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Study of the effects of the ultraviolet irradiation on the rheological properties of modified asphalt binders


The aging of asphalt binders is a natural phenomenon that starts during the construction of the HMA layers and runs slowly during the whole pavement lifespan of the . Hardening is the main consequence of aging and it is expressed in terms of modulus increase. A harder HMA mixture resists more to rutting during the first months after construction, but it can be detrimental in terms of strain-controlled fatigue resistance in long term. The importance of asphalt aging on the mechanical properties of HMA mixes is such that current specifications around the world impose limits for some aging indices or aging parameters in order to minimize the excessive hardening of the asphalt binder. The Superpave specification, for instance, deals apparently well with this phenomenon: it prescribes the simulation of the short-term aging, that occurs during the construction of the asphaltic layer, through the rolling thin film oven test (RTFOT), and the long-term aging, that occurs slowly during the whole pavement lifespan, through the pressurized aging vessel (PAV). These accelerated-aging procedures, as others available in the literature, are driven by the principle of thermo-oxidative simulation, based on the application of temperature and pressure combined with exposition to gas (air or oxygen) during a period of time. The ultraviolet radiation (UV) has an expressive effect on the oxidation phenomenon of the asphalt binders but it is usually neglected by the specifications, including the Brazilian one. Taking the limited number of studies on the UV effect on the oxidative aging of asphalt binders into account, a wide investigation is proposed in order to quantify the effects of UV radiation on the rheological properties of asphalt binders. Due to the increasing use of modified asphalt binders, it is also necessary to evaluate how the ultraviolet radiation affects the rheological properties of this kind of material. Twelve PG 76-XX modified asphalt binders will be prepared using a PG 64-XX as the base asphalt binder and the following modifiers: Elvaloy, crumb rubber from scrap tires, SBS, EVA, polyethylene (PE), SBR and polyphosphoric acid (PPA). The pure asphalt binder, one formulation of the type asphalt+PPA, five of the type asphalt+modifier and six of the type asphalt+modifier+PPA will be previously submitted to short-term aging in the rolling thin film oven and then to different UV-radiation levels at different temperatures. The UV-treated residues will be submitted to oscillatory-shear tests in the dynamic-shear rheometer (DSR) and the results will be compared to the tests performed with the long-term aged samples (aged only in the PAV without UV application). (AU)

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