The extensively used AASHTO structural design procedures for flexible pavement indicate the required pavement design in terms of a structural number. For a particular pavement thickness design, this structural number can be computed from the sum of each pavement layer's thickness multiplied by its strength parameter, called the structural layer coefficient. The research work reported herein presents methods for determining the structural layer coefficients for asphalt emulsion-aggregate mixtures. A hot plant-mixed asphaltic concrete was evaluated for structural layer coefficient, and the radial stress vs. fatigue failure relationship was developed using circular specimens and the Jimenez deflectometer. Relationships between structural number and load repetitions to failure for different loading conditions were developed. These relationships were used to evaluate the structural numbers of other specimens when tested to failure in flexural fatigue. Three asphalt emulsion-aggregate mixtures were designed using CSS-lh asphalt emulsion. The aggregates used for the three mixtures were: (1) Type I aggregate using dense-graded, crushed, river gravel; (2) Type II aggregate using pit-run, coarse sand; and (3) Type III aggregate using a silty sand. These mixtures were evaluated for Marshall stability, Hveem stability and cohesiometer value, unconfined compressive strength, double punch tensile strength and dynamic modulus of elasticity at various ages from 3 to 28 days. Flexural fatigue life, when tested in the deflectometer, was determined for all mixtures at 7 and 28 days. Structural numbers for the specimens and structural layer coefficients for the mixtures were determined. Relationships were developed between the evaluation tests performed and the structural layer coefficients at various mixture ages by using test results from the three mixtures and a regression analysis procedure. A fourth asphalt emulsion-aggregate mixture using CSS-lh asphalt emulsion and a Type II crusher-run aggregate was designed. Evaluation tests were performed at 3 and 7 days and layer coefficients for the mixture were predicted for 7 and 28 days using the regression equations developed. Layer coefficients at 7 and 28 days were also determined by testing specimens in fatigue in the deflectometer and computing their structural numbers and layer coefficients. Layer coefficients determined in these two manners indicated favorable comparisons. The results of this research provides information about the structural layer coefficients for asphalt emulsion-aggregate mixtures. The relationships between the evaluation tests and structural layer coefficient can be used for determining layer coefficients for other asphalt emulsion-aggregate mixtures. Because the evaluation tests used were tests commonly performed in most asphalt laboratories, these determinations can be made without the necessity of additional equipment or procedures in most cases.

No description available.

" The determination of strain is an important step when using a mechanistic-empirical structural design, such as the AASHTO 2002 Design Guide. This thesis investigated the use of accelerated pavement testing system on Hot Mix Asphalt pavements to determine actual transverse and longitudinal strains under loads of varying frequency at different temperatures. A Model Mobile Load Simulator (MMLS3) was used in this study. Laboratory compacted pavement slabs were instrumented with thermocouples for monitoring the pavement's temperature, and with strain gauges in transverse and longitudinal directions at the bottom surface to measure strain. The slabs were subjected to loading by the MMLS3, running at different speeds. The pavement slab and accelerated loading equipment were enclosed in an environmental chamber to control temperatures during testing. Strains were also determined from layered elastic analysis after determining modulus values by two different methods - Resilient modulus testing and Witczak’s dynamic modulus equation. Comparisons of pavement strains calculated through the use of layered elastic design software and actual strains obtained during loading were made. The test results have shown a significant difference between strain values obtained using an instrumented pavement slab and those obtained with the use of standard resilient modulus values or dynamic modulus values determined by using a typical layered elastic design model. To avoid the discrepancies, two approaches are proposed - The first is modeling strain with accelerated pavement testing and the second one is using a correction factor. "

Unlike in laboratory compacted asphalt mixtures, the distribution of viscoelastic properties in field layers is not uniform because of nonuniform air void distribution and aging. Therefore, characterization of field specimens is more challenging compared to that of laboratory compacted specimens. Formerly, characterization of field asphalt mixtures was based on binder tests which are useful but do not represent the properties of the asphalt mixtures because binder is only a component in the asphalt mixture. This study uses linear viscoelastic theory and numerical modeling to obtain the undamaged and damaged viscoelastic properties of both laboratory made and field compacted asphalt concrete. Additionally, it uses fracture mechanics principles to find the fracture and healing properties of aged asphalt specimens. The analytical models presented in this research have been successfully verified by testing the actual field specimens of different ages. The model developed in this dissertation is suitable to track the viscoelastic, fracture and healing properties of the field specimen with time and depth. The test protocols and analytical models described in this study can be used for the development of reliable performance models for field-aged asphalt layers.

