Partner: Tarmac
In the UK in 2020, 80% of freight was moved by road and 90% of passenger miles were travelled by road. It is considered a high-carbon form of transport today, but this is changing as new technology is rapidly making electric vehicles and alternative fuels more attractive.
The UK Government has indicated that sale of new petrol and diesel cars will be phased out by 2030 and the Transport Decarbonisation Plan puts Britain on a trajectory to do the same for heavy goods vehicles from 2040.
With the decarbonisation of road transport, its popularity is expected to increase, with traffic levels set to be higher in 2050 than they are today. Even juggernaut investments in rail such as High Speed 2 are expected to take just 1 to 3% of traffic off the Strategic Road Network. Those are the main roads and motorways managed by National Highways (formerly Highways England) rather than local authorities…
Road travel provides a convenient, low cost and practical way for ordinary people to travel outside of major cities. And this is reflected in preferences, with 80% of families owning a car in the UK.
National Highways has the usual Net Zero by 2050 target for road user emissions, but to be fair, that is only partly under its own control. What is more under its control are its own emissions – corporate and those created by maintenance and construction. And where it has control, helped by its industry partners and new innovations, it is being much more ambitious.
In this article we are looking at some of the key technologies it and the roads industry are exploring. Not just to bring the industry’s carbon emissions down in line with the Net Zero goals, but how they are thinking outside the box to make road transport more sustainable in other ways, to take a key waste product of motor travel, and find a use for it in the road itself.
Tarmac’s National Technical Director Brian Kent has three key technologies that he thinks will help make a difference in our efforts to mitigate the Climate Emergency. We will look at all of them, but one of his ideas is perhaps the single most important thing the roads industry needs to adopt… but has taken nearly 10 years to be accepted as standard practice.
But before we get to that, it is important to understand how things work in the UK roads industry, how new ideas are agreed, and what exactly it means… when they are.
Specification for Highway Works
National Highways has brought forwards its Net Zero target for road maintenance and construction ahead of the government’s 2050 target by 10 years, and a key part of this 2040 Net Zero ambition is of course what goes into our roads, and how it goes in.
Robin Hudson-Griffiths is the Senior Pavement Advisor for National Highways. He is responsible for a set of design manuals for road and bridge standards, they cover pavement design for new construction, and upgrading the existing road network. As well as the design manuals, he also undertakes traffic calculations to facilitate new pavement design (pavement refers to any asphalt surface, generally a road).
“Day to day, I run a collaborative research task with industry partners, Mineral Products Association, and Eurobitume UK, where we look at developing and research into new pavement materials, systems and processes,” says Hudson-Griffiths.
But the most significant part of his work as far as we are concerned is the Specification for Highway Works.
“It’s performance based. And it’s the specification that governs road materials that are used on national highways network. So it’s sort of like a toolbox, if you like, different materials that can be used to construct pavements.”
The specification has safety as a top priority, fitness for purpose too, but it also has regulations for the correct governance process, as well as routes to implementation through various technology readiness levels. So tech concepts through to trials and then to implementation into the specification, so it can be used anywhere without restriction on the Strategic Road Network.
It is constantly evolving. And one technology was included in the specification for the first-time last year. The technology that is, according to Tarmac, the most significant sustainability improvement for asphalt in a generation: warm-mix asphalt.
Warm mix
Tarmac first started looking at it back in 2011. It was part of a three-year project was the Carbon Trust, a not-for-profit entity that advises business on how to be green. The organisation is designed to be distanced from government, to speak to business on its own terms.
“The Carbon Trust’s incentive at the time was purely reducing the carbon footprint of the asphalt industry, which we’re still striving for now,” says Brian Kent. “After the three years we produced a report, working with the Transport Research Laboratory, which explained what Warm Mix Asphalt is, and its benefits.”
The quick run-down is that warm-mix is produced and transported at 150oC, compared to the 190oC of traditional hot-rolled asphalt. Additives allow this 40oC reduction in temperature, reducing energy consumption, and reducing carbon emissions from asphalt production by 15%. The UK produces some 25 million tonnes of asphalt every year in the UK, and if it entirely switched over to warm mix, the country would save around 60,000 tonnes of CO2 per year. Around 500 million kilometres of car journeys.
