8 Conference

code ISAP 8th Conference Titles & Abstracts
08001 Long-Life Flexible Roads
M. Nunn

A longer design life for flexible pavements, which carry the heaviest volumes of traffic, will yield a lower whole life cost. This will require strategies for design that decrease the need for maintenance and thereby cause less disruption to the road user.

This paper reviews the current philosophy and criteria for design and considers information on the performance of roads that has been collected since the last revision of UK design standards, in 1984. This has demonstrated that the deterioration of thick, well-constructed, fully-flexible pavements is not structural, and that deterioration generally occurs at the surface in the form of cracking and rutting. The evidence suggests that fatigue and structural deformation originating deep within the pavement structure are not the prevalent modes of deterioration. It also shows that changes that occur to the structural properties of the bituminous materials over the life of the road are crucial to the understanding of its behaviour. These changes can help to explain why conventional mechanisms of deterioration do not occur. They imply that a road built above a minimum strength will remain structurally serviceable for a considerable period, provided that non-structural deterioration in the form of cracks and deformation are detected and remedied before they have a serious impact on the structural integrity of the road.
08002 UK Design of Flexible Composite Pavements
A. Parry, S. Phillips, J. Potter, M. Nunn

The UK pavement design guide has recently been updated to include new options for the construction of flexible composite pavements for heavy traffic. They are summarised in this paper. These new designs, along with those they supersede, are based upon the principal that the flexural strength of the cement-bound roadbase should be greater than the combined traffic and thermal warping stresses experienced during service. The thickness of the asphalt layers is required to limit these stresses and to reduce the severity of reflective cracking.

A study of the construction and maintenance history of in-service flexible composite pavements, which have carried up to about 100 million standard axles, has revealed that the current designs are capable of carrying at least this traffic load. Ongoing studies which should lead to further improvements in the design of these pavements are identified and the results to date summarised.
08003 New Tools for Rational Pavement Design
B. Eckmann

The paper presents two developments aimed at the supporting of rational pavement design. In the field of probabilistic design, the possibilities of the ROSENBLUETH approximation have been evaluated. This technique consists in replacing a continuous data distribution by an equivalent discrete distribution (2 or 3 data points), which leads to considerable gains in calculation times. The validity of this approach is shown to be related to the shape of the "transfer function" which relates the considered input parameter to the calculated pavement response (e.g. a stress). The potential of the method is illustrated by an example. The NOAH software is a very powerful computation tool by which the user can investigate the sensitivity of pavement performance (as related to calculated stresses and strains) to variations of any of the involved input parameters (structural, environmental, loading). It incorporates the ROSENBLUETH method and many other specific facilities such as a built-in "Formula Generator". This confers NOAH an extreme flexibility so that it can easily be used by pavement engineers working according to different design methods.
08004 Pavement Design and Management Guide
R. Haas, T. Kazmierowski

A new Pavement Design and Management Guide, produced under the auspices of the Transportation Association of Canada, provides an up-to-date, comprehensive consolidation of knowledge in the field for a new generation of users. It promotes good practices among the owners of pavements and incorporates the best available technology within a systematic, organized framework. The Guide is intended to serve the needs of engineers and technologists in public agencies, industry, academia and consulting.

The Guide has ten major chapters which cover (1) an introduction to and focus of the document, (2) procedures and technologies for acquiring and processing identification of data, (3) identification of maintenance and rehabilitation treatments, (4) carrying out needs analysis and priority programming, (5) description of pavement materials and their characterization, (6) structural design and economic evaluation, (7) role of construction, (8) role of maintenance, (9) implementation guidelines, and (10) issues, opportunities and future prospects.
08005 Development of Performance Models for Ontario’s New Mechanistic-Empirical Pavement Design Method
Z. He, G. Kennepohl, Y. Cai, R. Haas

Ontario’s OPAC design method, developed in the early 1970’s, was mechanistic-empirically based. A key feature was the performance modeling approach which separated traffic and environment associated deterioration. A new, comprehensive "OPAC 2000" has been developed as the successor to the original OPAC. This new pavement design method is also mechanistic-empirically based, with separate load-associated and environment associated performance models. However, the updated models have been calibrated from an extensive, long-term performance data base (incorporating age vs PCI, layer thicknesses, ESALs, etc.). Moreover, they have been regionally adjusted using a clustering technique. As well, reliability analysis has been included based on the second moment approximation method to obtain variance estimates for the parameters. Validation checks indicate very reasonable results.

