Product certification following a successful motorway trial confirms the status of Tarmac’s waste tyre rubber modified thin surfacing as a pointer to the future of asphalt layers.
Ultipave R thin surfacing from Tarmac is based on a warm mix stone mastic asphalt to which has been added rubber milled from waste vehicle tyres.
The environment friendly system was trialled on the M1 before receiving BBA Hapas Clause 942 approval in June. Hapas certification scheme was established by Highways England, the County Surveyors Society and the British Board of Agrément (BBA) to facilitate testing methods for innovative products and systems for use in the highways sector.
The BBA Hapas approval of Ultipave R is good news on two fronts.
"There are distinct low grade polymer benefits in using rubber"
Firstly, Tarmac claims the rubber of up to 750 waste tyres can be effectively bound into every kilometre of road surfaced with 40mm of Ultipave R, substantially reducing the carbon footprint of tyre carcass disposal.
The process could help Britain overcome the problem of getting rid of waste tyres that can no longer be sent to landfill or burned. The UK currently relies heavily on exportation – up to 120,000t of tyres each year – but is vulnerable to recipient countries changing waste import policies.
Kuwait, for example, is likely to be forced to review its policy. At the small town of Sulabiya a mountain of 7M tyres is clearly visible from space. Dumping here will one day have to cease.
Secondly, adding rubber to what is otherwise a conventional thin surfacing mixture conveys physical advantages that include flexibility and waterproofing.
“The benefits are not just environmental ones,” says Tarmac technical director Brian Kent. “There are distinct low grade polymer benefits in using rubber.”
Tarmac’s knowledge of rubber modification was boosted in 2015 when it was acquired by United States conglomerate CRH. CRH had been using rubber since 1990 and possessed considerable data, to which Tarmac gained access.
This data revealed that asphalt containing tyre rubber enjoyed enhanced flexibility plus a delay in the formation of cracks – which, logically, pointed to delays in the formation of potholes.
Air voids
“And that’s not all,” says Kent Typically, SMAs have air voids of 4% to 6% by volume after compaction.
“We know particles of rubber can enter these voids, and thereby assist in reducing water penetration to lower levels that can lead to longer term underground movement,” he says.
His enthusiasm for rubber modified asphalt is shared in principle by Highways England head of lean and continuous improvement Martin Bolt.
“More flexibility and fewer defects to put right means less maintenance working, less road closures and fewer operatives at risk repairing roads. We can enhance safety while providing a better service to our customers.”
Highways England support has been crucial to the development of Ultipave R. In particular it has funded a comparatively onerous trial on the M1. There was exceptional interest in this trial because the asphalt used had a much higher proportion of rubber than normally employed.
“We’ve produced asphalt for some years now with a rubber content of 0.67%. On the M1 we upped the content in the mixture to 1%, which represents quite a steep increase,” Kent says.
The trial began in May 2019 along lane one of the M1 southbound carriageway, between junctions 23 and 22. Two sections were laid: a 280m length of Clause 942 thin surface course system incorporating rubber (designated Ultipave R) and a control section of similar length and material, but without rubber.
The binder type was a 70/100 penetration paving grade bitumen. The thickness of the surfacing was 50mm.
“Everything went well,” says Kent. “The mixtures came from one of our plants in Leicestershire using conventional kit to which had been added a silo for feeding in the rubber additive.”
The rubber was delivered as fine milled material, with granules of between 0.5mm and 0.8mm in diameter.
The cost of the silo, plus the associated automatic control equipment and software, was around £70,000, a sum which Highways England helped to meet.
“Total project cost to us was £181,000,” says Bolt, “This covered our contribution to the silo, modifying the software, the product itself and the trial report.” The money came from one of the government’s innovation funds.
"The inclusion of 1% ground tyre rubber represents a good opportunity to recycle asphalt materials without undermining durability and performance"
The report Bolt refers to was compiled by Aecom. “It presents the findings of the comprehensive lab work and on-site surveys carried out during the year-long trial,” Kent explains.
The principal objective was to assess the performance of both trial sections – the one with 1% rubber in its mix and the other without – to compare their properties. Nothing untoward showed up at all, says Kent. “Everyone was satisfied there were no detrimental effects in adding the rubber.”
To quote from the report: “The findings of this project showed comparable mechanical and performance properties for (both Ultipave R and the control asphalt) in line with a typical Clause 942 material.
“The inclusion of 1% ground tyre rubber represents a good opportunity to recycle asphalt materials without undermining durability and performance.”
Aecom’s report formed the basis of Tarmac’s successful application for BBA Hapas approval.
According to Hapas certificate 01/H052, Ultipave R – complete with 1% rubber – has been assessed as being fit for its intended use as a warm mix surface course on new and maintenance road construction.
“If installed correctly,” says the document, “the system provides a durable surface course for high and lower speed roads, including roundabouts.” A statement which obviously pleases Tarmac.
The company is a strong proponent of circular economy principles – it is reported to recycle 8M.t of waste and secondary aggregates from other industries every year, and is a net user of waste.
“We’re fully committed to developing sustainable construction materials – Ultipave R is just one example of the innovation we continue to invest in,” Kent says. “The onus rests increasingly on the UK’s client authorities to specify sustainable, low environmental impact road products and processes.”
Kent adds: “At Tarmac we believe we’re doing our bit – now it’s down to clients and the industry in general to exploit what’s available, for the benefit of all.”
(Credit: Ty Byrd. https://www.newcivilengineer.com/the-future-of/future-of-roads-adding-tyres-to-asphalt-to-bring-down-carbon-emissions-05-08-2021/)
Comentarios