Concrete Sleeper - Under Sleeper Pads

Under Sleeper Pads

Concrete sleepers lack the elasticity of wooden sleepers and therefore ballast tracks with Concrete sleepers usually have a much quicker degradation of the ballast when loaded. This is especially true in bends and turnouts/swithces. To reduce the wear on the ballast and in some cases offer vibration isolation pads are fitted to the base of the sleeper. The pads are usually manufactured of poluretahane foams with a stiffness tailored to meet the elasticity requirements of the track.

To reduce the wear of the ballast only, the best material to use is a very stiff semi-plastic polyuretane foam which mimics the plastic behaviour of wooden sleepers (the ballast stones are pressed into the surface of the sleeper, increasing contact area) typically these pads are 7-10 mm thick.

In order to achieve vibration isolation as well the elastic layer needs to be softer and in many cases thicker as well. A vibration isolation of 5-12 dB can be achieved, but the results will depend on many factors such as axle load, velocity, subsoil stiffness, ballast thickness, ballast quality and more. Therefore it is very difficult to predict the results exactly.