Research on Roadway Performance and Distress at Low Temperature

This research project investigated the performance and damage characteristics of Nebraska roadways at low-temperature conditions. To meet the research objective, laboratory tests were incorporated with mechanistic numerical modeling. The three most common pavement structures in Nebraska were selected and modeled considering local environmental conditions and pavement materials with and without truck loading. Cracking of asphalt overlay was predicted and analyzed by conducting finite element simulations incorporated with cohesive zone fracture. Parametric analyses were also conducted by varying pavement geometries and material properties, which could lead to helping pavement designers understand the mechanical sensitivity of design variables on the overall responses and performance characteristics of pavement structures. This better understanding is expected to provide NDOR engineers with more scientific insights into how to select paving materials in a more appropriate way and to advance the current structural pavement design practices

Impact of Truck Loading on Design and Analysis of Asphaltic Pavement Structures

Mechanistic-Empirical Pavement Design Guide (MEPDG) is an improved methodology for pavement design and the evaluation of paving materials. However, in spite of significant advancements to pre-existing traditional design methods, the MEPDG is known to be limited in its accurate prediction of mechanical responses and damage in asphaltic pavements. This restriction is both due to the use of simplified structural analysis methods, and a general lack of understanding of the fundamental constitutive behavior and damage mechanisms in paving materials. This is additionally affected by the use of circular tire loading configurations. Performance prediction and pavement life are determined based on the simple layered elastic theory and the empirically-developed failure criteria: the so-called transfer functions. To model pavement performance in a more appropriate manner, this study attempts finite element modeling to account for viscoelastic paving materials. Mechanical responses between the finite element simulations and the MEPDG analyses are compared to monitor any significant differences that are relevant to better pavement analysis and design. Pavement performance and the corresponding design life between the two approaches are further compared and discussed

Evaluation of Thin Asphalt Overlay Pavement Preservation in Nebraska: Laboratory Tests, MEPDG, and LCCA (17-2624)

Thin asphalt overlays offer an economical resurfacing, preservation, and renewal paving solution for roads that require safety and smoothness improvements. Recently, thin asphalt overlays have been used in Nebraska as a promising pavement preservation technique that needs evaluations

0-6839: Designing Pavements to Support the Heavy Loads in the Energy Development Areas

0-6839In recent years, rapid energy development in Texas has caused significant damage to many farm-to-market (FM) roads, which traditionally have a thin asphalt surface layer plus a stabilized base directly over the subgrade. These roadways were often rehabilitated with full-depth reclamation (FDR), and often 2 to 3 percent cement was added to the pulverized existing materials. These roadways performed well under normal traffic loads but failed dramatically under the energy-sector truck loads. Figure 1 shows the damaged FM roads. The impact of overloading traffic on pavement damage is not only limited to FM roads; it also has significant influence on the pavement life of state highways and even interstate highways. There is an urgent need to repair many of these badly damaged roadways in all energy development areas

CHARACTERIZATION OF VISCOELASTIC AND FRACTURE PROPERTIES OF ASPHALTIC MATERIALS IN MULTIPLE LENGTH SCALES

Asphaltic materials are classical examples of multi-phase composites in different length scales. The understanding of the mechanical behavior of asphaltic materials has been a challenge to the pavement mechanics community due to multiple complexities involved: heterogeneity, anisotropy, nonlinear inelasticity, and damage in multiple forms. The micromechanics-based models based on numerical methods have been receiving attention from the pavement mechanics community because the modeling method can account for those complexities of asphaltic materials by considering the effects of material properties and geometric characteristics of individual components on overall performance behavior of mixture or structure. As a step-wise effort, this study intends to identify some of key relevant mechanical characteristics such as linear viscoelastic, non-linear viscoelastic, and fracture properties of asphaltic materials in two different length scales, e.g., mixture scale and component scale. More specifically, this study developed testing-analysis methods to rigorously define the stress-dependent nonlinear viscoelastic material characteristics at various stress levels and the viscoelastic mixed-mode fracture properties at different loading rates and testing temperatures. The results from three-dimensional finite element simulations of the pavement structure presented significant differences between the linear viscoelastic approach and the nonlinear viscoelastic modeling in the prediction of pavement performance with respect to rutting. This implies that differences between the two approaches are considered significant and should be addressed in the process of performance-based pavement design. The Semi-circular Bend (SCB) fracture test presented reasonable and repeatable results. The test and analysis results in this study suggest that the rate-, temperature-, mode- dependent fracture properties are necessary in the structural design of asphaltic pavements with which a wide range of strain rates and service temperatures is usually associated. Advisor: Yong-Rak Ki

Rate- and Temperature-Dependent Fracture Characteristics of Asphaltic Paving Mixtures

