Track & Civil Construction

KiwiRail expands KLP Hybrid Polymer Sleepers application to tunnels and bridges

KiwiRail had to find an alternative solution for its aging timber sleeper infrastructure. With first positive outcomes using Lankhorst’s KLP Hybrid Polymer Sleepers on mainline and turnouts, KiwiRail is moving ahead with implementing KLP Sleepers in tunnels and on bridges.

Around 10 years ago, KiwiRail was faced with a maintenance challenge. Across the 4,128 kilometres of track, ageing timber sleepers needed replacing to ensure a safe and efficient rail network.“We were looking for a solid substitute for timber as an alternative solution for our track, designed for over 18 tonne axle loads and maximum speeds of 110 km/h.” explains Mark Fleet, Professional Head of Track at KiwiRail.

“We’ve been having difficulty with hardwood sleepers because we can’t find sustainable sources and as a smaller purchaser, our access to sustainably managed timber from South America and Africa was limited. The cost of timber sleepers is also going up and the required quality is hard to find. With new legislation prohibiting the use of creosote for the treatment of sleepers, their life expectancy can drop to as little as 10 years.”

The solution that KiwiRail turned to were sleepers made from alternative materials, such as fibres, plastics, composites, or hybrids. After an initial successful contract with a leading supplier of composite sleepers, and with more manufacturers entering the market, KiwiRail opened a Request for Tender in 2018 for the supply of composite sleepers designed for over 18-tonne axle loads and maximum speeds of 110 km/h.

“We were looking for a product that’s like timber, so it’s easy to train our staff and easy to use out in the field as well. We also wanted something that’s more environmentally friendly and uses recycled products,” said Fleet.

While other railways have turned to concrete sleepers to replace wooden sleepers, the high carbon cost of manufacturing and transporting concrete sleepers and its limitations due to set fastening locations meant that this was not always a solution for KiwiRail. In addition, as KiwiRail were primarily looking for sleepers to use in turnouts, flexibility was key.

“The sleepers are used in both mainlines and, in our yards, so there’s a big mixture of working environments that they’re subjected to. There’s a lot of areas where they’re high speed, high volume, high axle load and then alternatively in yards it’s a lot slower, a lot more forgiving, so a product that’s more versatile and not dedicated to one sort of infrastructure was required,” said Fleet.

“Our Request for Tender focused on whole- of-life cost, minimum maintenance and security of supplies” confirms Fleet. With an initial expression of interest from seven competitors in response to an RFT for the supply of more than 50,000 sleepers, KiwiRail went through a rigorous selection process.

Link Asia Pacific, the sole regional agent and service provider for Dutch manufacturer Lankhorst, informed them of the tender opportunity. Link Asia Pacific also successfully coordinated preparation, review, and submission of all tender documentation.

Ultimately, KiwiRail selected the KLP Hybrid Polymer Sleepers from Dutch manufacturer Lankhorst. A reassuring fact is that Lankhorst’s KLP Sleepers, with first installations in operation since 2006, are reliably operating in tracks in 11 countries globally.

As part of our due diligence, we witnessed factory testing in the Netherlands and conducted a site visit with Lankhorst. We’ve seen how they’re working, and we’ve seen the products in use as well. They arranged for us to go to the local infrastructure provider to get their firsthand reviews on how the product has benefited them,” said Fleet.

KLP sleepers best met KiwiRail’s requirements for functional performance, whole-of-life cost, minimum maintenance, and supply security. As Bernard Huitema, Account Manager Rail at Lankhorst, highlighted, the steel reinforcements within the KLP sleepers distinguishes them from other polymer sleepers on the market. “KLP sleepers are unique in combining the respective beneficial characteristics of both polymer and steel. Polymer dampens impact and sound, even better than wood, but if you have only the polymer you do not have the required bending stiffness. Steel rebar is optimally placed to provide high bending stiffness at low thermal expansion, which ensures that the required gauge is maintained.”

