What is fibre reinforced asphalt and how does it work?

Fibre reinforced asphalt is asphalt to which small, strong fibres — usually aramid or PAN — have been added during production to slow down cracking, ravelling and rutting. It is an alternative to polymer modified bitumen (PMB) and reinforcement mesh, with comparable or better real-world performance at generally lower environmental impact. This article is the starting point of our series on fibre reinforced asphalt.

Why does asphalt need reinforcement?

Asphalt consists of a mixture of crushed stone, sand, filler and bitumen as a binder. Under the influence of traffic loading, temperature fluctuations and ageing of the binder, cracks, ravelling (loosening of stones) and rutting (indentation from tyre loads) eventually develop. Open mixtures such as porous asphalt (ZOAB) — with a high percentage of void space for noise reduction and water drainage — are particularly susceptible to this, because the stone skeleton has less mutual contact than in dense mixtures.

How does fibre reinforcement work in asphalt?

Fibres are added dry during the mixing process: first the fibres are mixed with the aggregate, then the bitumen is added. Once well distributed throughout the mixture, the fibres act as a three-dimensional reinforcement at the micro level:

• Crack bridging: where a microcrack forms, the fibre spans the crack surface and slows further growth.

• Load distribution: loading from passing traffic is distributed more evenly across the mixture rather than concentrated on a single weak point.

• Mortar stabilisation: in porous asphalt, the fibre holds the mortar bridge between the stones of the stone skeleton more firmly in place, which counteracts ravelling.

Which fibre types are used?

The two most important fibre types in asphalt are:

• Aramid fibre: a very strong, heat-resistant fibre, typically dosed at around 0.05% of the mixture.

• PAN fibre (polyacrylonitrile): also widely used, typically dosed at around 0.15% of the mixture, often combined with a small proportion of cellulose fibre against binder drainage.

Both fibre types are covered in more depth in the following articles in this series.

Why fibres instead of PMB?

Traditionally, asphalt is reinforced with polymer modified bitumen (PMB) or with reinforcement mesh. PMB, however, is harder to recycle and requires a higher production temperature; reinforcement mesh requires a separate, time-consuming operation. Fibre reinforcement combines the best of both worlds: a standard penetration bitumen suffices (with a correspondingly lower production temperature), and no separate reinforcement layer is needed.

Real-world results

Field research on the A73 near Roermond, carried out as part of the European FIBRA project, showed that fibre reinforced asphalt performs comparably to PMB mixtures in terms of skid resistance, water drainage, noise reduction and visual condition after traffic loading — at a production temperature 15 to 20°C lower and with a lower environmental impact.

Where is it applied?

Fibre reinforced asphalt is applied, among other places, in asphalt on national and provincial roads, on N-roads, in heavily loaded construction roads, roundabouts and on business premises in the distribution and transport sector.

In conclusion

Fibre reinforced asphalt is a proven technology for extending the service life of asphalt, with demonstrable benefits in terms of production temperature, recyclability and environmental impact. In the following articles in this series, we go deeper into the specific fibre types, applications and real-world data.