“Unfortunately, since publication, that report then took another eight years to get into specifications in this country,” says Kent. “And I think that’s one of the issues we have in this country is how long it takes embrace innovation, and actually enjoy all the benefits coming from it. Now, as I said earlier, lowering the carbon footprint in industry is fundamental. And it’s so important to us. And it’s something all suppliers are striving for.”
The lower temperature also means more can be laid in one shift and the finished surface can be opened to traffic sooner, reducing the time taking to lay the asphalt and shortening the overall project. Nine-day jobs become eight-day jobs and so on. This has the benefit of reducing costs and public disruption. Plus for every 10% reduction in temperature, there is a 50% reduction in fumes, making it a more pleasant working environment, and more pleasant for nearby residents.
Hudson-Griffiths and National Highways decided to introduce warm-mix into the specifications in July 2019.
“Anything that we introduce into the specifications, needs to perform as well as what we currently have. If not better,” he adds. “It has to offer efficiency savings and carbon reduction benefits. And warm mix asphalt ticked all these boxes. We trialled war mix national on our Strategic Road Network first in 2014. The site was monitored and we had to collect data, gain assurance and confidence that it was performing as well as conventional asphalts.”
Also making sure the claimed benefits are real, then a draft specification is produced, engagement with the industry supply chain to make sure that introducing the new technology wouldn’t introduce any supply issues. Then they had to notify the EU commission in case introducing the technology caused barriers to trade.
A second specification was written and warm mix was fully implemented in 2021. The reason this is so exciting to Kent and the industry is that prior to this, if a company wanted to use warm mix asphalt for a job, they had to complete a ‘departure from standards’ form. Often the company in question would not be the Tier 1 contractor, so they would have to go to the Tier 1 contractor and cajole them into completing the necessary paperwork. And sometimes there would be approval delays. It was an administrative burden that stood in the way of implementing a superior technology.
But new it has been added to the toolkit, Kent expects to see it used more-or-less universally across the Strategic Roads Network, with the exception of one or two niche materials that are inappropriate for warm-mix. But as a rule, hot-mix will become unusual.
However for the suppliers, the job is only half done. They now need to convince local authorities to adopt warm-mix for their roads, otherwise the production plants are starting and stopping all the time to switch between warm mix and hot mix.
Kent explains, “What you’re doing is you’re stopping intermittently, you’re having to clean the plant out you have to feed aggregates in at different temperatures, which means we’re not actually achieving the true sustainability benefits we can, at present.”
If they can get warm-mix universally adopted, suppliers can remove this inefficiency by running at one temperature all day.
“Productivity is optimised, sustainability is optimised. it’s actually been worked out that if the industry takes us approach in the clients allow us to take this approach, approximately 61,000 tonnes of carbon can be saved annually in the UK,” says Kent.
That’s the equivalent of cutting nearly 500 million kilometres of car travel, every year, so Hudson-Griffiths says that this change should filter through to local authorities, which are responsible for roads not on the Strategic Roads Network.
“I would urge local authorities to make the switch because we all have to work together in achieving Net Zero. And to make this work we need the asphalt plants all operating at a warm mix temperature range, it’s not efficient to switch between warm and hot,” he adds. “And I can also advise the local authority’s that we’ve trialled over 300 schemes with warm mix asphalt over a duration of seven years.
“And we have not had any failures. That should provide some level of confidence that the material used on our heavily traffic network is, is fit for purpose. Warm mix asphalt does not require any specialist equipment. It can be used using conventional asphalt plants and equipment, and it performs as well as conventional asphalt.”
Above to below
The industry is looking for other sustainability wins, and not just related to carbon. Brian and Tarmac have identified another problem they think roads can mitigate. Tarmac became aware of this about four years ago – that the UK and rest of Europe has a big issue now in disposing of car tyres.
“Because in 2006, the European law changed to say you could not move car tires to landfill anymore. Now in the UK alone, there are 40 million tires a year that fall beneath the legal tread limit,” says Kent. “Trying to dispose of the tyres since the law changed is an enormous challenge.”
Many industries have tried to use rubber tyres. In the asphalt industry, they are burned in concrete kilns for fuel, they are also remoulded into new tyres and any number of creative solutions. But there are still 25% of these tyres being considered unusable and exported to Pakistan, India, China and the Middle East. Exporting the problem. Kent argues that we should be trying to keep UK tires in the UK and solve our own problems. One way of doing that is to use them in asphalt.
