Phase Angle Master Curves Research Articles

Impact of Water on Asphalt Aging

Atmospheric pressure aging experiments were conducted to determine whether the presence of moisture during aging at a pavement service temperature of 60°C had any significant influence on the aging kinetics of thin (100-micron) asphalt binders. The five binders studied were aged in both dry and humid atmospheres. Infrared spectra of the dry- and moist-aged binders were compared. Master curves (dry aged and moist aged) generated from dynamic shear rheometry tests were also compared. The results showed that moisture had no significant effect on the oxidation rate at atmospheric pressure. A first-order and zero-order aging kinetic model was applied to fit all the chemical results. The Arrhenius equation was employed to calculate the activation energy for carbonyl and sulfoxide formations on all of the asphalts. The observed activation energies indicated that asphalt AAD-1 was more sensitive to the aging temperatures than the other four tested asphalts on the rapid carbonyl formation. However, after the initial spurt, the reaction rate of asphalt AAD-1 became more stable than in the other four asphalts. Sulfoxide formation was also evaluated. Rheological property changes with aging correlated reasonably well with carbonyl and sulfoxide concentration changes of asphalt binders as a consequence of atmospheric pressure aging. The master curves of complex modulus and phase angle for dry-aged and moist-aged asphalt binders fall right on top of each other and indicate that aging in the presence of water (99% of relative humidity) at the ambient pressure at pavement service temperature does not influence the rheological properties of asphalt binders.

Anisotropic Viscoelastic Properties of Undamaged Asphalt Mixtures

A test protocol and a data analysis method are developed in this paper on the basis of linear viscoelastic theory to characterize the anisotropic viscoelastic properties of undamaged asphalt mixtures. The test protocol includes three nondestructive tests: (1) uniaxial com- pressive creep test, (2) indirect tensile creep test, and (3) the uniaxial tensile creep test. All three tests are conducted on asphalt mixture specimens at three temperatures (10, 20, and 30°C) to determine the tensile and compressive properties at each temperature and then to construct the master curve of each property. The determined properties include magnitude and phase angle of the compressive complex modulus in the vertical direction, magnitude and phase angle of the tensile complex modulus, and the magnitude and phase angle of the compressive complex modulus in the horizontal plane. The test results indicate that all tested asphalt mixtures have significantly different tensile properties from compressive properties. The peak value of the master curve of the tensile complex modulus phase angle is within a range from 65 to 85°, whereas the peak value of the compressive moduli phase angle in both directions ranges from 35 to 55°. In addition, the undamaged asphalt mixtures exhibit distinctively anisotropic properties in compression. The magnitude of the compressive modulus in the vertical direction is approximately 1.2 to ∼2 times of the magnitude of the compressive modulus in the horizontal plane. Dynamic modulus tests are performed to verify the results of the proposed test protocol. The test results from the proposed test protocol match well with those from the dynamic tests. DOI: 10.1061/(ASCE)TE.1943-5436.0000302. © 2012 American Society of Civil Engineers. CE Database subject headings: Asphalts; Mixtures; Anisotropy; Poisson ratio; Viscoelasticity; Material properties. Author keywords: Asphalt mixtures; Anisotropy; Viscoelasticity; Complex modulus; Poisson's ratio; Master curve.

Master Curves of Dynamic Modulus and Phase Angle for High Modulus Asphalt Mixtures

Two types of high modulus asphalt mixtures are introduced. Dynamic modulus and phase angle of these two mixtures are tested with Simple Performance Testing System under different temperatures, loading frequencies and confining pressures. Based on time-temperature superposition principle, dynamic modulus master curves and time-temperature shift factors at reference temperature are obtained using nonlinear square least square regression, and phase angle master curves are constructed utilizing the same time-temperature shift factors. The influence of confining pressure on mechanical properties of high modulus asphalt mixture is discussed.

