Jaeseung Kim

Determination of Shear and Bulk Moduli of Viscoelastic Solids from the Indirect Tension Creep Test

Because of its efficiency in analyzing complex viscoelastic problems, the finite-element (FE) analysis has been widely used to identify the time- and rate-dependent effects of viscoelastic materials on various structural conditions. When performing the FE analysis on a viscoelastic structure, most FE programs require fundamental material properties, shear and bulk moduli, of the given viscoelastic material as their input. However, the shear and bulk modulus tests are difficult to perform, so they have been commonly estimated from a single material test on the basis of the assumption that the Poisson’s ratio of viscoelastic materials is a time-independent constant. Such an assumption, however, might not be suitable because the Poisson’s ratio of the viscoelastic materials is also a function of time. Therefore, this study developed computation algorithms for determining the time-dependent Poisson’s ratio and shear and bulk moduli of asphalt mixtures, which have been well recognized as a viscoelastic materia...

General Viscoelastic Solutions for Multilayered Systems Subjected to Static and Moving Loads

Since the linear elastic layer solution for the layered systems was developed in the 1940s, the linear elastic layer analysis has been systemized and widely used for the designs of roadway pavements as a tool for evaluating the structural soundness of pavements. The primary assumption made in the analysis is that the layered system consisting of materials that are linear elastic; and hence, an application of the elastic layer analysis to asphalt mixtures, which is a well-known viscoelastic material, has been limited. Therefore, the intention of the study was to derive a viscoelastic solution able to take into account the time- and rate-dependent nature of the viscoelastic materials in the multilayered system. In this paper, a linear viscoelastic solution for the multilayered system subjected to a cylindrical unit step (static) load was derived from the elastic solution by using the principle of elastic-viscoelastic correspondence and the numerical inversion of Laplace transforms. The solution was then extended to simulating pavement responses subjected to a moving load by employing the Boltzmann’s superposition principle. The soundness of output from the viscoelastic solution was confirmed by comparing them to those of the finite-element analysis (FEA). Compared to the time and effort required in FEA, the analysis based on the viscoelastic solution was much faster. Therefore, it is expected that the viscoelastic solutions derived in this study will be an effective tool for the design of flexible pavements.

Performance of Polymer-Modified Asphalt Mixture with Reclaimed Asphalt Pavement

Reclaimed asphalt pavement (RAP) mixtures have shown good resistance to rutting for hot-mix asphalt (HMA) pavement. Mixtures with polymer-modified binders such as styrene-butadiene-styrene (SBS) have also shown good performance against rutting and cracking. This paper presents the laboratory evaluations used to determine the rutting and cracking performance of the RAP mixtures with SBS polymer-modified binders as virgin binders. The asphalt pavement analyzer (APA) test and indirect tensile (IDT) test were conducted for the laboratory evaluation. The properties of SBS polymer-modified binders blended with recovered RAP binders were also investigated. The binder tests included G*/sinδ as the rutting parameter and G*sinδ as the cracking parameter of the Super-pave® PG grade system. The multiple stress creep and recovery test, which has recently received attention as an indicator of the rutting potential of polymer-modified asphalt binders, was also performed. RAP mixtures with SBS polymer-modified binders were fabricated containing different amounts of RAP materials: 0%, 15%, 25%, and 35%. From the APA and Superpave IDT tests, RAP mixtures with modified binders showed good performance regardless of the amounts of RAP materials in HMA. Even though the parameters, G*/sinδ and G*sinδ, and the percentage of recovery indicated the different amounts of RAP binders in polymer-modified binders, the relationship between these parameters and mixture performance was not clearly identified.

Application of the Viscoelastic Continuum Damage Model to the Indirect Tension Test at a Single Temperature

The viscoelastic continuum damage model, developed based on Schapery’s correspondence principle and the continuum damage mechanics, has received a great deal of attention because of its mathematical soundness and effectiveness in describing damage growth in viscoelastic media and has been used to make reliable estimations on the fatigue lives of asphalt mixtures. Its applications to field mixtures, however, have been limited because the model requires performing the uniaxial tension test. As an alternative, this study developed an analytical methodology for applying the model to the indirect tension test, which has been successfully used in testing both laboratory-made and field-cored mixtures. From the results of the indirect tension tests conducted on asphalt mixture at three different crosshead-controlled rates, it was found that the stress-pseudostrain curves could be superimposed onto one equality line in the linear viscoelastic range of the given mixture, and its rate dependency was successfully eli...

Forensic Investigation and Validation of Energy Ratio Concept

The energy ratio (ER) concept was recently introduced as an accurate predictor of top-down cracking performance in Florida. Initial evaluation of ER with field projects in Florida confirmed its ability to distinguish between cracked and uncracked sections. To evaluate and validate the ER concept further, the Florida Department of Transportation designed and constructed two test sections at the National Center for Asphalt Technology test track. The primary difference between the two sections was the binder used in the upper two lifts. The first section used PG 67-22 and the second section used PG 76-22, which resulted in an ER of about twice the size. The section with the lower ER value cracked first and more extensively, though both sections experienced top-down cracking. This study was intended not only to look at ER as the primary factor to differences in performance but also to evaluate forensically the sections by using in situ strain measurements, coring, and interface bond strength testing. The strain regimes and bond strengths were found to be approximately equal between the sections, a finding that further validated the ER as a good predictor of top-down cracking performance.

Extension of Fracture Mechanics Principles to Viscoelastic Continuum Media

The fracturing of materials is well known on the basis of the theory of fracture mechanics. An important concept in fracture mechanics theory is that crack propagation is governed by the fundamental material properties of energy dissipation and energy threshold. However, to apply the fracture mechanics approach and measure these properties, a notch needs to be introduced into a continuum body. This requires additional effort to make the notch, which is often sensitive to the formation of materials surrounding the area near the crack tip. These effects become more complex for a material that exhibits time, rate, and temperature dependency. To overcome these complexities and problems regarding fracture testing, this study used the analogy between the material’s behaviors with and without a notch. A transfer of the fracture mechanics principle to continuum viscoelastic media was the key to the model developed in this study. For this purpose, the energy release rate (G) which is theoretically derived from a v...

Effect of Thermal Stresses on Pavement Performance Under Mild Climate Conditions

Thermal stress on the surfaces of pavements located in mild climates has been commonly considered to have a negligible effect on pavement performance. Current pavement design methodology focuses on maximum tensile stress rather than tensile stresses occurring over the design life of pavements. To identify the significance of thermal stress on pavement performance through structural stress analysis, this study investigated the predictive capability of the enhanced integrated climate model by comparing it with measured temperature data and introducing an analytical methodology of estimating thermal stress development using the dynamic modulus test. The identified thermal stresses were compared with the tensile stresses occurring at the bottom of an asphalt layer through the analysis method employed in the Guide for Mechanistic–Empirical Design of New and Rehabilitated Pavement Structures. Damage caused by the thermal and bottom stresses was evaluated on the basis of the damage ratio derived from the hot-mix asphalt fracture model. The conclusion drawn from the investigations was that the effect of thermal stress on pavement cracking performance, evaluated through the damage analysis considering the time-and temperature-dependent nature of asphalt mixtures, is much less significant than that of bottom stress under mild climate conditions. Under the nonaging condition, 1-year average damage occurring due to thermal stress at typical pavement structures would be slightly less than 0.5% of that which would be expected to occur at the bottom.