The effect of temperature and pressure on laboratory oxidized asphalt films with comparison to field aging
Abstract
Two aging models, the asphalt-aging model and the highway-pavement aging model, are developed to describe oxidative aging in asphalt. The first model is based on first principles accounting for carbonyl formation and unsteady-state variable diffusivity oxygen diffusion and reaction. The second model relates measurable properties of pavements to fundamental quantities in the asphalt-aging model. The long-term constant rate of carbonyl formation at isobaric and isothermal conditions is a function of both temperature and oxygen pressure. An Arrhenius equation models the temperature dependence, and these model parameters are functions of asphalt composition. Activation energies range from 66.7 to 80.5 kJ/gmol. The order of reaction with respect to oxygen pressure is 0.27 and independent of asphalt composition. Laboratory experiments at a single elevated oxygen pressure can be reliably extrapolated: however, multiple laboratory experiments at different elevated temperatures are required to estimate rate of carbonyl formation at highway conditions. Because of an initial non-linearity, the integration constant in the carbonyl formation equation can not be determined from neat material. The integration constant is a function of oxygen pressure: the model parameters are dependent on asphalt composition. Therefore, a single laboratory experiment at the highway pressure is required to determine the integration constant. Oxygen diffusivity in asphalt is estimated from laboratory data together with the asphalt-aging model. Oxygen diffusivity is a function of asphalt viscosity; the model parameters are independent of asphalt composition and temperature. Oxygen diffusivity in asphalt is approximately 1 x 10^-12 m^2/s for viscosity of 10,000 poise. Physicochemical models relating viscosity, carbonyl content, temperature, and molecule weight for oxidative aging in asphalts are developed. The model parameters in these equations are functions of initial asphalt composition. Field- and laboratory-aged asphalt are compared with physicochemical properties and the asphalt-aging model. Laboratory aging at relatively low temperature and high pressure simulates field aging based on the agreement between physicochemical properties. Comparisons between field data and values calculated from the asphalt-aging model are the foundation for the highway-pavement aging model. Hypothesized models relating oxygen pressure and film thickness in the asphalt-aging model to percent air voids, asphalt content, and time are developed.
Description
Vita.Collections
Citation
Lunsford, Kevin Michael (1994). The effect of temperature and pressure on laboratory oxidized asphalt films with comparison to field aging. Texas A&M University. Texas A&M University. Libraries. Available electronically from https : / /hdl .handle .net /1969 .1 /DISSERTATIONS -1551880.