Sustainability is a way of life in the province of Friesland in northern Netherlands, including in its infrastructure. An important showpiece project for this region was the doubling of the provincial road N381 between Donkerbroek and Oosterwolde.
The work was awarded to construction company Heijmans, on the basis of its sustainable approach and circular high recycled asphalt pavement (RAP) ZOAB (porous asphalt) mixtures, made possible by incorporating a rejuvenator.
The N381 paving project is the latest example in circular road construction. In line with the sustainability objectives of the province, circular implementation is the guiding principle.
“It’s very stimulating, given our own sustainable ambitions at Heijmans,” said Gerbert van Bochove, innovation manager at Heijmans Infra. “We are happy when our clients recognize that we have the people, the knowledge and the technology to realize their plans together.”
The old surfaces of the road construction of this part of the N381 are recycled and processed in a circular two-layer porous pavement. Maximum circularity requires the reuse of the old layers.
This new approach guarantees the maximum achievable circularity for this project. In the field of circular porous pavements, Heijmans is building the showpiece in Friesland: a two-layer ZOAB with 60 percent recycled asphalt in the bottom layer and a top layer with 40 percent upcycled RAP.
“Recycling old porous asphalt is not as easy as it seems,” Van Bochove said. “The bitumen of porous pavement milling material is more oxidized and aged than that of SMA milling material, which has lost its necessary flexibility properties in the asphalt.”
As a result, it may lack the qualifications for the production of asphalt that meets the required technical specifications of a project. In that case, it becomes crucial to use an asphalt rejuvenator. Heijmans used a bio-based Anova rejuvenator from Cargill Bioindustrial to bring the chemical composition of aged bitumen back into balance.
“Heijmans has developed a special technique to produce a high RAP mix with the necessary properties using rejuvenation,” said Jan Struik, business development manager at Cargill Bioindustrial. “Heijmans conducted a great deal of research into the effect and functionality of rejuvenation products and their suppliers. Anova turned out to be very suitable for this purpose and thus making circular road construction possible. Besides the technical functionality, reliability of the supplier, cost per ton of asphalt and the sustainability profile played an important role in the consideration.”