While the framework of OPAC 2000 will be summatized in terms of the major modules and subsystems, including a comprehensive economic analysis module, the paper concentrates on the performance modeling effort and results. It is suggested that even though the calibration has been carried out with the Ontario data base, the approach is generic in that the model form is transferable and could be calibrated to other regions.
08006 Computer Aided Overlay Design System for Flexible Pavements
F. Bayomy, F. Al-Kandari, W. Nassar

This study presents a mechanistic-based overlay design system and its implementation in a computer program named "FLEXOLAY" for the state of Idaho. The concept adopted is based on analyzing the pavement distresses in terms of rutting and fatigue and determining an overlay thickness using strain-based fatigue and rutting models. The developed design procedures consider the past and the expected future traffic to calculate the required overlay thickness. Evaluation of existing pavements is performed by nondestructive testing using Falling Weight Deflectometer. Effect of seasonal variation is considered by employing seasonal adjustment factors for pavement layers moduli to account for each season. Seasonal factors for different climate regions in Idaho have been established and used in the environmental data base of the computer program. The program allows for entering other seasonal factors for other locations. The user has the flexibility to enter different shift factors based on local experience.
08007 Progress and Pitfalls for a DOT-Developed Mechanistic Design Procedure
J. Corley-Lay, Y. Qian

For thinner asphalt concrete sections, the horizontal tensile strain at the bottom of the asphalt layers obtained using Jung’s technique was found to be in reasonable agreement with Thompson’s AUPP. It also was in good agreement for thinner sections with backcalculation of layer moduli and using these moduli in an elastic layer program to obtain the horizontal strain. Jung’s method appears to overpredict strain in thick asphalt sections.

Seasonal ratios of strain calculated using Jung’s method to the strain at the initial testing period were calculated. Similar seasonal ratios were obtained for pavements of similar type and subgrade stabilization type. The seasonal ratios could be used to incorporate seasonal effects for the wet-no freeze zone of North Carolina using three seasonal periods.

Fitting time series to the backcalculated moduli of the asphalt layers and to the subgrade moduli as suggested by Ali and Parker resulted in the most direct method to incorporate seasonal effects and calculate remaining life.

Serious difficulties were demonstrated in correctly estimating the time to failure and order of failure of three similar design sections.
08008 Research on the Design Method of Asphalt Pavement
Y. Menyu, Z. Qisen

China has moved its national economy into a continuous upwards and stable development stage since this country implemented economic reform and "open door to foreigners policy" in the mid-1980s. This has brought a good opportunity for booming its road construction and improving highway transportation. Over the last 10 years, a large quantity of high graded highways or freeways has been built within the country. As a result, a significant change has been made from backward traffic condition to a better highway transport facilities.

In order to meet the standards of high graded highways required by Ministry of Communications of China, we organized a research group, consisting of many scientists and engineers from universities, highway research institutes and highway design agencies, to study the design method of asphalt pavement at semi-rigid base conditions. Based on the study, the previous version of the Code of Flexible Pavement Design gf Highway, JTJO14-86, was revised and now it is renamed as Code of Asphalt Pavement Design of Highway, JTJ014-97. The new code will come into effect on the first of October, 1997. The key points and major contents of the new code is described explicitly.
08009 Dynamic Loading Effects on Flexible Pavement Performance
B. Pidwerbesky, B. Steven, J. de Pont

Research was conducted at the Canterbury Accelerated Pavement Testing Indoor Facility investigating the influence of dynamic axle loads on pavement response and deterioration. Measurements from an earlier pavement showed that the SLAVE units subject the pavement to realistic dynamic loading.

Two tests have been undertaken, comparing the effect of steel multi leaf, twin parabolic spring and air suspensions on pavement deterioration. The second test was part of the Organisation for Economic Co- operation and Development Dynamic Interaction between Vehicles and Infrastructure Experiment (OECD DIVINE project). The results to date show a good correlation between the dynamic wheel forces and pavement distress. The modes and level of pavement distress are dependent on the particular suspension characteristics. Analysis ranks the suspensions from worst to best as steel, parabolic and air.

