University, Company Engineers Research Safer Railroad Ties

Concrete rail ties (CXT Concrete Ties)

Engineers at Kansas State University in Manhattan and the company CXT Concrete Ties in Tucson, Arizona have received funding for research leading to safer railroad ties to support the nation’s new high-speed rail projects. The engineering team was awarded a grant for nearly $900,000 from the Federal Railroad Administration, with another $300,000 provided by CXT Concrete Ties and the K-State Transportation Center.

The engineers say high-speed rail requires prestressed concrete railroad ties, since the traditional wooden cross ties are too flexible. For these railroad ties to be effective, prestressing forces must be applied at a considerable distance before the rail load is applied. Rail planners call this prestressing force transfer length. To resist the heavier impact of the higher speeds, concrete ties employ about 20 steel wires, each stressed to around 7,000 pounds. If the prestressed force is not properly transferred, failures can occur in the track.

The project will focus on creating an adequate bond between the steel wires and surrounding concrete. All factors will be examined, including the mixtures of concrete, as well as the wires and indents that allow for better bonding. The team will also develop a test that prestressed concrete producers can use to determine the bond capacity of specific types of wire.

The team will then move to CXT Concrete Ties’s prestressed concrete plant in Tucson. At the plant, railroad ties with 12 different wires and three different strands will be produced, with measurements taken of the transfer length in those ties.

The team will use a transfer length measurement device based on laser-speckle imaging developed by the K-State research team. The laser-speckle device images the surface of the tie before and after de-tensing, and subsequently plots the strain profile of the tie. “We can tell by the strain profile how far from the end of the tie the prestressed force is transferred with each of the different reinforcing types,” says engineering professor Bob Peterman.

The team will then make recommendations to the Federal Railroad Administration on the appropriate methods to ensure good-bonding reinforcing steel, the best concrete, and related factors to create durable prestressed concrete ties.

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