Ask most people what wears out a road and you will hear about trucks, potholes, and rain. Heavy loads and water are the usual suspects.

But there is a slower culprit that gets almost no airtime: the sun. Ultraviolet light breaks down the sticky bitumen that holds a road surface together, and for years that kind of damage went largely ignored. Engineers knew heat, moisture, and traffic mattered. What sunlight was doing, and how to guard against it, was a question few had bothered to answer.

A group at RMIT University in Melbourne decided to look and their answer involves something you would normally think of as trash: the rubber from worn-out car tires.

The assumption worth correcting

Recycled tire rubber has a reputation problem. For a long time it has been treated mainly as a disposal headache, something to get rid of rather than a material that earns its place. Grinding scrap tires into “crumb rubber” and mixing it into road binder has usually been sold as a tidy way to make waste disappear. Useful, but the story stopped at “at least it’s not in a landfill.”

The RMIT work pushes back on that. The suggestion here is that crumb rubber is not just filler you tolerate for environmental credit. It may be doing real protective work in the binder. That turns it from waste management into a performance ingredient, which is a very different pitch to a road authority deciding what to lay down.

A quick note on what we are and are not: we are not materials engineers or road scientists, and nothing here is technical advice. This is our reading of one published study, a controlled lab experiment rather than the last word on how any real road will behave.

What the RMIT team actually did

In 2022, the RMIT group, working with the industry body Tyre Stewardship Australia, published their results in the Journal of Cleaner Production. They took plain bitumen, and bitumen mixed with crumb rubber from old tires, then aged both under a UV weathering machine. The exposure ran for about a month and a half, set to match roughly one year of Melbourne sun.

The team pointed out that sun damage had been a genuine gap. As lead author Filippo Giustozzi put it, “We knew that UV would be a factor in road degradation, but not by what degree or how to protect against it, as nobody has really been looking at this aspect.” That “nobody” probably overstates it a little, but the broader point holds.

They tested rubber at three concentrations, from 7.5% up to 22.5% by weight. The range mattered because more is not automatically better. A binder also has to survive trucks, not just sunshine. Giustozzi’s line on that tradeoff, in an interview, is blunt: “You don’t want something that is UV resistant but not truck resistant.” The study found a sweet spot in the middle, reporting that adding between 18% and 22% gave the best balance of resistance to rutting, cracking, and UV ageing.

The finding: a sunscreen effect

The high-rubber blend showed roughly 50% less UV damage than standard bitumen. Both plain and rubberised binder stiffen as they age, and that stiffening is what eventually cracks a road. The rubber slowed it down.

The numbers are worth seeing. Engineers use a threshold to judge when a binder gets brittle enough that cracking becomes likely. After UV ageing, standard bitumen sat only 13.2 kPa from that danger point, while the crumb rubber blend sat almost 60 kPa away from it. More distance from the threshold means more life left in the surface before it starts to fail.

Giustozzi described it in plain terms, saying the research suggests “the ageing trend is actually slowed down when you add crumb rubber, which is recycled from scrap tyres, into the top layer of a road.” He went further, calling it a sunscreen for roads: “This acts so effectively as a sunscreen for roads that it actually makes the surface last twice as long as regular bitumen.” That last claim deserves some care.

The “twice as long” comes from a UV machine, and it speaks to sun damage specifically, not to a guaranteed doubling of a real road’s overall lifespan.

What it tells us, and what it doesn’t

This is a lab study, and a fairly narrow one. The samples aged in a machine, not on a road carrying real traffic through real seasons. The tests were run on a single base bitumen, so how the effect holds up across the many types used in different climates is an open question. A month and a half in a UV machine standing in for a Melbourne year is a reasonable proxy, but a proxy is not a decade of weather.

Our read is that this is a clue, not a verdict. The high-rubber blend roughly halved UV damage in this experiment. Whether that translates into roads that genuinely last much longer is exactly what field trials exist to settle.

Even hedged, the potential is easy to see. Australia produced around 450,000 tonnes of worn-out tyres in 2021, only about 70% of which were recycled, and since December 2020 exporting used tyres has been banned, leaving the country holding more of its own scrap. Meanwhile Australian states and territories spent $2.9 billion on road maintenance in 2019 to 2020. A material that absorbs scrap tires and helps a surface survive the sun longer would be nudging both problems at once.

Waste as a useful ingredient is a better story than waste as a disposal problem, and the lab data gives it some legs. The question that decides everything now is whether a real road, under real sun and real trucks, ages the way a sample in a machine did.