In order to seek an appropriate mechanical model to describe the complex modulus and characterise the linear viscoelastic property of asphalt concrete, the Huet–Sayegh model was studied in this research. Laboratory tests of complex modulus were conducted on 20 different mixtures. Several mechanical models (Maxwell, Kelvin, generalised Maxwell, generalised Kelvin and Huet–Sayegh) and the mathematical model of sigmoidal function were applied to establish master curves of dynamic moduli. Results indicate that the Huet–Sayegh model can describe complex modulus more accurately using fewer numbers of parameters compared with other mechanical models.

Every year, a tremendous amount of toner is produced for copiers and printers by toner manufacturing companies throughout the United States. Some of this toner does not meet quality specifications and becomes a waste of the manufacturing process. This waste and the spent toner from copiers and printer cartridges are dumped in landfills for lack of a better way of utilizing them. A cooperative research project was undertaken by Texas Department of Transportation and the University of Texas to investigate the feasibility and potential benefits of utilizing waste toner in hot mix asphalt concrete. The research program included procurement of a number of different waste toners, blending them with asphalt cement at different ratios, and evaluating binder and mixture properties. The results indicated that as the amount of waste toner in the blend increases, the stiffness and viscosity of the modified binder increase. The mixture analysis also indicates higher strength and stability for toner-modified asphalt concrete compared with unmodified mixtures. The toner-modified binder is expected to perform satisfactorily in areas where permanent deformation is of great concern and some increase in low-temperature stiffness is not regarded as posing any cracking problems. It was found that a PG64-28 asphalt will grade as PG70-22 with the addition of 10 percent waste toner.

This paper presents the use of three dimensional (3D) finite element modeling (FEM) techniques to determine asphalt pavement response to loading. In mechanistic-empirical pavement design, the properties of materials used in pavement layers must be specified before the pavement response to imposed loads can be determined. A numerical method is used to obtain the relaxation modulus of linear viscoelastic materials, such as asphalt concrete, from the dynamic modulus measured on specimens procured from the field. Linear elastic behavior is assumed for granular materials. In addition, regarding finite element modeling, key factors such as model geometry, material properties, load and boundary conditions, element type, and mesh refinement are discussed in detail. The adopted Global-Local (GL) FEM approach is capable of simulating pavement responses to multiple axle loads with different load configurations, speed, and temperatures.

Proper characterization of asphalt concrete mixtures with respect to the changes in dynamic modulus (DM) with the applied loading frequency and test temperature is a key task for pavement structural design. This phenomenon is generally described through the use of a modulus master curve, which is an important input for mechanistic empirical pavement design tools. In the current abbreviated DM testing protocol, given in AASHTO TP-79-09, the limiting maximum modulus value, estimated through Hirsch model, is used to constrain the upper portion of the modulus master curve function. However, the predicted modulus values of higher shelf region can become an artifact of the presumed upper asymptote due to any inaccuracies in estimation of the limiting maximum modulus value. In this study, DM tests were coupled with a series of ultrasonic pulse velocity (UPV) tests to investigate the validity of the current limiting maximum modulus assumption. Three hot mix asphalt mixtures prepared using different binder performance grades, i.e. 52-28, 64-22, and 76-16, were investigated. Experimental program consisted of DM and UPV testing of the specimens at 4, 10, 25, and 40°C along with a series of additional UPV tests at -10°C. Polynomial shift factor function was used to construct the modulus master curves. It was concluded that the Hirsch model can result in underpredicting the actual limiting maximum modulus. Results indicate the potential advantages of using higher frequency-range nondestructive tests along with the conventional modulus tests to improve the prediction accuracy of higher shelf of modulus master curve.

Using recycled materials in construction of asphalt pavements yields both economic and technical advantages. Recycled asphalt shingles (RAS) and reclaimed asphalt pavement (RAP) are two major sources to serve this purpose for which proper design and characterization are key elements. In this study, engineering properties of asphalt concrete containing RAP and RAS under dynamic loading were investigated. Three asphalt mixes were designed and included in this research: a conventional mix with no RAP/RAS as a control, a mix with 35% RAP, and finally a mix with 35% RAP and 5% RAS. A conventional resonant column (RC) apparatus was retrofitted and used for testing the specimens in torsional mode. Testing was conducted at five temperatures ranging from 10 to 45°C. Damping ratios and moduli of the mixes were analyzed and compared to assess the effect of the recycled materials on dynamic properties of asphalt concrete. Results clearly show the impact of RAP and RAS in increasing the mix stiffness. The stud...