Heat-resistant asphalt: how fibres counter rutting caused by heat

With ever warmer summers, heat resistance of asphalt is getting more attention. At high temperatures asphalt becomes softer and more prone to rutting — the indentation that develops from repeated tyre loading. Fibre reinforcement tackles this problem via a different mechanism than the better-known light-coloured, reflective asphalt mixtures. This article explains the difference and how they relate.

Why does asphalt perform worse in heat?

Bitumen is a thermoplastic material: it becomes softer as the temperature rises. On hot summer days, the surface temperature of standard black asphalt can climb to 50-60°C. At these temperatures the binder loses some of its stiffness, so the mixture deforms more easily under repeated tyre loading — this results in rutting: gradual indentation in the spots where most tyres pass over.

Two different solution directions

There are two, complementary ways to tackle this problem:

• Lowering the temperature at the source. Light-coloured, reflective asphalt mixtures (such as those already developed by various Dutch municipalities) keep the road surface cooler by reflecting more sunlight — a difference of 10 to 15°C has been measured here. Less heat automatically means less rutting, simply because the binder becomes less soft.

• Making the mixture itself more resistant to heat. Fibre reinforcement intervenes at a different point here: instead of lowering the temperature, it improves the mixture's mechanical resistance against deformation, even at higher temperatures. Fibres distribute the load from passing traffic over a larger volume, which reduces the risk of local, permanent deformation — even when the binder has become softer due to heat.

How exactly does this mechanism work?

Fibres distributed through the mixture not only bridge crack faces, but also contribute to the overall stiffness and cohesion of the mixture under load. Where the binder softens in the heat, the fibres retain their mechanical strength — aramid and basalt fibre in particular are heat-resistant well above typical asphalt temperatures. This partly compensates for the loss of stiffness of the softened binder.

How well the two solutions combine

Temperature-lowering measures (light colour, reflective additives) and fibre reinforcement don't exclude each other — in fact, they reinforce each other. A light-coloured mixture that is also fibre reinforced benefits both from a lower surface temperature and from better mechanical resistance to the remaining heat effects.

Where is this most relevant?

• Residential streets and inner-city roads, where heat stress is becoming an increasingly important theme within climate adaptation policy.

• Heavily loaded motorway lanes, where rutting from a combination of heat and intensive heavy traffic occurs fastest.

• Commercial sites with a lot of stationary or slow-moving traffic (for example at loading and unloading bays), where concentrated, prolonged loading at high temperatures gives an increased risk of rutting.

In conclusion

Heat-resistant asphalt is not a single technology, but a combination of measures: temperature-lowering mixtures tackle the problem at the source, while fibre reinforcement makes the mixture itself more resistant to the remaining heat effects. For road authorities that are serious about climate adaptation, combining the two is a logical next step.