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United Kingdom: SP 25i Slipform Paver masters a special job

CANNOCK/UK, June 4, 2015 - Wirtgen SP 25i was used on the M6 motorway near Cannock together with a Wirtgen ISF 25i (independent side feeder) in order to pave a concrete slab under difficult conditions. With an overall length of 373 km, the M6 is the longest and one of the most heavily trafficked motorways in the United Kingdom.

The M6 connects the M1 motorway near Rugby with Carlisle near the Scottish border. Due to the steadily growing volume of traffic on this major artery, the Highways Agency as customer for the planned construction project decided that the service lane was to be upgraded for use as an additional traffic lane between junctions 10a and 13 near Cannock, 25 km north of Birmingham. The primary task of the consortium comprising Carillion as contractor of the Highways Agency and the construction company Extrudakerb Ltd was to completely replace the existing reinforced concrete slab with asphalt surfacing on the service lane in order to bring the new traffic lane onto a level with the adjacent pavement and create a homogeneous concrete pavement.

A Wirtgen SP 25i was used on the M6 motorway near Cannock together with an ISF 25i . | photo: Wirtgen Group

Project first of its kind in the United Kingdom

This unique project is the first of its kind in the United Kingdom. Work can only be carried out on this highly sensitive traffic artery during selected time frames and in exceedingly confined conditions. Following an intensive planning phase, project manager Mark Gladwell decided on a sophisticated timetable and logistics schedule covering every last detail. During the day, temporary steel barriers separate the service lane to be converted from the main traffic stream on the adjacent traffic lane. At night, when traffic is lighter, lane 1 and part of lane 2 are closed to traffic to provide an access route for the construction vehicles.

Paving concrete in challenging conditions

The project as a whole encompassed 16 km of new roadway, approx. 3 m wide and 300 mm deep. Around 14,000 m³ concrete of quality class C50 were delivered to the site just-in-time by Lafarge Tarmac from their mixing plant in Walsall using specially modified 8 m³ concrete mixer trucks. These trucks are equipped with GPS and an automatic system which monitors and adjusts the consistency of the concrete in order to ensure that exactly the required concrete quality is delivered at the right moment in time.

On arrival at the job site, the concrete is transferred over the top of the temporary steel barrier into the hopper of the ISF 25i and from there to the slab paving kit of the slipform paver via two synchronized conveyors. On account of the special site conditions outlined above, the time frame available for working was never more than six hours. This made it eminently important to maximize productivity within this narrow time frame so that the construction work could proceed efficiently. As a result, around 32 m³ of concrete were paved per hour, making almost 200 m³ per six-hour shift. The work was undertaken in 12 consecutive shifts followed by two rest days. All the other materials needed for the project as a whole, i.e. around 300 t of reinforcement, as well as 25,000 tie bars and 3,000 dowels, dowel bars and curing material, had to be delivered during the night, within the same time frame. Another major challenge, also in terms of the logistics.

The exceedingly short time frame during which the concrete slab could be paved on the M6 motorway during the night was never more than six hours. | photo: Wirtgen Group

SP 25i with Auto Pilot Field Rover

The compact slipform paver SP 25i is a multifunctional all-rounder for high-grade inset slipforming of narrow concrete roads, individual traffic lanes, minor rural roads and cycle paths. The multi-functional machine's features include the slipform paver's convenient operation, the speed at which it can be transported and repositioned and its fuel-saving engine concept.

Good-bye to stringlines

The Wirtgen Auto Pilot Field Rover has made it possible to produce concrete pavements fully automatically without stringlines. Stringline-free concrete paving works for a range of very different basic conditions from 3-m-wide pavements for a cycle path to concrete barriers on a motorway. If the concrete profile is to be slipformed on an existing roadway edging, the user can calculate the optimum virtual stringline on site in a matter of minutes. For the first time, the customary stringline can indeed be replaced in practice.