Glass Transition and Phase Stability in Asphalt Binders

Major aspects of the glass transition of asphalt binders are described and an extensive literature review of the phenomenon and its relation to chemical composition is presented. The glass transition of asphalt binders was studied by modulated differential scanning calorimetry and also via dynamic mechanical analysis. A certain analogy between the glass transition of amorphous polymers and asphalts is suggested. The overall transition was found to be very broad on the temperature scale. The effects of evaporation of light-end components and oxidation on asphalt phase stability and glass transition were studied. It was suggested that phase incompatibility may exist in asphalts; however, the phase separation is observable after long-term isothermal conditioning at a temperature within the glass transition range. Based on the presented results, it is suggested that phase incompatibility develops if there is a discontinuity in the molecular distribution. Such discontinuity may be present in some neat binders as well as in severely oxidized or aged asphalt binders.