7th Conference

7th International Conference on Asphalt Pavements – Volume contents
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A list of session titles and paper titles

Effects of different pavement rehabilitation types on the development of rut depth and fatigue cracking
H Beckedahl, H Buseck, A Gerlach, E Straube, S Velske

Pavement rehabilitations vary in general any part of the wearability of the pavement substance, no matter what reason led to the rehabilitation. In Germany the VESYS-program has been extended to a pavement rehabilitation design program. The calculated rehabilitation effects are compared with the measured ones and the effects of different rehabilitation types including an asphalt binder course with low strength against permanent deformation are shown. Several asphalt mixtures were tested with different laboratory test methods. Two of them and some test-results are described in this paper.

Two-stage mechanistic approach to asphalt pavement design
S F Brown, A R Dawson

A method is outlined for the design of asphalt pavements in two stages; the foundation under construction traffic followed by the completed structure under long-term loading. The results of research on soils and granular materials are incorporated to establish design criteria and allow for non-linear resilient behaviour. The method incorporates simple charts and equations and is illustrated by an example. The procedure is put forward as a framework for further progress and discussion rather than as a complete package.

Extending the use of the Nottingham Asphalt Tester
F Bullen, J N Preston

Present mechanistic pavement design procedures do not take into account creep deformation in thick asphaltic concrete layers. The Nottingham Asphalt Tester (NAT) and similar apparatus may be used to remedy this deficiency however, the use of the NAT in pavement design is restricted by the need for extensive sample testing and accompanying preparation. The use of simple mathematical models is able to extend the use of the NAT by predicting the behaviour of specimens more representative of the actual pavement.

Interface systems to prevent reflective cracking. Modelling and experimental testing methods.
L Francken, A Vanelstaete

This paper describes recent developments on design and evaluation of interface systems for the prevention of reflective cracking in asphalt overlays. The study deals with the following topics :
– Characterisation of the system components (asphaltic and interlayer products)
– Calculation models for the evaluation of the structural behaviour of such systems under thermal and traffic loads.
– Laboratory simulations for the study of the effect of thermal loads.
– Field surveys for the evaluation of their feasibility.

Thickness design of asphalt overlays on concrete pavements for airports
Y Hachiya, K Sato, A Kawakami

Two design methods of asphalt overlays on the structurally sound concrete pavements have been developed. The current design method gives extremely thick overlays on the condition that the existing concrete slabs are structurally sound. One is based on a multi-layered elastic theory in case that there is no danger of reflection cracking occurring, and the other is founded on a finite element method when reflection cracking is suspected. Loading test data on experimental pavements have been taken into consideration in the process of establishing both methods. The proposed design methods give thinner overlay thickness compared with the current one.

Application of the visco-elastic properties of asphalt concrete
P C Hopman, A C Pronk, P A J C Kunst, A A A Molenaar, J M M Molenaar

In this paper a visco-elastic approach to the rutting and fatigue behaviour of asphalt pavements is presented. For this the Burgers’ model has been adopted and several laboratory tests have been performed to characterize the parameters in the Burgers’ model both for fatigue and permanent deformation. From these tests it appears that the elements of the Burgers’ model are dependent on the mode of loading (tensile versus compressive). Furthermore evidence has been obtained that values for the elements can be estimated from mix composition and bitumen characteristics.

In order to be able to qualify the behaviour of a visco-elastic pavement structure, the pavement is characterized at this stage as a visco-elastic half-space, which is loaded by a moving point load. It appears that the velocity of the load and the viscous properties of the asphaltic material are important factors which control the deterioration of the construction.

This study enables a further detailed insight in the mechanical behaviour of asphalt pavements. It will be used to develop a better correlation between the mix composition and the mechanical behaviour of the road.

Cracking in asphalt concrete pavements
M M J Jacobs, A H de Bond, A A A Molenaar, P C Hopman

This paper describes the research efforts that are currently undertaken at the Road and Railroad Research Laboratory of the Delft University of Technology in the modelling of crack propagation in asphalt concrete mixes and the development of an overlay design method. From the research on crack propagation it appears that cracking in asphalt concrete mixes is a rather complex phenomenon. Micro crack zones, as well as small single macro cracks develop initially while later on these small macro cracks combine into one large macro crack. The incorporation of this complex crack behaviour in pavement and overlay design models would make these models not suitable for every day use. However it is shown that the complex crack process can be simulated by a much simpler single macro crack process. This approach has been used to characterize the cracking of asphalt concrete mixes and to develop a set of design equations which allow the calculation of stress intensity factors at the tip of cracks entering from the existing pavement into the overlay. It is believed that procedures are provided that can be used in practical overlay design problems.

Performance of asphalt pavements at Bibi new test road in Japan related to their bearing capacity
A Kasahara, K Himeno, K Kawamura, S Nakagawa

In order to transfer from the conventional and empirical asphalt pavement design method to theoretical one, it is important to ascertain performance of asphalt pavement designed based on the respective design method. For this purpose, Bibi New Test Road was constructed in July 1990 in National Highway Route 36 close to New Chitose Airport in Hokkaido area. To obtain the performance, measurements were made for the following items:
1) Weigh-in-motion,
2) Pavement distress, and
3) Surface deflection.

In particular, the relationship between elastic moduli in the asphalt pavement structure layer and a number of equivalent 49kN wheel load were determined, according to backcalculation of deflection data obtained by a falling weight deflectometer.

Rational concept in relating lab testing to pavement analysis
M S Mamlouk

A laboratory investigation is performed to evaluate the modulus of typical asphalt concrete using fourloading conditions; diametral (indirect tensile) pulsating, axial compressive pulsating, triaxila compressive pulsating, and axial compressive harmonic. The diametral modulus was considerably higher than those obtained from compressive loads, especially at low and intermediate temperatures. The laboratory results were related to typical pavement field conditions. Since the stresses are mostly compressive in the pavement asphalt layer, a significant error might develop if the tensile lab modulus is used in the analysis. In addition, the temperature correction factors reported in the 1986 AASHTO guide to be used with non-destructive testing of pavements are too sensitive. More accurate pavement analysis and temperature correction factors can be developed if both tensile and compressive moduli are considered.

Integrating flexible pavement mix and structural design
R W May, M W Witczak

Typically, asphalt concrete mix design and the structural thickness design of the pavement are performed separately. New analytical computer programs that allow the two design processes to be integrated into a rational system are described. The discussion is concentrated on the behavior and performance models used in evaluating the trial mixes for the intended pavement cross-section. Performance is examined in terms of fatigue cracking, permanent deformation, and low-temperature cracking. Finally, the performance of mixes in actual pavements is compared to the performance predicted by this system.

