Comparison of Uniaxial and Four-Point Bending Fatigue Tests for Asphalt Mixtures

Abstract

The fatigue properties of asphalt mixtures estimated with fatigue tests in the laboratory are difficult to compare with each other. One reason is that for so-called inhomogeneous tests that do not have a uniform stress–strain distribution, the measured stiffness is a weighted overall stiffness that does not really represent the stiffness of the damaged zone. For homogenous fatigue tests, the stress–strain field within the specimen is uniform in theory. In this case, the measured stiffness corresponds to a material property. It is supposed that the stiffness evolutions in the inhomogeneous tests might be described by the results from the homogenous test. In this paper, the results of the uniaxial tension and compression (UT–C) fatigue test and the four-point bending (FPB) fatigue test are described and compared. The evolutions of the stiffness and phase angle are simulated by means of the partial healing model. With the model parameters, the local stiffness for each volume unit of the beam is calculated. It is found that, on the basis of the measured overall stiffness, the classical fatigue life Nf,50 of the beam in the FPB fatigue test is larger than that of the cylinder in the UT–C fatigue test. However, in the midsection of the beam, the local stiffness evolution is similar to that observed in the UT–C fatigue test. On the basis of the local stiffness concept, comparable fatigue lines can be obtained from the UT–C and FPB fatigue tests.