Characterization of Road Profiles Based on Fractal Properties and Contact Mechanics

A major challenge in tire, as well as in road engineering, is to understand the intricate mechanisms of friction. Pavement texture is a feature of the road surface that determines most tire-road interactions, and can be grouped into two classes of macro-texture and micro-texture. Since the effects of microtexture and macrotexture dominate the friction measurements at low and high slip speeds, they can help provide sufficient resistance to skidding, if maintained at high levels. It is proven that road surfaces are of fractal nature on given ranges of scale. The fractal properties are used to predict road surface characteristics. It is shown that while global fractal quantities fail to classify pavement profiles, a local fractal parameter and some other texture parameters can separate road profiles that have different friction characteristics. To collect data, a non-contact profilometer is used to measure the macro- and micro-texture of several different road surfaces. The friction number for each surface is also measured using the MDOT single axle friction trailer. The texture and fractal parameters of the measured profiles are estimated, and it is shown that all measured profiles indeed display strong fractal behavior. The correlation between texture and fractal parameters and friction is investigated, in order to find out which parameters can discriminate profiles which have different friction properties. For five road surfaces, 2D characterization is done using 1D profile measurements. The coefficient of friction is estimated using the contact theory developed by B.N.J. Persson. Good correlation is observed between the friction measurements and friction prediction results.