Estudo do "fator Healing" em misturas asfálticas modificadas por polímeros utilizando o modelo S-VECD

Abstract

The delamination of asphalt coatings, caused by fatigue cracking, involves the formation of microcracks with nonlinear properties. Originating from repeated vehicle loads and influenced by aging and temperature, this phenomenon can lead to structural failure of the coating. For the evaluation of asphalt materials, it is crucial to understand fatigue and the "healing" process, i.e., the self-regeneration process of the asphalt coating when not subjected to loadings. Recent research has been using direct tension fatigue testing applied to the simplified continuous viscoelastic damage model (S-VECD) to understand these phenomena. This study aimed to analyze fatigue damage in polymer-modified asphalt mixtures, based on direct tension fatigue test results using the S-VECD model, as well as the analysis of the "Healing" phenomenon in the fatigue life of the studied asphalt mixtures. Three types of asphalt mixtures were analyzed: one with conventional asphalt binder (CAP 50/70), one modified by styrene-butadiene-styrene (SBS) polymer, and one proposed modification with a composition of 97.35% CAP 50/70 + 1.8% Ethylene Methyl Acrylate and Glycidyl Methacrylate (EMA-GMA) + 0.3% Polyethylene terephthalate (PET) + 0.15% Polyphosphoric Acid (PPA116%). Tests were conducted to estimate the physical and rheological properties of asphalt binders, as well as the effects of fatigue through the Linear Amplitude Sweep (LAS) test, applying the S-VECD model. Mechanical properties were measured from tensile strength tests, resilience modulus, fatigue with indirect tension by diametrical compression, moisture-induced damage, and permanent deformation FN. The linear viscoelastic behavior (LVE) was characterized based on the dynamic modulus test, while fatigue performance was studied through uniaxial direct tension testing, using the S-VECD model, and the "Healing Factor" was studied by applying rest periods to the uniaxial direct tension test using the S-VECD model. LAS test results indicated that the proposed modified binder studied showed superior performance compared to the conventional one, in terms of fatigue, being classified as intermediate according to the binder fatigue factor (FFL). Mixtures with polymer-modified binders indicated a trend of mechanical performance improvement. In the direct tension test, based on the GR failure criterion, modified mixtures showed superior fatigue performance. Based on the DR failure criterion and Sapp damage capacity, the proposed polymer mixture was classified as having better fatigue performance. Therefore, the use of polymer-modified binders resulted in asphalt mixtures with superior performance regarding fatigue damage. The healing process, based on the regeneration rate (%Hs), indicated more effective regeneration in the SBS mixture, while mixtures with proposed modified binder and base binder showed similar responses. Regarding the fatigue life gain (Nf), all studied mixtures showed a doubling in fatigue life. Knowledge of the "healing" factor from analytical observations of mechanical test results can lead to more realistic fatigue curves with conditions inherent to what actually happens "in situ," being crucial for estimating the service life of asphalt coatings.