Road to the future? New ways with used plastics

Viewing used plastic not as waste but as a material can reduce the problem of littered oceans. One promising approach is its use in road construction.

So far, only a small proportion of used plastic has been recycled worldwide. One reason for this is that recycling is complex and expensive. At least if you want to have high-quality material again afterwards, for which there are as many areas of application as for virgin material. On the other hand, there is little demand for low-grade recyclate, which does not require the complicated separation of different polymers. It can be used to make park benches, snow shovels or simple containers, but the demand for such items is limited. But what would it be like to find a field of application in which huge quantities of plastic waste could be easily processed? Even those made from films, for example, whose different layers would not have to be separated from each other beforehand. Waste that would otherwise end up in landfills or incinerators? One such area in the future could be road construction. 

For some years now, research has been going on in various places around the world into ways of using old plastic to build new roads. In the Netherlands, the construction company VolkerWessels has been pursuing its "Plastic Road" project since 2015 with the goal of even building roads entirely from recycled plastic in the future.

More precisely, from industrially manufactured plastic modules that are plugged together like Lego building blocks. The recycled plastic raw material for the modules comes from municipal waste. VolkerWessel points to numerous advantages of the plastic road over conventional roadways.  For example, the surface does not have to be prepared in any complicated way; the road virtually "floats" on it and adapts to it. Since the modules are hollow on the inside, electrical lines and sewer pipes can be laid there and, if necessary, replaced or supplemented quite easily. Subsequent excavation work is therefore no longer necessary. The hollow interior also makes it possible to install sensors that can be connected to existing traffic management systems. And the whole thing is also very light. One square meter weighs only 40 kilograms.  The plastic road also scores in terms of costs, according to VolkerWessel. Savings are made on the one hand because huge quantities of sand, chippings and asphalt can be dispensed with, but above all because the construction time is significantly shorter.

The first field tests have already been carried out. Part of the footpath to an amusement park was built from the plastic modules. A bicycle path, the first parking spaces and a residential street are to be put into operation in the Netherlands before the end of the year. A road for car or truck traffic is not yet included. Whether the advantages described will actually materialize in the harsh reality of a busy road is therefore not yet clear.

Nevertheless, the path seems promising. Also because important construction materials such as sand are becoming scarcer as the world's population grows and urbanization accelerates. The consulting firm McKinsey writes in a recent study on the future of road construction that new materials such as plastic could help meet such challenges. The first trials in the Netherlands showed that roads with or made of plastic were up to 60 percent more robust than conventional ones. The authors of the McKinsey study also assume that this would lead to cost reductions.  With an annual investment volume of 100 billion euros by 2030 in European countries alone, savings of around 30 billion euros per year would be possible. A large part of this would come from increasing digitization, but new materials would also play their part in reducing costs. Above all, they help to reduce the speed factor as the biggest cost driver. All in all, McKinsey predicts nothing less than a revolution for road construction in the coming years. As a result, costs are expected to drop from the current level of around two million U.S. dollars to 1.6 million U.S. dollars per kilometer of road.  

In the scientific community, the possibilities of using plastic in road construction have also been studied for some time. German road construction expert Prof. Johannes Beckedahl, who worked for a long time at the University of Wuppertal, thinks it's basically good to think about "upcycling" plastic waste, but is skeptical about prefabricated solutions like those used by VolkerWessels. He doubts that a durable road construction is possible with modules. The modules would have to be laid on the base in such a way that the same storage conditions exist everywhere. Otherwise, each module or precast element would settle unevenly under use. With the consequence of possible fractures or step formations. Beckedahl, on the other hand, takes a more positive view of processing plastic waste into granules. "A correctly produced asphalt modified with plastic granulate or rubber granulate, for example from used tires, and its high-quality paving can be an advantageous and service life-extending alternative to conventional asphalts," says the expert. However, he said, the prerequisite is always that the formulation for a modified asphalt mixture is determined and tested in the laboratory so that the mixture is optimized for the intended use. The environmental compatibility of roads with modified asphalt could be problematic, Beckedahl finds. Abrasion on roads with plastic content, for example, could release microplastics.

Roads made of or with recycled plastic waste nevertheless have the potential in principle to make a significant contribution to sustainability. They can help to conserve resources in terms of materials and land on a large scale - and that all over the world, because there are roads everywhere and plastic waste is a resource everywhere. However, it is not yet possible to predict the extent to which this type of construction will become established and which type will then prove to be the best.