An Equation-of-State approach to measure the surface free energy (SFE) of bituminous binders

To overcome the liquid set dependency of existing surface free energy (SFE) component approaches, this paper presents an Equation-of-State (EQS) approach to measure the SFE of bituminous binders. A succession of water-ethanol mixtures with varying surface tensions are first prepared as the test liquids. The Wilhelmy plate method is then adopted to measure the surface tension γL of each liquid as well as the contact angle θ between bituminous binder and each test liquid. A quadratic polynomial function is subsequently employed to fit the plot of γLcosθ versus γL. Combining Young's equation and Good's interaction parameter and then imposing a limiting condition in which the contact angle between bituminous binder and test liquid is exactly 0°, the SFE of a bituminous binder can be finally determined. This approach is verified to have capability to accurately measure the SFE of bituminous binders with a solid thermodynamic basis.