Fleet also commented on the benefits of the steel-reinforced polymer design. “Due to the ductility of polymers used, there is no risk of micro cracks under impact and overload situations, like concrete sleepers. Since it does not contain glass fibres, handling on site does not require special breathing apparatus, and does not cause skin irritation. Furthermore, it can be cut and drilled on site, like timber, making installation easy especially when used for turnouts.”

Holes are easily drilled into the polymer sleepers.

“Because you can drill where you need to use it, you’re not dedicated on a particular turnout angle or a particular turnout design,” said Fleet. “It’s quite flexible so the staff out in the field find that a big help. Because it’s so similar to timber, they find that just drilling it, moving it around and actually fastening to the sleepers themselves is quite easy as it’s something they’re used to with timbers.”

To date, 4,112 of Lankhorst’s KLP Hybrid Polymer Sleepers have been installed across the KiwiRail network and the feedback from staff installing the sleepers has been positive. With an expected useable life of above 50 years, the KLP sleepers are providing a competitive, whole of life option to timber, which Fleet noted had been decreasing in quality and life expectancy. When the sleepers do reach the end of their life, they are fully recyclable, contributing to the circular economy.

“Not only are the sleepers made from 100 per cent recycled materials but they are also 100 per cent recyclable without any degradation of the quality, which means you can make a new sleeper with the same material,” said Huitema. “This is a big difference because composite products with glass fibre are hard to recycle.”

Building on the successes of the installation of the KLP Hybrid Polymer Sleepers for turnouts, Link Asia Pacific and Lankhorst worked on a solution for the installation of KLP sleepers in tunnels. In this instance, concrete sleepers (which are cheaper to produce than composite sleepers) were not an option as the ballast bed, designed for timber sleepers, could not be lowered further to accommodate deeper concrete sleepers.

With limited height available and an axle design load increased to 22.5 tonnes, Lankhorst offered four different concept designs at a height of 130mm, 20mm lower than existing timber sleepers. KiwiRail selected Lankhorst’s internationally proven Type 102 KLP Mainline Sleeper. Its 53kg low weight allows for manual handling, while its tailored shape delivers a significant increase in the required lateral and longitudinal stability, due to increased integration in the ballast bed. KiwiRail has placed a first order for more than 18,000 tunnel sleepers, with Lankhorst investing in dedicated new mould developments, based on the unique requirement, given the narrow- gauge application.

Type 401 KLP Bridge
Sleeper being installed.

The most challenging demand for sleeper stiffness is that found in bridges, particularly when the gauge width and the distance between bridge girders differ (this difference is referred to as “Offset”). KiwiRail’s 22.5-tonne axle loads and offsets of more than 300mm was a new design challenge for Lankhorst. Despite this, Lankhorst offered a 150mm high bridge sleeper as solution. This also allows sleepers to be spaced 25 per cent further apart that the current timber sleepers. Based on experience and growing confidence in the KLP solutions, KiwiRail has placed an order for 160 high-strength Type 204 KLP Bridge Sleepers, to be trialled and installed in 2021.

KiwiRail posed another bridge-related request to Lankhorst: for bridges with girders that are riveted together, timber sleepers get slots machined on site for sleepers to fit over the rivet heads. In response, Lankhorst offered the Type 401 KLP Bridge Sleeper. This sleeper allows for machining and drilling slots in the bottom surface, very comparable to the operations done on timber sleepers. “With Lankhorst’s design, they have achieved that compatibility for us and all the time they’ve kept to our requirements around dimensions and specifications, so all in all it’s a win-win for us,” said Fleet.

Throughout the process of meeting unique requirements and installing a new product, all parties have had to collaborate and be open, something that Fleet reflected positively on.

“Lankhorst and Link Asia Pacific have been very forthcoming and honest about any questions we had with them. The communication is open, they provide solid technical and commercial offers in a timely manner. Both Lankhorst and Link Asia Pacific are good companies to work with.”

Interested in finding out how KLP Sleeper solutions can address your challenges? Contact Link Asia Pacific via

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