Recycling has never been more popular, with people encouraged to set aside paper, food, glass, plastic and more. But what about recycling our roads?
Roads deteriorate over time, and rehabilitating works have to be carried out regularly — road signs warning about roadworks are a common sight.
To make this rehabilitation more efficient, a time-saving and new environmentally-friendly technology has been introduced into the UK this year — having already been widely established in North America, Europe and China.
The cold recycling technology involves the milling and granulation of damaged asphalt layers, which are then rebound, placed again and compacted.
The cold recyclers — the machinery used in the process — recycle the underlying layers of the road. The old surface material is churned up with new binder in the machine’s mixing-chamber, before laying down the new, recycled mix immediately on the road behind.
Mike Reay, managing director at Lane Rental Services which owns and operates the first UK cold recycler, says: “The recycling layer is the layer beneath the surface. Following the recycling a brand new surface course is installed — first a new structural re-strengthen layer is provided by the recycler and then a brand new layer, running surface, is provided straight after that’s been completed.”
The cold recycler when operating in the project’s site needs the assistance of a second machine in order to complete the resurfacing work. “A final surfacing, after the recycling process, is always done with an asphalt paver,” says Martin Diekmann, Wirtgen’s recycling product manager.
“This means that an average 4cm hot mix asphalt layer as a wearing course is paved on top of the recycled layer.”
Wirtgen — the market leader in cold recycling technology — has sold 1,000 cold recycler machines worldwide so far, according to Diekmann, and this number is expected to grow.
The cold recyclers can be used for thin asphalt layers or minor roads, as well as for thick asphalt or heavily-trafficked motorways.
A UK first
The first UK cold recycler made its way into the country three months ago. “I was aware of the machinery used in the States and also in Europe. I visited a site near Toulouse in France in 2015 and was impressed with the equipment,” says Reay.
He adds: “This equipment has been tried and tested in the USA and Europe, therefore we had the confidence to introduce it to the UK.”
The cold recycling technology was first used in the UK on a Highways England project to resurface 1.6km of the A1 at Brownieside in Northumberland.
“I discussed it with AOne+ [the project’s contractor] and, obviously mindful of Highways England delivery programme requirements, we jointly decided the time was appropriate for this introduction to the UK. We ordered the machine and some trials schemes were authorised and have now been carried out,” says Reay.
The Wirtgen 3200 CR cold recycler is owned and operated by Lane Rental Services and was especially custom-made for the project. Reay adds: “It has been custom-made for the UK market, not only for the 2016 works. It will be the UK machine.”
The 3200 CR differs from the standard Wirtgen 2200 CR and 3800 CR on its operating width. While the 3200 CR cuts on a 3.2m width, the other two machines cut at 2.2 and 3.8m widths, respectively.
The cold recycler was used in the A1 project with the assistance of a Vögele Super 1900-3i tracked paver. “We chose a specific model which is a high-performance engine machine to have larger volumes of daily output,” says Reay.
Diekmann adds that the two machines work well together. “It is as easy as it looks like. The paver just follows and collects the already mixed material and paves it.”
Lane Rental Services — the A1 project’s subcontractor — chose the down-cut process for the A1. Reay says: “The down-cut process is designed to ensure that existing road material shutters to a smaller size, and therefore produces a better-graded material.”
Wirtgen describes the overall process as starting with cement being pre-spread on the road by a binder spreader, which is followed by water and binder tanker trucks. The milling and mixing rotor of the cold recycler then granulates the asphalt layers by a depth of up to 18cm, with the pre-spread cement mixed.
Then water and bitumen emulsion or foamed bitumen are injected into the mixing-chamber via injection bars. The recycled material is then picked up by a loading conveyor and transferred into the material hopper of the asphalt paver, which places it to line and level. After, compaction is carried out by rollers.
Alternatively, there’s the up-cut process, the main difference being the direction in which the rotor operates — in the up-cut process the rotor operates against the direction of travel, while in the down-cut process it operates in the direction of travel.
