the Leverkusen intersection and the Cologne-Mülheim junction.

The Cologne ring-road system is an endurance test dreaded amongst motorists – since the busiest section of motorway in Germany lies between the A1, A3 and A4, with a high risk of congestion. And it’s not just the drivers’ nerves that are under strain, but the asphalt as well: long-distance traffic winds its way from here through Europe and branches out across Germany. There is particularly heavy traffic on the section of the A3 between the Leverkusen intersection and the Cologne-Mülheim junction.

To ease traffic, it was therefore decided to widen the six-lane motorway to eight lanes. The technical focus lay mainly on the asphalt bearing the brunt of the HGV traffic, which covers around 100,000 square metres of road surface. The main priority alongside high stability was that the asphalt also com-plied with more stringent noise-control requirements to protect the residential areas bordering on the motorway.

To reduce noise levels for local residents, a significant five-decibel reduction in the sound pressure level was required in the A3 project. Due to these requirements, the only option for the road surface was open pore asphalt (OPA). OPA is characterised by having interconnected voids in the surface layer. This dampens the sound of vehicles and prevents “hissing” on the road surface, since the air in the tyre tread is distributed via the interconnected voids. Such sound absorption can-not be achieved with the more commonly used stone mastic asphalt. The void content of stone mastic asphalt is usually under four per cent. Consequently, to achieve the required noise reduction, the asphalt needed to have a void content of at least 24%.

the Leverkusen intersection and the Cologne-Mülheim junction.

Five decibel noise reduction achieved

“Ensuring this high void con-tent was the main challenge in the production and application of the mix,” says Guido Dreher from Kemna Bau West, the asphalt supplier of the A3 project. In the selection process, it quickly became apparent that Kemna would use Shell Cariphalte OPA as a bin-der in the A3 extension. The Shell product had already been used successfully by Kemna in previous projects, such as in the upgrade of the A40 between Bochum and Essen and in the new construction of the A46 at Tagebau Garzweiler.

Because of our positive experiences with Shell Cariphalte OPA in other projects, it was clear to us that we would use the product in the A3 project as well. What’s particularly noteworthy is the affinity of the asphalt (i. e. the bonding of aggregates and bitumen), an important factor in the required void content,” says Guido. Added to that is the high stability achieved with Shell Cariphalte OPA, which becomes increasingly important with extremely high traffic volumes.

Logistical master stroke

When the construction work started, around 2,000 tonnes of asphalt and 120 tonnes of bi-tumen were needed each day. “First of all, these quantities need to be produced in a short space of time,” notes Guido. Yet Shell Bitumen was able to deliver these high quantities of bitumen reliably: 300 tonnes of asphalt were delivered and applied on the construction site per hour. Two asphalt mixing plants working in parallel supplied the construction site for this remarkable paving output. The entire road section required 12,000 tonnes of OPA and 780 tonnes of bitumen for the production. The logistical challenge was not just down to the need for a short construction time: there always had to be enough material on hand for continuous laying of the road surface, which was the only way to achieve the required evenness of the pavement. To guarantee material replenishment, 35 trucks carrying 27 tonnes each were in constant circulation between the construction site and the mixing plants.

Work on such a critical traffic hub can only take place outside peak times. To minimise disruption to the traffic flow, the road works took place bet-ween 6 p.m. and 5 a.m. “A construction project on a motor-way as busy as this is in principle much more challenging than on a quieter stretch of road or a new build,” Guido points out. “So we also worked during the night to take advantage of the lower traffic volumes at those times.” In addition, half of each carriage-way was closed during the night time work, to allow construction on two lanes per carriageway at a time. But even minor restrictions can have a major effect when working at night: just lighting the eight-lane motorway evenly was a very challenging task.

Long-term planning with the best support

All in all, a massive coordination effort lay behind the major project. Several companies needed to work closely together to stay on top of the tight schedule: during the construction phase, the installation company Wolf & Müller and the asphalt supplier Kemna Bau West could rely on the on-time delivery of the asphalt haulier and Shell Bitumen, as well as the other suppliers for the asphalt production. The rapid completion of the challenging project is testament to the success of this efficient cooperation. It was planned and completed between the end of 2015 and May 2017.

Guido Dreher also regards the co-operation with Shell Bitumen as a resounding success: “The long-term planning worked well and was fully complied with, and the logistics in this complex project were also well coordinated bet-ween the suppliers. Even in the run-up to the project, Shell ensured excellent cooperation between the laboratory and quality management at Kemna. All customer requirements were implemented.” As reiterated in Guido’s positive summary of our overall cooperation: “Support was perfect from start to finish.”

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