Rainproof asphalts

The study of friction between surfaces using numerical simulation could give rise to 'super-draining' asphalts.

Michael Lebed/Rights-Managed

Driving on wet roads can be risky, we all know that. Although asphalts that drain water rather efficiently already exist, there is still no ideal solution for asphalt that minimizes the risks of driving in the rain, on the wet road or whith puddles. Nor is there an accurate description of the problem. In fact, there are many factors that interact in making the road more or less safe: in addition to the characteristics of the asphalt itself, the wear and tear on the vehicle's tyres, the friction created between the tyres and the asphalt road, the way in which rain or other liquids, e.g. oil, change the grip between the wheel and the ground, and so on.

Researchers from the MUSAM lab at the IMT School for Advanced Studies Lucca study how interactions between rough surfaces, such as those between tyres and asphalt, occur. In a study published in theInternational Journal of Solids and Structures with colleagues from the Department of Mechanical Engineering at Imperial College London, the scholars describe precisely the new computational method developed to simulate contact problems between rough and complex surfaces on the computer.

At the heart of the research is a tool called a profilometer, which is used to analyze surfaces and derive their geometry in terms of computer data. The asphalt geometry data was provided by the Faculty of Civil Engineering of the University of Rijeka (Croatia), a partner in the research project. "The surface is translated into a data structure corresponding to the coordinates of each point in space, which are then assigned by the programme to the virtual surface recreated on the computer," explains Jacopo Bonari, MUSAM researcher and one of the authors of the study. "The software then uses this virtual surface to simulate contact problems, such as friction." This method had already been introduced in recent years by MUSAM researchers, but without reaching the current level of detail. "The new study allows us to go from two to three dimensions, and therefore to simulate phenomena more realistically and with fewer approximations," Bonari continues. "In addition, it allows us to consider the presence of adhesion forces, a very important and non-negligible phenomenon when analyzing surfaces at a high level of detail."

The data acquired on the asphalt profile will also feed into the Wiki Surfacedatabase, an international collaborative project developed by the MUSAM unit that collects images of natural and artificial rough surfaces.

The model used in Lucca makes it possible to study on the computer what until now was studied experimentally in the laboratory at greater expense, using instruments such as the british pendulum , which is capable of measuring slip resistance. This 'pendulum' has a rubber tip, simulating a tyre's surface. By dropping and sliding it on a piece of pavement, for example, a piece of asphalt, one can measure how much the friction force generated brakes the pendulum's motion, and thus calculate the coefficient of friction between the two surfaces.

The simulation studies conducted in Lucca could also have an impact on the understanding of further phenomena, such as the degradation and damage of industrial elements. Future research will also allow these contact problems to be solved using alternative solutions that are simpler, but difficult to implement to date.

Marco Maria Grande

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