Showing papers on "Asphalt concrete published in 1976"

Rubberized asphalt paving composition and use thereof

Abstract: The dissolving and/or dispersing of relatively large proportions of reclaimed rubber into molten paving asphalts is facilitated by incorporating into the asphalt a minor proportion of a highly aromatic, high-boiling, high-flash-point mineral oil. The resulting mixtures can be held at temperatures above 300° F for substantial periods of time without becoming too viscous for convenient handling, thereby facilitating the application thereof to roadways. The rubberized asphalt mixtures are particularly useful in the form of stress absorbing membrane interlayers between old, damaged pavement surfaces and an overlayer of new asphalt concrete, for providing chip-seal coatings over old pavement, as crack fillers in Portland Cement concrete or asphalt concrete pavements, and bridge deck waterproofing membranes.

Structural design considerations

Abstract: This paper illustrates existing and potential pavement design (thickness selection) procedures for thick lift asphalt concrete sections resting directly on prepared subgrades. Four existing design procedures - namely (1) that described in AASHO interim guide, and those of (2) the state of California, (3) the Asphalt Institute, and (4) Shell, have been selected as representing a cross-section of methods which can be used to design pavements of this type. In addition, a procedure utilizing recent research developments, and based on concepts embodied in the Shell design procedure is also presented to illustrate how research can be implemented to develop solutions for design situations beyond the scope of procedures such as those developed by AASHO, the state of California, and the Asphalt Institute. /TRRL/

Rutting prediction in asphalt concrete pavements

Abstract: The state-of-the-art paper summarizes a number of procedures to either limit rutting to some specific amount or to estimate the expected quantity from repetitive traffic loading. Two methods are suggested for estimating permanent deformation from long-term loading. From a design standpoint, the procedue for limiting the rutting to some prescribed amount that is based on a limiting subgrade strain criterion is the procedure that could be used with more confidence since these criteria have been developed from analysis of existing design procedures and field trials. On the other hand, the methodology described for the estimation of the actual amount of rutting from laboratory repeated load or creep tests and either elastic or viscoelastic layered theory will require field documentation before it can be used with confidence. Nevertheless, such procedures can be used to compare alternatives in design by making rutting estimates for pavements made of different materials. /Author/

Predicting permanent deformation of asphalt concrete from creep tests (abridgement)

Abstract: A method of predicting permanent deformation characteristics of asphalt concrete under repetitive loading is described. In this mehtod, a relatively small number of creep tests are needed for the characterization of the constritutive equation for predicting permanent strains. The approach outlined here is applicable to a rich-mix asphalt concrete. For asphalt concrete with a low asphalt content, the total permanent strain due to repeated loading cannot be considered as due solely to viscous flow, and an equation is presented which would give an accurate prediction of deformation: irrecoverable strain = A (delta + N) sup alpha + gamma (N) sup xi. N=total number of repetitions. Three of the 4 coefficients in equation (A, alpha, gamma) can be determined from the creep and recovery test results, and the fourth coefficient, xi, can be determined from a repetitive loading test.

Pavement and process of providing the same

Abstract: A portland-cement stabilized soil base for a roadway is covered with an elastic rubber-asphalt layer and thereafter with a surfacing layer The elastic layer may be formed by reacting 1 to 30% by weight of asphalt with 99-70% by weight of rubber and be applied hot as by spraying; and the surfacing layer will ordinarily be asphalt concrete composed of asphalt binding aggregate particle such as coarse stone, together Preferably the elastic layer covered with a layer to prevent bonding of the elastic layer with an overlying asphalt concrete layer Such bonding-preventing layer may be finely crushed stone, roofing paper, non-woven fabric, or plastic film, or the like

Asphalt cooling rates: a computer simulation study

Abstract: A simple method is presented for predicting the rate at which a newly placed asphaltic concrete mat cools under a given set of environmental conditions. Application of this method facilitates decisions on a daily basis, on whether or not to proceed with paving operations under marginal weather conditions specific to a construction site. Thermophysical properties of asphaltic concrete and pavement base materials common in Ohio are considered, together with heat transfer variables including conduction, convection, radiation, wind velocity, solar flux and cloud cover. Mathematical development of existing numerical calculation methods permits solution of the heat transfer equations in the field with a hand-held programmable calculator. The use of a portable surrogate device is also considered, for direct observations of the pertinent heat transfer variables. A quasi-analytical mathematical treatment developed for the specific purpose is most effective with the surrogate device. /Author/

