With a joint project of the Swiss Federal Laboratories for Materials Testing and Research (Empa), the Federal Roads Office (Astra), the Federal Office for the Environment (Bafu), the cantons of Zurich and Graubünden and several industry partners, the researchers wanted to increase the proportion of recycled asphalt in roads.

Up to now, much more asphalt waste has been produced in Switzerland than can be reused, Empa said. Every year, 750,000 tonnes of asphalt from the Swiss road network end up in landfills.

Better mix

One obstacle to more asphalt recycling has been that the binder in asphalt ages and becomes stiff over time. This leads to a susceptibility to cracking. In addition, the material is sometimes very heterogeneous.

The Empa researchers have therefore developed calculation models that can be used to calculate the perfect mixture for a specific application. One model can be used to calculate the permissible variability depending on future use. Another model calculates the dosage of the rejuvenating agents to be added. These are oily substances that soften the old binder in the reclaimed asphalt and thus make it usable again.

Heavily trafficked and climatically difficult

On the Aathalstrasse in Uster, 30 per cent recycled asphalt was added to the surface course. Typically, recycled material is not used in the surface course of such a heavily trafficked road, according to Empa. Nevertheless, there were no cracks.

On the stretch over the Lukmanier Pass, the climatic conditions are considered difficult for the use of recycled asphalt. In the test, however, the material proved resistant to cracking despite temperature fluctuations. The two test sections will continue to be monitored over the next two years.