James C. Holste

MOISTURE DAMAGE EVALUATION OF ASPHALT MIXTURES BY CONSIDERING BOTH MOISTURE DIFFUSION AND REPEATED-LOAD CONDITIONS

Two moisture damage models based on major moisture failure mechanisms are proposed. The adhesion failure model was developed to analyze the adhesive fracture between asphalt and aggregate in the presence of water. Cohesive and adhesive fractures in an asphalt-aggregate system are directly related to the surface energy characteristics of asphalt and aggregate. The surface energy of adhesion with or without the presence of water can be calculated from the surface energies of asphalt and aggregate. A moisture diffusion model was developed based on the one-dimensional consolidation of soil and a gas adsorption model. The moisture diffusion model was used to obtain the moisture diffusion characteristics of asphalt binders, including the amount of moisture that can permeate a binder and the diffusivity of the binder. The amount of moisture that permeates a binder is identified as a key factor in the moisture damage. Finally, mechanics-based experiments conducted on asphalt mixtures validated the results from the adhesion failure and diffusion models.

SURFACE ENERGY MEASUREMENT OF ASPHALT AND ITS APPLICATION TO PREDICTING FATIGUE AND HEALING IN ASPHALT MIXTURES

Cohesive and adhesive bonding within the asphalt—aggregate system are directly related to the surface energy of the asphalt. The thermodynamic changes in the surface energy of adhesion and cohesion are related to the de-bonding of the interface between asphalt and aggregate and to cracks that may occur within the mastic, respectively. However, it is also true that thermodynamic changes in the surface energy are required to heal a fracture between the surfaces of the asphalt and the aggregate or within the mastic. The methodology and testing protocol for measuring the surface energy of asphalt are presented. Both the surface energy of dewetting (fracture) and the surface energy of wetting (healing) can be obtained from the contact angle measurement with the Wilhelmy plate method. Ten asphalts were tested; surface energies varied substantially as a function of asphalt composition and the level of aging to which the asphalt was subjected. By using thermodynamic theory, the adhesion and cohesion bonding energy within the asphaltaggregate systems were further analyzed. This analysis has the potential to select the most compatible asphalt—aggregate combination for mixtures. The surface energy is also a very important parameter in the fatigue and healing analysis of the asphalt pavement.

Experimental (p, Vm, T) for pure CO2 between 220 and 450 K

Abstract Densities of pure carbon dioxide were measured using Burnett, Burnett-isochoric, and isochoric techniques. The measurements were made at temperatures from 217.01 to 448.15 K and pressures up to 47.7 MPa. Eleven vapor-pressure measurements were also made. Second and third virial coefficients were derived. Three saturated-liquid and five saturated-vapor densities were also derived from the measurements.

A SIMPLE RELATION TO PREDICT OR TO CORRELATE THE EXCESS FUNCTIONS OF MULTICOMPONENT MIXTURES

Hwang, C.-A., Holste, J.C., Hall, K.R. and Mansoori, G.A., 1991. A simple relation to predict or to correlate the excess functions of multicomponent mixtures. Fluid Phme Equilibria, 62: 173-189. Semi-theoretical relations for the excess functions (e.g. excess Gibbs energies GE, excess chemical potentials) developed previously for binary mixtures have been extended to multicomponent mixtures. We postulate that contributions from two-body and three-body interactions are significant, and we propose an expression relating unlike three-body interactions to binary interactions. We have tested the relation with ternary vapor-liquid equilibria (VLE) having various chemical interactions and have found good agreement between the experimental excess functions and the predictions from the relation based solely upon binary data. Predicting fluid phase equilibria of multicomponent mixtures using existing binary data is relatively simple and, for the systems tested, appears to be considerably better than the NRTL model for VLE systems having partially or wholly negative GE. For the systems tested having wholly positive GE, the new model (H’M) is superior to the NRTL model except for ethanol-water. While the model is less satisfactory for liquid-liquid equilibria (LLE) than for VLE, it is significantly better than the NRTL or UNIQUAC model for the (randomly selected) system tested. The current model is also extremely flexible for either correlating or predicting multicomponent data, and it always converges to a solution.

Experimental cross virial coefficients for binary mixtures of carbon dioxide with nitrogen, methane and ethane at 300 and 320 K

Densities of five mixtures of carbon dioxide + nitrogen (xCO2=0.10560, 0.25147, 0.50365, 0.71105, 0.90921), pure nitrogen, four mixtures of carbon dioxide + methane (xco2=0.09990, 0.29858, 0.67607, 0.90112), pure methane, and five mixtures of carbon dioxide + ethane (xCO2=0.10043, 0.25166, 0.49245, 0.73978, 0.90367) were measured at 300 and 320 K using the Burnett technique. Second and third virial coefficients and densities were derived for each mixture from the measurements. Cross second and third virial coefficients were determined for each system.

