems leading to loss of train detection and therefore limits of application have been imposed. The development of alternative, novel adhesion enhancing materials with higher electrically conductivity may mitigate the risk of electrical insulation and allow for larger amounts of material to be applied to improve wheel/rail adhesion. As well as not interfering with track circuits, these new materials must demonstrate good deposition efficiency using conventional sanders as well as providing a significant increase in friction levels under low adhesion conditions. This work describes the testing of proprietary coatings which can be applied to sand and other particles to improve conductivity and deposition efficiency. Laboratory scale testing of the deposition efficiency, adhesion enhancing and electrical characteristics of these materials were carried out at the University of British Columbia and LB Foster facilities in Canada and field testing of the influence on track circuits was carried out in the UK by The University of Sheffield under an RSSB funded project. Laboratory results indicated an improvement in deposition efficiency compared to non-coated particles as well as improved electrical conductivity in comparison with standard sand with no reduction in adhesion enhancement performance. Field trials showed that, even at relatively high deposition rates, train detection in track circuits was unaffected which may allow such materials to be used at higher application rates to further increase adhesion without any risk to train operations. Further work to test these materials has been proposed including flow characteristics in equipment and full scale braking tests under a range of low adhesion conditions.

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