Determination of relative damage of Asphalt pavement from reduced tire contact area

Considering the traditional contact area which is a full circular contact area without any tread, in the current pavement design procedure, is an extreme overestimation of contact area and hence extreme underestimation of the real contact stress. Since the relationship between the contact stress and pavement damage is not linear but exponential, even a trivial difference between tire contact areas leads to significant difference in terms of induced pavement damage. This study was conducted to quantify the relative damage caused by realistic tire-pavement contact area with respect to the full contact area and incorporated three objectives: To design a wheel tracking and instrumentation system, to establish a method for determination and analysis of effective tire contact areas, to quantify the relative damage of asphalt pavement due to various tire-pavement contact areas. In this study, a new equipment called Rotary Compactor and Wheel Tracker (RCWT) was designed and fabricated for capturing the effective tire contact areas, resembling the compaction effort of Stone Mastic Asphalt (SMA) site rollers, and conducting simulative wheel tracking test. In order to capture the effective contact area, 155/70R12 tire was selected with the six most common treads in the market besides a completely worn-out tread resembling the full contact area without any tread. The footprints of these treads were captured at five tire load groups of 1.50 kN, 2.0, 2.5, 3.0, and 3.5 kN and four tire inflation pressures of 137.90 kPa, 172.37, 206.84 and 241.32 kPa. Using the developed tire imaging procedure, the obtained footprints were very clear and free of any image noises. The footprints were then scanned and uploaded in a MATLAB-based image processing program to calculate the effective contact areas. Comparison between effective and traditional contact areas indicated that the current pavement design procedure overestimates the actual tire-pavement contact area up to 92 percent. Among the tested treads, Dunlop Ec201, Dunlop SP Sport J3, and Sime Astar 100 induced minimum, intermediate and maximum contact areas besides the full contact area which was caused by the worn-out tread. Therefore, these treads were selected for further wheel tracking performance study at three different load groups (three normal loading of a Kancil car) of 1.43 kN, 1.91 kN, and 2.13 kN by preparing 12 slabs. Permanent deformation and permanent strain profiles of different contact areas in each tire load group were obtained and the relative damage analyses were done between tires with and without tread from various aspects. These aspects include operational life reduction ratio, rutting rate, linear and nonlinear relative damage concepts. Based on nonlinear relative damage analyses, real tire with tread induced about three times more rutting compared to the worn-out control tread. In addition, the induced permanent vertical strain by the real tire with tread was two times higher compared to the worn-out control tread. Finally, the current pavement design, by using the full circular contact area, underestimates the amount of rutting significantly, and it is recommended to incorporate the realistic tire-pavement contact area in the design procedure to obtain an optimum design.

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