EVALUATING ACCELERATED RUT TESTERS

To avoid costly pavement failure and to ensure that rehabilitation and maintenance efforts are maximized, state Departments of Transportation have adopted the use of accelerated rut testers and/or servohydraulic testing devices to help predict pavement performance. The Federal Highway Administration tested several devices at the Turner-Fairbank Highway Research Center in McLean, Virginia, to determine which device offers the most accurate prediction of pavement rutting resistance. Accelerated rut testing devices, such as the Georgia Loaded-Wheel Tester, French Pavement Rutting Tester, and Hamburg Wheel-Tracking Device, try to simulate the distresses caused by many years of exposure to traffic within a matter of hours by rolling a wheel across a sample of asphalt concrete under specific temperature and humidity conditions. These devices apply a fixed load at a fixed temperature and do not account for seasonal changes in traffic, temperature, or environment. Servohydraulic equipment, such as the Superpave Shear Tester, offers the option of changing temperature and load configuration; however, tests are still performed under fixed conditions. Comparison tests showed that no device was clearly better than the others. For the most part, all devices were able to separate good from bad mixtures when these had been made with the same aggregate and different binders. However, when mixtures with two different aggregate gradations were tested, no device was able to distinguish the mixtures that performed well from those that did not, even though accelerated loading facility testing showed significant differences in pavement performance.