Old road markings are recycled in unique project

An environmental project led by the Swedish National Road and Transport Research Institute (VTI) is testing the manufacture and properties of recycled road markings. This trial is the first of its kind globally and thus far the results have been very promising. That said, the road from prototype to commercial product is long.

A row of small glass jars in Svevia’s Linköping laboratory provides a pedagogical view of the materials road markings consist of: resin, reflective glass beads, wax, sand and seven additional substances. The subject of the study is thermoplastic road markings, the most common form of road marking in Sweden, even if there are a couple of other types.

In the recently completed project, VTI and industry partner Svevia have added an additional ingredient: old, recycled road markings. As far as we know, this is the first such attempt.

“We knew each other and had previously discussed various collaborations on several occasions. Could we reuse pigment, improve the quality of fillers or something else? In the end, we settled on this project,” explain Hanna Fager, a senior researcher at VTI, and Martin Gunnarsson, works manager for emulsions and thermoplastics at Svevia.

The first issue facing the project was identifying suitable road markings that could be recycled. Several candidates were rejected, but a suitable stretch of road was found in Stockholm that would be subject to diversions during the construction of the Stockholm Bypass. Other questions included how to process the old road markings. Water blasting proved ineffective, but mechanical grinding was more successful.

The main task however was to clean the recycled road markings. In the end, the project team was confronted with an enormous pile of debris.

“We used a sieve to sift out gravel, asphalt and stones. This was all done manually and it took me and a colleague a full day,” Gunnarsson recalls.

“And when we received the material at VTI, we had to clean it one more time,” says Fager.

The cleaned material was then melted down, sieved through sheet metal with 3-mm holes and cast into large blocks, which were then broken up and mixed into new road marking compound. The mixture was produced in three different concentrations of 10, 20 and 30 per cent. Ane then, the crucial question was: Would it work?

The answer is yes, the initial evaluation is very positive. While the goal of the project was that a 10 per cent mix would meet requirements, tests reveal that a mix of up 20 per cent meets all functional parameters: retroreflectivity, luminance, friction and colour. Extended trials are now underway at the NordicCert test facility in Norway, conducted by VTI and consultancy company Ramboll. New measurements will be taken in September this year and next year.

“So far, it looks very promising. Certain attributes even appear to have improved since the markings were laid out,” says Gunnarsson, who visited the test facility a week before this interview was conducted.

The production of raw materials for road markings generally consumes large amounts of energy and other resources and recycling would create significant environmental and climate benefits. It may also prove profitable, as costs associated with waste management and raw materials will decrease. Eventually, it may also lead to increased incentives for sustainable procurement.

Meanwhile, there is much work left to do before recycled road markings become a reality, the promising results notwithstanding.

“There’s no denying that this has been the easy part. The next step will pose a challenge. That said, recycling and circularity are very much in favour at the moment. I both hope and believe that we will be able to find a way to proceed,” says Fager.

Remaining issues include how to go about collecting old road markings on a large scale and how to wash the material. Sifting by hand is off course out of the question. It is also vital to recruit a road operator to a future project, such as the Swedish Transport Administration or a municipality. Other issues that need to be addressed include certification – the process is underway but must be completed – and developing business models, policy instruments and regulations.

More stakeholders also need to be engaged in the project, such as materials manufacturers and waste management and logistics companies.

“For Svevia’s part, this is very much in line with our environmental work. Still, another project is clearly necessary,” says Gunnarsson.

The project Recycling of Thermoplastic Road Markings has been funded by Vinnova, the Swedish Energy Agency and Formas as part of the strategic innovation programme InfraSweden. In addition to VTI and Svevia, water-blasting company Stripe Hog Scandinavia has also participated in the project.

Text: Mikael Sönne

Translation: CBG