Tayside Seeks Olympic Green

In conjunction with the University of Dundee and Nynas, Scottish local authority contractor Tayside Contracts has launched a new product to maintain the country’s roads it says could lead to an annual carbon dioxide emissions saving of 17,160tonnes, or enough to fill an Olympic sized swimming pool 3,800 times. MQR chatted to MD Iain Waddell and Tayside project and quarry manager Grant Milne to find out more.

For Tayside Contracts quarry manager and project leader for the Scottish firm’s new Tayset road maintenance product Grant Milne, it is more than a simple matter of figures. OK, the cold-mix system could save £6million compared with traditional asphalt methods, he says, but there’s much more to it than that.

“There are about 500,000tonnes of road planings taken up in Scotland each year,” he explained to MQR. “We could turn that into 700,000tonnes of cold-mix a year. This would save 17,160tonnes of CO₂ being released into the air each year. We may be in business but we have a moral obligation to do what we can for the environment as well.”

Scottish politicians appear to agree. On 20 June, Tayside MSP and Minister for Finance and Sustainable Growth John Swinney officially launched Tayset at the company’s Collace Quarry at Kinrossie near Perth (see main picture). “This unique production process that emits less carbon… will bring numerous benefits to Scotland,” he said. And anything that can get a politician into a quarry has got be worth looking at. So, what is Tayset?

Well, developed in conjunction with the University of Dundee and bitumen specialist Nynas, Tayset is a cold-mix asphalt system. But rather than adopting what Milne refers to as the “hit-and-miss” processes of foam-mix, the product takes a different route.
Milne: “We didn’t want to use cement as they do to make foam-mix given the levels of CO₂ used in its production and we didn’t want to get into firing high pressure water to produce foam so instead we use an emulsion based material using penetration grade bitumen.

“I can’t tell you too much but when the material is rolled over the emulsion breaks, the water squeezes out and the asphalt bonds.”

The production process, however, is quite straightforward. Planings are removed and taken back to the quarry. Here they are screened to 20mm with a Powerscreen Warrior 1400 or if too large crushed to size with a tracked OM Apollo jaw. Samples are then taken for testing at its on-site laboratory.

Tayside Contracts rolls out the cold-mix black carpet for local MSP and Scotland’s Minister for Finance and Sustainable Development John Swinney at its Perth-based Collace Quarry.

Material then enters a old Titan 2000 coating plant that has been modified for the new process – although, again, Milne is keeping quiet about how it has been tweaked. Here it goes into the mixer and virgin aggregate added. “We add 10-30% primary to ensure a solid aggregate matrix for structural strength,” says Milne.

The Nynas modified bitumen is added and the product is ready to be transported to site. Milne is keen to stress that it is a system rather than a collection of isolated links: “Controlling the product, monitoring, production it is all connected. There can’t be any chinks in the chain,” he says.

It all started four years ago when Tayside earmarked a need for a sustainable, low cost, low carbon, recycled road paving system. Tayside had a number of recycling centres that it found were simply giving planings away or selling them at a low price. Tayside MD Iain Waddell: “We decided we needed a higher value product to use the material in. There was the carbon issue as well. Half the transport miles were clocked up by empty trucks making deliveries,” he told MQR.

Tayside started off with using recycled in a hot-mix. Waddell: “It didn’t work. We could only use about 10% recycled. So we looked into cold-mix.”

After about a year Tayside took its ideas to the University of Dundee through the Knowledge Transfer Network. Another year or so on – and five different mix combinations later – and they felt they were ready for the next step.

Milne: “By 2007, after work by the Concrete Technology Unit at Dundee, we felt we had a product that was ready for live trial. We decided a road leading into the quarry would be the perfect choice given the tonnages it had to support.

“We ripped the road out and laid the cold in the morning, put on the hot surface layer in the afternoon and opened it to traffic in the evening. There hasn’t been any rutting. It is quick to lay and performs really well,” he told MQR.

Waddell says the company viewed the product as a material that would ease pressure on local council maintenance budgets, while offering a greener, cost effective solution that would perform as well as traditional asphalts.

And Tayside certainly knows about local councils. It is the commercial contracting arm of Angus, Dundee City and Perth & Kinross councils.

So no surprise that Dundee City Council has certainly taken the Tayset material to heart. To date, Tayside has worked on two urban carriageways and three footpaths. And there are plans to widen this much further. Milne also says the company is keen to explore the possibility of a surface coat cold-mix product as well.

Milne: “The focus has very much been on the structured layers below because of the amount of material that can be reused. But I am confident we could move to testing a surface layer product within a year that could be used on English equivalent B-class roads,” he said.

The CO₂ savings promised by the system come directly from not having to use a hot-mix rather than through other means such as using plant derived binders.

And Waddell and Milne are not the only ones to see the benefit of the system. Waddell has had tentative enquiries about franchising. So, would he be interested in such an option?

“Possibly. I need to be sure about robustness. I could easily see mobile plant offering what we do here but I would need to be sure that the franchisee followed the system to the letter.

“At the end of the day I don’t want to be transporting Tayset across Scotland. It is supposed to be a green option, after all.

Tayside: 01382 812721