Ballastless track system without continuous reinforcement

RAIL.ONE has developed a ballastless track system without continuous reinforcement. In its structural configuration and its functional principles, this new system is analogous to the state of the art in the engineering and construction of concrete slabs. The new ballastless track system, however, differs from the previous RHEDA 2000® system in that the innovative development does not implement continuous reinforcement. This elimination of part of the reinforcement now enables reduction in construction time and lowering of costs. The new development also minimizes the influence exerted by the reinforcement on the earthing facilities and on the railway signalling systems. As a result, the new system is also particularly effectively suited for applications in France, Spain, and Asia, where the UM71 DC circuit system is used.

Structural configuration

In the RHEDA 2000® system, the reinforcement uniformly distributes the cracks that develop from restraint stresses arising from shrinkage and temperature effects, and limits these cracks to a width less than 0.5 mm. The new ballastless track system without continuous reinforcement prevents uncontrolled formation of cracks on the basis of technology resulting from long years of experience in the engineering of concrete slabs. Analogous to concrete slab technology, these new track systems are produced with lateral dummy joints to achieve controlled formation of cracks. The cracks that subsequently develop begin from these joints. They arise in accordance with reduction of the thickness of the concrete track supporting layer, as a result of temperature-related influences as well as of shrinkage of the concrete. The dummy joints therefore represent planned fracture points, whereby the objective – soon after the concrete has hardened – is to achieve fracturing at all lateral dummy joints that is as uniform as possible. Controlled formation of cracks is achieved by notching the early-age concrete at a notch depth of approx. 30% of the thickness of the concrete layer. The joints are then sealed to prevent or reduce the penetration of water into the joint structure.

In this case, the lateral transfer of forces at the cracks takes place by aggregate interlock for small crack widths, as well as through the reinforcement itself. These cracks develop through the continuous longitudinal reinforcement at relatively short intervals. In the case of non-reinforced concrete track supporting layers, excellent lateral transfer of forces is achieved by lateral-force dowels (bolt anchors) installed into the fresh concrete, as well as by active aggregate interlock. These dowels are fastened approximately in the middle of the concrete layer, each under a joint at the lattice girder of the sleeper. As an alternative, however, they can also be fastened to a reinforcement cage installed on the concrete supporting layer. Similar to concrete road construction, these dowels are 500 mm long, with a diameter of 25 mm. They have a plastic coating 0.3 mm thick to protect them from corrosion.

An additional effective option is to replace the previously used concrete of C30/37 strength with stronger C35/45 concrete. This solution achieves greater frost resistance, leading in turn to longer life cycles, and likewise reduces track structural height.

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Installation on hydraulically bonded layer (HBL)

A configuration with a concrete track supporting layer on a hydraulically bound support layer (HSL) and a frost-resistant layer is approximately analogous to the standard configuration for roads built in German Construction Class SV (for heavy-haul traffic). Very good experience has been gained with road configurations of this type. With respect to dimensional and stiffness characteristics of the individual supporting layers, the only difference between the new ballastless track system without continuous reinforcement and the RHEDA 2000® with continuous reinforcement lies in the reduced height of the supporting concrete slab (enabled by the greater concrete strength). Key data of the two options are summarized as follows:

  • A supporting concrete slab, 220 mm thick, in C35/45
  • As alternative, a supporting concrete slab, 240 mm thick, in C30/37
  • A hydraulically bound support layer (HSL), 300 mm thick
  • A frost-protection layer, with EV2 ≥ 120 N/mm2

The ballastless track system without continuous reinforcement can be implemented with or without a hydraulically bound support layer (HSL).

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Installation on ballast supported layer (BSL)

The chief difference between the ballastless track system without continuous reinforcement and without hydraulically bound support layer (HSL), and its predecessor models, is the elimination of the HSL. In order to achieve the required load-supporting behaviour of the system, a ballast supporting layer is installed, thereby raising the EV2 value of the unstabilized supporting layer to 180 N/mm2. In addition, the height of the concrete track supporting layer is increased to 300 mm. In order to achieve sufficient load-bearing distribution in the sub-grade, the width of the concrete layer is increased to 3200 mm: this is necessary because – in a ballastless track system without continuous reinforcement and without a hydraulically bound support layer (HSL) – the load-distributing characteristics of the lacking HSL are not available. The ballastless track system without continuous reinforcement and without a hydraulically bound support layer (HSL) therefore concurs with the definition of a “thick concrete slab on a ballast supporting layer,” as it is applied to the renewal of roadways by deep construction work. In German Construction Class SV (for heavy-haul traffic), the concrete slab rests directly on the non-bound support layer: with, however, a slab of C35/45 concrete strength. Application is also possible with C30/37 concrete strength, but here the thickness of the supporting concrete slab must be increased to 330 mm. As represented in the following, it is also possible here as well to eliminate the four longitudinal reinforcement bars:

  • A concrete track supporting layer, 300 mm thick, in C35/45
  • As alternative, a supporting concrete slab, 330 mm thick, in C30/37
  • A ballast supporting layer, 300 mm thick, with EV2 ≥ 180 N/mm2
  • Frost-protection layer (FPL), 400 mm thick, with EV2 ≥ 120 N/mm2

The ballastless track system without continuous reinforcement on a ballast subbase.

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TRAVERTEC is a 100% subsidiary of RAIL.ONE, Germany. We offer an extensive line of concrete sleepers and railway track systems for passenger traffic as well as freight- and heavy-haul transport.

System structure without reinforcement

The illustration here shows an example of the system structure, without reinforcement, on a ballast supporting layer.

Test section

In September of 2006, a test section 30 m long was built at the Coswig sleeper plant, in Germany. After successful conclusion of this work, the German Federal Railway Authority (EBA) in March of 2007 granted official approval for field testing. In 2010 the system has been employed for the first time in the metro Athen in Greece.