Identification and prediction of durability and weathering properties of paving asphalts are problems faced by highway material engineers. Correlation between accelerated laboratory durability tests and asphalt field performance is established on four asphalts. Double beam multiple internal reflection spectra are obtained for both laboratory-aged and field samples up to 48 months. Rheological properties and chemical analyses are also made. The kinetic model for weathering is found to be Δ y = T/( a + bT) where Δ y is the property change, T is the weathering time, and a and b are constants. Weathering of asphalts is characterized by changes in absorption at wavelengths of 5.88 µm and is correlated with chemical changes and aging index defined by viscosity change.
The surface free energy of wetting of E-glass by water and benzene vapors was calculated from Bangham and Razouk's free-energy equation. The method of F'u and Bartell for determining specific surface area was used to analyze the microstructure. The surface free energies, which were computed from adsorption isotherms obtained at temperatures from 18" to 2Q"C, had values from -235 to -254 ergs/cm2 and -71.1 to -72.4 ergs/cm* for water and benzene adsorption, respectively, depending on temperature, surface geometry, and sample treatment. The lower affinity of E-glass for benzene, which resulted in a smaller work of adhesion, suggests that active adhesion of hydrocarbons is impossible in the presence of bulk water. Microstructural analysis indicated that the water-modified E-glass surface contains micropores 23 A in diameter.
The thermodynamics of a water-vapor-E-glass system were studied by adsorption-isotherm analysis. The seven isotherms completed were Brunauer type IV with permanent hysteresis.The first adsorbed water layer could not be removed by p u m p ing, indicating permanent hydrolysis. AppIication of heat removed the remaining water to close the hysteresis loop. Calculation of isosteric heat of adsorption indicates that the adsorbed state is between the solid and the liquid states, equivalent to the loss of one vibrational and one translational degree of freedom. A new plot of energy vs thickness is proposed which describes the adsorption independent of surface area, as contrasted to the usual energy-vs-volume plot which was found to depend on surface area. A modified ClausiusClapeyron equation is proposed for computing the isosteric heat of adsorption.
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