An overnight OPA job –– Wirtgen Group technologies pump up the speed
During rehabilitation of the A1, Wirtgen Group machines worked hand in hand, paving thin layers and carrying out fine milling work. The new high-quality surface course was paved economically in just 42 nights, as opposed to the scheduled 55.
Around 15 years ago, Straßen.NRW had the first section of federal highway paved with noise-reducing open-pore asphalt on the A1 between the Westhofen interchange and the Dortmund/Unna junction in the Ruhr region – by far the most densely populated area in Germany. By 2016, the surface course was worn and the three-lane highway including the hard shoulder needed rehabilitation. On the right-hand lane and the hard shoulder, the binder course also needed replacing.
Project planners wanted to prevent full closure, as this 7.2-km highway section is one of the main arteries of the German federal highway system and is used daily by an average of 100,000 vehicles in each direction, with heavy goods vehicles accounting for around 17% of this total. In the end, the starring roles in the project fell to Wirtgen milling machines and Vögele pavers, which took to the road each night and rehabilitated the asphalt pavement section by section and lane by lane. Some of the mix was supplied by a Benninghoven mixing plant. They all did an excellent job – so excellent, in fact, that the project was completed after just 42 nights.
Innovative rehabilitation concept
To minimize traffic obstructions during rehabilitation, Straßen.NRW developed an innovative concept: Every night a 700 to 900-m section of each of the 3.75 m-wide lanes was rehabilitated when the traffic frequency was at its lowest in the hours between 8 p.m. and 5 a.m. Heike Gerlach, Head of Road Construction at the highway subsidiary of Straßen.NRW in Hamm, summarized the project as follows: “If you don’t notice during the day that there was a construction site here at night, then we have done our job properly.”
For the left and center lanes, this meant blocking the respective section, removing the surface course with fine milling drums, cleaning the milled surface, placing a SAMI layer (Stress Absorbing Membrane Interlayer), paving a new surface course, applying the road markings and cooling. There was slightly more to do on the right-hand lane, where cold milling machines removed the surface and binder courses in two passes. The binder course material was then paved to a thickness of 12 cm. In another night shift, the right-hand lane and the hard shoulder of the highway were milled to a depth of 4 cm and replaced with a new OPA surface course of the same thickness. Next came the final step: creating 2 cm-deep joints at the seams. These ensure that the individual paved lanes are permanently bonded without impairing the drainage of water in the open-pore asphalt.
Hand in hand for high quality: Fine milling and thin overlay paving
GEHRKEN Straßen- und Tiefbau GmbH & Co. KG from Dortmund carried out the work as the general contractor and project coordinator. The company used Wirtgen Group machines for the key jobs. For example, the milling contractor GMS Fahrbahnsanierungen GmbH exclusively worked with Wirtgen cold milling machines – two large milling machines of type W 210i and the new compact milling machines W 100 CFi and W 150 CFi. After cleaning the milled surface, a Vögele SUPER 1800-3i SprayJet spray paver carried out two jobs at the same time: With the integrated spray module, it placed the new SAMI layer and immediately overlayed the new surface course "hot on hot" (thin overlay). Some of the asphalt for the job site was supplied by a Benninghoven BA 3000 mixing plant belonging to KEMNA BAU Andreae GmbH & Co. KG in nearby Kamen-Heeren.
The customer was thoroughly thrilled with the machine performance across the board. Engineer Udo Mattigkeit, Project Manager at Straßen.NRW, reported; “In the end, the machines proved even more efficient than previous calculations had led us to expect. This prompted our decision to extend the length of the sections after the first few nights, enabling us to rehabilitate up to 1,300 m per night. We ultimately finished the job 13 nights ahead of our original schedule. And the quality of the new surface course is absolutely superb.”
Fine milling: Wirtgen large and compact milling machines create basis for thin overlay
One of the machines used was the W 150 CFi, the most powerful cold milling machine in the Wirtgen Compact Class. With its low transport weight, it can be conveyed on most roads without a special transport permit – a great advantage when it comes to providing flexible and fast milling services.
With a capacity of 283 kW and a milling width of 1.50 m, this front loader is ideal for larger job sites with limited space. In such conditions, the sophisticated vision concept combined with the camera systems help the machine operator to maneuver the milling machine. The many cameras around the milling machines were particularly helpful to the operators when working on the A1 at night. “I can see exactly where the milled material lands in the truck. I can also recognize what is happening immediately in front of and behind the milling drum,” explains Milling Machine Operator Jens General. The brilliant illumination of the entire working area of the milling machines by bright LED lamps is a further boon. The excellent visibility not only enhances safety, but also helps the operators achieve the required precision. A large front axle steering angle also ensures very small turning circles and the large conveyor slewing angles of 60° to the right and left make it possible to load material under difficult job-site conditions.