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High Speed | Pushing slab track engineering

Madrid-based contracting giant Acciona, part of the Acciona/Sisk High Speed 2 JV, is agnostic when it comes to trackbed choice. Whether it is ballast or slab-track it is happy; it just wants to see innovation – as innovation is its passion.

Just a stone’s throw away from Acciona’s swish Madrid HQ is its technology and innovation centre; a five storey building where some real magic happens – and right now the focus of the magic is very much high speed rail.

Whether it is in the chemicals lab developing its eco-friendly ballast bonding method to prevent ballast pick-up on high speed lines, or in the composites lab expanding its range of auxiliary elements to reduce whole life maintenance costs, a team of technicians is on the case.

All have great potential. But probably of most interest is its work to make slab track a more palatable option for those concerned about construction tolerances and adaptability.

acciona slab track test

acciona slab track

Acciona is pioneering small precast track bed sections

The core goal is to develop a fast-assembly, modular slab track system with multiple vibration attenuation levels.

“We have tried to go for smaller slabs for the ease of changing geometry. We also have a top-down alignment system – which means positioning of the slabs doesn’t have to be so precise.”  says Acciona international innovation and technology manager Javier Bonilla Díaz.

Acciona’s modular system features slabs just 1.2m long by 2.7m wide. These provide rail support via two embedded blocks per rail per slab at a spacing of 600mm.

acciona slab track test

acciona slab track test

Precast units undergoing lab tests

These shorter slabs are laid on a flexible bituminous sub-base to adapt better to terrain settlements (see below), and the coarse bottom-up slab alignment is complemented by the ability to fine tune individual blocks.

“Our slabs hold just two blocks. These gives some modularity and it means you can correct alignments if you have settlement,” explains Diaz.

The system also features three elastic levels – rail pad, block pad and slab mat – for maximum noise and vibration absorbtion.

“It has a very good capability to absorb noise and vibration,” he notes.

The size of the slabs also lends itself to industrial production and precasting, and makes it a realistic to create precast untits even in the tight confines of a tunnel.

The modular nature means damaged modules can be replaced with minimal interference, meaning maintenance costs and on-track time are drastically reduced.

“We expect to see a 10% reduction in the cost of installation and faster repairs in service,” notes Diaz.

Right now the system is undergoing tests under the auspices of Spanish research agency Cedex.

“We’ve finished the resistance under vertical load test – and the results were good. We’re waiting on durability test and then we’ll test it on a high speed line in Spain,” explains Diaz.

The durability test simulates up to 3M axle loadings. Once it passes that, it moves to real-life testing on a section of Spanish high speed rail line dedicated for testing new products.


Acciona could complete an innovation double-whammy if its innovative new slab track system was to be approved and used with its equally innovative Recytrack sub-base.

Currently being developed by Acciona with the help of the European Union through its LIFE +2010 programme, Recytrack would turn shredded end of life tire resin into an elastomeric mat for ballasted conventional rail system and slab track.

The main objective of the project is to demonstrate its environmental benefits and the product’s technical and economic viability.

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