Fatigue of asphaltic mixtures and paving cracking
J Medina, L Motta, S Pinto, R M Rodrigues

Fatigue test data of fifteen asphaltic mixtures under stress controlled diametric compression are presented. Creep testing under diametric compression is compared to repeated load diametric compression. Some results of strain controlled flexure tests are compared to stress controlled tests. Fracture parameters of Paris’s law are obtained from the analysis of the diametral compression test. Models of crack propagation – vertical, horizontal, and reflection cracking – are presented. A model for pavement management system with its application is shown.

Resilient modulus of granular materials under repeated loading
A Nataatmadja

Several models presently available for characterisation of granular materials under repeated loading are reviewed and a new simple elastic model is subsequently proposed. The model can predict the dynamic stress-strain relationship (yielding and locking) during loading and incorporates both the first invariant of stress and the repeated deviator stress. The model is dimensionally stable, requires only straightforward calculation for parameters, and offers a practical application in the analysis and design of flexible pavements as well as in the evaluation of material performance.

Guidance on the design of fine dense bituminous material
E O Donnell, D Fordyce, K Khweir

A rational approach to the design of fine dense bituminous materials is outlined which extends current procedures. The approach is based on the characterisation of the dry compacted fine aggregate-filler structure. A profile of voidage allows for: an appraisal of the effectiveness of the packing of the blend, calculation of binder content at a target blend and an appraisal of mix tolerance to material ingredient variation. Placement performance is appraised using a stiffness-temperature profile defined using a high temperature triaxial cell and from compaction data. Service performance can be measured from current fundamental techniques.

The effect of maximum nominal aggregate size and the coarse/fine ratio to permanent deformation of continuously graded mixtures
G Tsohos, A F Nikolaides, D Leondarides

Six typical gradings of asphaltic concrete mixtures for surface course and two types of bitumen (40/50 and 60/1OOpen) were examined in order to investigate their effect to permanent deformation. The evaluation was carried out using the unconfined creep test. The results show that mixtures with high coarse aggregate content and large maximum aggregate size possess better resistance to permanent deformation. A minimum coarse/fine aggregate ratio of 1.O is justified and proposed for better deformation performance of the mixtures. The effect of using harder bitumen is only apparent on rich mixtures. Air voids is a critical factor and there should be a limiting permissible value depending on the maximum aggregate size.

The case for tapered pavement sections
A H Rhodes

This paper assesses the potential for using tapered pavement sections on dual two-lane and dual three-lane roads. The taper is formed by varying the depth of the base layer which is overlayed by a conventional surfacing. The study demonstrates that either the design life of a conventional pavement section can be almost doubled by redistributing the base material to form a tapered section, or the base material can be reduced by at least 20 per cent without reducing design life.

Micromechanical modelling of asphalt concrete in connection with pavement rutting problems
L Rothenburg, A Bogobowicz, R Haas, F W Jung, G Kennepohl

Rutting of asphalt concrete can be modelled using discrete element techniques that are able to simulate the interactions of individual aggregate particles binded with bitumen. The particles are treated as elastic elements and the binder as a linearly visco-elastic material. Creep displacement of the particles involves a viscous flow of the binder, whose rate is affected by binder viscosity, film thickness, contact stress and other parameters. The binder within voids is treated as a compressible Newtonian fluid. Simulations are carried out by numerically solving Newton’s equations of motion for individual particles. Results of the simulations illustrate the effects of cohesive and frictional contacts on creep behavior. Rutting occurs when the number of frictional contacts is below a certain minimum.

Critical condition mechanistic analyses for structural evaluation and rehabilitation design
B E Ruth, L Guan, M Tia

A computer program for the REhabilitation Design of Asphalt Pavement Systems (REDAPS) was developed to mechanistically analyze and design flexible pavements. The analysis segment of the program uses non-destructive deflection test methods (e.g., FWD or Dynaflect) in combination with asphalt mixture properties to assess the effect of thermal contraction and load induced stressing conditions during periods when the pavement is at its worst structural support (critical) condition. Description of the key functions built into the program are presented along with the testing requirements needed to provide input parameters for the asphalt concrete pavement layer(s).

Use of the Pencel pressuremeter in pavement design
P J Sanders, E Horak

The paper describes the use of a special pressuremeter and associated in-situ equipment for shear strength measurement and compares test results with those of a Heavy Vehicle Simulator (HVS) and laboratory shear tests on one site. Results are given for tests on a subgrade and a crushed mine dump rock basecourse. From the limited data the pressuremeter shows promise for use in mechanistic design and provides data that can be used to predict stress-dependant elastic moduli. An iterative technique to predict elastic moduli under wheel loads is also described using equations derived from pressuremeter test results and multi-layer linear elastic analysis.

High modulus asphalt mixes – Laboratory evaluation, practical aspects and structural design
J P Serfass, A Bauduin, J F Garnier

High Modulus asphalt mixes can be obtained using various technologies, the main ones being special very hard bitumen, asphaltite-modification and polyethylene-modification. The laboratory characterization of these types of High Modulus mixes is presented and discussed. It comprises gyratory compaction test, compressive and tensile strength, determination of static moduli, rutting resistance, complex moduli, fatigue response, and low-temperature behaviour. Practical aspects are briefl y dealt with. In-place characteristics and performance are then analyzed, special attention being paid to linking laboratory- and site- results. Examples of pavement condition evaluation and modulus backcalculation are given. They show that practice matches research.

Modelling strain distributions in flexible pavements for variable loads and tire contact pressure distributions
H F Southgate, K Mahboub

A modified Chevron N-layer program permitted application of 150 discrete loaded areas and contact pressures to a given flexible pavement structure. This paper presents sensitivity analyses for three loadings:
a) variable loads and pressures,
b) variable loads and constant pressure, and
c) constant load and constant pressure.

Static load analyses indicated that the severest combination of load and location corresponds to the variable load, variable tire contact pressure, for the location under the edge of the tire. Tire-pavement interaction proved to be too important to be neglected in the pavement response analyses.

Water conditioning of asphalt concrete mixtures using the environmental conditioning system (ECS)
R L Terrel, S Al-Swailmi, A Al-Joaib, W L Allen

As part of the SHRP contract, the Environmental Conditioning System (ECS) was developed to evaluate the water sensitivity of asphalt paving mixtures. The ECS includes cyclic hot-cold conditioning following partial saturation under flow-through vacuum. The integrity of the mixture is monitored by measuring dynamic resilient modulus (MR) and permeability after each cycle. Repeated loading can be applied continuously or only during M, measurements. The ratio of original (dry) to conditioned (wet) M, appears to be a good indicator of expected deterioration. Also, visual observations of stripping and change in permeability provide a further indication of asphalt-aggregate compatibility.

ILLI-PAVE based conventional flexible pavement design procedure
M R Thompson

The basic concepts and the development of a CONVENTIONAL FLEXIBLE PAVEMENT THICKNESS DESIGN PROCEDURE are presented. The proposed procedure is based on resilient soil and material testing procedures, the ILLI-PAVE structural model, and design algorithms developed from an extensive ILLI-PAVE data base. Traffic (Equivalent Single Axle Loads), subgrade modulus, location (pavement temperature effects), asphalt concrete modulus and design reliability are considered. Comparisons of ILLI-PAVE, SHELL, and the Asphalt Institute thickness requirements are made.

