On track for success

A promising technology could be set to revolutionize future track construction. The Frenzel-Bau group, a company specializing in railway construction, has developed the innovative track system Durflex in conjunction with Bayer MaterialScience and its wholly owned subsidiary Hennecke.

It is characterised by its outstanding noise damping properties and longevity. With this innovative system, gaps between the ballast stones are completely filled with a polyurethane foam. The displacement of ballast stone that typically occurs as a result of the dynamic forces associated with rail traffic is prevented, as is the wear normally associated with this displacement.

In the Lower Saxony town of Uelzen, a 300-metre-long pilot section of the new system is being trialed and is due to be opened up to regular rail traffic this month.

Construction of the test section has been subsidized by the German Federal Railway Department, the Federal Ministries for Transport, Construction and Urban Development, and the Federal Ministry of Economics and Technology.

Many residents living near railways are bothered by the noise produced by rolling goods vehicles. Up until now, railroad network operators have relied on the erection of noise barriers to reduce noise pollution in residential areas. These measures are costly and the barriers are frequently regarded as blots on the landscape – disadvantages that are largely eliminated with the new track system.

'The polyurethane foam fixes the ballast stone and dampens its movement. The structure-borne noise is dampened by Durflex at the very point where it is normally generated,' said Dr. Andreas Hoffmann, a polyurethane expert at Bayer MaterialScience.

The movement of goods by rail is regarded as more environmentally sound than transporting them by road. Yet in time heavy goods trains leave their mark on the trackbed, forcing track network operators like DB Netz to undertake considerable expenditure on maintenance.

'Maintenance work has high costs associated with it, because if the ballast bed has to be replaced, the stretch of track has to be closed for a period of time,' explained Jürgen Frenzel of Frenzel-Bau. 'With Durflex, the maintenance cycle for routine ballast work can be extended considerably. The system can be used both for the building of new sections of track and for existing stretches.'

In preparing the 300-metre-long pilot track in Uelzen, the Durflex track system was applied by a rail vehicle specially designed for this purpose by Hennecke.

In use, it injects the liquid polyurethane system via a mixer head straight into the gaps between the ballast stone, and foams up to fill them completely. The desired effect is achieved, when the foaming takes place in the load transfer area of the track ballast. Within a short time, the polyurethane system is completely set and the track can be used again.

Similar foam systems have already proved highly successful in rock consolidation and in the form of assembly foam for the construction industry.