With eight structures, thirteen roundabouts and a total route length of 20km, the Northern Distributor Road (NDR) being built for Norwich County Council, is no small project. When completed, this £178m infrastructure project will create a dual carriageway link that sweeps eastwards from the A1067 Fakenham Road across the northern edge of Norwich City, around the airport, to link up with the A47 at Postwick. As part of the construction process, the NDR project will use more than 150,000 tonnes of asphalt to complete the dual carriageway and the various side roads leading from it. Such a logistical exercise has resulted in the temporary installation of an on-site batching plant to ensure consistency of supply with asphalt materials for the duration of the project. And putting the finishing touches to the black top for main contractor, Balfour Beatty, is Tarmac engineering supervisor, Ben Howard and his team, making full use of a satellite-guided Volvo P8820C tracked paver. “We opted to bring the Volvo tracked paver onto this job for
many different reasons,” explains Ben. “We do get tremendous traction and stability from its tracked undercarriage which makes it much easier to push 44-tonne walking floor bulk- trailers when they’re in front of the paver’s feed hopper.” While positive traction enhances productivity, and choosing no-tip walking floor bulk-trailers boosts on-site safety, the P8820C paver also offers a 7.5 - 9.5m adjustable working width for its asphalt screed. And on each of the NDR’s 8.3m wide carriageways, this lets the team deliver on productivity with a forward speed of around four metres per minute, while creating a high-quality finish.
“The variable width vibrating screed lets us lay both lanes simultaneously, without joints or seams,” Ben says, “and a seamless finish is very important for the road’s longevity, which makes it much easier for us to get it right first time.”
While laying both lanes in one pass does boost productivity, it demands a constant flow of hot asphalt to the paving machine. And this is where an on-site batching plant has an important role to play.
“Once we get the go-ahead to pave each section, we can then guarantee a constant delivery of material from our own plant to keep the paver moving until it reaches the end of its prescribed run.” With the road’s sub-base having been stabilised in-situ, the asphalt layers are being progressively built up to achieve the finished profile and gradients required by the client. “We’re putting down two layers of binder material onto which a wearing course will be applied,” he says. “These layers comprise a 60mm base, followed by a 55mm binder and a 35mm wearing course.”
Machine control and guidance comes from Topcon’s LPS/GPS to provide a high-quality and stable guidance, so each finished layer provides a very accurate and even surface to accept the next layer. In addition to creating exact layers, the machine also regulates the lateral pitch of the screed box to create the desired fall across the road surface. Ultimately, such precision will give motorists a smooth, finished road with highly effective surface drainage. “We are working to a tolerance of +/- 6mm at finished road level, which meets Highways England’s specification.”
Using digital design models of the road, Ben Howard and his team load the asphalt paving plans into the machine’s controller via a USB stick. This process avoids the need for traditional conductive roadside pins while simultaneously eliminating a trip hazard from the work area. In his experience, Mr Howard reports that using machine guidance has been found to speed up the entire paving project, and has made it almost impossible to lay asphalt outside the prescribed area of the road design.
CONTINUED OVERLEAF a
“The variable width vibrating screed lets us lay both lanes simultaneously, without joints or seams. And a seamless finish is very important for the road’s longevity, which makes it much easier for us to get it right first time.”
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