Direct tension test results for some asphalt concretes

Abstract: Several thickness design and analysis techniques that have recently been made available utilize tensile strain as part of the procedure. A study was undertaken to determine the effect of some mixture and environmental variables on strain at failure (limiting strain) for some asphalt concretes. Cylindrical specimens were loaded to failure in direct tension and strain at failure was calculated from axial deformations. The information can be used to establish working values for rational mixture and thickness designs for mixtures where experimental and field parameters are essentially the same. These fundamental data can also be used to correlate direct tension values with those that are obtained with simpler indirect tension test methods.

Analysis of subgrade rutting in flexible airfield pavements (abridgement)

Abstract: This paper reports studies in which the amount of rutting occurring in the subgrade soil of prototype accelerated-traffic test pavements has been computed, and the rutting characteristics of subgrade soil as related to factors such as pavement thickness, subgrade strength, magnitude of load, and load repetitions have been investigated. Computations wer also made on subgrade soils of many pavements designed by the CBR equation for different loads and different subgrade strengths by using the procedure suggested by Monismith and others. The BISTRO computer program was used to compute the stresses in the subgrade. The test pavements analyzed in this study were conventional flexible pavements and full-depth asphalt pavements. The selections of modulus values for the asphalt concrete, unbound granular materials, and subgrade soils are explained. The study results indicate that the surface rut depth measured at the time the pavement is judged to be failed may increase as the thickness of the pavement is increased, even though the material in each layer of the pavement has been properly selected and compacted. Since the surface rut depth is not limited by the failure criteria, when 2 pavements are designed for the same performance level the surface rut depth and the subgrade rutting will be greater for the thicker pavement, while the elastic vertical strain at the surface of the subgrade will be nearly the same for the 2 pavements. If it is desired that pavements designed for the same performance level have the same degree of rutting in the subgrade, the elastic vertical strains at the subgrade surface induced by the load will have to be varied, with the smaller elastic strains allowed for stronger subgrades.

Rut depth perception

Abstract: This paper describes a method for the prediction of rut depth in asphalt pavements that is based on a combined mechanistic-empirical approach. Three methods, viscoelastic, elastoplastic and linear-elastic, were originally evaluated. The viscoelastic methods are under study by the Federal Highway Administration. The elastoplastic procedures offer the best longrange solution, but cannot yet be implemented for a multilayered structure such as an asphalt pavement. Therefore, this paper concentrates on linear-elastic procedures to relate the various mechanistic responses, stress, strain, and deformation to the rate of rutting observed on 32 sections at the AASHO Road Test. The rate of rutting was influenced by the season of the year and the number of years for which traffic is applied. Correlations with the surface deflection, the vertical compressive stress in the asphalt concrete, the vertical strain in the subgrade, and the traffic previouly applied to the section were obtained. Correlations could be obtained by converting heavy axle loads to equivalent 80-kN (18,000-lbf) single-axle loads using AASHO load equivalency values. The prediction model inlcudes calculations for estimating rut depth in terms of reliabilty. /Author/

Performance of asphalt concrete pavement mixtures produced by the drum mixer process

Abstract: The paper reports on a study to evaluate the performance of several projects constructed with drum mixed asphalt concrete. A 1970 prototype plant was used on one project, while the others were completed in 1972-73 using commercial models on large volume highway and airport jobs. Each site was visited in 1975, samples obtained and tested, and the findings evaluated with respect to overall quality and comparisons made with conventional pavements. Evaluations were made of overall quality in terms of Present Serviceability Index (PSI). The results were compared to original construction data and evaluated in terms of general quality as well as compared to similar projects constructed with conventional asphalt plant mixes.

