Showing papers on "Asphalt concrete published in 1998"

Viscoelastic Continuum Damage Model of Asphalt Concrete with Healing

Abstract: A viscoelastic constitutive model of asphalt mixtures that accounts for the rate-dependent damage growth and microdamage healing is presented in this paper. An elastic continuum damage model, which is based on thermodynamics of irreversible processes with internal state variables, is first reviewed and extended to a corresponding viscoelastic model using an elastic-viscoelastic correspondence principle. A rate-type internal state evolution law is employed to describe the damage growth and microdamage healing in asphalt concrete. An analytical representation of the model is established for the uniaxial loading condition. Tensile uniaxial cyclic tests were performed under the controlled-strain mode with different strain amplitudes to determine model parameters. The resulting constitutive model successfully predicts the damage growth and recovery in asphalt concrete under multilevels of loading, varying rates of loading, different modes of loading (controlled-strain and controlled-stress), and random rest periods.

Viscoelastic constitutive model for asphalt concrete under cyclic loading

Abstract: 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.

Pavement Strain from Moving Dynamic 3D Load Distribution

Abstract: This paper presents the formulation and the application of a continuum-based finite-layer approach to evaluate pavement strain response under actual traffic loading. The model incorporates important pavement response parameters such as the dynamic tire-pavement load variations and corresponding complex contact stress distributions (normal and shear), vehicle speed, and viscoelastic material characterization. Results of a parametric study in which two typical thin and thick pavement sections were subjected to traffic loading moving at different speeds are included. As an important application of the proposed method, pavement strain responses generated by wide-base and dual tires have been presented. This study reveals that contradictory to the past studies, the impact of tire-pavement contact shear stress on tensile strain at the bottom of asphalt concrete is insignificant.

Aggregate tests related to asphalt concrete performance in pavements

Abstract: The properties of coarse and fine aggregates used in hot mix asphalt (HMA) are very important to the performance of HMA in pavements. Many of the current aggregate test methods were developed to empirically characterize aggregates and, therefore, may not be related to the performance of HMA. This research was undertaken to recommend a set of aggregate tests which are related to performance of HMA in pavement. The following aggregate properties were considered: (a) aggregate particle shape, angularity, and surface texture; (b) plastic fines in the fine aggregate: (c) toughness and abrasion resistance; (d) durability and soundness; and (e) characteristics of the material passing the 75 micrometer (No. 200) sieve (P200). Both current and new aggregate tests were identified and evaluated in the laboratory in terms of their relationship to three HMA performance parameters: (a) permanent deformation, (b) fatigue cracking, and (c) raveling, popouts and/or potholes. HMA performance parameters were measured by laboratory tests such as superpave shear tester (permanent deformation and fatigue cracking), Georgia loaded wheel tester (permanent deformation), and Hamburg wheel tracking device (stripping). A set of nine aggregate tests, related to HMA performance in pavements, are recommended. New tests include uncompacted void content of coarse aggregate, methylene blue test of fine aggregate and P200 material, particle size analysis of P200 material, and Micro-Deval test.

Aggregate toughness/abrasion resistance and durability/soundness tests related to asphalt concrete performance in pavements

Abstract: Numerous tests have been developed that empirically characterize aggregate without, necessarily, having a strong relationship to the performance of the final products incorporating these aggregates. This seems to be particularly true for aggregate toughness and abrasion resistance and durability and soundness. Toughness/abrasion resistance and durability/soundness tests for characterizing aggregate used in asphalt concrete were identified and evaluated, and those test methods that best correlate with field performance were determined. Based on a review of literature and specifications, laboratory tests for characterizing aggregate toughness/abrasion resistance and durability/soundness were selected. Sixteen aggregate sources with poor to good performance histories were identified for evaluation with the selected suite of tests. Performance histories of pavements containing these aggregates in asphalt concrete layers were established through personal contacts with state transportation agencies and performance evaluation questionnaires. Aggregate properties from laboratory tests were correlated with field performance. The micro-deval and magnesium sulfate soundness tests provide the best correlations with field performance of asphalt concrete and are recommended for characterizing aggregate toughness/abrasion resistance and durability/soundness.