Development and validation of realistic pavement response models
J Uzan, M W Witczak, T Scullion, R L Lytton

In this paper constitutive models are presented for both the resilient modulus and Poisson’s ratio of granular materials. They are based on an extensive review of laboratory test data and incorporate the dilation effects which have been measured to exist at high stress ratios. These constitutive equations have been incorporated into a finite-element computer code. A comparison is made of the influence of using either a fixed or varying Poisson’s ratio on the induced layer stresses. Validation is attempted using deflection data from instrumented test sections. The proposed nonlinear equations show a distinct improvement over the linear approach in matching both surface and depth deflections.

The Shell pavement design method on a personal computer
C P Valkering, F D R Stapel

A version of the Shell Pavement Design Manual has been developed for use on personal computers. The Manual, based on a rational method for the thickness design of flexible pavements, was published in 1978 in the form of a series of design curves. The separate computer modules of the new version provide for the prediction of material properties and for the calculation of the critical stresses and strains. The method now has greater flexibility in that the user can introduce his specific material properties, traffic or climate without extensive interpolation effort.

Structural design of road structures with unbound granular bases and subbases
E Vos, P J Galjaard, A P Allaart

A mechanistic approach of the structural contribution of unbound granular bases and subbases has been developed. It is based on a non-linear elastic constitutive model, the parameters of which can be determined with cyclic load triaxial tests. The model has been implemented in the finite element code DIANA. Validation has been carried out by comparison of calculated and measured asphalt strain data of full scale test pavements. For full depth asphalt structures and structures with unbound granular base courses a good compatibility has been found. Comparison has been made between the results of the developed non-linear elastic approach and traditional linear elastic analysis. Consequences for practical road design are discussed.

A reliability analysis of flexible pavement design
Q S Zhang, Li Yun

Based on the Design Code (JTJO14-86) for Highway Flexible Pavement issued in 1986 by the Ministry of Communications of China, this paper has put forward a method of analysing the reliability of flexible pavement with multi-indexes. It has carried out a probability statistics and simulation analysis for the design indexes and parameters, thus obtaining their probability distribution. Also, it has calculated and analysed the reliability and sensitivity of pavement structure by using different mean parameters and coefficients of variation. Finally, it has discussed the application of reliability analysis in areas of construction and quality control.

Aging of asphalt-aggregate mixtures
C A Bell, Y Ab Wahab, J E Klliewer, D Sosnovske, A Wieder

This paper presents the development of laboratory aging procedures for asphalt-aggregate mixtures as a part of project A-003A of the Strategic Highway Research Program (SHRP). A short-term oven aging method to represent aging of the mixture when it is hot during the construction process is described. Alternate long-term aging methods are considered, involving oven aging, or forcing oxygen through a specimen. The development of tests to evaluate the extent of aging is also described together with the extensive data gathered (to date), and a description of testing yet to be done. Finally, a validation program is outlined, which compares the aging of mixtures in the field with that achieved in laboratory made specimens.

Assessing the nonlinear behavior of subgrades and granular bases from surface deflection basins
R Bonaquist, M W Witczak

Linear elastic basin analysis methods often yield unrealistic layer moduli when stress dependent subgrade soils and unbound base materials are encountered. The objective of this study was to develop and verify a method for assessing the nonlinear behavior of subgrade soils and granular base course materials from surface deflection basin measurements. The method that was developed is not a rigorous nonlinear solution, but uses numerical integration of the Boussinesq point load solution to estimate stresses and to calculate deflections using stress dependent moduli. Field derived nonlinear modulus relationships were developed with this method for a silty sand soil, and a dense graded crushed aggregate base.

A new initiative in measuring the fatigue performance of bituminous materials
M J Brennan, F Clancy

Cylindrical test specimens are manufactured using a double acting static load of 100 or 125 kN. The specimens are tested in uniaxial sinusoidal loading with zero mean stress. Failure is defined by the complete fracture of a specimen. The materials that have been tested include SBS modified and unmodified bitumen macadams, EVA modified and unmodified rolled asphalts, graves-emulsion, asphaltic concrete, heavy duty macadam and polymer modified slurry seal. The paper presents the results of statistical comparisons between the performances of the different materials together with analyses of the effects of test temperature, aggregate grading, bitumen content and rest periods.

Performance of bituminous road pavements in Malaysia
K P Chong, R B I Hasnur, J K Han

The primary mode of pavement distress in Malaysia is cracking in the bituminous surfacing due to a reflection of cracks from existing pavement and age-hardening of the bituminous materials. Rutting is not a major problem except at highly stressed areas such as on climbing lanes and junctions. Extensive research has been carried out by the Training and Research Institute, Public Works Department of Malaysia, to address the problems of pavement distress accordingly. Some early findings from the research work are discussed and presented in this paper.

Full scale pavement testing in the Netherlands
L J M Dohmen, A A A Molenaar

Response studies have been carried out on several test pavements, equipped with strain measurement devices. From the results it appears that the actual strain under a circular, uniformly distributed load as produced by a falling weight deflectometer can easily be predicted with linear elastic multi layer programmes, like e.g. BISAR. The agreement between the measured and calculated strain due to a moving dual and single wheel was less then was obtained from the F.W.D. tests. The measured strains were lower than the predicted ones. It is believed this is mainly due to the non-uniform contact pressure distribution but effects of visco-elasticity might have attributed to this as well.

Furthermore it appeared that there was a very good agreement between the asphalt layer stiffness back calculated from deflections profiles and the laboratory determined mix stiffness.

Effect of polymer modified bitumen on rutting and cold cracking performance
J Eisenmann, U Lempe, U Neumann

The paper presents extensive laboratory tests to determine the influence of different kinds of polymer modified bltumen in opposition to a usual bitumen as it appears in practice. Tests were run to investigate each binders’ performance in asphalt courses at high and low temperature and under dynamic load repetitions. Full scale tests were run in a special device to estimate the influence of the used binders on rutting. The results of the different tests show a good conformity that is partly proved by theoretical studies.

Effects of asphalt properties on low temperature cracking of asphalt pavements
H Kanerva

The effect of the following asphalt properties on low temperature pavement cracking are studied: penetration at 0, 5, 10 and 25C, viscosity at 60 and 135C, Fraass brittle point, softening point R&B, ductility at different temperatures, force-ductility at OC, sliding plate-stiffness at -10C and OC, glass transition point (DSC), impact strength at different temperatures and cracking temperature on a glass plate. All these properties are correlated with a cracking temperature measured in a laboratory using the restrained stress beam test. Based on the data from nine asphalts, the penetration at 5C of the TFOT residue together with PI are the best predictors for the cracking temperature of the mixture.

