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A laboratory study has been carried out to develop mechanical models for the dynamic modulus, fatigue life, and rutting performance of asphalt concrete as a function of air void content. The experimental program includes an axial compression complex modulus test, indirect tensile (IDT) fatigue test, and triaxial repeated load permanent deformation (TRLPD) test on the two most commonly used asphalt-aggregate mixtures in North Carolina. The dynamic moduli are determined using axial compression tests with and without confining pressure, and the results are compared to evaluate the effect of confining pressure on the dynamic modulus. The relationship between the dynamic moduli that are determined from the uniaxial compression test and the air void content is developed. The growth of the tensile strain and axial permanent strain is measured from the IDT fatigue test and TRLPD test, respectively, and is used to determine the fatigue life and rutting behavior of the mixtures. The fatigue and rutting models adopted in the new NCHRP 1-3714 Mechanistic-Empirical Pavement Design Guide have been refined to represent the IDT and TRLPD test results more accurately and to incorporate the air void content as an input parameter. DOI: 10.1061/(ASCE)0899-1561(2007)19:10(874) CE Database subject headings: Fatigue; Cracking; Deformation; Asphalt; Concrete; Parameters.

This paper develops a dynamic prediction model of a highway pavement contractor's quality-based performance using a panel (longitudinal) data analysis. This panel data modeling uses as-built roughness measurements and pavement and contractor's characteristics for reconstructed, replaced, and resurfaced pavement projects in Wisconsin from 1998 through 2002. Several random effects models were first developed in in-sample specification, and their modeling performances were measured by Akaike's information criteria, which combines goodness of fit and model complexity. Out-of-sample specifications validated the developed random effects models by comparing out-of-sample forecasting accuracies. The results show that the best model has approximately a 16% mean absolute percentage error. The results finally show that asphaltic concrete pavement quality of construction can be predicted based on the contractor's past quality-based performance and other construction parameters. Therefore, the dynamic prediction model developed in this study could be implemented in the contractor's prequalifications required for advanced contracting methods. DOI: 10.1061/(ASCE)0733-947X(2007)133:2(90) CE Database subject headings: Data analysis; Roughness; Performance characteristics; Models; Predictions; Asphalt pavements.

This note outlines the experimental investigation of the factors affecting bond development between pavement layers. The tests involved the use of an apparatus known as the Nottingham shear box. To establish a realistic stress distribution at the interface, which would facilitate the analysis of the test results, finite element models of bonded and weakly bonded specimens were developed. It was concluded that care must be taken when interpreting test results from the shear box experiments. Several materials and four interface conditions were investigated. Bond stiffness and strength were assessed under repeated dynamic and monotonic static test conditions. The analysis of the experimental results showed that the interface properties depend more seriously on the type of materials in contact, rather than on the amount of the applied tack coat and the interface condition. It was suggested that the interface bond should be described by introducing a vertical shear reaction modulus, as well as using the horizontal shear reaction modulus. CE Database subject headings: Asphalt pavements; Asphalt concrete; Bonding; Interfaces; Shear; Finite elements; Experimentation.

Abstract: Stone Mastic Asphalt (SMA) technology has been introduced to Malaysia since the 1990's. Since then, several trial lay projects had been initiated for purpose of evaluating the mix on [...]

Asphalt concrete has been recognized as an anisotropic material, but the degree of anisotropy and its implications for pavement design and analysis have not been well understood. This paper illustrates the difference between the stress fields of an isotropic and an anisotropic pavement under wheel load through analytical solution and finite-element simulation for several cases. A servocontrolled true triaxial (cubical) testing device was used to test 4-in. cubical asphalt concrete specimens under general stress states to characterize the anisotropic properties of asphalt concrete. It was discovered that (1) the stiffness of a cored field specimen has significant differences in the vertical and horizontal direction; and (2) the significant difference may result in larger shear stress and tensile stress in a pavement. These findings indicate that characterization and modeling of the anisotropic properties of asphalt concrete are an important area that deserves further investigation. CE Database subject headings: Anisotropy; Asphalt concrete; Asphalt pavements; Pavement design; Tensile stress; Shear stress.

