Avaliação do dano por fadiga de misturas asfálticas modificadas por adição de polímero a partir do modelo S-VECD.

Abstract

One of the main asphalt pavements mechanisms of degradation is the fatigue cracking. This defect is characterized by the initiation, expansion, and connection of microcracks, with a high degree of localization and non-linear characteristics (CHEN et al., 2021). The formation and propagation of cracks in the asphalt mixtures, in general, occurs due to the repeated loads applied by the vehicles, generating tensile stresses, also associated with aging and temperature. In more critical situations, this process leads to structural failure of the asphalt mixtures. In recent years, the use of direct tensile fatigue tests associated with the simplified viscoelastic continuous damage model (S-VECD) has been shown to be an effective tool for evaluating fatigue in asphalt materials. This model uses fundamental material properties to characterize the asphalt mix performance from an efficient and simplified laboratory test protocol. This study aims to evaluate the fatigue damage of asphalt mixtures modified by the addition of polymer from the results of the direct tensile fatigue test with the application of the S-VECD model. Three asphalt mixtures were produced with the same granulometry (maximum nominal size of 19mm and designed by the SUPERPAVE methodology), varying only the binder. Three asphalt binders were selected to compose this research: a) CAP 50/70 as base binder for comparison; b) AMP 55/75, a commercial product prepared with the addition of SBS and c) CAP 50/70 modified by the combination of EMA-GMA+HDPE+PPA. The binders were evaluated for physical and rheological properties (Performance Grade - PG and MSCR), and fatigue using the Linear Amplitude Sweep - LAS test, using the S-VECD model. The asphalt mixtures were evaluated for stiffness using the tensile strength (RT) and resilience modulus tests (MR), to permanent deformation from the uniaxial repeated load test (Flow Number), the LVE behavior was characterized based on the dynamic modulus test, and fatigue performance was evaluated from the uniaxial direct tensile test with application of the viscoelastic damage model S-VECD.The results of the LAS test indicated that the modified CAP 50/70 presented the best fatigue performance, being classified according to the FFL as excellent. The mixtures with modified binders presented the highest values of RT and MR, indicating greater rigidity in relation to the mixture with the base binder. Regarding permanent deformation, from the Flow Number parameter, mixtures with modified binders are classified for heavy traffic, which is consistent with the MSCR result in which the AMP 55/75 and modified CAP 50/70 binders are indicated for heavy traffic with based on the Jnr parameter. As for the LVE behavior, the mixture with modified CAP 50/70 showed the expected behavior, with higher dynamic modulus values at high temperatures (low frequencies), and the lowest modulus values at lower temperatures (high reduced frequencies). Furthermore, for the entire spectrum of frequencies and temperatures, the mixtures with modified CAP 50/70 presented the lowest phase angle values, indicating a more elastic and less viscous behavior. From the direct traction test, based on the failure criterion Gr , the asphalt mixture with modified CAP 50/70 showed better fatigue performance, with a higher FFM value and following the same trend as the FFL. Based on the ܦ Dr failure criterion, from the damage capacity ܵSapp the mixtures with modified CAP 50/70 and AMP 55/75 were classified as having the best fatigue performance. Therefore, the use of binders modified by addition of polymers promoted asphalt mixtures with better fatigue damage performance.