Road rehabilitation and widening in a single pass

During a recent road upgrade project in Silkeborg, Denmark, the deployment of a Wirtgen W 380 CRi cold recycler demonstrated the efficiencies of insitu rehabilitation as a cost-effective and sustainable solution.

With conventional asphalt paving methods, the work would have involved milling off the entire road surface in several stages and then widening and repaving from the ground up. In contrast, with in-place cold recycling, the contractor was able to use the existing asphalt material to produce a new bitumen-stabilised material (BSM) base layer.

Leading the paving train, the Wirtgen W 380 CRi cold recycler first milled off the existing asphalt surface to a depth of 15 cm and then added foamed bitumen and cement to directly produce the new mix in the machine’s milling and mixing chamber. Around 300 tph (tonnes per hour) of BSM was transferred to the Vögele

Super 2100-3i road paver following behind, which then established the new 5.5 m wide and 12 cm deep pavement profile – all in a single pass.

The cold recycling train worked its way forward along the 3 km section at a rate of 4 m/min. Then as soon as the rollers had taken care of the final compaction, the road was able to be temporarily reopened for local traffic.

Significantly lower construction costs

According to lead contractor Arkil A/S, the costs were 30% lower than for a conventional rehabilitation project. Here, savings on materials played the biggest role in the reduction of the overall project costs.

Thanks to foamed bitumen technology from Wirtgen, considerably less bitumen needed to be added as a binding agent when compared to the production requirements for a new asphalt mix. During the project, hot bitumen was delivered to site and automatically injected in place during the milling and mixing process via

Wirtgen’s Vario injection bar system. The latter automatically matches the feed volume to the travel speed and ensures the homogeneity of the mix transferred directly to the Super 2100-3i paver.

Another advantage of this technology is that the final asphalt surface layer can be paved thinner. In this case, only 3 cm of high-quality surface layer material was used, instead of the usual 4-5 cm. This also helped to reduce the construction costs.

Streamlined logistics and lower carbon emissions

Lower transportation costs led to further cost savings. The recycling area of over 12 000 m2 produced almost 4 000 t of material that did not have to be removed from the site. This in turn helped to lower CO₂ emissions with the elimination of some 400 truckloads of material to and from the site that would otherwise have been required.

Some 3 800 t of fresh hot-mixed asphalt would also have been needed for the base layer in the case of conventional asphalt paving. This clearly underscores the cold recycling approach as a far more efficient and environmentally friendly method.

The versatility and durability of BSM have been proven on decades of projects around the globe. The required minimum thickness for a sustainable BSM base layer is 10 cm; in Silkeborg, the Super 2100-2i paved the material with a thickness of 12 cm