Cargill gives Highways an international briefing on the art and engineering of bio-based road rejuvenation.
In the province of Friesland in northern Netherlands sustainability is a way of life, including when it comes to infrastructure. A flagship project for this region is the widening of the provincial road N381 between Donkerbroek and Oosterwolde.
In 2015, the route was expanded from 1×1 lanes to 2×1 by construction company Heijmans. Then in 2018 Heijmans won a contract to widen the road again to 2x2 lanes over a length of 8km. A key reason for the company being chosen for the work was its sustainable approach and circular, high RAP (reclaimed asphalt pavement) ZOAB (porous asphalt) mixtures.
These mixtures are made possible by incorporating a rejuvenator and by 2023 Heijmans wants to be able to process 100% circular asphalt on all projects.
The N381 paving project is a cutting edge example of circular road construction. In line with the sustainability objectives of the province, circular implementation is the guiding principle.
In the field of circular porous pavements, Heijmans is building a showpiece in Friesland: two-layer ZOAB with 60% recycled asphalt in the bottom layer and a top layer with 40% upcycled RAP. The top layer of the road was replaced to a depth of 3-4 cm.
The old two-layer porous pavement on the N381 was reused in the circular mixtures developed by Heijmans and validated by Rijkswaterstaat (Directorate-General for Public Works and Water Management) for the new top layer.
‘It’s very stimulating, given our own sustainable ambitions at Heijmans,’ says Gerbert van Bochove, innovation manager at Heijmans. ‘We are happy when our clients recognise that we have the people, the knowledge and the technology to realise their plans together.’
‘[But] Recycling old porous asphalt is not as easy as it seems,’ Mr van Bochove adds.
‘The bitumen of porous pavement milling material is more oxidised and aged than SMA (stone mastic asphalt) milling material, which has lost its necessary flexibility properties in the asphalt. As a result, it is simply not directly suitable for the production of asphalt that meets the required technical specifications and the desired lifespan.’
It becomes crucial to use an asphalt rejuvenator and Heijmans used Cargill’s bio-based Anova to bring the chemical composition of the aged bitumen back into balance.
For the N381 scheme, the Anova 1817 rejuvenator was added in liquid form at Heijmans’ asphalt mill in Amsterdam. The exact dosage is calculated based on the percentage of RAP and its pen-grade.
The asphalt mix was applied at around 160°C; though Anova 1817 rejuvenator can work with lower temperature production with excellent compaction properties.
‘We have gained a lot of experience with Anova, especially in bringing the bitumen to the desired specification,’ says Mr van Bochove. ‘We have already produced multiple high RAP mixtures in large volumes.
The composition varies from 30% to more than 60% of old asphalt that has been brought to specification. We are increasingly working with circular asphalt with high percentages of reuse.’
Jan Struik, business development manager at Cargill Bioindustrial, says: ‘Heijmans has developed a special technique to produce a high RAP mix with the necessary properties using rejuvenation.
‘Cargill’s Anova rejuvenator allows the increasing usage of RAP to nearly 100%. Our unique chemistries not only reverse the impact of ageing on pavement to help maintain and build better roads but provide a more sustainable, economically beneficial advantage that is easy to implement.
‘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 tonne of asphalt and the sustainability profile played an important role in the consideration.’
Mr Struik concludes: ‘Using high RAP containing asphalt mixes is very good for emissions reduction as well as for economic benefits for the road constructors.
‘It’s possible to go for 100% recycling in top layers without compromising on quality. We have US customers for which this is business as usual. Some governments across Europe still have reservations on higher RAP contents and, mostly, limits are in place for 10-20% RAP in top layers. The Netherlands are an exception in this. Rijkswaterstaat is pushing the Dutch road construction industry for circularity.’
Cargill is co-operating with authorities to be part of developmental trials in other countries too. One such scheme is in Belgium on the REjuveBIT-programme, where the Government together with the University of Antwerp tested 40% RAP in top layers.
Heijmans is a listed company that combines activities related to property development, construction and technical services and infrastructure
This is one of a series of articles in the March issue of Highways magazine on the theme of rejuvenation.
