A STUDY ON FATIGUE CHARACTERIZATION OF BITUMINOUS MIXTURES USING THE FOUR-POINT BENDING TEST

This thesis focuses on the characterization of the fatigue resistance of bituminous mixtures following the European standards, by means of the four-point bending test. The effects of material type and test temperature on fatigue properties were investigated. The effects of material type were taken into account by considering two different bituminous mixtures, one mixture prepared for a base layer and the other mixture for a binder layer, compacted at a reference air void content. The effect of temperature was investigated by performing tests on the binder course material at two test temperatures, 10 °C and 20 °C. As indicated in the European standard, three strain levels (140 µm/m, 200 µm/m, 300 µm/m) and a minimum of six replicates at each strain level were considered. Five fatigue failure criteria were selected from the literature to analyse the fatigue resistance of the mixtures: 50 % reduction in the initial modulus taken at the 100th cycle (50%E0); 50 % reduction in the extrapolated modulus (from the phase of linear decrease) that is based on the modulus reduction (50 % E00); the Peak in the Phase angle; and the Energy Ratio Approach and Dissipated Energy Ratio approach. From the outcomes of the experimentation, it was found that both temperature and mixture composition strongly affected the fatigue behaviour, as demonstrated by the better performance showed by the binder course material at the higher temperature. Moreover, it should be pointed out that different failure criterion led to distinct fatigue lines. A statistical analysis was used to highlight how the fatigue behaviour is significantly affected by both air void content and initial stiffness variability.