Rheology of polyacrylate binders produced via catalytic chain transfer polymerization as an alternative to bitumen in road pavement materials

Catalytic chain transfer polymerization has been successfully used to produce a range of methyl acrylate (MA) and butyl acrylate (BA) synthetic polymers of specific, targeted molecular weights, with polydispersity index values in the range of 2–4.5. The rheological properties of a subgroup of these synthetic binders consisting of four MA homo-polymers and one MA–BA co-polymer were then determined by means of oscillatory testing using a dynamic shear rheometer (DSR). The rheological tests consisted of a combination of stress/strain amplitude and frequency sweeps using a standard 8mm diameter parallel plate testing geometry. The rheological parameters of phase angle and complex, storage and loss moduli were then shifted to form master curves at a reference temperature of 25°C and isochronal plots at 0.1, 1 and 10Hz. The rheological properties of the synthetic polymers were also compared to those of standard road pavement bitumens. The results show that it is possible to produce a range of synthetic polyacrylates with different rheological responses by altering the reactant type, reactant concentration and polymerization conditions to match the rheological properties of road bitumens. All the polyacrylate binders showed a similar rheological profile with a unique viscoelastic response as represented by the phase angle master curves together with an upper limiting stiffness and intermediate temperature/frequency ‘plateau’ region as shown in the complex modulus master curves. The results of the rheological examination of the binders showed that the key material property that influenced the performance of the polyacrylates in these specific application tests was glass transition temperature rather than molecular weight. Over this range of investigated molecular weights, it is the ratio between the two polymers which determines the glass transition and as such determines the material properties. These findings suggest that such sustainably sourced polyacrylate binders may allow for a move from petrochemical feed stocks to be made and allow for targeted road pavement design based on local climates, offering improved mechanical robustness.

Evaluation of asphalt mixtures' viscoelastic properties using phase angle relationships

A recent study at Arizona State University has shown that the phase angle, φ, was a good laboratory parameter to distinguish the asphalt mixture's tyre/pavement noise characteristics in the field. The phase angle is obtained simultaneously from the E* dynamic complex modulus test (AASHTO TP 62-03). In particular, the peak or maximum phase angle obtained from the range of the E* test frequencies provided the best indication of the mixture's noise-dampening response. The objective of this study was to utilise the φ–E* relationships to develop appropriate master curves for the phase angle parameter. In addition, the objective was to develop predictive phase angle models so that they can be used to assess the dampening response, and therefore the tyre/pavement noise characteristics of the different asphalt mixtures. E*–φ results from 217 conventional and crumb rubber-modified asphalt mixtures were used in the analysis. The beta distribution was found to best fit the phase angle master curve relationship and the statistical goodness-of-fit parameters were found to be excellent. Phase angle predictive equations were modelled with combinations of mixture properties such as aggregate gradations, binder viscosity–temperature susceptibility parameters, asphalt content, mixture air voids, temperature and loading frequency. Over 6510 data points were included in the development of the phase angle predictive equations. They included equations for both conventional and crumb rubber-modified mixtures. The predictive equations had very good to excellent goodness-of-fit statistics.

Dynamic Modulus Testing of Asphalt Concrete in Indirect Tension Mode

This study presents the results from an analytical and experimental study on the dynamic modulus testing of hot-mix asphalt using the indirect tension (IDT) mode. An analytical solution for the dynamic modulus in the IDT mode was developed with the use of linear viscoelasticity. To verify the analytical solution, temperature and frequency sweep tests were conducted on 12 asphalt mixtures commonly used in North Carolina; both axial compression and IDT test methods were used. A modified dynamic modulus test protocol is introduced to reduce the required testing time by using more frequencies and fewer temperatures on the basis of the time-temperature superposition principle. A comparison of results from the axial compression and IDT test methods shows that the dynamic modulus master curves and shift factors derived from the two methods are in good agreement. It also was found that Poisson's ratio was a weak function of the loading frequency; its effect on the phase angle master curve is discussed.

Study of rheological properties of pure and polymer-modified Brazilian asphalt binders

In recent years, many authors have suggested techniques to study asphalt binders and establish structure-property correlations for these materials. Several works have shown that rheological analysis provides reliable information about the stability, elasticity, thermal susceptibility, and also that rheological behavior depends on chemical composition and structure of pure and modified binders. The objective of this work was to study the effect of the asphalt binder chemical composition and modifier polymer type on the linear viscoelastic properties and to correlate these properties to the PMB's thermal susceptibility. A set of polymer-modified asphalt binders (PMB) was prepared using two Brazilian asphalts. Both pure binders and PMB were analyzed by classical and dynamic rotational rheology tests. The rheological analysis results were also compared to storage stability data and PMB's morphology. The fitting capability of the Christensen-Anderson and Christensen-Anderson-Marasteanu rheological models was analyzed for the two pure asphalt binders. Both models presented lack of fitness in the regions of lowest and highest frequencies. When using elastomeric modifiers, it was possible to state the existence and interrelation between the width of the phase angle master curve plateau and the PMB's thermal susceptibility and stability. This interrelation was supported by PMB's storage stability data and microscopy analysis.