As it would be thought with any new technology and machine, some training and tests were carried out before the technology could be properly applied and used. “There was a trial scheme carried out in June 2016. The first 100 meters was a bit of a learning curve, but after that everything was installed very well,” says Reay.
He adds: “The machine operators were provided with on-site training. German technicians and engineers were on site on the first two schemes to assist our operators and ensure that they became fully familiar with operating the machine on their own, which they now are.”
With the new method, 500 to 1,000t per hour can be resurfaced — a significant increase when compared with the 100t per hour of conventional techniques.
Additionally, it reduces the quarried stone used by 75%, the waste taken to landfill by 66%, and undertakes 70% fewer lorry trips to and from site.
Reay adds: “The main benefit is cost saving. The carbon emissions are considerable improved and there is a massive reduction in waste disposal. Schemes are completed more quickly using this system and road work site safety is considerable enhanced.”
Moreover, the road asphalt is expected to last for a decade. “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,” says Steve Bishop, Highways England project manager.
Reay, however, recognizes a disadvantage on the whole process and technology. “It’s not a process that can be carried out in winter time. That’s the main downside, but fairly most schemes are carried [out] during summer months, for obvious reasons.”
According to Reay, two projects in the UK have already been completed — the A1 at Newton on the Moor and the A1 at Brownieside — while a third one is on the line for completion in September 2016.
With both projects a success, Reay is already thinking in future acquisitions: “We would like to think that this process will be adopted by clients and designers and that shortly will lead to buy a second machine, because the idea is to carry out this work throughout the UK road network.”
US Cold Recycling Award 2012
The cold recycling technology has been widely available and used in the US. Its successful application at the Interstate 81 in Virginia won the project the US Cold Recycling Award 2012.
The Roads & Bridges magazine and the Asphalt Recycling & Reclaiming Association’s (ARRA) award recognises top asphalt road recycling projects in North America — winners are selected based on the amount of recycled pavement material used, cost savings and project challenges.
Governor of Virginia Robert F. McDonnell said at the time: “Using the cold recycling method has the potential to revolutionize how we rehabilitate our aging roads, both in Virginia and nationally.”
The interstate I-81 is a major route in the eastern United States of America, which runs across the state of Virginia. The continuously-increased traffic volumes and the loads imposed by heavy-vehicle traffic left the two-lane road surface covered with huge cracks, wheel ruts and patches where minor repairs have been carried out. In previous years the Virginia Department of Transportation (VDOT) solved the problem with extensive repair operations.
However in spring 2011, a 6km-long stretch near Staunton on the right-hand truck lane required complete rehabilitation due to structural damage and an inadequate load-bearing capacity. The left-hand passenger lane also required rehabilitation.
According to Wirtgen, this construction project involved three different recycling methods. The truck-lane was rehabilitated with the assistance of W 210 and W 2100 large milling machines, which removed the asphalt material to a depth of 25cm in a single pass.
The granulated material was transported to the mobile mixing plant KMA 220 for recycling — ‘in-plant’ process.
The WR 2400 cold recycler then started on the soil stabilising operation to restore the subgrade to the required bearing capacity. Following recycling, the asphalt pavers placed the material, effectively compacted by tandem rollers from Hamm. At last, a 5cm-thick asphalt layer was placed on top.
The ‘in-situ’ process was used on the left-hand passenger lane. The W2100 milled off the 5cm thick surface course, and straight after pure cement was spread. The Wirtgen 3800 CR cold recycler integrated with a 3.8m wide paving screed milled off and granulated the damaged asphalt to a depth of 12cm in a single pass, while the milling and mixing rotor mixed in foamed bitumen, cement and water at the same time. Then, the machine proceeded to the paving and pre-compacting of the recycled mix with the integrated Vögele paving screed.
Final compaction was carried out by Hamm’s tandem and rubber-wheeled rollers. The work was completed with an asphalt course on top of the recycled layer.
Greg Whirley, VDOT Commissioner, added: “Savings on the I-81 in-place pavement recycling project go beyond time, money and materials.”