Technology and in-situ trial of a noise absorbing pavement structure
E U Hiersche, H-J Freund

The porous surface bituminous wearing courses which are employed for traffic noise reduction are capable of reducing rolling noises of traffic by approximately 3 dB(A). A pilot study and trafficable pavement test section showed that a full depth of 45 cm and an air void content of 20 – 25 Vol.- % is necessary to reduce rolling noises by approximately 7 dB(A) and engine and driving noises by 6 dB(A). Bitumen and Cement, as well as synthetic materials (as a wearing course alternative of bituminous subsection) were utilized as binding agents. After a service life of approximately 2.5 years further investigations (in regard to materials, construction and cleaning procedures) of the bituminous mix design were carried out.

The performance and behaviour of bitumen emulsion treated road bases in South Africa
E Horak, F C Rus

Emulsion treatment of granular bases is used mostly as a rehabilitation option in South Africa. Emulsion treated bases (ETBs) have been used on an ad hoc basis in South Africa in the past. Considerable work has gone into the mix design of ETBs, but in general, the modelling of ETB pavements lacks performance data. Accelerated testing with the Heavy Vehicle Simulator (HVS) fleet in South Africa has proven to be the ideal way of evaluating and modelling the performance of ETB pavements. Experimental sections and previously constructed ETB sections were tested. The outcome of these tests has contributed significantly towards the increased use of ETBs in South Africa. Research on ETB with natural gravels are also reported on.

The impact and management of the Heavy Vehicle Simulator (HVS) fleet in South Africa
E Horak, E G Kleyn, J A du Plessis, E M de Villiers, A J Thomson

Accelerated testing of pavements is accepted as an important decision tool in road design and behaviour analysis world-wide. Accelerated testing with the Heavy Vehicle Simulator (HVS) system in South Africa has enhanced an understanding and knowledge of material, pavement behaviour and modelling specific to the South African environment. The HVS system proved to be a unique and cost-effective decision tool and facilitator of cooperation between researchers, practitioners, clients and administrators. The impact of the HVS system in South Africa is clearly demonstrated by the extent of successful technology transfer projects.

The structural performance of the thinly surfaced road pavements
D A B Hughes, C D F Rogers, H A R Faddaoui

The performance of a number of surface dressed, unbound pavement structures has been assessed under repeated standard axle loads. The structures consisted of variable thicknesses of sand and gravel and well graded crushed limestone subbases overlying a clay subgrade. Transient surface deflections, to define the deflection bowl, permanent surface deflection and radius of curvature were measured. Well defined and consistent patterns of the various performance indicators were found, with good correlation between radius of curvature, measured by a curvature meter, and Surface Curvature Index. Interesting trends were found in the transient surface deflection measurements.

Mechanistic performance modeling: a contradiction of terms?
A M Ioannides

Most current pavement performance prediction models incorporate a two-step approach. Mechanistic structural responses are passed to statistical/empirical "transfer functions," predicting distress as a function of load repetitions, It is argued that algorithms like the AASHO PSI equation, the ESAL concept, and Miner’s hypothesis are descriptors of past pavement performance and are unreliable as predictors of future perfomance. Predictions of current programs are, therefore, erratic. The constructs noted should be replaced by more fundamental approaches, calibrated using laboratory and field observations. Pending such changes, mechanistic performance modeling will remain a contradiction of terms.

Full-depth asphalt pavement fatigue under accelerated loading
G W Jameson, K G Sharp, N J Vertessy

This paper describes the recent Accelerated Loading Facility (ALF) trial conducted in Australia on full depth asphalt pavements nominally 120 mm thick. The aim of the trial was to investrgate the fatigue performance of dense-graded asphalt. Extensive laboratory and field testing was conducted to complement the ALF trial. Relationships were established between back-calculated asphalt stiffness, determined from Falling Weight Deflectometer deflection bowls, pavement temperature and the severity and extent of surface cracking. The asphalt stiffness was found to decrease markedly with an increase in the number of loading cycles before surface cracking was apparent. Fatigue relationships, derived for various extents and severities of surface cracking, suggested that, for the trial mix tested under ALF loading, the Shell fatigue relationship was associated with about 50% of the loaded area having severe fatigue cracking.

Primary response under heavy truck traffic
W J Kenis, G Rohde

The Federal Highway Administration’s Test Road located at the Turner-Fairbank Highway Research Center (TFHRC) in McLean, Virginia, is an experimental in-service roadway used for monitoring the primary response of the pavement. The Test Road was constructed and first tested in August 1990. It contains two full scale flexible pavement test sections. It will accommodate truck traffic at speeds up to 73 Km/h. The main feature of the test road is the strain and deflection instrumentation located in the pavement. This paper presents an analysis of information obtained from the deflection devices.

Measuring pavement deflections using laser imaging
H Lee, D I McLean, H Oshima

The paper demonstrates the feasibility of automatically measuring pavement deflections using a laser imaging method. A sheet of laser light, created using a cylindrical lens, is projected on a concrete slab at a small angle to create a straight line image. The straight laser line bends as the slab is deflected. The shifted laser images are captured using a video camera and then digitally processed to determine the vertical deflection. Deflections obtained using the proposed laser imaging method closely match the measured deflections using LVDT’s at various points along the length of the slab. It is concluded that this automated deflection measuring procedure using a laser sheet is a precise and inexpensive method of measuring pavement deflections at multiple locations

Assessment of radar technology for determining the thickness of pavement layers
M Livneh, M H Siddiqui

Use of GPR is proposed as a non-destructive technique for pavement thickness determination, and its possibilities and limitations are discussed. It is found that for the zero product variability case the maximum error anticipated in determining asphalt layer thicknesses may be at the 15-20 percent level, mainly due to the biased errors resulting from the measuring method of the relative dielectric constant. The error can be reduced to about 10 percent when several readings are taken for each measuring point. For the heterogeneous case, the maximum error anticipated in determining asphalt layer thicknesses can be higher. However, this can be avoided if the relative dielectric constant is determined for each measuring point.

Use of radar technology for pavement layer evaluation
K R Maser, T Scullion, R C Briggs

This paper describes the use of non-contact Ground Penetration Radar to measure asphalt surfacing thicknesses at speeds ranging from 8 to 64 km/hr (5 to 40 mph). On four SHRP sites in Texas it was determined that by using radar alone it was possible predict asphalt thicknesses to + or – 7.6 mm (0.32 ins). However when a single calibration core was taken on each site the accuracy improved to + or – 2.8 mm (0.11 ins). The accuracy in predicting granular base thickness was + or – 25 mm (0.99 inches). The impact of using actual layer thicknesses on FWD analysis is demonstrated.