The results have provided the first measured evidence of a direct link between peak dynamic loads and pavement damage reported thus far.
08010 Distribution of Tire Contact Pressure of Vehicles and Its Influence on Pavement Distress
K. Himeno, T. Kamijima, T. Ikeda, T. Abe

This study places an emphasis on precise measurement of distribution of tire contact pressures. Komatsu Corporation has developed a new device using piezo electric ceramics sensors, which measures weight distribution within a contact area of a tire in motion. From the measured data at all the pixels, distribution of contact pressure and its average value can be obtained. The measurement was performed in summer in Tsukuba, Japan, varying tire type, traveling speed, air pressure, and wheel load.

Based on the measured data, effect of the difference between the modeled uniform and the actual distributed pressures on the pavement distress, especially fatigue cracking, is discussed, employing the multilayered elasticity theory and energy dissipation theory for prediction of the initiation of cracking.
08011 Investigation of Flexible Pavement Response to Truck Speed and FWD Load Through Instrumented Pavements
S. Dai, D. Van Deusen, M. Beer, D. Rettner, G. Cochran

Falling weight deflectometer (FWD) and truck tests have been conducted on the Minnesota Road Research project (Mn/ROAD) in an effort to (1) study truck speed effects on flexible pavements, (2) compare pavement response under FWD and truck loads; and (3) investigate the effects of wheel path offset on the pavement response.

Three flexible pavement sections were used for this study. The truck tests were performed at various speeds ranging from 10 to 103 km/h.

The results showed that on a smooth pavement (IRI=O.97 m/km) strains in the bottom of the pavement continuously reduced with the truck speed. While on a relatively (relative to the smooth pavement) rough pavement (IRI=l.74 m/km), strains in the bottom of the pavement decreased as the speed of the truck increased to a speed about 65 km/h, but the strains increased when the speed was further increased from 65 km/h to 103 km/h. The effects of the pavement surface roughness were also investigated and the influence of truck suspension type was discussed.
08012 Mechanistic Determination of Equivalent Damage Factors for Multiple Load and Axle Configurations
J. Prozzi, M. de Beer

The increase of the maximum axle load limit in South Africa sparked renewed interest into methods of quantifying traffic load associated damage on pavements. Extensive research with the Heavy Vehicle Simulator (HVS) over the past 20 years has led to improved fundamental understanding of pavement performance and has permitted the development of Equivalent Damage Factors (EDFs) for single-axle loads. A major limitation of this approach is that it does not directly facilitate the calculation of EDFs for multiple axle contigurations, i.e. tandem or tridem axles.

This paper describes a method for extending the existing HVS-based method to the determination of EDFs for multiple axle configurations. This, in principle, facilitates the development of guidelines on permissible axle loads and tyre inflation pressures for different axle configurations. The method assesses the effects of: wheel load, contact stress, single and dual wheels, and single, tandem and tridem axle configurations. The method, therefore, enables determination of EDFs for the accurate estimation of equivalent traffic loading for design purposes and performance analysis enhancing life predictions and management decisions.

Initial determinations indicated the advantage to road friendliness of grouping axles together into tandem or tridem configurations. Additionally, the use of dual-wheel instead of single-wheel axles could result in the axle load being increased by up to 30 percent without any increase in pavement damage.
08013 Determination of Pneumatic Tyre/Pavement Interface Contact Stresses under Moving Loads and Some Effects on Pavements with Thin Asphalt Surfacing Layers
M. de Beer, C. Fisher, F. Jooste

This paper describes the quantification of three-dimensional tyre/pavement contact stresses for vehicle tyres. The Vehicle-Road Surface Pressure Transducer Array (VRSPTA) system was developed to measure contact stresses under moving loads, i.e. Stress-In-Motion (SIM). Prediction equations for quantification of these stresses, based on tyre inflation pressure and loads for seven (7) different tyre types, are given. Tyre inflation pressure predominantly controls the vertical contact stresses on the pavement at the tyre centre, whereas the tyre load controls those at the tyre edges.