Cracking in asphaltic pavement layers causes primary failure of the roadway structure, and the fracture resistance and characteristics of asphalt mixtures significantly influence the service life of asphaltic roadways. A better understanding of the fracture process is considered a necessary step to the proper development of design-analysis procedures for asphaltic mixtures and pavement structures. However, such effort involves many challenges because of the complex nature of asphaltic materials. In this study, experiments were conducted using uniaxial compressive specimens to characterize the linear viscoelastic properties and semi-circular bending (SCB) specimens to characterize fracture behavior of a typical dense-graded asphalt paving mixture subjected to various loading rates and at different temperatures. The SCB fracture test was also incorporated with a digital image correlation (DIC) system and finite-element model simulations including material viscoelasticity and cohesive-zone fracture to effectively capture local fracture processes and resulting fracture properties. The test results and model simulations clearly demonstrate that: (1) the rate- and temperature-dependent fracture characteristics need to be identified at the local fracture process zone, and (2) the rate- and temperature-dependent fracture properties are necessary in the structural design of asphaltic pavements with which a wide range of strain rates and service temperatures is usually associated

Layer Moduli of Nebraska Pavements for the New Mechanistic-Empirical Pavement Design Guide (MEPDG)

As a step-wise implementation effort of the Mechanistic-Empirical Pavement Design Guide (MEPDG) for the design and analysis of Nebraska flexible pavement systems, this research developed a database of layer moduli — dynamic modulus, creep compliance, and resilient modulus — of various pavement materials used in Nebraska. The database includes all three design input levels. Direct laboratory tests of the representative Nebraska pavement materials were conducted for Level 1 design inputs, and surrogate methods, such as the use of Witczak’s predictive equations and the use of default resilient moduli based on soil classification data, were evaluated to include Level 2 and/or Level 3 design inputs. Test results and layer modulus values are summarized in the appendices. Modulus values characterized for each design level were then put into the MEPDG software to investigate level-dependent performance sensitivity of typical asphalt pavements. The MEPDG performance simulation results then revealed any insights into the applicability of different modulus input levels for the design of typical Nebraska pavements. Significant results and findings are presented in this report

Impact of Truck Loading on Design and Analysis of Asphaltic Pavement Structures- Phase II

In this study, Schapery’s nonlinear viscoelastic constitutive model is implemented into the commercial finite element (FE) software ABAQUS via user defined subroutine (user material, or UMAT) to analyze asphalt pavement subjected to heavy truck loads. Then, extensive creep-recovery tests are conducted at various stress levels and at two temperatures (30oC and 40oC) to obtain the stress- and temperature-dependent viscoelastic material properties of hot mix asphalt (HMA) mixtures. With the viscoelastic material properties characterized and the UMAT code, a typical pavement structure subjected to repeated heavy truck loads is modeled with the consideration of the effect of material nonlinearity with a realistic tire loading configuration. Three-dimensional finite element simulations of the pavement structure present significant differences between the linear viscoelastic approach and the nonlinear viscoelastic modeling in the prediction of pavement performance with respect to rutting and fatigue cracking. The differences between the two approaches are considered significant and should be addressed in the process of performance-based pavement design. This also implies the importance of proper and more realistic characterization of pavement materials

Impact of Truck Loading on Design and Analysis of Asphaltic Pavement Structures- Phase III

This study investigated the impact of the realistic constitutive material behavior of asphalt layer (both nonlinear inelastic and fracture) for the prediction of pavement performance. To this end, this study utilized a cohesive zone model to consider the fracture behavior of asphalt mixtures at an intermediate temperature condition. The semi-circular bend (SCB) fracture test was conducted to characterize the fracture properties of asphalt mixtures. Fracture properties were then used to simulate mechanical responses of pavement structures. In addition, Schapery’s nonlinear viscoelastic constitutive model was implemented into the commercial finite element software ABAQUS via a user defined subroutine (user material, or UMAT) to analyze asphalt pavement subjected to heavy truck loads. Extensive creep-recovery tests were conducted at various stress levels and multiple service temperatures to obtain the stress- and temperaturedependent viscoelastic material properties of asphalt mixtures. Utilizing the derived viscoelastic and fracture properties and the UMAT code, a typical pavement structure was modeled that simulated the effect of material nonlinearity and damage due to repeated heavy truck loads. Twodimensional finite element simulations of the pavement structure demonstrated significant differences between the cases: linear viscoelastic and nonlinear viscoelastic modeling with and without fracture in the prediction of pavement performance. The differences between the cases were considered significant, and should be addressed during the process of performance-based pavement design. This research demonstrates the importance of accurate and more realistic characterizations of pavement materials