Reflection of model and measurement errors on stiffness estimates
K Matsui, T Inoue, T Sanpei

Some problems encountered in backcalculation of pavement structure are examined in this paper. The problems considered are errors in layer thickness, Poisson’s ratio, deflection measurements and possible existence of rigid bottom. The effect of errors on stiffness estimates are presented by both simulation and analysis. Optimal design sensitivity is introduced in the analytical approach.

The effect of rigid bottom is also presented in terms of the sensitivity of layer stiffnesses with respect to the thickness change of the layer overlying the rigid bottom.

Mechanism of longitudinal surface cracking in asphalt pavement
S Matsuno, T Nishizawa

Longitudinal Surface Crack (LX) is one of the major problems of the asphalt pavements in Japan. This type of cracking is basically different from the scope of current structure design concept. In this paper, our assumption, that LSC is induced by tensile strains in the pavement close to the tire edges at high temperature, is discussed based on visual condition survey and FEM analysis. From the visual condition survey conducted in highway sections, it is confirmed that LX occurs more in the sunshine than in the shadow cast by overpass bridges. The FEM analysis shows that large tensile strains occur in the pavements close to a tire edge at high temperature and that the strain is concentrated at the tip of a small crack induced at the surface.

The evaluation of six modified binders for retardation of crack reflection through laboratory studies and field work
F C Rust, K Coetser, B M J A Verhaeghe

Three bitumen-rubber binder technologies and three polymer-modified binders were evaluated both in field trials and extensive laboratory work to assess their ability to retard reflection cracking. The work conducted included the measurement of crack activity and fatigue testing under simulated crack movement. Laboratory results and field performance data were related in a model to assist in the selection of surface treatments for the retardation of reflection cracking.

The appraisal and evaluation of an asphalt base pavement on a sandy subgrade
P J Sanders, G Verwey, C J van der Merwe

The paper describes the appraisal of a pavement using a variety of test measurements and life prediction methods. When the pavement was built over 20 years ago the base consisted of a crushed mine dump rock layer. Since then two asphalt overlays and a chip and spray surfacing have been laid, effectively forming an asphalt base. The pavement is to be rehabilitated and upgraded to take increased traffic flows, hence the pavement investigation. The pavement is shown to perform well under Heavy Vehicle Simulator loading and has a significant residual life.

Field and laboratory evaluation of specialist high performance binders
A F Stock, L Planque, B Gunderson

The circular test track facility of the University of Canterbury was used to compare the performance of four specially prepared polymer modified binders and one high stiffness binder, with that of a conventional binder in an asphalt concrete mix. The study showed that the special binders outperform the conventional binder by a significant margin, and also that there is variation in performance between different polymer systems.

Modelling of pavement performance
P Ullidtz, R N Stubstad

Pavement structures are amongst the most difficult civil engineering structures to treat using analytical (or mechanistic) methods. Since the very first "Ann Arbor" conference in 1962, a lot of effort has been put into changing pavement design from being a purely empirical craft to being part of the engineering science.

Some success has been achieved in applying the analytical-empirical method to day-to-day engineering problems, but the gap between research and practice is far from closed. An important reason for this is the complexity of the problem. Models are necessarily simplifications of reality, but oversimplifying often leads to a lack of realism, which again leads to a rejection of the model for practical use.

This paper presents a model called PERS (for Performance and Economic Rating System) that tries to strike a balance between simplification and realism, giving the user the possibility to verify or calibrate the model to conform to practical experience. It is hoped that this approach may contribute to paving the gap.

Quality of bitumens in asphalt hot-mixes with emphasis on the durability of constructed premix surfacings
E J van Assen, M Vlok, F C Rust

The chemical and physical properties (quality) of bitumens and the durability of hot-mix surfacings placed in various locations have been investigated over a four-year period. Performance-related properties of the residual bitumen subsequently recovered, were identified and quantified by comparing asphalts from early failures to those which have performed well. There is a significant relationship between ductility and chemical composition of the residual bitumen and the durability of new hot-mix surfacings. A rapid test for the semi-quantitative estimation of asphaltenes in bitumen is described. The method based on the Oliensis spot test, can be used for on-site bitumen quality control.

Impact of season on the structural condition of asphalt pavements
C van Gurp

Results of a study on the effect of season on the structural condition of asphalt pavements and subgrade response in non-frost areas is presented. Changes in subgrade response and deflection were measured with a falling weight deflectometer. Each of the 60 test sites was visited 15 times in a two-year period. Moisture content and groundwater table level were recorded at each visit. Analyses of the moduli show a sine shaped variation throughout the year. The influence of the subgrade soil type on this variation is presented. Repeated triaxial tests were performed at some subgrade soils. The results indicate that use of meteorological data, and measuring deflections can result in reasonable estimates of the subgrade modulus at any date in the year.

An assessment of the increased damage potential ot wide based single tires
R Bonaquist

In 1989, the Federal Highway Administration (FHWA) initiated a research program to assess the impact of wide based single tires on flexible pavement response and performance. This study was conducted at the FHWA Pavement Testing Facility. Using the Accelerated Loading Facility pavement testing machine to simulate traffic loading, pavement response and performance data were collected for comparable dual and wide based single tires. Comparisons of the response and performance data for the two types of tires were used to assess the relative damage potential of the wide based singles.

Seven years experience of pavement evaluation
J M Brunton, R J Armitage, S F Brown

Since the back-analysis program PADAL was written in 1985 extensive experience has been gained in the practical implementation of the program and the associated rehabilitation design techniques based on analytical methods. A number of case studies are discussed which cover a range of pavement types and conditions. Comparison of measured and back-analysed effective stiffnesses are made, and correlations between stiffness and deflection parameters presented. Consideration is given to non-linearity of the subgrade. A simple procedure for assessing load transfer across joints in rigid pavements when designing bituminous overlays is also illustrated.

Development of an overlay design method for flexible pavements on lateritic soils
G Claros, W R Hudson

A mechanistic-empirical overlay design method (in terms of cracking and rutting) applicable to Nigerian conditions is presented in this paper. The basic steps of the new overlay design procedure include field evaluation of existing pavement (with condition and deflection surveys), in situ materials sampling and testing, laboratory testing, analysis of the existing pavement to determine remaining life, and the structure layers design method. The procedure was tested during the evaluation of over 3,500 kilometers of roads in Nigeria.

Developments in the failure criteria of the South African mechanistic design procedure for asphalt pavements
M de Beer

Effective implementation of the widely accepted mechanistic design method for asphalt pavements requires calibrated failure criteria and transfer functions. This paper describes various criteria developed and verified in South Africa in association with the full-scale accelerated testing of pavements, using the Heavy Vehicle Simulator (HVS) technology. Criteria such as the effective fatigue failure; compression (crushing) failure; erodibility of lightly cementitious (stabilized) pavement materials, and subgrade strain are discussed. Aspects of in situ pavement response measuring techniques are discussed, and include dynamic pavement characteristics; asphalt creep response; temperature and load correction, as well as effects of vehicle speed on pavement response.

