Nigel Keightley
Since 1980, Sekisui has engineered and manufactured synthetic wooden baulks made from Fibre-reinforced Foamed Urethane (FFU) and, in 2014, Network Rail engineers installed the first FFU baulks and cross-sleepers as replacements for traditional hardwood on Military Canal & Blockhouse bridges in Kent (Rail Engineer 209, Aug/Sept 2024). Since then, FFU has been used to provide track support on more than 70 railway bridges in the UK & Ireland.
FFU was first introduced on Japanese Railways in 1980 where early installations are still performing to specification. It is now widely used on railway infrastructure in 33 countries to support track on bridges, decking for level crossings, plain line sleepers, and Switch and Crossing (S&C) bearers.
Background
Developed in conjunction with Japanese National Railways, FFU synthetic sleepers are made using a pultrusion process. Continuous glass fibres are soaked and mixed with polyurethane, and then hardened at a raised temperature, moulded, pulled and cut to length. This creates a high-quality material that has the life expectancy of plastic and the weight of natural wood, which can be worked like natural wood.
First installed in Japan in 1980, and adopted for standard sleepers and turnout sleepers, FFU has subsequently been installed on numerous projects in Europe over the past 20 years, particularly turnouts and bridges. Up to the end of 2023, there was more than 2100km of track with FFU sleepers around the world.
Tests of the original 1980 sleepers undertaken by the Railway Technical Research Institute in 2011 predicted that the FFU sleepers could safely continue in use for another 20 years, giving a total life of at least 50 years.

An opportunity
In the Autumn of 2023, Sekisui was contacted by Jonny Rayson, Network Rail’s work delivery manager, Carlisle. Jonny told us that he had been to look at the FFU baulks which had recently been installed at Bridge 140 Eskmeals Creep on the Cumbrian Coast Line. He was impressed, particularly by the regular geometry of the product when compared to hardwood and said that his team had experienced warping and twisting of timbers prior to installation on previous projects.
Jonny asked us to visit Carlisle Depot during December 2023 to present on the suitability of FFU for use on a significant project at Eskmeals Viaduct on the Cumbrian Coast Line. We were delighted to attend along with our UK fabrication partner BSSL who prepared sample FFU joints, transoms, cleats, and holding down arrangements. Jonny and his team were impressed and FFU was incorporated into the design for this prestigious project which was to be delivered in a blockade from 6 to 23 September 2024.
This was great news for Sekisui as the project required 137m³ of FFU to be produced at our Ritto factory in Japan. This twin track viaduct at 285 metres in length, provided not only the largest bridge project we have completed on Network Rail infrastructure, but also the largest Sekisui FFU global bridge project in 2024.
Project underway
In January, Network Rail’s designer HBPW confirmed the requirements. FFU production was completed in May and the FFU baulks were shipped to the UK for final fabrication into panels at BSSL’s facility in Middlesborough. These panels were then transported to Network Rail’s Doncaster Woodyard in August to be loaded onto engineering trains for transportation to site during the blockade.
Network Rail’s endorsement of FFU, citing reduced life cycle costs, extended longevity, and decreased maintenance requirements, aligns perfectly with the growing global emphasis on sustainable infrastructure solutions.
Jonny said: “The £4.5 million upgrade will make journeys more reliable for years to come and using synthetic materials instead of wood means there is an increased life expectancy, reduced maintenance costs for Network Rail, and reduced disruption for passengers and freight operators.”
Network Rail added: “The viaduct has stood for more than 150 years, and the improvements completed will future proof the structure for generations to come. Climate change means that more intense storms, greater rain fall, and rising sea levels will put the viaduct under more pressure, so the work we’re doing will stand it in good stead.”
Achievements during the blockade included:
- 188 longitudinal FFU baulks installed in the place of timber waybeams.
- Replacement of approximately 600 transom bars over the structure.
- Removal of existing non-compliant cleats and holding down arrangements and the installation of 1,060 new compliant cleats and HDAs.
- Removal and installation of over 1.1km of rails.
- Rail joints converted to Finlube and hardlock bolts from previous black oil.
- Over 43 tonnes of packing pieces installed to accommodate for the out of level steel works on the structure.
- Replacement of 80 defective softwood sleepers for new composite sleepers.

A great success
Jonny applauded the efforts of everyone on site: “The works were not without issues, however the way everyone responded and dealt with them, really proved that we could not have asked for a better group of people to complete this job.”
Sekisui was honoured to be invited to site on three occasions during the blockade, taking the opportunity to talk with staff on the projects about their experience. On completion of the work, we took time for discussion with Jonny and Chris Bibby, Network Rail’s regional track engineer Northwest & Central. They both reflected positively on the decision to use FFU.
The driver for change is to improve sustainability within track. The FFU product will deliver a wide range of performance, value, and environmental benefits to the network, as well as helping us transition to a circular economy by keeping our materials in use for as long as possible.
“Following this success, the FFU product will be subsequently installed on more bridges on Network Rail’s Northwest & Central Routes,” said Chris.
Sekisui welcomes the opportunity to build on this accomplishment and greatly appreciates the opportunity to supply FFU for future projects. We would like to thank Jonny Rayson and the wider Network Rail team for choosing FFU, facilitating the site visits, and contributing to this article. Many thanks to Network Rail for giving us the opportunity to supply FFU for this project and to work with all the partners involved.
Special thanks go to Quattro Plant Ltd, Bottomley Site Services Ltd, Torrent Trackside Ltd, QED Scaffolding Ltd, HBPW & PBH, Vital Human Resources, Sekisui Chemical, all Network Rail team members, and everyone who contributed to the projects nominated charities: Eden Valley Hospice, and Jigsaw – Cumbria’s Children’s Hospice.
Image credit: Sekisui
