Warm mix asphalt – the future of roads

Reducing the carbon emissions associated with construction projects is vital if the UK government is going to meet its 2050 net zero carbon ambitions, so how can the roads sector help?

One way is by using warm mix asphalts (WMAs), which are also referred to as low energy asphalts, lower temperature asphalts, energy reducing asphalts or lower carbon asphalts. They can help cut the CO² emissions associated with asphalt production by 15% or more as they are produced and laid at lower temperatures, using less energy and delivering significant carbon savings.

These asphalts also offer a range of other benefits to contractors and road users – without compromising performance – and are suitable for use on the strategic road network as well as local roads.

A lower carbon, low energy asphalt option

WMAs are produced using special techniques and/or additives to reduce the production temperature of the asphalt to between 100⁰C and 150⁰C. This compares with conventional hot mix asphalt products which are generally produced at temperatures of up to 200⁰C. The lower production temperatures use less energy, cutting carbon emissions.

They perform to the same standards as – and sometimes better than – hot mix asphalts and, as well as reducing carbon emissions, also offer reduced disruption for road users and improved health and safety for asphalt contractors.

WMAs have been available since the late 1990s and, worldwide, account for a significant proportion of all the asphalt laid. According to the National Asphalt Pavement Association, for example, WMAs account for around 40% of production in the USA and, in France, this figure is 12% (source: EAPA).

Take-up in the UK has been much lower at around 4% but this is anticipated to increase significantly following National Highway’s (formerly Highways England) announcement in August 2021 that the use of WMAs, as standard, is encouraged on the strategic road network. National Highway’s approach is also expected to lead to the wider use of WMAs on the local road network.

Benefits of WMAs

Environmental:

Less energy used as production temperatures are up to 40⁰C lower than conventional hot rolled asphalt
Cuts the carbon emissions associated with asphalt production by 15%+
Fume generation is reduced by around 50% for each 10⁰C decrease in temperature, improving air quality at production and laying sites.
The lower temperature of the asphalt allows earlier re-opening to traffic, which reduces vehicle emissions from lower speed/stationary vehicles at road works and improves fuel efficiency.
WMAs are 100% recyclable back into new asphalts, helping prevent waste going to landfill and conserving natural resources for future generations.

Safety:

Minimises fumes and odour emissions for improving conditions for workforce at production and laying sites.
Lower temperatures create a cooler, more comfortable working environment for road laying, reducing risk of burns.
Creates less steam, allowing better visibility for night-time and winter working.

Efficiency:

Lower laying temperatures means WMAs need less time to cool before roads can be reopened to traffic. This allows less money to spent on traffic management and reduces disruption for road users.
Reduced cooling times between courses increases workforce productivity, allowing more material to be laid in a standard sift, saving time and money.

Performance:

Can be used to produce base, binder and surface course materials suitable for all types of roads.
Performance equivalent, if not better, than hot mix products.
Improved workability allowing a higher compaction density to be achieved, improving durability by reducing hardening of the bitumen and preventing water ingress.
Lower production temperatures can decrease bitumen binder ageing which can improve cracking resistance.
WMAs can include recycled content.
WMAs are laid using conventional asphalt paving equipment.

Resources:

European Asphalt Pavement Association: https://eapa.org/warm-mix-asphalt/
National Asphalt Pavement Association: https://www.asphaltpavement.org/expertise/sustainability/sustainability-resources/warm-mix-asphalt

Hanson ERA range

Hanson ERA 100 uses a micro-foaming process to reduce the temperature of the asphalt to below 100⁰C, cutting the carbon emissions associated with asphalt production by up to 50% while enhancing durability and improving health and safety for contractors.

Hanson ERA 140 warm mix asphalts incorporate a specialist bitumen that allows asphalt to be produced at temperatures up to 40⁰C lower than conventional hot mix asphalt. This reduces energy use, saving an average of 2.4kg of CO₂ per tonne of asphalt, and can result in enhanced durability and faster completion of resurfacing work. We have BBA HAPAS extended scope of accreditation for warm mix asphalt, ERA 140 Cl 942 materials.