Saskatchewan Ministry of Highway and Infrastructure (SMHI) currently use the Marshall compaction method for the preparation of hot-mix asphalt laboratory samples. Due to increases in commercial truck traffic on most provincial highways, there has been an observed increasing trend in the occurrence of permanent deformation within the hot-mix asphalt concrete (HMAC) layer. One of the most important material properties found to influence the resistance of HMAC to structural permanent deformation is volumetric air voids within the mix.<p> End product air voids within a hot mix asphalt concrete pavement in the field is simulated by the method of compaction used during the laboratory design process. Based on findings of the Strategic Highway Research Program (SHRP), the gyratory compactor is believed to better simulate field compaction of asphalt mixes at the time of construction, as well as better predict mix consolidation over the field performance period. However, the SuperpaveTM sample preparation protocol specifies a fixed angle of gyratory compaction, which may not be the optimal parameters to evaluate Saskatchewan hot-mix asphalt concrete mixes during the laboratory mix design phase.<p> The primary objective of this research was to investigate the relationship between laboratory characterization and field evaluation of Saskatchewan SPS-9A asphalt mixes across alternate laboratory compaction protocols. A second objective of this research was to quantify the effect of gyratory and Marshall compaction energy on the physical and mechanical properties of Saskatchewan SPS-9A asphalt mixes in the laboratory. The third objective of this research was to compare field ground penetrating radar dielectric permittivity profiles and rutting performance across Saskatchewan SPS-9A test sections.<p> The hypothesis of this research is that gyratory laboratory compaction will provide improved sensitivity in the characterization of physical asphaltic mix properties. It is also hypothesized that varied volumetric properties of HMAC mixes influence the mechanistic triaxial frequency sweep material properties of both conventional Saskatchewan and SuperpaveTM dense graded HMAC mixes.<p> The laboratory portion of this research included volumetric and mechanical properties of the seven Saskatchewan SPS-9A asphaltic mixes. The scope of this research included an investigation of the Saskatchewan Specific Pavement Study-9A (SPS-9A) asphalt mixes constructed in Radisson Saskatchewan in 1996. Physical volumetric properties as well as mechanistic triaxial frequency sweep properties were characterized across all seven Radisson SPS-9A mixes. Rutting after ten years of performance in the field was quantified as well as in situ ground penetrating radar dielectric permittivities of the Radisson SPS-9A test sections.<p> Based on the findings of the study, there was a significant reduction in VTM with an increase in Marshall compaction energy from 50 to 75 blows. Marshall stability was observed to be higher at 75 blow compared to 50 blows across the test sections.<p> Similarly, with regards to gyratory sample preparation, there was an observed reduction in VTM with an increase in gyratory compaction energy. VTM of SuperpaveTM mixes were higher than VTM SMHI Marshall mixes. VTM of the SuperpaveTM mixes were above acceptable SMHI limits at all angles of gyration at Ndesign. SuperpaveTM gyratory compactor accurately predicted field air voids of the Radisson SPS-9A asphalt after ten years of traffic loading at 2.00° angle of gyration.<p> In general, this research showed significant sensitivity of volumetric material properties across both Marshall and gyratory compaction energy.<p> This research also demonstrated that there was an improvement in the triaxial mechanistic material properties of the Radisson SPS-9A HMAC mixes with an increase in gyratory compaction energy. Dynamic moduli across all test section mixes increased with an increase in gyratory compaction energy. Similarly, it was shown that Poissons ratio generally increased with an increase in compaction energy across all test sections. Phase angle also increased with an increase in gyratory compaction energy. Radial microstrain (RMS) displayed the most significant sensitivity to increased gyratory compaction energy.<p> This research concluded that compaction energy in the laboratory can significantly influence the volumetric and mechanistic properties of hot-mix asphalt concrete mixes. As indicated by the field performance of the Radisson SPS-9A test sections, it is known that both volumetric and mechanistic properties can influence field performance. Mechanical material properties of HMAC may be improved by increasing compaction energy, as long as volumetric properties are adhered to. The use of rapid triaxial frequency sweep testing demonstrated the ability to characterize mechanistic material properties as a function of varied compaction energy.<p> Based on the findings of this research, it is recommended that Saskatchewan asphalt mixes, both Marshall and SuperpaveTM types, be characterized using gyratory compaction with 2.00° angle of gyration and the SHRP specified number of gyrations. Further, the gyratory compacted samples provide the ability to characterize the mechanistic material constitutive properties of asphaltic mixes for mechanistic based road structural design purposes.<p> Future research should evaluate the relationship of laboratory material properties to the field performance of various Saskatchewan asphalt mixes across various field state conditions.