The circular test track facility and road maintenance studies on flexible pavements
A de Boissoudy, J C Gramsammer, J P Kerzreho

We describe the behaviour of three thin bituminous overlays placed on flexible pavements which have been first damaged by the Nantes circular test track and we compare their behaviour with that of equivalent newly-made pavements. The pavements are modelised with the help of the rational method and we use a simplified law to describe rutting evolution. We show, among other things, the important part played by the sealing effect in the case of overlays and how the law, chosen for flexible pavement rutting, confirms the validity of the limits usually selected for the vertical strain of untreated courses. It seems that a 50% increase can be chosen in the case of overlaid pavements in relation to newly-made ones. Let us note that the French routine design method already applies it.

Analysis of asphalt test pavements with a subbase of expanded polystyrene foam
M Duskov, R Bull-Wasser

Flexible pavement structures with an EPS sub-base were investigated by measurements on six full-size test pavements and by a numerical analysis using a finite element program. The measurement program included registration of horizontal tensile strain at the bottom of the asphalt layer, surface deflections, compaction degree in the gravel layer, and rut depths during long-term loading tests. Numerical analysis is performed by the DIANA program which contains a non-linear material model. The pavement structures are compared with each other and calculated stresses and strains are compared with allowable material values.

A system for evaluating the impact of truck characteristics and use on flexible pavement performance and life-cycle costs
E G Fernando, R L Lytton

Florida COMPAS is a project level pavement management tool for evaluating the effects of different forecasted truck characteristics and use on flexible pavement performance and life-cycle costs. This is accomplished through a comprehensive approach involving the combined application of models for load-shift analysis, vehicle simulation, load equivalency calculations, performance prediction, overlay design, and life cycle cost estimation. This comprehensive pavement analysis system is described in this paper together with examples that illustrate program applications.

Use of subnormal local aggregates in high modulus asphalt mixes
H Goacolou, A Dimitri, F Prudhomme, L A George

The construction of the A 71 Motorway in France raised the problem of the use of local materials which could only give a low percentage of standard crushed aggregates. The use of High Modulus Mixes (HMM) with better mechanical properties than those of the standard base course mix allowed an optimal use of the local pit and a considerable reduction in aggregate extraction and elaboration. Laboratory and in situ test results are discussed and shown to confirm the pavement design initial assumptions.

The effects of dynamic axle loads on the response and life of flexible pavements
M S A Hardy, D Cebon

In order to assess the influence of dynamic wheel loads on pavement wear it is necessary to understand the way in which such loads are carried by the structure.

A method for calculating the transient response of road surfaces to dynamic wheel loads is presented. The key assumptions of this method, the system’s dynamic linearity and structural isotropy, are investigated and the theory is validated by experiments on an instrumented test track.

The theory is then used to:

i) Investigate road response to static and dynamic loads;

ii) Investigate the conditions under which dynamic road models are required for accurate response predictions;

iii) Examine theoretical road damage due to dynamic loads.

Prediction of airfield pavement response employing nondestructive testing procedures and elastic layered theory
D R Hiltunen, J R James, R Roque, A J Bush III

The deflections of airfield pavements predicted using elastic layered theory are compared with deflections measured under actual aircraft loads. The predictions are made using elastic moduli backcalculated from falling weight deflectometer data. The deflections under actual moving aircraft loads were determined via velocity transducers (geophones) placed both on and within the pavement system. In all cases analyzed, the predicted deflections agree well with the measured deflections in the vicinity of the wheel load. The predictions become progressively worse, however, for increased distances from the load. It is felt that the discrepancies observed are due to nonlinear effects in the subgrade materials.

Comparative tests of FWD and Lacroix Deflectograph
W Th Hoyinck, J M M van der Loo, J Mulderij, R Kuijper

Parallel tests of the FWD and Lacroix-Deflectograph were carried out in order to explore the possibilities of using both types of equipment side by side in everyday practice. This paper provides the necessary tools to convert certain parameters from LAC to FWD and vice versa. It also presents a new approach to the theoretical analysis of LAC deflection bowls. Subsequently, the results of this analysis are compared with the FWD analysis. Strain levels appear to compare favourably, both for direct LAC analysis or after conversion to FWD profiles.

New concepts on load equivalency measurements
M Huhtala, J Pihlajamaki

The equivalencies of 100 kN and 115 kN were compared within the OECD/FORCE circular track test and the "powers" of the fourth power law were calculated. A comparison of the effects of different tyres and the lateral wander effect is based on response measurements made at Virttaa. The strains in pavements in transverse and longitudinal directions are different if measured by non-elastic gauges. That phenomenon was studied also with computer simulation based on Burgers’ model.

Towards improved procedures for the mechanistic analysis of cement treated layers in pavements
G J Jordaan

The horizontal tensile strain at the bottom of cement treated (CTB) layers in pavements is generally used to assess the expected behaviour of such layers. However, this strain parameter alone does not adequately allow for the description of the observed behaviour of many pavements containing cemented layers. In this paper measurements of an accelerated pavement test with the Heavy Vehicle Simulator, are used to develop an approach for the mechanistic analysis of CTB layers which is in line with the observed behaviour. This procedure includes the modelling of the CTB layer using a relatively low effective elastic modulus, a test to establish the position of maximum strain which is not always at the bottom of the CT6 layer and an adjustment of the fatigue curve for CTB layers to allow for field performance.

Evaluation of various field measurement techniques for the assessment of pavement interface conditions
P Lepert, J P Poilane, M Bats-Villard

A brief overview of the construction and maintenance faults which causes lacks of bond between the road base and the bituminous wearing course (one of the major causes of distress of treated base pavements) is presented. Experiments were carried out on special test sections, with different interlayer conditions, to compare the ability of existing NDT equipments to support a definite diagnosis of such a flaw. Results from these equipments are compared. A new dynamic testing method is presented: it was applied on the test sections, and proved to be one of the most efficient methods to detect lacks of bond. Finally an equipment applying the method is described: the COLIBRI system.

Fatigue of asphalt materials for Norwegian conditions
J Myre

Fatigue cracking is a frequent failure mechanism causing extensive structural damage of flexible pavements. This study presents results from fatigue testing in the laboratory. The project involved three types of fatigue test apparatus. Based on this study fatigue criteria have been established for asphalt mixes commonly used in Norway. The influence of load environmental and mix variables have been studied. The experimental work has also resulted in development of one single fatigue criterion for all examined mixes.

Determination of pavement aging by high frequency body and surface waves
S Nazarian, M Baker, R C Boyd

An economical field methodology for determining the degree of aging of the AC layer is presented. The assessment of aging involves relating the propagation velocities of shear and compression waves to elastic modulus and Poisson’s ratio of the layer. These parameters are directly related to the stiffness and brittleness of the AC layer. The ultrasonic wave propagation techniques have the potential to yield valuable information with respect to aging of AC layers. Much research is needed to establish relationships between temperature, environment, stiffness, Poisson’s ratio and aging. The methods described here may facilitate the development of these relationships.

