Korea's rail research institute accelerates rollout of recycled composite sleepers

The new sleepers offer 1.8 times the rail-fastening strength of wooden ones and have been installed at two Airport Railroad stations

Resource-cycling composite sleepers (CCS) installed on the Airport Railroad line. [Korea Railroad Research Institute]

An eco-friendly composite sleeper designed to replace conventional wooden railroad ties — which rot and crack over time — is being deployed on an active Airport Railroad line. Made from recycled materials, it holds rails 1.8 times more firmly than its wooden counterpart and is expected to improve both rail safety and maintenance efficiency.

The Korea Railroad Research Institute announced Monday that its resource-cycling composite sleeper (CCS), developed in-house, has been replacing deteriorated wooden sleepers in mainline switch sections at Geomam and Unseo stations on the Airport Railroad since September.

Switches are devices that split or merge tracks to change a train's direction of travel. Because of their complex geometry, wooden sleepers — which can be easily cut and drilled on site — have long been the material of choice.

Over time, however, wooden sleepers rot and crack, degrading the performance of the fastening hardware that holds rails in place. The problem has grown more urgent this year, as domestic production of wooden sleepers was halted entirely due to environmental and health concerns over creosote oil used in wood preservation, making the search for alternatives a pressing priority.

The CCS is a composite sleeper made of recycled thermoplastic material reinforced with fiberglass. Unlike wood, it does not rot or crack, giving it superior durability, and it can be recycled after use by crushing and reprocessing.

Particularly notable is its spike pull-out resistance — the force required to extract the screw spikes that secure the rail — which stands at approximately 90 kilonewtons (kN), about 1.8 times stronger than the roughly 50 kN of conventional wooden sleepers.

Durability tests confirmed strong performance. After 3 million cycles of inclined repeated loading simulating actual train loads, deformation, lateral displacement and rail movement at the fastening points all met the required standards. The sleeper also sustained no damage after more than 2 million cycles of repeated bending-load tests.

The most significant feature of this installation is that only the worn sleepers can be selectively replaced without dismantling the entire switch assembly.

Because the CCS is similar in size and workability to conventional wooden sleepers, it can be installed alongside existing ones. Replacements can be carried out quickly during nighttime hours after train operations end, targeting only the sections that need attention and reducing the maintenance burden on operating rail lines.

CCS units for switch sections stockpiled at the site ahead of Airport Railroad track installation. [Korea Railroad Research Institute]

The Airport Railroad plans to replace a total of 134 deteriorated wooden sleepers in mainline and depot switch sections with CCS units in stages this year.

The institute completed CCS installation in June on an aging switch section of the Yangsan turnback line on Busan Metro Line 2.

Going forward, the institute plans to conduct long-term monitoring alongside the Airport Railroad on active train-operating sections, observing the movement of composite sleepers versus wooden ones and tracking overall track conditions. The data will be used to establish maintenance standards and assess the feasibility of expanding the technology to additional sections.

"The application of composite sleepers on an active Airport Railroad commercial line offers a realistic alternative to the halt in wooden sleeper production," said Kim Ji-hwan, a senior researcher at the institute. "We will continue gathering field data to advance the technology and expand its deployment."

Institute President Sagong Myeong said the technology addresses a growing replacement demand created by the production halt. "We will expand research aimed at commercializing carbon-neutral rail technology and spreading it across the industry," he said.

nbgkoo@heraldcorp.com