Minimizing cracking of asphalt concrete pavements

Abstract: Asphalt pavements are extremely complex structures or systems whose performance is influenced by a myriad of factors ranging from the nature of traffic (weight and volume) to the whims of the environment (rainfall and temperature). It is the objective of the pavement design system to produce, on the roadway, a pavement capable of exposure to traffic and the elements, which will provide a desirable level of performance. The paper describes a project aimed at developing designer controlled recommendations which will provide a level of uniformity in the performance of asphalt pavements without the occurrence of unanticipated cracking. Various types and causes of cracking are discussed, asphalt concrete properties, aggregates, foundation materials, and other factors.

Impermeable Asphaltic Concrete Pond Liner

Abstract: An impermeable dense hydraulic asphaltic concrete solar evaporation pond liner was developed by the Southern California Edison Co. for the Mohave Generating Station, Clark Co., Nevada. Laboratory apparatus was developed and tests performed on native site materials to form an asphalt pond lining material. Quality control procedures were developed and monitored during construction to assure compliance with the rigid specification. The project proved that high density (97% of Marshall density) could be placed using standard construction and paving equipment. A brief description of the economics of the project, as well as the peculiar constraints imposed by the weather and plant operating procedures is included.

A bituminous mix of improved resistance to deformation

Abstract: The article describes the development of grave-bitume (gravel-bitumen) which has high resistance to permanent deformation under heavy loading. The bituminous mix has a strong stone skeleton with a high filler content incorporating a harder than normal bitumen and a higher proportion of crushed aggregate than previously used in French roadbases. Aggregate gradings are similar to those used in the UK for dense bitumen macadam, but the harder binder used is likely to make gravel-bitumen twice as stiff and possess a better fatigue behaviour. It is suggested that the material could be used in thinner layers than other roadbase materials, providing comparable structural performance. Experience with gravel-bitumen as a roadbase has led to its application as an overlay both in conjunction with asphaltic concrete surfacings or with a surface dressing as a seal. Measurements have shown that the material has a higher stiffness and elastic modulus than asphaltic concrete. /TRRL/

Application of fracture machanics for improved design of bituminous concrete, volume 2: evaluation of improved mixture formulations and the effect of temperature conditions on fatigue models

Abstract: In this study, the State-of-the-Art of fatigue and fracture concepts and matheamtical developments of stress-intensity factor were reviewed. The interrelation between normalized stress-intensity factor crack length and beam on elastic foundation are discussed. The effect of material consitituents influencing the fatigue and fracture response of asphaltic mixtures are discussed. The sensitivity analysis included the effect of mixture constituents such as asphalt, filler and polymeric and fibrous additives. In this study, a number of fatigue models for asphaltic concrete were also investigated. In this volume, a sensitivity analysis of mixture variables and a study of fatigue models as related to fracture mechanics is presented. The sensitivity analysis included the effect of mixture constituents, such as aggregate, asphalt and filler content as well as influence of mixture additives. Numerous polymeric and fiberous additives were investigated and effects of treatment levels and additive types on fatigue parameter A were evaluated. In this investigation a number of fatigue models for asphaltic concrete were investigated. These models ranged from the simplest form to the most general form. Variation of the parameters in these models were studied and relationships to asphalt mix were investigated. /FHWA/

Pavement Performance Models. Volume I. Repeated Load Fracture of Pavement Systems.

Abstract: : This report volume presents a state of the art for fatigue cracking of pavement systems. The report deals with prior research relating to the fatigue of asphalt concrete, asphalt emulsions, cement-modified emulsions, lime-treated material, lime fly ash, lime cement fly ash mixes, cement-treated material, and portland cement concrete. A comprehensive summary touching upon laboratory test procedures, test methods, influence of mix factors upon fatigue, generation of typical fatigue curves, development of fatigue fracture subsystems, and verification studies is presented. The state of the art is summarized and qualitatively rated relative to eleven different features felt to be necessary for the development of a fatigue subsystem. In addition, this summary formed the basis for recommendations dealing with future research on fatigue. The basis of the fatigue subsystem is formulated upon the concept that any such methodology proposed for fracture distress must ultimately be founded upon a functional pavement failure. Accordingly, the major results for future research, regardless of material type, appear to be focused upon the development of a distress-to-performance model that can be accurately used in pavement design and management systems.