Volumetric behavior of near-equimolar mixtures for CO2+CH4 and CO2+N2

Abstract Burnett-isochoric measurements are reported for gravimetrically prepared, nominally equimolar binary mixtures of CO2 with CH4 and with N2 at temperatures from 205 to 320 K and pressures from 0.1 to 48 MPa. Densities, real gas (compressibility) factors, second and third virial coefficients, and phase boundary conditions derived from the measured pressures and temperatures are presented. The phase boundary results indicate that vapor—liquid critical points do not exist and that gas—gas phase equilibrium occurs for certain compositions of CO2 +N2 mixtures.

Thermophysical properties of gaseous carbon dioxide- water mixtures

Abstract A Burnett-Isochoric (B-I) apparatus was used to obtain precise, experimental, vapor-phase P-ϱ-T data for mixtures of 2%, 5%, 10%, 25%, and 50% water in carbon dioxide for temperatures from 323.15 K to 498.15 K at 25 K intervals, and pressures from 27 kPa to 10.34 MPa or the dew point at each temperature. Separate experimental measurements for pure water, along with corrected compressibility data from the literature, were used to characterize physical adsorption within the B-I apparatus using the Brunauer-Emmett-Teller (B-E-T) adsorption model coupled with the sequential Burnett equations. The resulting adsorption constants were used to correct the compressibility data for the present mixtures and precise values were obtained for the second virial coefficients, enthalpies, and other derived thermodynamic properties. Interaction second virial coefficients, B12, and interaction third virial coefficients, C112 and C122, were also determined from the mixture virial coefficients. The densities are considered accurate to 5/10,000, and the mixture second virial coefficients to ±3 cm 3/mol. In addition, dew points (±1 K and ±14 kPa) were also measured for the above mixtures by noting the change in slope of the isochores.

Isochoric (p, Vm, x, T) measurements on (methane + ethane) from 100 to 320 K at pressures to 35 MPa☆

Abstract Comprehensive isochoric (p, Vm, x, T) values have been obtained for {xCH4 + (1 − x)C2H6} with x = 0.35, 0.50, and 0.69 at amount-of-substance densities from 1 to 25 mol·dm−3. The measurements for each composition cover a temperature range from approximately 100 to 320 K at pressures up to 35 MPa. For each mixture the results have been fit to a 32-term modified Benedict-Webb-Rubin equation of state. Further development of the extended corresponding-states model has been accomplished using the results presented here. Comparisons with values from independent sources have been made where possible.

An algebraic method that includes Gibbs minimization for performing phase equilibrium calculations for any number of components or phases

The most widely used technique for performing phase equilibria calculations is the K-value method (equality of chemical potentials). This paper proposes a more efficient algorithm to achieve the results that includes Gibbs minimization when we know the number of phases. Using the orthogonal derivatives, the tangent plane equation and mass balances, it is possible to reduce the Gibbs minimization procedure to the task of finding the solution of a system of non-linear equations. Such an operation is easier and faster than finding tangents or areas, and appears to converge as fast as the K-value method. Examples illustrate application of the new technique to two and three phases in equilibrium for binary and ternary mixtures.

The density of gaseous ethane and of fluid methyl chloride, and the vapor pressure of methyl chloride

Abstract The amount-of-substance density ϱn of gaseous ethane was measured in a Burnett-isochoric apparatus from 323 to 473 K in 25 K increments. Thirteen isochores ranging from 15.94 to 1489.0 mol m−3 nominal ϱn provide pressures from 43.0 to 5390kPa. For methyl chloride values of ϱn were observed at the same temperatures covering the vapor, gas, and near-critical regions. Seventeen isochores ranging from 20.42 to 8653.1 mol m−3 nominal ϱn provide pressures from 55.4 to 14908 kPa. Dense-vapor values near saturation are corrected for adsorption by a new technique. Second and third virial coefficients as well as derived thermophysical properties are reported for both ethane and methyl chloride. Optimal Lennard-Jones and Stockmayer force constants are calculated for ethane and methyl chloride respectively. Two sets of vapor pressures for methyl chloride are reported for the temperature range 313 to 408 K (T68c = 416.27 K).