When it is hot, asphalt can heat up considerably and deform depending on the load. If ruts occur, this can be dangerous. In Hessen, therefore, work is being done on innovative road surfaces.
Kassel/Offenbach (dpa/lhe) - Heat not only puts a strain on many people, but also on the streets. Concrete, for example, is trying to expand, explains Dirk Kronewald from the Hessen Mobil road and traffic management team. "This creates stresses in the concrete roadways. Old and/or previously damaged concrete can then break, the so-called blow-up." Asphalt softens with heat and deforms when heavy loads are repeatedly applied to it by trucks. "Then ruts form over time." Surface water can collect in these longitudinal depressions in the road surface, which can lead to aquaplaning.
In Hesse, therefore, work is being done on alternatives to conventional asphalt. In Offenbach, for example, there has been a test track since mid-2020 in which the patent-pending "Klimaphalt" road surface has been installed. "It consists of a road structure with a depth of 60 centimeters and a light surface that reflects the sunlight better than dark asphalt," explains press spokesman Fabian El Cheikh. The material, which the Offenbach civil engineering and road construction entrepreneur Lutz Weiler developed, is able to store water that evaporates under the sun's rays and can thus contribute to cooling the environment.
According to El Cheikh, regular buses also drive on the 150 square meter test area. So it's a field test under normal conditions in an inner-city area. There are good conditions for such a test on the test track on Oberen Grenzstrasse: "The asphalt can be exposed to sunlight almost all day long, there are no cables and pipes laid in the ground and there is regular stress from bus traffic."
The test is accompanied by the Baucontrol Institute for building material, soil and environmental testing in Bingen. For three years, among other things, findings are to be collected on how resilient the material is and whether there is a measurable cooling of the environment in summer. According to El Cheikh, whether the new road surface in Offenbach will continue to be used depends on these results. Ultimately, this is also a political decision, "since the costs for climate asphalt are higher than for normal road rehabilitation on the surface, also because of the necessary and complex road construction".
At the University of Kassel, research is currently being carried out as part of a doctorate on a geothermal system that can be used to cool asphalt in summer and at the same time prevent it from becoming icy in winter. For this purpose, pipes are installed in the top layer of asphalt through which cold water flows in summer and thus cools the street. "The thermal energy gained is stored in a heat exchange system and released again in winter," explains Konrad Mollenhauer, professor in the Department of Civil and Environmental Engineering and supervisor of the doctoral thesis.
The basic idea is not new, but it is being optimized in the Kassel research project. "For example, investigations are being carried out into what distance the lines should ideally be and which aggregate is most suitable," explains Mollenhauer. At best, the system can cool the asphalt by up to 20 degrees. The road surface is currently being tested on test areas in Cologne.
So far, the streets in Hesse's major cities have withstood the heat this summer. In Kassel and Darmstadt, for example, no significant heat damage has occurred so far, the municipalities said. According to the cities themselves, they regularly check the condition of their roads.
In Frankfurt, a material mixture that is used to fill potholes in winter only recently softened in a section of road, said the senior building director Michaela Kraft. However, the deformations did not pose a traffic hazard and would smooth out again over the coming weeks. "Apart from that, we are not aware of any heat damage to our road surfaces."
The asphalt mixtures used by the city have proven themselves and proven to be very resilient to high temperatures, Kraft said. "We have already installed brightened asphalt in various places." However, it is only used in exceptional cases, since installation is associated with significantly higher costs. "We don't yet have concrete experience as to what extent this differs from conventional asphalt in terms of its heat resistance."
So far, the heat has not affected the state roads and motorways in Hesse. In principle, ruts could also occur on heavily loaded federal or state roads, explains Dirk Kronewald from Hessenmobil. This is prevented by using stiffer asphalt. "Therefore, no problems are known in this area." According to Kronewald, all federal, state and district roads in Hesse are checked for their condition at least weekly.
No heat damage has currently occurred on the highways in Hesse, said Benedikt Dederichs, press spokesman for the federal Autobahn GmbH. So far, almost no corresponding damage has been recorded nationwide. Nevertheless, the following applies: "At high temperatures, you should drive with particular care."