Analysis indicated that during instantaneous overloading / under-inflated conditions the maximum strain energy of distortion (SED) in the asphalt surfacing occurs close to the tyre edges, while under instantaneous uniform vertical stress conditions the SED is within the asphalt surfacing at the tyre centre. In addition to improved load/contact stress idealization for modelling, this finding may have important implications for the design of relatively thin asphalt surfacing layers for pavements.
08014 Measured and Theoretical Comparisons of Traffic Loads and Pavement Response Distributions
B. Chadbourn, D. Newcomb, D. Timm

The correlations between traftic load distributions and tensile strains in flexible pavements are discussed in this paper, and these relationships are compared against theoretical strains computed from layered elastic theory. Six flexible pavement test sections at the Minnesota Road Research Project (Mn/ROAD) were selected for the analysis presented in this paper. Wheel-weight data from the weigh-in-motion station at the Mn/ROAD site were taken for a number of time periods during 1995. Weight data distributions were then matched to temperature-corrected transverse strains measured at the bottom of the asphalt concrete in the test sections. Finally, a layered elastic analysis was performed, the results of which were compared to actual measurements under traflic. It was found that the measured strains and the strains computed from the analytical model matched well when the loads were modeled as dual wheels with constant tire pressure and a varying load magnitude.
08015 Modification of the Austrian Guideline for Standardized Asphalt Pavements
R. Blab, C. Molzer, J. Litzka

The Austrian guideline regulating pavement design is currently being revised in the light of increasing heavy vehicle traffic and changes in the technical equipment of heavy freight vehicles. To calculate the expected traffic load for the design period the modification will not longer employ the well-known Fourth Power Law. Instead the damaging impact on the pavement structure (with fatigue as the criterion) is determined in a direct approach from the fatigue effects due to the passage of different axle loads and axle configurations.

A comprehensive sensitive analysis examines the key components of fatigue caused by single and twin tyres and different axle configurations on asphalt pavements by taking into account their lateral distribution in the cross section of a road lane. Detailed data for lateral distributions of loads evaluated due to field measurements and comprehensive information on the distribution of axle loads and heavy vehicle types found in Austria’s federal road network provide the basis for computation of mean equivalency factors for different vehicle types and characteristic collectives of heavy freight vehicles. These are used to determine the relevant design load for routine design purposes and will be incorporated in the modified Austrian design guideline for asphalt pavements.
08016 Maximizing Shear Resistance of Asphalt Mixtures by Proper Selection of Aggregate Gradation
R. Roque, S-C. Huang, B. Ruth

A better understanding of the influence of aggregate gradation on the shear resistance and volumetric properties of asphalt mixtures is needed to maximize the shear and rutting resistance in asphalt mixtures. Eighteen mixtures were prepared with different coarse aggregate (> 2.0 mm) gradations ranging from Stone Matrix Asphalt (SMA) to those corresponding to the maximum density line. The Gyratory Shear (Gs measurements indicated the gradation of the coarse aggregate fraction (> 2.0 mm) was related to the shear resistance of the mixtures. Coarseness, shape, and position of the gradation curve relative to the maximum density line affected the shear resistance. Mixtures including both coarse and fine aggregate fractions verified the test results obtained from the coarse-aggregate only mixtures. It was evident that coarse aggregate gradations controlled the shear resistance of the mixtures even though fine aggregate dilated the coarse aggregate structure. Crumb rubber modified (CRM) asphalt binders were generally found to have little effect on the air void content and shear resistance (Gs) of coarse- graded (e.g., SMA) mixtures.
08017 Design and Fatigue Behaviour of Emulsified Bitumen Macadams for Highway Reinstatement
H. Khalid, K. Eta

A mix design method has been developed for Emulsified Bitumen Macadam materials (EBMs) used in trench reinstatement operations as wearing and base course layers in flexible pavement constructions. The method considers the effect of mixing, compaction, curing, strength development and moisture sensitivity. The influence of polymer-modified emulsions on the stiffness and permanent deformation characteristics of the EBMs has been investigated. EVA and SBS copolymers have been incorporated into a conventional 100 pen emulsion at various levels in the investigation, and the resulting EBM properties were compared to the specifications advocated by the Highway Authorities and Utilities Committee (HAUC) to arrive at suitable mixes that are capable of performing adequately in service.

