Short-term aging procedures, either the thin-film oven test or the rolling thin-film oven test (RTFOT), are used to approximate the aging that occurs by asphalt binders during the hot-mix process. For unmodified binders, both of these procedures do a reasonable job of duplicating this aging not only with respect to physical property changes in the binder but also with respect to oxidation, as measured by changes in the infrared absorption spectrum. For modified binders, however, significant difficulties exist, among them surface skin formation and poor flow in the bottles. A new apparatus specifically designed to age modified binders as well as unmodified binders has been developed. This apparatus consists of a temperature-controlled vessel, a tube for introducing either nitrogen or air, a dispersing impeller for mixing the air and binder, and a condenser for collecting volatiles. Besides temperature, gas flow rate and mixing speed are controlled to desired values. The collection of volatiles allows a direct, rather than indirect, measure of volatiles loss. The required aging time of 30 min is less than the RTFOT's 85 min. Tests of the process with unmodified binders achieved excellent comparisons with RTFOT aging in both physical properties (dynamic shear rheometer) and oxidative aging (Fourier-transform infrared analysis). Trials with modified binders achieved uniform aging with no complications caused by the rheology of these materials. Modified binders studied included polymer-modified styrene butadiene diblock copolymer and styrene butadiene triblock copolymer materials.
Abstract