Tests have shown warm mix asphalts to be more cost-effective and more ecological than traditional hot mix asphalts.
Highways England has been specifying warm mix asphalt (WMA) since 2015 but only under special conditions. After several years of research it can now be used more freely across the strategic road network (SRN) for which the organisation is responsible.
Previously requiring an application for a departure from standard, Highways England is now asking all those involved in the construction and/or maintenance of the strategic road network, particularly designers and main contractors, to use WMAs as standard as part of its drive for net zero carbon emissions.
WMA has been shown to make 15% carbon savings compared to conventional hot mix asphalts.
While typical asphalts are produced at up to 190°C, WMA is made at reduced temperatures down to 150°C but with additional additives, thereby using less energy without compromising performance.
If all road surfacing in the UK switched to WMAs, it would save around 61,000 tonnes of CO2e a year, Highways England said, or the equivalent of eliminating 300 million miles of car journeys.
Reduced laying temperatures also mean that WMAs take a shorter time to cool so greater volumes of asphalt can be laid in one shift, reducing lane closures. This also means fewer construction joints in the road are required, and hence less maintenance is needed, tests have shown.
And the reduced risk of workers getting burned or exposed to fumes brings a health and safety benefit. With WMAs, fume generation is reduced by around 50% for each 10°C reduction in temperature.
Highways England procurement director Malcolm Dare said: “This is a big step forward for Highways England that allows us to not only achieve huge efficiency savings but also reduce carbon as we strive for net zero. Carbon reduction, along with ensuring our roads provide smooth, safe, and efficient journeys for motorists, are key and something we are constantly striving to improve for generations to come.
“That’s why we are altering our way of working to encourage and enable the use of warm mix asphalts as standard across the supply chain, which has efficiency, sustainability, and health and safety benefits whilst not compromising performance.”
According to a report from the All Party Parliamentary Group on Highways’ in September 2019, WMAs account for almost 40% of overall asphalt production in the USA and more than 15% in France, but less than 4% in the UK.
At Highways England, WMAs previously required an application from the supply chain for a departure from standard.
Having already received more than 250 applications to use WMAs on the strategic road network at more than 300 locations, including on the M1, M4, M5, M6, A36, and A303, the change in policy will now make that process easier for the supply chain.
Contractors using WMA on Highways England jobs include include Balfour Beatty, Kier, Morgan Sindall, Costain, Skanska, Galliford Try, BAM Nuttall and Osborne.
Paul Gott, project sponsor from Morgan Sindall Infrastructure, said: “Warm mix asphalt is the first carbon efficiency project on the groups extensive carbon reduction plan, which is evolving and already identifies several short, medium and longer-term goals.”
Malcom Simms, director of the Mineral Products Association, added: “We and members have been working closely with Highways England for a number of years to provide the evidence of the benefits of warm mix asphalts in order to give specifiers the confidence to make a shift to these solutions.
“This is a significant first step on our collective and challenging net zero journey, and it’s great to see lower carbon asphalts being enabled as a matter of routine, rather than by exception.”
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