Use of sand asphalt in highway construction

Abstract: Sand asphalt construction is being utilized by states in the Coastal Plain area of the Southeastern United States to alleviate the scarcity of high quality coarse aggregates. The paper summarizes current State Highway Department sand asphalt practice in the Coastal Plain. Representative local sands were selected from the state of Georgia. Tests were performed to determine aggregate characteristics, mix design, and the stress deformation properties of the sand asphalt mixes. An elastic layered analysis was used to determine the types of pavement sections in which sand asphalt could be successfully substituted for asphalt concrete. Finally, economic advantages of sand asphalt are discussed.

Improved techniques for prediction of fatigue life for asphalt concrete pavements

Abstract: Predictions for traffic-induced fatigue damage with time for asphalt concrete pavements are usually based on Miner's hypothesis and fatigue characterization of materials obtained from laboratory fatigue tests. In general, considerably greater damage is predicted than actually occurs in the field. This is partly due to inequities between the meaning of fatigue failure in laboratory testing and in a pavement layer in service, differences in stress states between laboratory specimens under test conditions and a pavement layer under wheel loads, and variability in strain and material characteristics in the field. Wheel tracking tests as developed by Shell Laboratories and analytical developments based indirectly on American Association of State Highway Officials (now American Association of State Highway and Transportation Officials) experimental data may be used for establishing much more rational fatigue relationships for asphalt concrete materials than those obtained from standard laboratory fatigue tests. Means for rationally revising the fatigue relationships to consider the effects of changes in temperature on fatigue life are presented. These two improvements allow considerably improved predictions for fatigue damage. Promising concepts for calculating an expected damage index to consider materials variability are discussed. Apparent shortcomings in the current stochastic formulations in VESYS IIM are described along with recommendations for further development. /Author/

Structural overlays for pavement rehabilitation

Abstract: Research in California on the use of deflection measurements for asphalt concrete overlay design resulted in a revision to the California overlay design method presented at the Western Summer Meeting of the Highway Research Board in August 1970. Deflection reduction characteristics and tolerable deflection levels of asphalt concrete were revised based on the performance of highway projects under study since 1960. A higher initial deflection level will result in a slightly greater percentage of reduction for a given overlay thickness. An evaluation of the design method compares predicted versus measured deflections on 69 reconstructed highways. The deflection level after reconstruction can be predicted within plus or minus 0.008 in. (plus or minus 0.2 mm) with a 95 percent confidence limit by using the deflection reduction guide. Pavement deflections are measured by using the California traveling deflectometer, which provides a dynamic type of measurement while traveling along the roadway at 1/2 mph (0.8 km/h). An asphalt concrete overlay design guide was developed that simplifies the procedure for determining overlay thicknesses, but other factors such as the condition of the structural section and reflection cracking potential may alter the design. Since 1960, the overlay method has been used on approximately 450 different roadways. /Author/

Surface treatments for asphaltic concrete for high speed traffic

Abstract: The most generally used traffic surfacing in Australia and New Zealand is the bituminous seal coat or chip seal. Increased use of hot laid asphaltic concrete mixes as part of a heavy duty structural pavement or as a shape correction treatment has brought with it problems of high speed skid resistance under wet conditions, even when new. The accepted alternative treatments for such conditions are: A chip seal; embedment of select chips in the hot-mix surface during construction; and use of a open textured asphaltic paving mix. Experience in use of chip seals and permeable friction course surfacings is discussed with particular reference to design, construction, and subsequent performance as measured by wet skid resistance (including speed/friction gradient) and surface texture change. Recommendations are made on method of choice of treatment for most effective construction and service. /Author/

Performance of coarse aggregate, hot sand and asphaltic concrete bases in oklahoma

Abstract: During the late 1940's and early 1950's Oklahoma experienced considerable success with road mix sand asphalt bases. This success encouraged the trial and subsequent use of hot mix sand asphalt based with the advent of the interstate system. This paper depicts the experience in Oklahoma of not only the sand asphalt bases but also the coarse aggregate and asphaltic concrete bases which have been in service since the late 1950's.

