UK: Cemex has developed a concrete sleeper for use on 200 m radius curves between Whitechapel and Aldgate East on the London Underground.
LU previously used timber sleepers on these curves, but they tended to shrink over time. According to Cemex, the main challenge when designing a longer-lasting concrete replacement was finding a way to attach the cast iron base plates to the sleeper. This would normally be done by casting plastic dowels into the concrete to allow the base plate to be bolted down, but analysis by Durham University found complications when using standard attachment methods, related to the forces in pre-stressed concrete which may induce cracking.
Instead, the plastic inserts normally used for the attachment of conductor pots were replaced with steel inserts with reinforcement around the plastic dowels, significantly reducing the risk of cracking.
Three variants of the sleeper have now been produced, and two more are planned.