Effect of Aggregate Gradation on Fatigue Life of Asphalt Concrete Mixes

Abstract: Four-point bending fatigue tests following the Strategic Highway Research Program (SHRP) M009 test protocol were executed to investigate to what extent gradation has an effect on fatigue performance of asphalt aggregate mixes. Gradations and mixes were selected that would satisfy all volumetric Superpave designs passing below the restricted zone. Other mixes were prepared with gradations passing through and above the restricted zone. The measured fatigue lives of 130 actual laboratory tests were compared with predictions by the Shell, Asphalt Institute, and SHRP-A003A fatigue-predictive equations.

Analysis of creep data from indirect tension test on asphalt concrete

Abstract: The purpose of this paper is to present several useful techniques for analyzing data from the indirect tensile (IDT) creep test. Furthermore, the intent is to explain and demonstrate these techniques in enough detail so that other interested engineers and researchers will be able to evaluate and apply these methods in analyzing their own data.

Aggregate orientation and segregation in asphalt concrete

Abstract: Asphalt pavement is a complex material that consists of aggregates, air voids and asphalt. The performance of asphalt concrete mixtures is influenced by its internal structure, which refers to the arrangement of aggregates and their associated voids. This paper focuses on developing computer automated image analysis procedures and parameters to quantify the aggregate orientation and segregation in asphalt concrete mixes. Aggregate orientation is described by a directional function with its components determined experimentally. Aggregate segregation is quantified by means of spatial statistics. The new parameters of orientation and segregation are used to study the variation of aggregate orientation and segregation in an asphalt concrete mix during compaction using the Superpave Gyratory Compactor (SGC). The measured parameters of the SGC compacted specimens are compared with those of field cores

Improved surface drainage of pavements

Abstract: The purpose of this project was to identify techniques for improving the drainage of multi-lane highway pavements and to develop guidelines for implementing the most promising of these techniques. The drainage of highway pavement surfaces is important in the mitigation of splash and spray and hydroplaning. This study focused on improving surface drainage to reduce the tendency for hydroplaning. The main factor affecting the propensity for hydroplaning is the thickness of the water film on the pavement surface. Three general techniques were identified for reducing the water film thickness: controlling the pavement geometry, the use of textured surfaces to include porous asphalt surfaces and grooved surfaces, and the more effective use of drainage appurtenances. The prediction of the water film thickness is based on the use of the kinematic wave equation as a model to predict the depth of flow on pavement surfaces. Data supporting the model were obtained from the literature and from studies conducted to measure Manning's n for a brushed concrete surface and for porous asphalt surfaces. Expressions for Manning's n as a function of Reynold's number were developed for portland cement concrete, concrete, asphalt concrete, and porous asphalt surfaces. Full-scale skid testing was also conducted on grooved and brushed concrete surfaces and on porous asphalt surfaces; texture measurements were obtained for all of the tested surfaces (laboratory and field). The results have been integrated into an interactive computer program, PAVDRN. This interactive program allows the pavement design engineer to select values for the critical design parameters. The program then predicts the water film thickness along the line of maximum flow and determines the hydroplaning potential along the flow path. If the predicted hydroplaning speed is less than the design speed, the designer is prompted to choose from alternative designs that reduce the thickness of the water film.

Pavement method and composition with reduced asphalt roofing waste

Abstract: A method of manufacturing and applying a novel pavement and patch material for roadways, driveways, walkways, patch for potholes and like surfaces, including the steps of reducing recycled asphalt roof waste to granules, adding aggregate and other solid recyclable materials to the granules, adding rejuvenating oil, adding emulsifier, adding asphalt concrete oil, adding anti-strip additives, adding liquid silicone, mixing the composition, heating the composition, applying the composition to the roadway or the like and compacting a new paving material

Mechanistic-based model for predicting reflective cracking in asphalt concrete-overlaid pavements

Abstract: One of the most common types of pavement on the national highway system is composite asphalt concrete (AC) over portland cement concrete (PCC). With a large percentage of PCC pavements either approaching or at the end of their design lives, AC overlay of PCC pavements has become one of the most common methods of rehabilitation. This has resulted in several thousand kilometers of composite AC/PCC pavements. As the level of heavy truck traffic loading continues to increase on a majority of pavements, it is likely that the total length of composite pavements in the nation will continue to increase considerably in the coming years. A common type of distress that occurs on these composite pavements is reflective cracking. This occurs when the joints or cracks in the underlying PCC pavement reflect through the AC overlay. A performance model that can be used to predict accurately the amount of reflective cracks in composite AC/PCC pavements has enormous potential uses. The development of a mechanistic-based per...