Saskatchewan Ministry of Highway and Infrastructure (SMHI) currently use the Marshall compaction method for the preparation of hot-mix asphalt laboratory samples. Due to increases in commercial truck traffic on most provincial highways, there has been an observed increasing trend in the occurrence of permanent deformation within the hot-mix asphalt concrete (HMAC) layer. One of the most important material properties found to influence the resistance of HMAC to structural permanent deformation is volumetric air voids within the mix.<p> End product air voids within a hot mix asphalt concrete pavement in the field is simulated by the method of compaction used during the laboratory design process. Based on findings of the Strategic Highway Research Program (SHRP), the gyratory compactor is believed to better simulate field compaction of asphalt mixes at the time of construction, as well as better predict mix consolidation over the field performance period. However, the SuperpaveTM sample preparation protocol specifies a fixed angle of gyratory compaction, which may not be the optimal parameters to evaluate Saskatchewan hot-mix asphalt concrete mixes during the laboratory mix design phase.<p> The primary objective of this research was to investigate the relationship between laboratory characterization and field evaluation of Saskatchewan SPS-9A asphalt mixes across alternate laboratory compaction protocols. A second objective of this research was to quantify the effect of gyratory and Marshall compaction energy on the physical and mechanical properties of Saskatchewan SPS-9A asphalt mixes in the laboratory. The third objective of this research was to compare field ground penetrating radar dielectric permittivity profiles and rutting performance across Saskatchewan SPS-9A test sections.<p> The hypothesis of this research is that gyratory laboratory compaction will provide improved sensitivity in the characterization of physical asphaltic mix properties. It is also hypothesized that varied volumetric properties of HMAC mixes influence the mechanistic triaxial frequency sweep material properties of both conventional Saskatchewan and SuperpaveTM dense graded HMAC mixes.<p> The laboratory portion of this research included volumetric and mechanical properties of the seven Saskatchewan SPS-9A asphaltic mixes. The scope of this research included an investigation of the Saskatchewan Specific Pavement Study-9A (SPS-9A) asphalt mixes constructed in Radisson Saskatchewan in 1996. Physical volumetric properties as well as mechanistic triaxial frequency sweep properties were characterized across all seven Radisson SPS-9A mixes. Rutting after ten years of performance in the field was quantified as well as in situ ground penetrating radar dielectric permittivities of the Radisson SPS-9A test sections.<p> Based on the findings of the study, there was a significant reduction in VTM with an increase in Marshall compaction energy from 50 to 75 blows. Marshall stability was observed to be higher at 75 blow compared to 50 blows across the test sections.<p> Similarly, with regards to gyratory sample preparation, there was an observed reduction in VTM with an increase in gyratory compaction energy. VTM of SuperpaveTM mixes were higher than VTM SMHI Marshall mixes. VTM of the SuperpaveTM mixes were above acceptable SMHI limits at all angles of gyration at Ndesign. SuperpaveTM gyratory compactor accurately predicted field air voids of the Radisson SPS-9A asphalt after ten years of traffic loading at 2.00° angle of gyration.<p> In general, this research showed significant sensitivity of volumetric material properties across both Marshall and gyratory compaction energy.<p> This research also demonstrated that there was an improvement in the triaxial mechanistic material properties of the Radisson SPS-9A HMAC mixes with an increase in gyratory compaction energy. Dynamic moduli across all test section mixes increased with an increase in gyratory compaction energy. Similarly, it was shown that Poissons ratio generally increased with an increase in compaction energy across all test sections. Phase angle also increased with an increase in gyratory compaction energy. Radial microstrain (RMS) displayed the most significant sensitivity to increased gyratory compaction energy.<p> This research concluded that compaction energy in the laboratory can significantly influence the volumetric and mechanistic properties of hot-mix asphalt concrete mixes. As indicated by the field performance of the Radisson SPS-9A test sections, it is known that both volumetric and mechanistic properties can influence field performance. Mechanical material properties of HMAC may be improved by increasing compaction energy, as long as volumetric properties are adhered to. The use of rapid triaxial frequency sweep testing demonstrated the ability to characterize mechanistic material properties as a function of varied compaction energy.<p> Based on the findings of this research, it is recommended that Saskatchewan asphalt mixes, both Marshall and SuperpaveTM types, be characterized using gyratory compaction with 2.00° angle of gyration and the SHRP specified number of gyrations. Further, the gyratory compacted samples provide the ability to characterize the mechanistic material constitutive properties of asphaltic mixes for mechanistic based road structural design purposes.<p> Future research should evaluate the relationship of laboratory material properties to the field performance of various Saskatchewan asphalt mixes across various field state conditions.

