A73 case study: results of the FIBRA research
On the A73 near Roermond, BAM and Rijkswaterstaat built a FIBRA trial section with four mixtures. The set-up, results and conclusions.
One of the most extensive practical trials of fibre reinforced asphalt in the Netherlands took place on the A73 near Roermond, as part of the European FIBRA project. This article walks through the set-up, results and conclusions of this research.
Background of the project
FIBRA (Fostering the implementation of fibre reinforced asphalt mixtures by ensuring its safe, optimized and cost-efficient use) was a CEDR research project, carried out by a consortium of five research institutions and two industrial partners from six countries, including BAM and Rijkswaterstaat in the Netherlands. Goal: to close the technical knowledge gaps that made National Road Administrations (NRAs) reluctant to apply fibre reinforced asphalt more widely.
The test location
In the last week of August 2020, BAM and Rijkswaterstaat built a trial section on the A73, on the southbound carriageway directly after Tunnel Swalmen, near Roermond. The stretch has 2 traffic lanes and 1 hard shoulder, with around 50,000 vehicles per working day.
The four tested mixtures
The trial section consisted of four variants of the same surface course of a two-layer porous asphalt (2L-PA 8):
• Section 1 — Reference with PMB (Styrelf); 330 m; chainage 23,600-23,270.
• Section 2 — Reference with penetration bitumen + cellulose fibre; 350 m; chainage 23,270-22,920.
• Section 3 — PAN fibre (Panacea), 0.15%; 350 m; chainage 22,920-22,570.
• Section 4 — Aramid fibre (Twaron 1080), 0.05%; 320 m; chainage 22,570-22,250.
Key results
• Production temperature. The fibre reinforced mixtures were produced at around 159-165°C, compared with around 181°C for the PMB reference mixture — a difference of 15-20°C.
• Mechanical performance. All four mixtures amply met the Dutch requirements for water drainage (Becker test), longitudinal evenness and skid resistance. The PMB reference performed slightly better on indirect tensile strength in the laboratory, but this did not translate into a noticeable difference in practical performance on the road.
• Skid resistance. The fibre reinforced sections (PAN and aramid in particular) performed even slightly better than the PMB reference during the first three weeks after opening.
• Noise. CPX measurements after 12 weeks showed negligible differences between all four mixtures.
• Visual inspection. After three months of traffic loading, all four sections were in good condition, with no visible damage.
• Environmental impact. The life cycle assessment showed that the PMB mixture had the highest environmental impact at cradle-to-gate level (more than 10% difference in the Environmental Cost Indicator), while this difference narrowed to less than 4% over the full life cycle (cradle-to-grave).
Long-term monitoring
The test sections on the A73 are being monitored long-term by BAM in cooperation with Rijkswaterstaat, with video inspections planned for year 2 and year 5, in addition to Rijkswaterstaat's regular annual monitoring programme for visual inspection and skid resistance.
Conclusion of the research
The FIBRA research concluded that porous asphalt can be successfully reinforced with synthetic fibres (both polyacrylonitrile and aramid), with practical performance comparable to the common PMB mixture, at a lower production temperature and environmental impact — without requiring any adaptations to existing production or paving equipment.
In conclusion
The A73 case study is one of the most thoroughly documented practical trials of fibre reinforced asphalt in Europe, and forms strong substantiation for the use of aramid and PAN fibre in porous asphalt on heavily loaded trunk roads.