Behavior of Construction and Demolition Debris in Base and Subbase Applications

Abstract: The design performance of a pavement system is evaluated based on the predicted number of load repetitions it will be subjected to throughout its service life. Mechanistic pavement design predicts pavement failure due to cracking and/or rutting. The pavement system includes a bound bituminous layer and unbound base, subbase, and subgrade layer. An investigation is carried out on two types of constructed and demolition debris, recycled asphalt pavement (RAP) and recycled concrete (RCA). A comparison of these two construction with dense graded aggregate (DGA) revealed that RAP and RCA yielded higher resilient modulus values than DGA. Laboratory test results concluded these models could be used for evaluating resilient modulus and permanent deformation.

Influence of aggregate type and gradation on voids of asphalt concrete pavements

Abstract: Air voids in an asphalt concrete pavement highly influences its performance. Careful consideration of void requirements in compacted bituminous mixtures is more important than stability consideration, since the latter is always higher than necessary. Lack of attention to void requirements may be a direct cause of instability of asphalt concrete pavements. The present work studied the influence of aggregate type and its gradation on the voids in mineral aggregate and air voids of asphalt concrete paving mixtures as compacted according to the Marshall method. Three types of aggregates and five different gradations were employed. Aggregate gradation may be used to control the void requirements in a specific asphalt concrete mixture, influencing and/or affecting other important engineering properties such as water permeability of that specific mixture. On the other hand, aggregate type can provide the necessary voids requirements for an aggregate-asphalt mixture without sacrificing other important engineering properties. Two of the aggregates easily satisfied the void requirements. The third aggregate could not satisfy the same void requirements unless a porous gradation was used. Porous mixtures have more air voids, resulting in an increased permeability to water. This increase in permeability is not the same for different aggregate gradations. The coarser the mix, the higher the rate of increase in the water permeability for the same type of aggregate.

Effects of Aging on Viscoelastic Properties of Asphalt-Aggregate Mixtures

Abstract: The effects of aging on asphalt-aggregate mixtures is a topic that has been gaining attention in recent years. Of special interest is how the fatigue performance of asphalt concrete mixtures changes with time because of changing material properties. The fatigue performance of a mixture is related to its viscoelastic material properties. An investigation of the effects of aging on viscoelastic properties of an asphalt-aggregate mixture, such as creep compliance, relaxation modulus, dynamic modulus, and phase angle, is discussed in this paper. The framework for including the effect of aging in an existing uniaxial constitutive model is established, and the applicability of Schapery's elastic-viscoelastic correspondence principle to aged mixtures is validated.

Fatigue Behavior of Rubber-Modified Pavements:

Abstract: Over the last 18 years, a number of rubberized pavement projects have been built in Alaska. Initial laboratory and field investigations sponsored by the Alaska Department of Transportation and Public Facilities (AKDOT&PF) and conducted by Raad et al. indicated improved fatigue performance of the rubberized sections in comparison with conventional asphalt concrete pavements. The results of a follow-up investigation to develop design equations for rubberized pavements in Alaska are presented. Laboratory studies were conducted on field specimens using the flexural fatigue test in the controlled-displacement mode. Specifically, the rubberized mixes included asphalt-rubber concrete with AC-2.5 (wet-process) and PlusRide RUMAC with AC-5. Tests were performed for a range of temperatures varying between 22°C and —29°C. Fatigue relationships were developed in terms of repeated flexure strain, dynamic flexure stiffness of the mix, and repetitions to failure. Relationships for the dynamic flexure stiffness as a func...