Towards a performance specification for bituminous roadbase
M E Nunn, G Bowskill

Work on the development of an end-product or performance specification for bituminous roadbase material is described. Practical methods of measuring the most important structural properties are being identified and assessed. The study has so far concentrated on evaluating a method for measuring the load spreading ability or elastic stiffness of the roadbase and has found the indirect tensile test to be suitable.

Pavement deflection analysis on sections where the subgrade vary in stiffness with depth
G T Rohde, R E Smith, T Scullian

This paper deals with an improved method of analyzing nondestructive deflection measurements. From the shape of a measured deflection bowl the depth to an apparent rigid layer is determined. This apparent rigid layer then accounts for bedrock, subgrades stiffening with depth, or both during the backcalculation of layer moduli. The procedure, incorporated in the layered elastic backcalculation program MODULUS4, has been validated by laboratory tests and results from instrumented pavements. The paper covers how to determine the depth to an apparent rigid layer and illustrates typical changes in stiffness with depth expected in clay and sandy subgrades. Results from a deflection analysis on an instrumented pavement section are also presented.

The use of linear elastic analysis to predict the nonlinear response of pavements
R Roque, P Romero, D R Hiltunen

A comprehensive analysis was performed to determine whether linear elastic layer analysis can be used to accurately predict the nonlinear response of pavements. The analyses showed that fairly accurate predictions of deflections, stresses, and strains resulted within the surface layer when a single effective layer modulus was used to represent the surface and base layers. However, it was found that the upper portion of the subgrade must be modeled as a separate layer in linear elastic layer analysis to approximate the effect of stress dependency on response. Effective layer moduli determined at design wheel load levels resulted in accurate prediction of nonlinear pavement response at load levels of + or minus 25% of the design wheel load level at which the moduli were determined.

Towards analytical mix design for large-stone asphalt mixes
F C Rust, J E Grobler, P A Myburgh, F Hugo

Increasing traffic volumes and axle loads in South Africa has recently resulted in traffic loading beyond the current design classes. In addition, there is a strong lobby to increase the legal axle load limit. A need was expressed by the Southern African Bitumen and Tar Industry for an investigation into Heavy Duty Asphalt Pavements. A project focusing on the use of large-aggregate asphalt mixes (37.5 mm and 53 mm) was defined. This paper addresses the development of an analytically based design procedure for large-aggregate asphalt and its application in thirteen trial sections. In addition, the physical and engineering properties of the various materials are discussed and related to the constructability of the mixes. The performance of these trial sections under accelerated trafficking are related to laboratory results.

Relationships between climatic conditions and the structural parameters of flexible pavements.
A A Shaat, M A Kamal, N S Matter

An extensive programme of Deflectograph deflection testing of typical highway sections is being conducted since early 1990 by the authors in co-operation with the Research and General Services, Roads Service of the Department of the Environment in Northern Ireland. This paper describes the technique being developed for quantifying the variations in pavement effective stiffnesses due to environmental (seasonal) effect. Monthly collection of deflection data, ground water-table variation, moisture content and temperature distribution in bituminous layer etc. are being carried out on 200 m in-service flexible pavement test sections. The analysis of this data will provide reliable information about the seasonal variation in strength of the tested pavements.

Field performance, laboratory testing and predictive models for modified binders used in reflection cracking
P J Strauss, E Kleyn, J A du Plessis

Cracks in flexible pavements allow surface water to enter and wherever marginal material has been used in foundation layers, structural failures are to be expected. Design and construction of overlays on cracked pavements are therefore aimed at avoiding reflection cracking. The development of modified binders has greatly improved the rate of success in this regard, but it also has emphasized the lack of understanding of and design methods to design against reflection cracking. This paper discusses the modelling of crack behaviour, the sensitive parameters in predicting performance and actual field experiences of different strategies. The conclusion is made that although fatigue principles are to be applied in predicting performance, cracks develop under brittle failure and re-heal during periods of warmer weather which complicates predictive models.

Evaluation of the rehabilitation design of a BTB pavement and the effects of artificial ageing using accelerated wheel load testing
C J van der Merwe, H L Theyse, E Horak, F Hugo, J A du Plessis

A number of flexible rehabilitation design methods that are used in South Africa were evaluated by Heavy Vehicle Simulator (HVS) test loading. The predicted mechanisms of failure and structural life of a Bituminous Treated Base (BTB) pavement were compared to actual test results. All design methods required shift factors to correlate the test results with the respective design performance predictions. The effects of accelerated ageing by heat were then studied under full scale HVS testing, as well as scaled down laboratory testing using the ITT’s 1:lO model Mobile Load Simulator (MLS). Shift factors were found to be affected by and dependant upon the mode of failure.

Harmonisation of Falling Weight Deflection evaluation procedures
C Van Gurp, W Th Hoyinck, A Van de Streek, B Thewessen

A novel procedure for the structural evaluation of falling weight deflection data on all types of asphalt pavements in The Netherlands is presented. Results of repeatability and reproducibility experiments in FWD comparisons are given. These tests point at the influence of the pulse load shape on the magnitude of the deflection. The FWD test procedure and the obligatory additional testings are described. Backcalculated moduli are adjusted for thermal gradient effects and normalized to a reference air temperature. The data processing procedure shows how the results of FWD testings and the other testings should be combined for a proper structural evaluation. A brief description of the effects of lateral wander and travelling speed of truck traffic is given.

Thermal cracking resistance of asphalt concrete: an experimental approach
T S Vinson, N M Jackson, D-H Jung

Low temperature and thermal fatigue cracking of asphalt concrete pavements are serious problems in many regions of the world. Based on research conducted to date under the Strategic Highway Research Program (SHRP), thermal stress restrained specimen test (TSRST) results for 5x5x25 cm beam specimens at a rate of cooling of lOC/hr provide an excellent indication of low temperature cracking resistance and TSRSTs performed under cyclic cooling provide an indication of thermal fatigue cracking resistance. The energy rate integral (C*-Line Integral) and direct tensile strength do not correlate to thermal cracking resistance.

The elasto-plastic behaviour of crushed stone bases in flexible pavement structures under accelerated testing
H Wolff, E G Kleyn, A T Visser, M de Beer

A model based on the S-N curve principle is developed to predict rutting in crushed stone bases from Heavy Vehicle Simulator (HVS) testing. The model is intended for use in the mechanistic analyses of pavements together with Miner’s damage law. The benefit in terms of less rutting over the lifetime of the pavement by compacting the crushed stone base to 89 instead of 84 per cent of apparent density is illustrated by the development of the model. The model is developed for the equilibrium moisture condition of crushed stone bases only, as an important aim of pavement design and management is to prevent ingress of water into the pavement layers.

