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This paper deals with the aging characteristics of SBS polymer modified binders in porous asphalt pavements. Field cores were taken from test roads of different ages and structurally analyzed using X-ray tomography. Binders were extracted from the upper and under layers of the field-aged cores and characterized using gel permeation chromatography, Fourier transform infrared spectroscopy, dynamic shear rheometer, as well as conventional penetration test. The chemical and mechanical characterization was also carried out on the binders recovered from loose mixes, and on the binders aged in laboratory by RTFOT and PAV.
The study indicated that the structure of porous asphalts can be visualized using X-ray tomography. The distributions of air voids, mortars and stone materials were displayed over the pavement depth; however, for an accurate quantification of the mix components, the boundary conditions must be validated. It was found that at the earlier time of service (< 2 years), the polymer modified binders aged quite uniformly over the pavement depth. With increasing years of service, the modified binders in the upper layer were more aged than those in the under layer even though both layers consist of high air void contents. Degradation of the polymer was found to occur mainly during asphalt production and during earlier stage of pavement service. The polymer degradation may compensate for the oxidative hardening of bitumen components, thus mitigating overall age-hardening of the binders. Rheological evaluation showed that, after four years in the porous asphalt pavement, the modified binders continue to perform well. The study also implied that a proper selection of base bitumen is of importance in achieving long-term durability of a modified binder in porous asphalt. As regards laboratory aging tests, field aging prediction by PAV was found to vary substantially, depending on air void content in the asphalt and asphalt position (layer) in the pavement.
X. Lu, B. Sandman, P. Redelius
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