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A comprehensive literature study on road durability has indicated that the aging susceptibility of bituminous binders in surface layer is a key parameter determining the life time of an asphalt pavement.
A comprehensive literature study on road durability has indicated that the aging susceptibility of bituminous binders in surface layer is a key parameter determining the life time of an asphalt pavement. To simulate bitumen aging in laboratory, several test methods are currently used, including RTFOT, PAV, and RCAT (Rotating Cylinder Aging Test). In this paper, the aging of bituminous binders (unmodified and SBS polymer modified) were studied using (i) RTFOT, followed by PAV at 100°C for 8 to 48h; (ii) RTFOT, followed by PAV at 75°C for 48 to 220h; and (iii) RCAT at 163°C for 4h, then continued at 90°C for 17 to 140h. For field core sampling, several roads of different ages were selected from the Swedish LTPP (Long Term Pavement Performance) database.
The study showed that RCAT at 163°C/4h, proposed as a short-term aging test, was similar to RTFOT. The long-term aging tests PAV (100°C, 20h), PAV (75°C, 120h) and RCAT (90°C, 140h) were also more or less equivalent when applied to unmodified bitumens. However, for polymer modified bitumen, these tests were significantly different with respect to the resulted aging kinetics. As regards aging in the field, it was found that after 10 – 30 years service on the road, the extracted bitumens displayed a relatively low degree of age-hardening, to which equivalent laboratory aging durations were much shorter than that being standardized or proposed. The low degree of field aging may be attributed to low air voids in the asphalt mixtures and/or prevention of bitumen oxidation by surface sealing or overlaying. Field aging also considerably differed from laboratory aging in terms of the formation of sulfoxides and carbonyl functionalities in bitumen.
Compared to the laboratory aging, much higher level of sulfoxides but lower level of carbonyls was found for the binders aged in the field. This suggests that oxidation mechanisms in the field may not be the same as in the laboratory aging tests.
Xiaohu Lu, Yohann Talon, Per Redelius
The 4th Eurasphalt & Eurobitume Congress, Copenhagen, 21-23 May 2008