Wetting Characteristics of Asphalt Binders at Mixing Temperatures
Patricia Hennig Osmari, Zelalem Arega, and Amit Bhasin, October 2013
Conventional hot mix asphalt (HMA) is produced by heating the aggregate and the asphalt binder to elevated
temperatures that are typically in the range of 150C to 160C. These temperatures ensure that the viscosity of the asphalt binder is low enough to effectively coat the aggregate particles. During the past decade, warm mix asphalt (WMA) has been introduced to reduce the mixing temperatures by approximately 30C compared to HMA. Workability at these reduced temperatures is typically achieved by the use of chemical additives in the asphalt binder or by foaming the asphalt binder using small percentages of water. The use of WMA is associated with advantages such as reduced emissions during mixture production, extended paving season and reduced aging in the asphalt binder. In case of the WMA and the HMA, one of the important physical properties that dictates the quality of coating is the surface tension of the asphalt binder at mixing temperatures. In this study, the surface tension of different liquid asphalt binders was measured at typical mixing temperatures. The effect of binder type, temperature, and chemical additives used to produce WMA on the surface tension of the binder was evaluated. Three different binders with and without three different chemical additives were used in this study. The dynamic surface tension was measured using four different rates of surface formation and at several different temperatures within the range of 140C and 170C. Results show that the surface tension of asphalt binder depends on the rate of surface formation, temperature and source of the asphalt binder. Dynamic surface tension of asphalt binders suggests that asphalt binders behave similar to surfactants. The addition of chemical warm mix additives did not significantly reduce the surface tension of the binder compared to the control.
Keywords: Warm Mix Asphalt, Hot Mix Asphalt, Workability, Surface Tension, Asphalt Binder
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