Paved to last

When we think of climate change, we first tend to think of polar bears wandering helplessly on fast melting icebergs, cities buried under a thick curtain of smog, or wheat fields filled with withering crops. Behind these apocalyptic scenarios hide other more realistic and often insidious threats to our lifestyle that affect not only our natural environment, but our built environment as well. They can be found in infrastructure we rely on every day of our lives, but have grown so accustomed to that we take it completely for granted, such as road pavements. And that, despite the fact that “on any given day, more people walk on asphalt than brush their teeth,” as Professor André-Gilles Dumont, Professor at the Traffic Facilities Laboratory, likes to say.

Dumont’s group works mainly on a wide range of problems related to today’s primary means of mobility: motor vehicle transport. Over the past decades, the infrastructure comprising the road network has hardly changed, but the number of cars and trucks that use it has gone through the roof. Coming to terms with this increase in load requires not only more robust construction materials, but also better traffic management schemes. On top of that, these advances have to be sustainable, from an environmental, social, and economic perspective. “Through our work, we try to build a knowledge base to assist those in charge of coordinating the rehabilitation of traffic infrastructure.”

“We received a mandate from the Swiss Federal Roads Office to find out whether climate change would impact our roads, and if so, how best to prepare them in the face of these impending challenges,” says Dumont. Roads are designed to provide a safe surface to carry traffic, whatever the weather. They freeze and thaw during the winter, expand and contract, and harden and soften with changing temperatures. All the while, cars, trucks and busses mercilessly drive up and down them. These effects add up and can lead to the formation of cracks and rutting. Roads are designed to endure this treatment for about two decades, but if the environmental conditions that they are exposed to change, their longevity can take a hit.

For his PhD project, Patrick Rychen, a former student in Dumont’s lab, developed a framework to evaluate the impact of climate change on the Swiss road network, basing himself on predictions of future weather patterns from 18 global climate models. In Switzerland, he says, climate change is likely to have the strongest impact on roads in the warmest parts of the country – the Lake Geneva area and southern Switzerland. In the colder areas, especially at higher altitudes, some roads may actually benefit from climate change due to the reduction of freeze thaw cycles they will experience.

The road network is in a perpetual state of renewal. There are over 70’000 km of roads in Switzerland, and ensuring that they are in good condition is already a formidable feat of logistics and planning. “If all of a sudden we were to notice that increased rut formation made the average lifespan roads drop from 20 to 17 years, our budgets would explode!” says Dumont. Rychen’s research shows that, by anticipating the changes in temperature expected for the next decades, this situation can be avoided. While in the cooler regions adapting the composition of the pavement would suffice, the warmer regions need a more thorough upgrade. High performance asphalts may provide the most optimal solution.

Other research projects analyze innovative asphalt mixtures, which are composed of different type of additive – water, wax, or some more complex chemical or polymer cocktail, bestowing the final road pavement with properties that are fine-tuned to address the required specifications. They are but one of a series of developments that are making our roads more sustainable. Hot mix asphalts are being replaced by a newer warm mix variant that can be rolled out with much lower greenhouse gas emissions. And asphalt recycling is increasingly becoming the norm. The impact is significant, says Dumont. “If you consider the extent of the road network, and the amount of asphalt that is consumed every year, these innovations, which may appear incremental at first glance, can go a long way.”