Asphalt research in the Netherlands.

The paper gives a state of the art and the latest results of the asphalt research performed within the TWAO-research group as sponsored by the Dutch Roads and Hydraulic Department of Rijkswaterstaat. The final goal of the research program is to develop an easy-to-handle pavement design method based on a visco-elastic material model concerning both fatigue and rutting. This research program is closely related to the SHRP-NL program. The fatigue phenomena in asphalt concrete is described in terms of dissipated energy. One part of the research is devoted to calculating the dissipated energy in road structures during the passing of lorry axles. Another part of the research covers the determination of fatigue properties, including healing, for a number of different mixes and the optimization of the mix design for fatigue properties. The material model used is Burgers' model. Assuming that each individual loading pulse "damages" the elements in Burgers' model, it is shown that the fatigue behaviour is related to these elements. As from experimental studies it appears that the Burgers' models, elements are directly related to the mix composition, the change in fatigue properties due to a charge in mix composition can be predicted. The development fatigue model in terms of dissipated energy will be validated by the LINear TRACKing device "Lintrack" of the Delft University of Technology. In the Netherlands rutting of asphalt concrete is tested in, among other tests, the wheel tracking test. The first part of the research was devoted to qualifying the effect of the boundary conditions of the test which have a significant influence on the test results. In the second part four different calculation models were used to simulate the wheel tracking test and to compare the results among each other. One of the calculation models, a finite element program with a visco elastic material model is the most promising. This one is used to simulate rutting ina semi full scale test, the so called Hextrack, to hopefully validate the chosen approach.