London Underground’s curved track problem has been solved thanks to a new type of concrete sleeper produced by Cemex Rail Solutions.

Until now, the sleepers on rail track curves have been made out of wood, but the first new concrete sleepers have recently been laid at a section of track between Aldgate East and Whitechapel.

London Underground had previously found it challenging to produce the right type of sleeper that would be sufficient to guide the track around curves of less than a 200 metre radius, while ensuring that the Tube trains remain on the track.

Previously, sleepers designed for curves were made out of timber, which can affect the gauge of the track as they tend to shrink over time.

As a result of this design flaw, London Underground have been searching for a solution to this problem and it now seems that Cemex have come up with the solution after 12 months of development work.

Cemex has said that the main challenge was how to attach the cast iron base plate to the sleeper, as this would typically be done by casting plastic dowels into the concrete to allow the base plate to be bolted down.

Durham University conducted analysis into the issue, which highlighted complications when using the normal attachment methods, relating to the forces in pre-stressed concrete that may lead to more cracks.

Replacement of plastic inserts normally used for attachment of conductor pots by steel inserts and reinforcement around the plastic dowels, adopted from industry practice in Germany, has significantly reduced the risk of any possible cracking.

The Derbyshire-based Cemex Rail Solutions factory has now started to produce three varieties of the sleeper, with two further models in the pipeline.

A further 2 variants of check rail bearer were designed (short ended at either end) at the same time to allow for drainage catch pits which are sometimes in the way trackside.