The Wirtgen Group production system cuts emissions and conserves resources during an in-place cold recycling project near Paris
The high-performance machines from the Wirtgen Group bring sustainability to the road construction industry. Conservation of resources, reduction of emissions and fast project completion are the overriding priorities on today’s construction sites. The combination of all machines and specialist technologies supplied by the Wirtgen Group delivers precisely these benefits. As here in the case of Colas, the interplay of the components of a so-called production system enables the exploitation of the full potential of each individual machine.
France | Saint-Léger-en-Yvelines
French road construction contractor Colas deployed a cold recycling train supplied by the Wirtgen Group for the rehabilitation of a link road in the French Department of Yvelines. As a globally active concern, Colas is always on the lookout for new solutions for more environmentally friendly and sustainable road construction. With precisely this goal in mind, Colas rehabilitated a 4 km section of the road with the cold recycling method. The existing road surface was milled off and used for the production of bitumen-stabilised material (BSM) for the new base layer. The machines deployed on the project were a Wirtgen W 240 CRi cold recycler with a Vario foamed bitumen injection system, a Vögele SUPER 1800-3i tracked paver and two Hamm tandem rollers, an HD 120i VO and an HD 90 PH with Hamm’s fuel-saving Power Hybrid technology.
The cold recycler was made available to the contractor as a demonstration machine by Wirtgen France. Colas has recognised the advantages of the technology and has since purchased a cold recycler for its own fleet.
The construction site was the link road between the communes of Gambaiseul and Saint-Léger-en-Yvelines. The key advantage of the cold recycling method is the short construction timeframe, which is one of the most important factors for assuring minimal disruption of traffic. The construction site with an overall area of 22,800 m² was completely recycled within only 8 working days. With conventional construction methods, the section would have had to have been completely closed to traffic for between three and five weeks.
Another key concern was the greatest possible minimisation of carbon emissions. Both lower CO₂ emissions and the reduction of environmental impact by the elimination of the need to move material to and from the site play an essential role in such projects. In-place cold recycling is an outstanding technology with regard to both of these factors.
‘The main advantage of a method like this is that the recycling takes place on the spot. We don’t have to move any material with trucks. With in-place cold recycling, the material is taken up by the machine and processed to produce a high-quality paving mix by the addition of foamed bitumen. This in-place recycling process avoids the need for all otherwise necessary transportation of material to and from the site and reduces CO₂ emissions in the foamed bitumen mixing process by up to 60 %.’
Jean-Paul Ripolli, Head of the Equipment Division at Colas
The reduction of site logistics plays a particularly important role. Fewer trucks for taking away the old material and just as few for bringing new material to the site. In the case of this construction site, this results in calculated savings of around 20 trucks an hour and about 11,000 t of material that would have had to be moved.
These savings are only possible as a direct consequence of the innovative method and the use of foamed bitumen. Colas, a recognised international specialist in the processing of bitumen, delivered the ideal raw material – hot bitumen – itself.
‘Alone that we recycle such a valuable construction material as asphalt means that we no longer have to draw on new resources or dispose of removed material.’
Alexandre Ludovic, Crew Manager Asphalt Paving at Colas
From left to right: Hadrien Brousson, Alexandre Ludovic
With the existing road pavement material and hot bitumen in the form of foamed bitumen, the Wirtgen Group production system produced a new, high-quality construction material and processed it in-place. As roads with base layers produced by cold recycling can be temporarily reopened for use by traffic immediately after final compaction, this meant that the disruption of normal traffic flow by the roadworks was able to be reduced to a minimum.
The Colas laboratory team prepared and analysed material samples from the construction site with Wirtgen laboratory equipment before the work began. These pre-project analyses delivered the quantities of binding agents that would be required when the cold recycler began the structural rehabilitation of the road bed. As binding agents, 1 % lime, 2.4 % foamed bitumen and, to ensure optimal compaction, 2.5% water were mixed in.
The aim of the project was to widen the D111 to a width of 5.1 m on 5.7 m to improve traffic safety. The cold recycler made the widening possible in a single construction process, without the need for new asphalt surfacing material. This meant that around 500 t of raw materials and a whole construction phase could be saved. In some cases, rehabilitation measures of this kind also enable communes to construct a separate bike lane, which can be a significant economic factor for a region.
A Wirtgen W 60i cold milling machine milled off the hard shoulder to a width of 60 cm and a depth of 10 cm. The milled material was left in the middle of the cut for direct processing by the cold recycler. Finally, a SW 19 SC binding agent spreader distributed the calculated quantity of 1 % lime over the first recycling cut. The W 240 CRi picked up the pre-milled material and the lime by means of the down-cut cutting process to a working width of 2.35 m. The working depth of 10 cm achieved exactly the required minimum thickness for a sustainable BSM layer produced by cold recycling. A homogeneous BSM base layer was produced by the simultaneous addition of standard bitumen in the form of foamed bitumen by the recycler’s integrated Vario injection system for foamed bitumen emulsion. ‘From a cold recycling system, I expect the material to be laterally homogeneous and that it produces a particle distribution curve tailored to the mix, delivers a finish that looks good and that it produces consistent quality’, said Rosine Confais, who performed the quality assurance checks.
The big advantage of BSM material is its outstanding endurance and long life. In contrast to conventional base layers, BSM is resistant to cracking for a much longer time. Numerous years of international experience from reference projects confirm its endurance and have since established cold recycling with foamed bitumen as an alternative standard method.
With a presentable speed of 5 to 7 m/min and a resulting productivity of around 220 t/h, the cold recycling train made excellent progress. The cold recycler’s maximum production rate of 800 t/h was not required for this project. The material produced was fed directly into the hopper of the Vögele SUPER 1800-3i following the recycler, which paved it at a working width of 2.85 m. The perfect, true to line and level paving of the mix was guaranteed by an AB 500 TV extending screed with Niveltronic Plus. As a result of this, the perfectly true to line and level, new BSM base layer behind the paver was already ready for final compaction.
‘The production system from the Wirtgen Group, consisting of a spreader, a recycler, a paver and rollers, is ideal for achieving perfect results. When you’ve finished, what you get is ready to use. You can drive on it right away – it’s just like a perfectly surfaced road.’
Rosine Confais, Quality Assurance
The final phase of the construction project was completed by a pair of Hamm road rollers. An HD+ 120 VO tandem roller performed the initial compaction of the BSM layer. Here, its active oscillation delivered the fastest compaction results. The second road roller, an HD 90 PH, took over from here and, thanks to its Power Hybrid technology, very efficiently completed the compaction process – bringing additional fuel savings and a further reduction of emissions. The new BSM layer was able to be temporarily reopened to traffic after a pneumatic tyre roller had finished its job.
The paving of the four-centimetre asphalt surface layer followed some time later.
As a construction method, in-place cold recycling differs significantly from conventional road rehabilitation methods. The site logistics are different, but the advantages are abundantly clear.
The 100 per cent recycling of the construction material results in:
Maximum usability of traffic infrastructure