Nonlinear visoelastic behavior of asphalt concrete in stress relaxation

Abstract: It is accepted that asphalt concrete for paving roads us a viscoelastic material. For engineering purposes, the stress-strain relationship for asphalt concrete has been assumed to be linear visoelastic. An earlier study (1) indicated that the material has a linear limit of only 0.1 percent deformation or less, implying that the material is nonlinear in normal service conditions of pavements. The actual nonlinear properties, the practical effects of the nonlinearity, and the best way to characterize asphalt concrete remain obscure. This study is to investigate the nonlinear viscoelastic behavior of asphalt concrete in stress relaxation under uniaxial-stress conditions at temperatures and at strains that a pavement might undergo. Priority is given to thermal stress prediction in asphalt pavements, since, in cold regions, such as central Canada, thermal cracking is a most serious problem.

Image Analysis Evaluation of Aggregates for Asphalt Concrete Mixtures

Abstract: The performance of asphalt concrete mixtures is influenced by the properties of the included aggregates, such as grading, shape (angularity and elongation), and texture (roughness). Complete and accurate quantification of aggregate properties is essential for understanding their influence on asphalt concrete and for selecting aggregates to produce high-quality paving mixtures. Recent developments in the use of digital image analysis techniques for quantifying aggregate morphological characteristics in asphalt concrete are summarized. Image morphological characteristics were used to quantify flatness and elongation of coarse aggregates, to estimate the proportion of natural sand in fine aggregates, and to correlate aggregate characteristics with engineering properties of asphalt concrete mixtures. Image analysis of sections also revealed information about the grading, shape, and orientation of coarse aggregates in a mixture. An overview is presented of the broad range of useful pavement engineering applications of this relatively new approach for evaluating aggregate characteristics.

Asphalt surfacings: a guide to asphalt surfacings and treatments used for the surface course of road pavements

Abstract: Contents: 1. Introduction; 2. Aggregates and fillers; 3. Binders; 4. Required characteristics; 5. Rolled asphalt surface courses; 6. Asphalt concrete (and macadam) surface courses; 7. Porous asphalt surface courses; 8. Mastic asphalt (and gussasphalt) surface course; 9. Stone mastic asphalt surface courses; 10. Thin surface course materials; 11. Veneer coats; 12. Specialized materials; 13. Recycling materials; 14. Summary

Model prediction of rutting in asphalt concrete

Abstract: 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. Good agreement exists between the model predictions and experimental data that include data published by other researchers.

Asphalt concrete damage associated with extreme low temperatures

Abstract: 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.

Polymer Modification of Arab Asphalt

Abstract: Neat asphalt binders lack the proper viscoelastic balance that usually occurs when an effective elastic network is created by molecular association. It is hypothesized that proper viscoelastic balance can be formed by creating molecular entanglement in asphalt through the use of high molecular weight polymeric additives. In this research, a procedure for modifying asphalt binders was developed, together with criteria to evaluate the effectiveness of the polymer modification process. The procedure and criteria were used to modify Arab asphalt binders to satisfy the performance requirements of the Gulf countries, in terms of rutting, fatigue, and low-temperature cracking. The data collected clearly indicated that polymer modification is effective in improving the rheological properties of neat Arab asphalt binders to satisfy the performance requirements of the Gulf countries. Furthermore, life cycle cost analysis of various polymer modified mixtures indicated that polymer modification is feasible and economically justified.

Relationships among rate-dependent stiffnesses of asphalt concrete using laboratory and field test methods

Abstract: As the application of nondestructive testing on pavements in service becomes more frequent, it is increasingly important to relate the resulting stiffnesses to those from laboratory test methods. The relationship among stiffnesses measured from five test methods currently used for asphalt concrete is addressed: creep compliance, complex modulus, impact resonance, falling weight deflectometer, and surface wave. Established relationships from linear viscoelastic theory are used to relate stiffnesses, including a comparison of creep stiffness, S(t), and relaxation modulus, E(t), calculated from creep compliance, D(t). Using laboratory and field measured stiffnesses, a linear relationship was discovered between stiffness and frequency on a log-log scale.

Probabilistic Method of Asphalt Binder Selection Based on Pavement Temperature

Abstract: The Strategic Highway Research Program, conducted in the United States and Canada from 1987 to 1992, included a significant asphaltic concrete study. The study included a new grading method for asphalt binders, performance grading, resulting in what is termed PG asphalt. The grade selection process is based on air temperature distribution. Since 1994, the Long-Term Pavement Performance program has established a seasonal monitoring program that consists of a number of sites with air and pavement temperature sensors and a data logger that records the air and pavement temperatures hourly. These data are now available for prediction of the extreme temperatures that are needed for the selection of the appropriate PG asphalt binder. On the basis of the review of the recent pavement temperature studies and statistical analysis of the pavement temperature data available, an empirical prediction model has been developed from the original data set and validated from the expanded data set. The model is compared with...