The deleterious effect of moisture on the structural integrity of asphalt mixtures has been recognized as one of the main causes of early deterioration of asphalt pavements. This phenomenon, usually referred to as moisture damage, is defined as the progressive loss of structural integrity of the mixture that is primarily caused by the presence of moisture in liquid or vapor state. Moisture damage is associated with the development of different physical, mechanical, and chemical processes occurring within the microstructure of the mixture at different intensities and rates. Although there have been important advancements in identifying and characterizing this phenomenon, there is still a lack of understanding of the damage mechanisms occurring at the microscopic level. This situation has motivated the research work reported in this dissertation. The main objective of this dissertation is to formulate and apply a numerical micromechanical model of moisture-induced damage in asphalt mixtures. The model focuses on coupling the effects of moisture diffusion—one of the three main modes of moisture transport within asphalt mixtures—with the mechanical performance of the microstructure. Specifically, the model aims to account for the effect of moisture diffusion on the degradation of the viscoelastic bulk matrix of the mixture (i.e., cohesive degradation) and on the gradual deterioration of the adhesive bonds between the aggregates and the asphalt matrix (i.e., adhesive degradation). The micromechanical model was applied to study the role of some physical and mechanical properties of the constitutive phases of the mixtures on the susceptibility of the mixture to moisture damage. The results from this analysis suggest that the diffusion coefficients of the asphalt matrix and aggregates, as well as the bond strength of the aggregate-matrix interface, have the most influence on the moisture susceptibility of the mixtures. The micromechanical model was further used to investigate the influence of the void phase of asphalt mixtures on the generation of moisture-related deterioration processes. Two different probabilistic-based approaches were used to accomplish this objective. In the first approach, a volumetric distribution of air voids sizes measured using X-Ray Computed Tomography in a dense-graded asphalt mixture was used to generate probable void structures in a microstructure of an asphalt mixture. In the second approach, a stochastic modeling technique based on random field theory was used to generate probable air voids distributions of the mixture. In this second approach, the influence of the air voids was accounted for by making the physical and mechanical properties of the asphalt matrix dependent on probable voids distributions. Although both approaches take into consideration the characteristics of the air void phase on the mechanical response of the mixtures subjected to moist environments, the former explicitly introduces the air phase within the microstructure while the latter indirectly includes its effects by modifying the material properties of the bulk matrix. The results from these simulations demonstrated that the amount, variability and location of air voids are decisive in determining the moisture-dependent performance of asphalt mixtures. The results from this dissertation provide new information on the kinetics of moisture damage mechanisms in asphalt mixtures. In particular, the results obtained from applying the micromechanical model permitted identification of the relative influence of the characteristics of the constitutive phases of a mixture on its moisture-related mechanical performance. This information can be used as part of design methodologies of asphalt mixtures, and/or as an input in life-cycle analysis models and maintenance programs of road infrastructure.