A viscoelastic (VE)-viscoplastic (VP) model for characterizing asphalt concrete behavior is described. The parameters of the model are determined in the prepeak region of the loading, under small load. It includes two separate damage functions, one for each component of the deformation, to describe the material behavior under heavy load and in the postpeak region of the fracture. In order to extend the material characterization to the postpeak region, the size of the fracture process zone (FPZ) is evaluated from mapping the strain in a fracture test. The deformation in the FPZ, in the continuum framework is computed from total and local measurements. Uniaxial tests, including frequency sweep for the undamaged, linear VE component, repeated triaxial load for the undamaged VP component are conducted and used to derive the material properties in the prepeak region. A tension up to failure test is used to determine the damage functions. CE Database subject headings: Viscoelasticity: Viscoplasticity; Damage; Fracture mechanics; Asphalt concrete.

Aggregates are an important constituent of asphalt concrete, hydraulic cement concrete, and granular base. The shape, angularity, and surface texture of aggregates are basically variations of asperities at different dimensional scales and affect mixture properties in different ways. This paper presents a unified Fourier morphological analysis method to quantify the shape, angularity, and surface texture of aggregates. Evaluation of these characteristics of 10 aggregates of known quality indicates that Fourier morphological analysis quantitatively ranks these aggregates in consistence with qualitative evaluations. CE Database subject headings: Fourier analysis: Shape: Aggregates: Image analysis: Asphalt concrete.

This paper presents a computational micromechanics modeling approach to predict damage-induced mechanical response of asphalt mixtures. Heterogeneous geometric characteristics and inelastic mechanical behavior were taken into account by introducing finite element modeling techniques and a viscoelastic material model. The modeling also includes interface fracture to represent crack growth and damage evolution. The interface fracture is modeled by using a micromechanical nonlinear viscoelastic cohesive-zone constitutive relation. Fundamental material properties and fracture characteristics were measured from simple laboratory tests and then incorporated into the model to predict rate-dependent viscoelastic damage behavior of the asphalt mixture. Simulation results demonstrate that each model parameter significantly influences the mechanical behavior of the overall asphalt mixture. Within a theoretical framework of micromechanics, this study is expected to be suitable for evaluating damage-induced performance of asphalt mixtures by measuring only material properties and fracture properties of each mix component and not by recursively performing expensive laboratory tests that are typically required for continuum damage mechanics modeling. CE Database subject headings: Damage; Models; Asphalt mixes; Viscoelasticity; Micromechanics; Finite element method; Fractures.

Asphalt concrete has been used for low permeability barriers in numerous applications over many centuries. In recent times, asphalt concrete barriers have been used for waste containment applications. The hydraulic conductivity of asphalt concrete specimens can be measured in the laboratory; however, there is no expedient, efficient way of accurately measuring the in situ hydraulic conductivity of low permeability asphalt concrete shortly after its placement and compaction in the field. A method has been developed to efficiently check the in situ hydraulic conductivity of asphalt concrete in the field. Asphalt concrete specimens with varying asphalt cement contents and unit weights were prepared in the laboratory and their hydraulic conductivity measured. The measured hydraulic conductivity data were grouped into different ranges and plotted as a function of unit weight and asphalt cement content. An acceptable zone was specified for a combination of asphalt cement content and unit weight that resulted in a specified hydraulic conductivity. In the field, a quality control inspector can check the unit weight and asphalt cement content of the in-place barrier to make sure it lies within the acceptable zone. The asphalt cement content and unit weight can be readily measured, thereby allowing rapid acceptance or rejection of the asphalt concrete barrier shortly after compaction. CE Database keywords: Asphalt concrete; Quality control; Barriers; Hydraulic conductivity.

A fatigue performance prediction model of asphalt concrete is developed from a uniaxial constitutive model based on the elastic-viscoelastic correspondence principle and continuum damage mechanics through mathematical simplifications. This fatigue model has a form similar to the phenomenological tensile strain-based fatigue model. Therefore, a comparison between the new model and the phenomenological model yields that the regression coefficients in the phenomenological model are functions of viscoelastic properties of the materials, loading conditions, and damage characteristics. The experimental study on two mixtures with compound loading histories demonstrates that the fatigue model maintains all of the strengths of the constitutive model such as its accuracy and abilities to account for the effects of rate of loading, stress/strain level dependency, rest between loading cycles, and mode-of-loading on fatigue life of asphalt concrete.