“So we fine-mill all the rubber down to 0.5mm, very, very small particles. We mix it into the asphalt at the production plant. The rubber itself has the benefit of holding bitumen during transportation. and the rubber also introduced other benefits in terms of some added flexibility to the payment. So, rubber by nature absorbs movement. So, if you can imagine all these fine particles a rubber enter space through the matrix of the asphalt, you will never see movement with your eye. But there’s a small degree of movement there.”
They also hope that this will delay the onset of potholes as well, because these tend to form through brittle bitumen – the material not being flexible enough to cope with traffic – or some underground movement that the material can’t cope with.
The data here comes from the CRH Group, the largest asphalt supplier in the US. It has used rubber in its materials for nearly 30 years, so the data showing delayed crack propagation is there.
“Having the rubber in the mat should reduce some of the crack propagation and perhaps some of the potholes start to form will take longer to become an issue.”
With this material, the rule of thumb is that a kilometre of highway would use up 750 tyres. And the environmental benefits come when you follow the statistics. It’s 1% of rubber in the material. But that’s equivalent to one tyre per tonne of asphalt.
“Well, if you think that the UK actually lays somewhere in the region of 24/25 million tonnes of asphalt a year, we could dispose of these 10 million tires if we put our mind to it,” says Kent.
There is now approval to use this on the National Highways network without departure from standards, and again both organisations are looking for uptake from local authorities.
Layers in development
Kent says that a number of changes have entered the roads industry in the last 50 years. The most noticeable one being that historically, roads would have been much thicker.
“Because in those days, perhaps budget constraints weren’t as tight as they are now. And obviously, when you’re building a road, initially, you have to take a full structural approach to it has to be thick enough to perform over the 40-year design life you’re looking for.”
When it comes to maintenance, road owners have to try to minimise costs.
“So we may need to take more depth out of the pavement to truly tackle the problem. But we can’t afford to. So we take off a thinner half of the pavement or 20% of the pavement and we replace that which looks great to the public there and then and will perform better than the material taken out… But you’re really just sticking a plaster on over an issue that’s further down in the payment. Bitumen has developed.
“So we didn’t have polymer modified versions, in the old days, PMB’s now give you more flexibility in a payment. So when you’re wanting to be underground movement, where the whole pyramid may have moved over time.”
With a polymer it’s now absorbing that movement.
“So there have been fundamental significant improvements in asphalt technology over the years. Which means if we were to go out now and lay a road that relate 50 years ago, we would do it very differently, we would do it thinner, because we’ve got better tougher, more flexible materials, more flexible bitumens, a range of additives we can use and better laying plant technology.”
And herein is the final easy win that Kent, and many others in the industry are hoping to see adopted.
“One of the other innovations many suppliers are pushing towards At the moment, as is a single layer technology. So if you think about specifications, your specifications have been present for 20, 30, 40, 50 years, and they were developed a long, long time ago for technology that was very different. So we have a very outdated approach of, if we’re going to replace a carriageway, we will take off 100 millimetre of material, we will lay 60 mil of binder coarse and 40 mil of surface coarse.. And that’s what we tend to do.”
The reason we do this is that decades ago, workers would be worried if you laid the material too thickly, then it would not compact well enough. And the road would be brittle.
“Innovation and technology has moved on tremendously. The type of pavers we use now are so much better. A paver can give you 90% compaction now before the roller even gets to it… the type of we use now are bigger and more powerful. The material technology has moved on, we have different bitumens, we have different additives, that really shouldn’t be a concern anymore about laying the material little bit thicker.”
If you can lay the material thicker, you can lay the road in one layer. This allows for shorter programmes, shorter intervention times. Meaning a job isn’t one or two days, you might be there for half a day, or a full day. The first layer doesn’t have to cool before the second layer is placed, so there is a huge advantage in costs and disruption.
“And I think that’s a message now the industry has to the client is we’ve been encouraged to innovate and develop for over a decade now,” says Kent. “We spend a lot of money as suppliers in research and development we have our own laboratories, we work with universities, we work with material suppliers, we come forward with innovations, but they need to be embraced.”
