Innovation is essential to meeting the challenges that Britain’s highways face, from managing the effects of long-term funding pressures, to hitting ambitious carbon reduction targets. Our road surfaces also need to be equipped to handle the changing weather patterns and evolving user behaviour.
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By Mark Flint, technical director, FM Conway
Taking all this together, it’s clear we need to embrace new ways of designing and building roads. But where to start? The first piece of the puzzle is in the lab as we evolve materials specifications to deliver better performance. At FM Conway our research and development work in this area is showing promising results. Here’s what the next frontier of highways materials looks like from where we’re sitting.
If we want to deliver better value from funding and to cut emissions, we need to boost the durability of our highways network. Longer-lasting roads can be game changing in terms of reducing maintenance costs and whole-life carbon, not to mention minimising disruption for road users.
One of the most exciting fields of research is the role of polymer modified bitumen (PMBs) and other additives in boosting resilience. PMBs’ ability to help prevent cracking thanks to their greater elasticity is well known but there is still so much more potential to be explored in this area. To take just one example, we’ve been looking at how the use of a vegetable-based liquid additive can slow down the ageing process of the binder and improve long-term performance by lowering the mix temperature by up to 30 degrees.
The benefits of new mixes can be made even greater when combined with new single layering techniques. Leapfrogging traditional two-layer surfacing, single layers incorporating PMBs can be laid as thinly as 70mm and without the need for a bond coat application. Single layering has not only proven to have excellent load bearing capabilities but also cuts the risk of multiple layers separating over time and therefore the chance of potholes forming.
Trial results suggest that some PMB variations can extend a road’s typical lifespan from seven to 15 or even 20 years. That’s a huge jump. And, of course, this has the potential to bring down the embodied carbon of the specifications over time as we carry on experimenting with higher levels of recycled asphalt. We are now routinely testing mixes containing up to 70% recycled material.
While tackling cost and carbon here and now is important, we mustn’t lose sight of future pressures. More frequent 40-degree days and higher levels of rainfall are all adding stress to our roads. Vehicle traffic is changing too. The Department for Transport predicts a 22% climb in all traffic on roads in England and Wales between 2025 and 2060, and as government encourages society to shift to low or zero emission alternatives, these vehicles are getting heavier. A 2022 report by the University of Edinburgh calculated that electric vehicles could cause between 20-40% additional road wear.
Again, lab work has a vital role to play in how we model these new scenarios, ensuring that any innovation can stand up to real-world use. Applied heat and air are able to mimic the short-term and long-term ageing of bitumen caused by the weather, while machinery can be used to replicate the impact of heavier tyre revolutions.
This kind of analysis shows that PMBs must be part of our future highways specifications, at least in the near term. While traditional bitumen has a softening point of 50°celsius, additive-enhanced PMBs can withstand the mercury climbing to more than 90°celsius. And since PMBs are also less prone to cracking, rainfall is less likely to infiltrate and so create potholes.
Traditional bitumen is made from crude oil in a notoriously energy-intensive process producing significant carbon emissions in addition to those associated with extracting fossil fuel in the first place. To mitigate this carbon impact, researchers have been looking at bio-based binders to replace bitumen.
Experiments with new materials to replace varying percentages of bitumen content have produced encouraging results. What’s more, bio-modified binders have proved more suitable for low-temperature applications while supporting equal rut resistance as traditional bitumen.
The significant positive environmental impact of blending these bio-materials into asphalt is clear. The key will be to see how far we can increase the ratio of these bio-based mixes without compromising performance. Once again, the answer lies in our lab work, in our appetite for experimentation and in our willingness to push the envelope on new products and techniques to achieve truly sustainable innovation.
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