The distresses of asphalt pavement, which include fatigue, rutting, and low temperature cracking, are related to the elastic modulus of asphalt concrete (AC). In addition, the elastic modulus of AC is a design variable for asphalt pavement structural design when elastic-layer system theory is employed. However, in the most commonly used AC design methods (the Marshall, Hveem, and Superpave methods), the elastic modulus is not used as a control variable. Therefore, these design methods do not ensure that the desired elastic modulus of AC will be obtained. In this paper, AC is treated as a two-phase composite with aggregates dispersed in the asphalt matrix. based on this treatment, a two-layer built-in micromechanical model of AC is developed by embedding an asphalt-coated circular aggregate into an equivalent AC medium. Using this model, an equation predicting the elastic modulus of AC is derived. The elastic modulus of AC predicted by the present model is compared with the Hashin and Shtrikman theoretical bounds and the Heukelom and Klomp equation. Using these comparisons, the proposed model is shown to be reasonable and applicable for predicting the elastic modulus of AC. Thus, the existing mix design approaches can be improved by using the modulus prediction model presented in this paper.

Current distress analysis practices and material specifications associated with low temperatures, including recent developments by the Strategic Highway Research Program, do not address the potential for localized damage associated with thermal incompatibility of asphalt concrete components. The analytical approach used to explain transverse surface cracking assumes a homogeneous pavement material. Although this approach produced satisfactory results for the prediction of low temperature cracking, it may obscure other forms of damage related to exposure to extreme low temperatures. This paper discusses localized forms of damage related to the vast difference in the coefficients of thermal contraction of asphalt concrete components (binders and mineral aggregates). Microscopic examination of asphalt concrete samples exposed to low temperatures revealed the presence of hairline cracks within the asphalt matrix. The examination also revealed deterioration of the bond at the aggregate/binder interface. The observed damage patterns explain the results of mechanical testing conducted using indirect tensile strength and three point bending procedure. Analysis demonstrates the potential impact of the observed forms of damage on pavement performance. It also explains results published by other researchers.

This paper is intended to verify the concern expressed by researchers that stiff asphalt-mineral filler mastics may lead to the cracking of flexible pavements in the brittle-ductile region. Test results obtained from the direct tensile test show that both tensile stress and tensile strain increase with increasing mineral fillers. The failure energy of asphalt-mineral filler mastics also increases with filler concentration because of increases in strength and strain. With increasing tensile strength, it is implied that there is a good adhesion between asphalt binders and mineral fillers. The tensile strength of asphalt-mineral filler mastics decreases as the size of filler particles increases. However, at very low temperatures plain asphalts and mastics exhibit low strains, indicating that mineral fillers may not be the cause of cracking. Interaction mechanisms between mineral fillers and asphalt binders are proposed to explain the increase of stress and strain. After reviewing various composite models, a particulate-filled composite model is selected to accurately predict the tensile strength of asphalt-mineral filler mastics.

A new elastoplastic model is presented for predicting the stress/strain response of asphalt concrete under cyclic loading. The model utilizes multiyield surfaces and isotropic hardening. Rowe's stress dilatancy theory is used to obtain the relationship between the permanent volumetric and vertical strains as well as the hardening law for the changes in the sizes of the plastic moduli caused by cyclic loading. These relationships considerably simplify the task of predicting the plastic deformation under cyclic loading of both triaxial compression and extension tests. A complete description of the plastic deformation of asphalt concrete under cyclic loading is treated, including the elastic, viscoelastic, and plastic components as well as the relationship between rutting and cracking. A computer program, called Rutting in Asphalt Concrete, RUT, determines the plastic deformation under cyclic loading. There is good agreement between the model predictions and experimental data that includes data published by other researchers.

This paper presents a mechanistic approach to uniaxial viscoelastic constitutive modeling of asphalt concrete that accounts for damage evolution under cyclic loading conditions. Schapery's elastic-viscoelastic correspondence principle is applied as a means of separately evaluating viscoelasticity and time-dependent damage growth in asphalt concrete. The time-dependent damage growth in asphalt concrete is modeled by using a damage parameter based on a generalization of microcrack growth law. Internal state variable formulation was used in developing the analytical representation of the model. Tensile uniaxial fatigue tests were performed under the controlled-strain mode to determine model parameters. Then, the resulting constitutive equation was used to predict the stress-strain behavior of the same materials under controlled-stress mode. The constitutive equation proposed in this paper satisfactorily predicts the constitutive behavior of asphalt concrete all the way up to failure under various loading conditions including different stress-strain amplitudes, monotonic versus cyclic loadings, and different modes of loading.