Rut depth prediction and test procedures for permanent deformation in asphalt pavements (abridgement)

Abstract: This article appeared in Transportation Research Record No. the basis for the current version of the VESYS II M rut Embankment on Varved Clays, and Foundations. incremental creep tests are presented. The rutting predicted by the VESYS II M structural subsystem is in good agreement with the observed on 2 experimental pavement sections. The close agreement between the results of the incremental creep tests and the interrupted repeated load tests and the simpler incremental creep test could be used in lieu of continuous repeated load tests to determine the rutting behavior of asphalt concrete at temperatures above 21 deg C (70 deg F). A fundamental creep law that separates the recoverable from the nonrecoverable strain was developed. Such a law can be modified to include temperature and stress effects and can be included in any structural subsystem for the prediction of rutting.

Dynamic analysis of asphaltic-aggregate mixtures

Abstract: Ultrasonic probes have been constructed for use in dynamic nondestructive testing of asphaltic concrete specimens. Use of the probe systems was superior to use of their main components alone, the piezoelectric crystals. The probes have the advantages of reducing ringing time, concentrating ultrasound in one direction, elimination of noise due to unshielded connections, and increased durability. The probes were used in a limited testing program. Compression and transverse wave velocities in the specimens tested were measured simultaneously. Sample conditions suitable for maximum wave velocity corresponded to conditions producing maximum strength and minimum voids in the mineral aggregate. A relationship of increasing wave velocity with increasing strength was noted. Wave velocity was observed to increase as the percentage of voids in mineral aggregate decreased. Various elastic constants were calculated from the wave velocities measured. Maximum values of E and G moduli as well as Poisson's ratio corresponded to minimum voids of the test specimens. Relative attenuation measurements were conducted by using water as a standard material. An evaluation of relative attenuation with changes in asphalt content indicated maximum damping at asphalt contents associated with high stability values.

Mechanistic structural subsystems for asphalt concrete pavement design and management

Abstract: Pavements are extremely complex physical systems involving the interaction of numerous variables. Their performance is influenced by factors such as material properties, environment, traffic loading, and construction practices. Pavement design procedures currently in use depend heavily on empirical relationships based to a large extent on long-term experience and field test such as the AASHO Road Test. It is generally recognized that such relationships between traffic loading and pavement performance apply only to the conditions under which they were developed. Application of these relationships to other sets of conditions is quite difficult. Considerable research has been conducted over the past 10 to 15 years with the objective of applying mechanistic technology to the structural analysis and design of pavements. This paper discusses realistic approaches to implementation of mechanistic technology resulting from the previous research and two specific studies culminating in usable structural subsystems. The subsystems, in the form of computer programs, are similar in some respects, but each has unique features. After further verification and calibration, they should be useful tools in the fields of asphalt pavement research, analysis, and design. /Author/

Fatigue criteria development for flexible pavement overlay design (abridgment)

Abstract: A fatigue model based on analysis and observations of numerous different pavement designs are presented for use in asphalt concrete overlay design. New overlay design procedures are being based on elastic layered theory, and fatigue curve analyses are being based on the analysis mentioned. Thus a compatability exists between development and application. The fatigue model presented is based on one asphalt concrete only; therefore, procedures should be investigated to adjust for mix design by using laboratory data.

Maintenance-free life of heavily trafficked flexible pavements

Abstract: Results obtained from a nationwide survey and analysis of the performance of 18 heavily trafficked flexible pavements are presented. The pavements surveyed are located in nine states, and interviews were held with highway engineers at each location. Results show that the major types of distress requiring maintenance for heavily trafficked flexible pavements are fatigue or alligator cracking, transverse crakcing, longitudinal cracking, and rutting. The major causes are heavy traffic loadings, inadequate pavement structures, low temperature shrinkage of asphalt concrete, poor lane joint construction, aging of asphalt cement, and disintegration of cement-treated bases from deicing slats and freeze and thaw. The maintenance-free life of conventional flexible pavement depends on several factors including environmental region. For wet regions having significant freeze-thaw cycles, maintenance-free life ranges up to 10 years; for dry freeze-thaw regins, maintenance-free life ranges up to 15 years. In non-freeze-thaw wet or dry regions, maintenance-free life ranges up to 15 years. Several design recommendations are given that were found to improve the maintenance-free life of flexible pavements and whose use may be justified after the high maintenance and user delay costs of heavily trafficked highways are noted. /Author/