This could be the year that warm mix asphalt finally takes off in the UK, with Highways England shortly due to approve a specification for this more sustainable method of laying road materials.
Warm mix asphalts are produced and applied at temperatures up to 40°C lower than conventional hot mixes, using less energy and improving efficiency and safety on site.
The concept has been around for the better part of the last century. But uptake in the UK has not been significant to date, despite warm mix now accounting for a third of asphalt production in the USA and its use starting to increase across continental Europe.
However efforts by the industry to promote the advantages of using warm mix in the UK now appear to be paying off.
“There is a strong evidence base to prove that warm mix is viable and delivers similar performance to that normally specified,” says asphalt director of the Mineral Products Association and spokesman for the Asphalt Industry Alliance, Malcolm Simms.
He adds that it is incumbent upon the industry to keep clients up to date with emerging opportunities and instil confidence that they are getting a quality product.
“We are a relatively energy intensive industry, so mixing materials at lower temperatures can contribute towards wider sustainability and climate change objectives,” he explains.
He also argues that, because using warm mix means the bitumen is “younger and fresher” when it goes down, it may actually offer increased durability over traditional hot mixes.
Some local highways authorities are now beginning to deploy warm mix asphalt on parts of their networks. But its use on strategic roads – where it represents a departure from standard – has so far been much more limited.
“Authorities working with local suppliers may be more willing to trial innovations to gain the potential benefits in light of their stretched budgets and where there may be an element of risk sharing,” speculates Malcolm.
He adds that local highway authority trials, combined with experience from overseas, have helped to build the evidence of performance for the wider use of warm mix asphalt in the UK.
“Highways England has traditionally been more risk averse to large scale trials and generic application,” he says.
However the strategic road network operator has now confirmed that it is shortly to incorporate a specification for warm mix asphalt into its Specification for Highways Works, subject to regulatory procedural clearance.
The company says it recognises the material’s potential carbon savings and durability benefits and adds that mixing at lower temperatures will mean that the materials cool quicker, allowing greater productivity and roads to be re-opened to live traffic sooner.
Warm mix asphalt also creates fewer fumes than hot mix, bringing health and safety benefits to road surfacing teams and creating cooler, more pleasant working conditions.
Health and safety is our number one priority as an industry,” emphasises Malcolm Simms. “We can develop all the best products in the world, but if we can’t deliver them safely then we are wasting our time.”
He says that the benefit of Highways England’s specification will be to enable and encourage warm mix asphalt’s more general use, with carbon and efficiency savings more likely to be achieved when these materials are produced more routinely.
Following the introduction of the specification later this year, the Mineral Products Association is considering setting some “hard, rational targets” for annual volumes of warm mix production in the UK.
Warm mix is currently estimated to represent less than 1% of UK asphalt production. “We would like to see that rise further towards millions of tonnes a year,” says Malcolm Simms.
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