The purpose of this study was to characterize the micromechanical properties of various structural components in asphalt using Atomic Force Microscopy (AFM). The focus of the study was based on nano-indentation experiments performed within a micro-grid of asphalt phases in order to determine micromechanical properties such as stiffness, adhesion and elastic/plastic behavior. The change in microstructure and micromechanical behavior due to oxidative aging of the asphalt was also a primary focus of the study. The experiment was performed with careful consideration of AFM artifacts, which can occur due to factors such as geometry of the cantilever tip, hysteresis, filtering methods and acoustic vibrations. The materials used in this study included asphalts AAB, AAD and ABD from the Materials Reference Library (MRL) of the Strategic Highway Research Program (SHRP), chosen due to variations in crude source, chemical composition and elemental analysis for each asphalt type. The analysis of nano-indentation creep measurements corresponding to phase-separated regions ultimately revealed heterogeneous domains in asphalt with different mechanical properties, and oxidative aging was found to induce substantial microstructural change within these domains, including variations in phase structure, phase properties and phase distribution. The form and extent of these changes, however, were different for each asphalt studied. Data analysis and information collected during this study were used for comparisons to existing models and asphalt data, which validated results and established correlations to earlier, related studies. From these comparisons, it was found that data parallels followed expected trends; furthermore, analogous interpretations and distinctions were made between results from this study and the micellar and microstructural models of asphalt. This study of micromechanical properties that govern asphalt behavior has yielded information essential to the advancement of hot mix asphalt (HMA) performance, including a new asphalt “weak zone” hypothesis and a foundation of data for implementation into new and existing asphalt models.

This dissertation presents the integration of a damage viscoelastic constitutive relationship with a viscoplastic relationship in order to develop a comprehensive anisotropic damage viscoelastic-viscoplastic model that is capable of capturing hot mix asphalt (HMA) response and performance under a wide range of temperatures, loading rates, and stress states. The damage viscoelasticity model developed by Schapery (1969) is employed to present the recoverable response, and the viscoplasticity model developed at the Texas Transportation Institute (TTI) is improved and used to model the irrecoverable strain component. The influence of the anisotropic aggregate distribution is accounted for in both the viscoelastic and viscoplastic responses. A comprehensive material identification experimental program is developed in this study. The experimental program is designed such that the quantification and decomposition of the response into viscoelastic and viscoplastic components can be achieved. The developed experimental program and theoretical framework are used to analyze repeated creep tests conducted on three mixes that include aggregates with different characteristics. An experiment was conducted to capture and characterize the three-dimensional distribution of aggregate orientation and air voids in HMA specimens. X-ray computed tomography (CT) and image analysis techniques were used to analyze the microstructure in specimens before and after being subjected to triaxial repeated creep and recovery tests as well as monotonic constant strain rate tests. The results indicate that the different loading conditions and stress states induce different microstructure distributions at the same macroscopic strain level. Also, stress-induced anisotropy is shown to develop in HMA specimens.

Thesis (M.S.)--West Virginia University, 2003. / Title from document title page. Document formatted into pages; contains viii, 106 p. : ill. Vita. Includes abstract. Includes bibliographical references (p. 104-105).