EVALUATION OF A MODIFIED ROTAVAPOR AGING APPARATUS FOR SIMULATION OF HOT-MIXING ON CRUMB RUBBER-MODIFIED ASPHALTS

摘要

In the evaluation of an asphalt binder for use in a hot-mix asphalt, it is important that the properties of the asphalt binder after aging in the hot-mixing process be determined. At present, two standard methods are used to simulate the effects of hot-mixing on asphalt binders in the U.S. These two standard methods are (1) the Thin Film Oven Test (TFOT) [ASTM D1754], and (2) the Rolling Thin Film Oven Test (RTFOT) [ASTM D2872]. These standard procedures have been successfully used on conventional asphalts for many years. However, recent studies by the University of Florida and other researchers in the country have shown that problems were encountered when these procedures were used on some modified asphalts. It was found that asphalts modified with crumb rubber (CR) and SBR tended to spill out from the RTFOT bottles during the RTFOT process. When the TFOT was used, a thin skin tended to form on the surface of some modified asphalt samples, which reduced the homogeneity of the aging of the samples. There is a need to develop a suitable laboratory aging procedure to replace the TFOT and the RTFOT, so that the aging characteristics of modified asphalts could be properly determined. The rotavapor apparatus, which is commonly used for recovery of asphalts from solutions (ASTM D5404), was modified into an aging device as an alternative to the standard thin film oven and rolling thin film oven. The vacuum connection of the rotavapor apparatus was replaced by an air pump with a controlled air flow. The oil bath of the rotavapor apparatus was covered with an insulated box to reduce the temperature variation in the oil bath. To further improve the temperature uniformity in the oil bath, the standard distillation flask was also replaced with a Morton flask. The performance characteristics of the modified rotavapor aging apparatus and its applicability for use as an alternative for the RTFOT procedure in the Superpave binder specifications were evaluated. The results indicated that equivalent aging severity between the modified rotavapor aging process and the standard short-term aging methods (TFOT and RTFOT) could be established. The modified rotavapor aging process using a process temperature of 163℃, process duration of 210 minutes and a sample weight of 200 g produced aging effects similar to that of the RTFOT. Using a test configuration of 163℃, 160 minutes and 200 g sample produced aging severity similar to the TFOT.