Rational relationship between the fatigue curves of asphalt mixes obtained from tension/compression and 4-point bending tests

The fatigue properties of asphalt mixes are usually established according to a series of laboratory cyclic loading tests at fixed temperature (theta) and frequency (f). Unfortunately, the results are different when considering different types of tests. This paper proposes a rational method to link the 4-point bending (4PB) and tension/compression (TC) fatigue test results. First a theoretical analysis of the 4PB fatigue test is presented. This analysis allows to introduce a link between the fatigue curves (modulus or damage versus number of cycles) of this type of test with the results from uniform TC tests. The 4PB fatigue curve is superimposed with the TC fatigue curve if the reference strain amplitude is correctly chosen. This amplitude must not be the maximum strain at the boundary fibre of the beam (epsilon(0max)), as usually considered, but a lower proposed value (epsilon(0h0)). Then, the previous approach is extended to the fatigue failure Wohler's law, which is a line in the Log-Log plot of the number of cycles at failure versus the loading amplitude (stress or strain). An experimental campaign on a Canadian asphalt concrete (HMAC) validates the developped approach. It is an important output from this research as fatigue life from one type of test can be obtained from the other type of test in the case of strain (or displacement) control tests.