The distribution of stresses at the interface between tyre and road and their effect on surface chippings
A R Woodside, J Wilson, G Xin Liu

Contact stresses induced at interface between tyre and road surface may cause crushing, polishing and abrasion of surface chippings. Two computer-aided testing systems are used to measure the contact stresses under static and dynamic conditions using various loads and inflation pressures. The effect of different surface texture depths is assessed and the contact forces on individual chippings obtained. Results indicate that a surface chipping of 1 mm macro-texture endured a contact force of twice that induced on a chipping at zero texture depth. These stresses are also analyzed mathematically.

Evaluation of field measurements of the Ankara-Eskisehir flexible experimental road
R Yuce, U Anliatimer. E Bostanci

This study includes some of the field results for the Ankara- Eskisehir Flexible Experimental Road which was constructed in 1988 and 1989. Since September 1989, axle load repetitions, surface deflections, rut depth and crack measurements, air and plant temperatures and aggregate stock moisture contents are recorded to find correlation in between selected parameters. The MAPCON computer program is used to estimate the appropriate modulus of elasticity values for each layer to match the deflection bowl obtained under a 50 kN FWD load, whereas the ELSYM5 computer program is used to determine the critical deflections, tensile stresses and strains created in the pavement structure. lt is attempted to determine the remaining fatigue life of the flexible pavement by the use of the design time concept and a flow chart is proposed for the design of flexible pavements.

Treatment of reflection cracks in Queensland
M A Caltabiano, R E Rawlings

This paper details the steps undertaken to arrive at a recommended code of practice for the treatment of reflection cracks in Queensland. The process followed firstly identified the problem, then used a detailed experimental site on the Bruce Highway at Beerburrum to trial the use of a range of treatments, conducted a parallel research program to further understand the mechanism of cracking, and finally confirmed the results through a series of trial sites before establishing a recommended code of practice.

Mastering the quality of bituminous pavement courses
M L Gallenne, E Layerle

The experiment that led to the monitoring of spreaders is part of a joint action by the USAP (Association of toll Motorway Companies) and contractors, with two objectives: to establish correlations between execution processes and pavement properties (evenness, density, and macrotexture) and to develop a system for the real-time monitoring of placement (contribution to operating assistance).

Design and construction of sandwich pavements for airports on soft ground
Y Hachiya, T Ogishima, K Sato

For constructing new facilities at Tokyo International Airport and New Tokyo International Airport, sandwich type pavements have been proposed. The principle of this pavement structure is to decrease the subgrade vertical stress by introducing a stiff subbase right on the subgrade. As the sandwich pavement is not included in the current airport pavement design manual in Japan, detailed research including construction of various test pavements has been conducted. The design procedure developed through these experiences has been used successfully on two projects. This paper describes the whole process of adopting the sandwich pavement design method for airports.

End-result smoothness specifications for acceptance of asphalt concrete pavements
W R Hudson, T Dossey, R Harrison, D G Goulias

This paper documents the development and evaluation of end-result smoothness specifications for asphalt concrete pavements in Texas. Based on available equipment and prior studies, the California Profilograph was selected as the instrument for use in developing the specification. Because there are several types of California profilographs, the study team compared two instruments by two different manufacturers. This paper presents the results of this comparison, along with a methodology for defining a recommended specification.

Evaluation of heavy duty asphalt pavements for rutting
P S Kandhal, S A Cros, E R Brown

34 pavements across Pennsylvania were evaluated to identify the material properties, mix design parameters, pavement construction properties, and in-service properties which are responsible for premature rutting. Cores were tested to determine pavement properties. The mix was recompacted by three different compaction methods, and analyzed for voids and strength. Transverse surface profiles of the pavements were taken to determine maximum rut depths. Correlation analysis, and linear regression analysis methods were used to analyze the effect of 60 independent variables on rutting. Threshold values of significant independent variables were also established.

Improving the properties of asphalt pavements through the use of Amir Compactor: laboratory and field verification
A E H Omar A El Halim, R Haas, W Phang

Results of previous research work carried out in the field of asphalt compaction showed that under currently designed rollers, construction induced cracks are inevitable. As a result a new compactor, Asphalt Multi-Integrated Roller – AMIR, was designed and built. The new roller overcomes the problems associated with current rollers and as a result produces pavements without construction cracks. The use of laboratory AMIR models confirmed the analytical findings and suggested that elimination of "hair checking" during compaction can significantly improve the mechanical properties of the compacted mix.

Asphalt concrete pavement preservation with cold in-place recycling
D F Rogge, T V Scholz, R G Hicks, D Allen

Since 1984, the Oregon Department of Transportation (ODOT) has utilized cold in-place recycling (CIR) as one alternative to conventional asphalt concrete pavement preservation techniques. Through September 1990 over 800 Km of pavement have been recycled with most projects showing good success. This paper describes the project design and selection process for CIR. Also presented is a summary of the field performance. Recycled pavement condition, ride data, and mixture properties are presented. Expected service lives and the economics of CIR versus hot mix preservation techniques are discussed.

Performance-related specifications for asphalt concrete
J F Shook, M A Diaz, M Stroup-Gardiner

This paper reports the results of a study to continue development of performance-related specifications (PRS) for asphalt concrete pavement by conducting a laboratory experiment to study the relationships between materials and construction (M&C) variables and fundamental response variables. The most relevant relationships between M&C variables and performance responses have been selected for presentation in this paper. All these relationships are expressed in algebraic form, and their statistical information is included. Also, included in this paper is a demonstration PRS for asphalt concrete developed using a computerized spreadsheet program. The description of the spreadsheet program addresses many of the significant factors that ought to be considered in assessing contractor bonus/penalty.

Application of new compacting technique for deep lifts and large aggregate asphalt mixes
O J Svec

Conventional asphalt compaction is characterized by geometric and material incompatibilities at the interface between the drums and the hot asphalt mix. As a result, surface and internal cracks are frequently generated during the compacting process. To avoid these problems, a new concept for compaction was introduced. Subsequently, a prototype was built as a joint project between the NRC and a Canadian manufacturer. This prototype was termed "Asphalt Multi-Integrated Roller" – AMIR, and its performance tested in four experimental trails and one commercial project This paper describes the results of AMIR compaction of two large aggregate and two standard mixes compacted in deep lifts with or without geogrid reinforcement.

The construction and performance of polymer modified asphalt concrete pavement
J A Scherocman, O W Schlitz

The use of polymer modified asphalt concrete mixes has increased in the United States in the last few years. The use of stone mastic asphalt mixes was also recently introduced. The mix designs used to construct three polymer modified asphalt concrete pavements, one in Germany and two in the United States, are described. Also discussed is the performance of these mixes during limited time under traffic.

Keyword Index

Note 1: This index is based on keywords provided by authors. Unfortunately, only about half the papers carried keywords and users should therefore recognise this index does not provide complete coverage.

Note 2: Roman numerals refer to the volume number and Arabic numerals to the first page of the relevant paper.