Evaluating accelerated rut testers

Abstract: To avoid costly pavement failure and to ensure that rehabilitation and maintenance efforts are maximized, state Departments of Transportation have adopted the use of accelerated rut testers and/or servohydraulic testing devices to help predict pavement performance. The Federal Highway Administration tested several devices at the Turner-Fairbank Highway Research Center in McLean, Virginia, to determine which device offers the most accurate prediction of pavement rutting resistance. Accelerated rut testing devices, such as the Georgia Loaded-Wheel Tester, French Pavement Rutting Tester, and Hamburg Wheel-Tracking Device, try to simulate the distresses caused by many years of exposure to traffic within a matter of hours by rolling a wheel across a sample of asphalt concrete under specific temperature and humidity conditions. These devices apply a fixed load at a fixed temperature and do not account for seasonal changes in traffic, temperature, or environment. Servohydraulic equipment, such as the Superpave Shear Tester, offers the option of changing temperature and load configuration; however, tests are still performed under fixed conditions. Comparison tests showed that no device was clearly better than the others. For the most part, all devices were able to separate good from bad mixtures when these had been made with the same aggregate and different binders. However, when mixtures with two different aggregate gradations were tested, no device was able to distinguish the mixtures that performed well from those that did not, even though accelerated loading facility testing showed significant differences in pavement performance.

Mechanistic-empirical evaluation of the Mn/ROAD low volume road test sections.

Abstract: This study utilized Illinois Department of Transportation (IDOT) mechanistic-empirical (M-E) procedures and Mn/ROAD low-volume road (LVR) data and information to verify/refine/modify analysis and design concepts and procedures for LVR flexible pavements. The Mn/ROAD LVR flexible pavements include conventional flexible, full-depth asphalt, surface-treatment and aggregate-surface sections. Laboratory test results, field distress measurements, and falling weight deflectometer (FWD) test data were used to study the effect of granular material quality on pavement performance and deflection response. The results from the rapid shear tests, permanent deformation tests and field rutting measurements show that granular material rutting potential can be characterized by a rapid shear triaxial test at 15-psi confining pressure. For conventional flexible pavements, granular material quality did not affect the pavement deflection response, but material quality effects were significant for aggregate-surface and surface-treatment pavements. ILLI-PAVE predicted pavement responses were fairly accurate for sections with thicker asphalt concrete (AC) surfaces. The FWD deflection basin parameter AUPP (Area Under Pavement Profile) can be used to predict the strains at the bottom of the AC layer. Effect of subgrade type on pavement response and performance was studied. Sandy subgrades showed little or no change in pavement structural response due to spring-thaw effects. For the cohesive subgrade sections, moisture changes and spring-thaw effects increased surface deflections. The study showed that the IDOT LVR flexible pavement M-E design concepts and procedures are valid and adequate.

Low-Temperature Cracking and Aging Performance of Modified Asphalt Concrete Specimens

Abstract: The thermal stress restrained specimen test (TSRST) was used to evaluate the low-temperature cracking resistance and aging performance of modified asphalt concrete (AC) specimens. One aggregate, two asphalt cements (AAA-1 and AAB-1), five modifiers (latex polymer, ethylene acrylate copolymer, rubber powder, elastomer, and a blend of polypropylene and Kevlar fibers), and four 85°C oven aging levels (0, 5, 25, and 50 days) were considered. The results of the bending beam rheometer test (BBRT) on binders at -20°C showed that AAA-1 displayed a smaller creep stiffness than AAB-1. Only two modifiers increased the deflection and softness of AAB-1. The additives in AAA-1 did not improve its lowtemperature rheological behavior. These results served as the basis for comparison with those from the TSRST. The fracture strength and temperature of AC specimens are sensitive to asphalt type (4.11 MPa and -32.2°C for AAA-1, 3.28 MPa and -25.4°C for AAB-1) and degree of aging (from 4.11 to 2.04 MPa and from -32.2 to -21.2...