Pavement Distress Under Accelerated Trafficking

A test pad was closely monitored for a 6-month period, with 640,000 axle load repetitions applied to the test pavement. The load was applied by the Texas Mobile Load Simulator, a full-scale accelerated loading device. Pavement performance data, such as rutting and cracking, were collected at intervals of 0; 2,500; 5,000; 10,000; 20,000; 40,000; 80,000; 160,000; 320,000; and 640,000 axle repetitions. Falling weight deflectometer (FWD) tests were performed at these same data collection intervals to characterize the structural capacity of the pavement system. Although there is a trend indicating that locations with higher FWD deflection result in higher rutting, a unique relation to predict rutting accurately from the surface deflection alone was not found in the study. The back-calculated asphalt concrete pavement moduli were reduced by 50 percent of the original value at the end of 320,000 repetitions. However, the test was not terminated until 640,000 repetitions, when moduli were reduced to 40 percent of the original values. Both FWD deflection and percent of cracked area share the same trend; the left wheelpath had higher initial FWD deflections and later yielded a higher percentage of cracked area. Approximately 50 percent of the wheelpath area was cracked at the end of 80,000 repetitions, as measured by counting the number of cracked squares on a 100 mm by 100 mm grid. However, most of the cracks were hairline cracks. The percentage of cracked area is strongly related to the grid size used. A grid size of 100 mm by 100 mm has been recommended by other researchers and was adopted in this study. Eighty-five percent and 90 percent of the area in the wheelpaths was cracked at the end of 320,000 and 640,000 repetitions, respectively. These numbers are higher than those adopted by the Asphalt Institute, which defines failure as 45 percent cracking in the wheelpath.