Researchers have completed the first stage of a project studying the use of railroad track connected to concrete slab instead of traditional ties and ballast as a construction method that may prevent tracks from buckling in hot weather, causing derailments.
When the track heats up, expansion can cause it to buckle. The phenomenon, known as sun or heat kink, may have caused the July 30 Amtrak derailment in Maryland that injured 97 people. Investigators discovered rails at the accident site were displaced 30 inches. Heat-related speed restrictions issued because of the possibility of heat kink also slow train service in the summer.
Cold weather causes safety problems as well because contraction can make welds in the track pull apart.
“Railroads in this country have been short of cash,” said David Bilow, director of engineered structures at the Portland Cement Association, of why concrete slab tracks haven’t been used in the United States as much as in Europe and Japan.
Slab tracks cost more than ties and ballast initially, but maintenance is much cheaper, Bilow said. “The tests will demonstrate that this slab technology can help the railroads reduce their maintenance costs and reduce delays,” he said.
Heat kink occurs because ballast systems are not strong enough to keep tracks in alignment, Bilow said.
The Portland Cement Association is sponsoring the research project at Construction Technology Laboratories to develop a track requiring no ballast. The track would be stable enough to resist buckling in hot weather and pulling apart during cold snaps. It would also be able to accommodate heavy freight cars and high-speed passenger trains. The system is widely used in Europe and Japan.
During the first stage of the project, researchers subjected a full-size concrete slab with rails and fasteners to 3 million cycles of simulated train loading. The lab tests simulated 315,000-pound freight cars, the largest in use today.
Next year engineers will build and test the concrete track at the federal government’s high-tonnage loop in Pueblo, Colorado. Fully loaded 70-car trains will operate over the track for two years to evaluate the long-term performance of concrete track.
Slab track is already being used in the United States in some tunnels, bridges and light rail projects. Bilow said any high-speed rail systems built to carry both passengers and heavy freight will have to use slab track as well.
Data gathered during the project will be used to establish design precedents for slab track installations. Slab track construction is similar to roadbuilding, Bilow said, so contractors specializing in concrete paving would probably be comfortable installing the tracks.
