Cold Repave

Leading the way in use of a pioneering technique, for Britain, of Cold recycling with the potential to achieve outputs of 2000t per shift is A-one+ and Highways England.

October will see the latest outing on the English strategic road network for a road strengthening technique that is new to the UK but that has the potential to become standard practice nationwide.

The pioneering Cold Recycling system employed by contractor A-one+ in Highways England’s Area 14 in the north east is an example of genuine innovation in UK road maintenance. It is one of the early successful outputs from Highways England’s challenge to contractors to find £1.2bn of savings to set against the £15bn currently being spent on its network.

The cold recycling is carried out by using a £1.7M Wirtgen CR3200 road recycler purchased by A-one+ subcontractor Lane Rental Services.

Cold repave is a form of road rehabilitation which simultaneously removes the old road material, re-grades the retained asphalt product and treats it with new emulsion, then places the material in to a tracked paving machine which lays it to correct line and level. This is all done at bitumen emulsion temperatures of 25 to 30 degrees C compared to the traditional new material delivered at 130 degrees C, making it safer to work with and helping reduce fumes and emissions. The process is popular in the US, Europe and China but the A-one+ work is the first of its kind in Britain.

Outputs being achieved are 11,000t of recycling in 10 working days in the initial trial, with the potential for 2000t per 10 hour shift compared to an average of 350t per shift using conventional methods.

Other quantified results include 40% cost savings, a 70% increase in daily outputs and a 33% reduction in carbon emissions. There was also a 75% reduction in quarried stone, a 66% reduction in waste taken to landfill (100% if you count using old surface material for new farm tracks alongside the trace of the projects) and 70% fewer lorry movements.

This month (October) on the A66M the Wirtgen machine will be at work refining and improving on these results. Initial trials of the technique were on 8.4km of lane carriageway on the A1 Felton Bypass in June, followed by the first formal use of cold recycling on 1.5km of road at Brownieside, also on the Northumberland A1, in August this year.

The projects so far have recycled the carriageways to depths of 160mm but the process can go to 200mm.

It was Highways England’s ‘1000t challenge’ to its contractors to find ways of carrying out 1000t of resurfacing in a single shift that encouraged A-one+ to rethink traditional practice.

“We hit the target by stretching what we do conventionally,” says A-one+ Area 14 asset manager Graeme Watt. “But we needed a lot more resource – more people, more trucks and the pace of work wasn’t safe or sustainable for our operatives. Throwing the kitchen sink at it did provide efficiency in terms of the amount of carriageway resurfaced but only saved less than £100,000 on a £1.6M scheme. Clearly we had to think completely differently and look at how to reduce the use of imported aggregates and hot mix as well as a way to increase productivity.”

The answer came with the help of A-one+ supply chain hub member Lane Rental Services. The planing contractor’s boss Mike Reay came forward with the idea of a technique used in Europe that could be employed on the English strategic road network – cold recycling.

“We went to see Wirtgen cold recycling in use in France and then discussed the next moves with Highways England, saying we would pursue the technique if it could provide the Departures from Standard that would allow us to use it,” Watt says.

These came swiftly, in the course of just 10 months. “From October 2015 to February this year we had a number of meetings with Highways England’s technical specialists along with Lane Rental Services, Paving Testing Services and Wirtgen to develop and agree the departures,” Watt says.

There was also a visit to Orlando in the US to see the technique in action and understand the contracting issues which gave everyone the confidence to go ahead. Then Lane Rental Services put in the order for the Wirtgen equipment which was delivered to the UK in June for the first trial.

This was where the investment demonstrated its value. Under the watchful eyes of Highways England, A-one+ and Wirtgen experts from the manufacturer’s home base in Germany and the US, including European head of recycling Walter Gruber, the CR3200 successful resurfaced a 4.2km of dual carriageway over 10 shifts. Costs were cut from £2.24M to £1.2M.

“And we got a depth of repair that would never have made it into the budget normally,” Watt says.

Watt describes the process. “We have to strip off the top course material first. Then the Wirtgen paver slowly drives forward, milling the rest of the old surfacing out and stripping it down to its constituent parts of hardened bitumen and aggregate, producing a pre-determined material grading. As the material passes under the milling drum it is mixed with bitumen emulsion and a small amount of water to aid compaction, with the newly graded and mixed material passed up the conveyor and into the traditional paving machine that follows behind to be laid like traditional hot mix material, but cold.”

“It’s fair to say,” says Lane Rental Services managing director Mike Reay “the old road becomes new road in one pass of interlinked equipment.”

All that is needed is for a new thin surfacing running course to be laid on top to complete the job. Timing is weather dependent but in the trial A-one+ followed with laying the surface course once the recycling was completed.

One lesson from the trial for the follow up Brownieside scheme was to spray the surface with 0.5% cement before the machine passed so the material was taken into the mix and helped absorption of water to aid compaction. “When we saw the technique in the US they didn’t need the cement but they were operating in 30 degree C heat which is not so common in Northumberland. We need a bit of help to drive the water out here,” Watt says.

The technique is gaining a head of steam in Highways England, Watt believes. Certainly Highways England project manager for the Brownieside job Steve Bishop is an enthusiast.

“There are lots of benefits to using this new way of working,” he said during the work. “It means we can resurface larger areas of road, there are fewer construction vehicle trips and the road surface is designed to last for at least 10 years, meaning that we shouldn’t need to go back to carry out further repairs any time soon meaning less disruption for drivers.”

A-one+ is planning to use cold recycling for all its Highways England areas and is going on tour to explain the technique to other contractors. Other clients are also very interested, particularly county councils which can see the potential for major savings. They have tried cold foam mix recycling in the past but that still involves removing all the material from site and bringing it back again; the work has never been done in situ.

“The best way for us to achieve the efficiencies Highways England requires is to utilise this technique,” Watt says. “It is currently difficult to see how this isn’t the future of sustainable road maintenance on the Highways England network and beyond.”