A viscoelastic solution of the diametral compression of short cylinders has recently been presented by Zhang et al. The solution is based on Hondros's elastic solution and applies to any load history. In this paper, the viscoelastic solution is used for analyzing the haversine load history. Expressions are derived for the real and imaginary parts of the complex compliance, as functions of phase angles and amplitudes measured in tests, and algorithms are presented for their evaluation. The theoretical solution is illustrated with a series of tests on two asphalt concrete mixtures, subjected at room temperature to haversine loading over a wide range of frequencies. It is shown that power-law creep compliance satisfactorily describes the deviatoric viscoelastic behavior of the tested materials. The volumetric behavior, on the other hand, is nearly frequency-independent and can be approximated by a purely elastic law. The results of this paper demonstrate that incorporating viscoelasticity in the interpretation of the diametral compression test is viable and provides valuable information on asphalt concrete viscosity-related properties.

Stripping has damaged some of South Carolina's asphaltic concrete pavements. It is not known whether the material properties of stripped asphalt pavement will allow its use for recycling. A field and laboratory study was initiated to investigate the feasibility of reusing moisture-damaged asphaltic concrete; to determine the effects of antistrip additives on recycled mixtures; and to evaluate the recycled mix design procedures that use cored reclaimed asphalt pavement (RAP) instead of milled RAP. A total of 144 laboratory Marshall specimens were made and tested. In addition, field cores were obtained and tested before and after recycling. The dry and wet modulus resilience (MR) and indirect tensile strength (ITS), visual strip rating (VSR), and air voids (AV) of all specimens were obtained. Marshall specimens containing moisture-damaged asphaltic concrete mixtures produced significantly higher strength values than those using only virgin material. Antistrip agents were found to be effective in increasing the strength of specimens in the saturated condition. The results also showed no significant differences among strengths of samples prepared with cored and milled RAP.

This paper presents an experimental analysis of the relationship between the relative quantity of a particular-size molecule in asphalt cement and the mechanical properties of asphalt concrete. Three AC-20 grade asphalt cements (AC) and recovered asphalt cements from four sources were used for high pressure-gel permeation chromatography (HP-GPC) testing and for preparing asphalt-concrete mixtures. Specimens of laboratory-prepared asphalt concrete and field cores were tested for tensile strength and resilient modulus in dry and wet conditions. Multiple-regression analyses indicate that tensile strength and resilient modulus had significant correlations with certain areas of chromatograms that are divided into 10 slices. Tensile strength appears to be sensitive to variation of the relative areas of the second and third slices (T(sub 2) + T(sub 3)) and resilient modulus vary with the area of the first, second, and third slices (T(sub 1) + T(sub 2) + T(sub 3)). In general, higher relative quantity of larger size molecules cause lower tensile strength and resilient modulus. However, there was no threshold value of the relative quantity of large molecules that showed a peak value for a mechanical property.

Current adhesion theories fail to explain completely the stripping phenomenon. Quantification of stripping potential prior to mix design, and based on variables described in current adhesion theories, remains difficult. Current laboratory evaluation procedures are not completely reliable and fail to predict, with accuracy, the stripping susceptibility of various asphalt concrete mixes. This paper evaluates the existing adhesion theories and stripping mechanisms suggested in the literature. Factors contributing to the lack of success in predicting stripping susceptibility of asphalt concrete in the laboratory are also discussed. An earlier comprehensive investigation of the stripping phenomenon revealed serious deficiencies in the current approach to the problem. First, the interaction between the different components of the asphalt-concrete mixture under a wide temperature range is neglected. It is proven that differential thermal contraction, as a result of the large difference in the coefficients of thermal contraction, is an important factor. This paper addresses another deficiency, which is the lack of a precise description of the location where debonding associated with moisture occurs. Observations made during the experimental investigation revealed that initial separation in the compacted mix takes place between the asphalt matrix (mix of asphalt cement and fine material) and coated aggregate particles.

Permanent deformation in asphalt concrete pavements manifests itself as depressions along the wheel paths, ruts. The prediction of rut depth requires a knowledge of materials characteristics that relate the asphalt concrete permanent strains to stress and temperature. This paper analyzes the character of permanent strains as inferred from a creep/recovery test. It is shown that the separation of the strains into the time-independent elastic and plastic strains and the time-dependent viscoelastic strains requires tests with various times to unloading. The analysis is illustrated with the results of a series of uniaxial compression creep/recovery tests on one asphalt concrete mixture. The tested material exhibits temperature-dependent elastic and plastic strains that are proportional to the level of stress. The time- and temperature-dependent viscoelastic strains are nonlinearly related to the stress level and stress history. An approximate constitutive equation that disregards this nonlinearity is presented.