Study of the Fatigue of Asphalt Mixes Using the Circular Test Track of the Laboratoire Central des Ponts et Chaussees in Nantes , France

The conventional French fatigue test has yielded significantly different results for two asphalt materials with the same grade of pure asphalt. A research program was begun to study the influence of the asphalt nature on the fatigue behavior of asphalt materials. The program included full-scale experimentation on the circular test track of the Laboratoire Central des Ponts et Chaussees, laboratory tests, and mechanical analysis. Four asphalt mixes with pure asphalt were tested on the experimental pavement: two asphalt concretes with asphal~s 50/70 of A and B origin, a high-modulus asphalt mix (bitumen 10/ 20), and a classical asphalt road base (bitumen A). The asphalt materials were fatigue tested in the laboratory according to several procedures: two-point bending fatigue tests on trapezoidal samples, with controlled strain, with and without rest periods, and with controlled stress, without rest periods; and three-point bending fatigue tests on parallelepiped-like samples, with controlled stress, with and without rest periods. The ranking of the materials according to their laboratory fatigue behavior depends strongly on the test procedure. The mechanical analysis carried out on the basis of the laboratory test results and the behaviors observed on the test track indicate that the controlled stress fatigue tests lead to results closer to the test track behavior and that the shift factor to be applied to the high-modulus asphalt mix should be 1. All these results have to be confirmed by a repetition of this experiment still in progress.