The conventional and selected modified EBMs were then used in a laboratory study to evaluate their fatigue behaviour, together with an equivalent hot-applied mix containing 200 penetration grade bitumen. Controlled stress three-point bending fatigue tests were conducted to arrive at strain/fatigue life relationships for the hot and cold-lay mixes. Linear elastic theory was then applied to evaluate the response of the materials to traffic loading in a typical flexible pavement model using BISAR-PC Program developed by Shell. The calculated strains were used to determine the life of the pavements with candidate mixes from the developed fatigue relationships. Structural equivalency factors for the cold-lay materials in conjunction with the hot-applied mixes were computed from the resulting fatigue lives. The fatigue analysis revealed that certain modified EBMs have the potential to perform equally to, or even better than, the equivalent hot-applied material.
08018 Recent Activities of RILEM TC 152-PBM "Performance of Bituminous Materials"
L. Francken, E. Eustacchio, U. Isacsson, M. Partl

A general overview on recent activities of the Technical Committee "Performance of Bituminous Materials" TC 152-PBM of the International Union of Testing and Research Laboratories of Materials and Structures (RILEM) is given, including a state of the art study on testing and appraisal of polymer modified road bitumens. All activities are within the framework of performance related mixture design and part of a basic general testing methodology. Results of three large interlaboratory tests on binder rheology and both design and repeated mechanical loading of mixtures are presented, showing general agreements and suggesting advanced methods to be implemented in the near future. The tests provided new information in addition to already known principles in the field of bitumen and bituminous materials testing methods. This opens the way for further developments to obtain better performance related standards and more durable roads.
08019 A Reliability-Based Mix Design and Analysis System for Mitigating Fatigue Distress
J. Harvey, J. Deacon, A. Taybali, R. Leahy, C. Monismith

A reliability-based mix design and analysis system has been developed for mitigating fatigue distress in asphalt pavements. Design decisions consider not only fundamental mix properties but also the level of design traffic, the temperature environment at the site, the pavement structural section, laboratory testing and construction variabilities, and the acceptable level of risk. This paper describes the mix design and analysis system, discusses its calibration, illustrates its use, and assesses the consistency of current California design practice vis- a-vis the control of fatigue distress. It reveals possible inconsistencies in current California design practice, discusses effects of construction variability, highlights advantages of rich-bottom pavement structures, and illustrates the integration of mix and structural components into a reliability-based mix design process.
08020 Properties and New Developments of High Modulus Asphalt Concrete
J-P. Serfass, P. Bense, P. Pellevoisin

The use of High Modulus Asphalt Concrete (HMAC) for base and subbase has steadily increased for the last fifteen years. Several technologies are suitable: selection of very hard bitumen, addition of asphaltite, addition of polyolefins. Rich or lean mixes can be designed. Richer mixes are easier to compact and less sensitive to water. The resistance to rutting and the stiffness moduli are similar, irrespective of the richness. The long term in-place behaviour can be rated as satiafactory. A new type of HMAC has been designed to obtain high fatigue resistance. It contains a high amount of binder, which is a composite of very hard bitumen and polyolefin. The first trial sections are being monitored. HMAC for binder and wearing courses began to be used recently. They are designed to reach not only high stiffness and excellent rutting resistance, but also sufficient surface macrotexture. The observation of the first sections laid shows no rutting under extremely heavy traffic and an overall satisfactory performance to date.
08021 Design and Evaluation of Large Stone Asphalt Mixtures
J. Button, E. Fernando, W. Crockford, B. Coree

A mixture design procedure was developed for large stone mixtures with maximum aggregate sizes of 25 mm to 63 mm. The design procedure makes use of existing contractor stockpile gradations with the intent of maximizing the load carrying role of the stockpile containing the largest aggregate. Evaluative laboratory test procedures were developed and tested. A full scale test pavement demonstrated the effectiveness of the procedure.
08022 Effect of Tack Coat on Bonding Characteristics at Interface between Asphalt Concrete Layers
Y. Hachiya, K. Sato

The effect of a tack coat on the bond between asphalt concrete layers was investigated. First, the stresses at the interface caused by aircraft loads were calculated. Second, the effect of using a tack coat was evaluated by examining samples taken from in-service airport pavements. Third, laboratory tests were conducted to investigate how bonding characteristics were influenced by dirt adhering to the existing surfaces. Finally, measures to ensure sufficient bonding were developed.

The following conclusions were obtained. The interval between the construction of the wearing and binder coarses influences the bond strength: the strength decreases as the interval increases because dirt accumulates on the binder course. Adhesion between the courses can be improved by applying a tack coat. The curing time of the tack coat, however, also influences the strength, and the strength after one hour of curing is much less than that after 24 hours of curing. However, satisfactory strength can be obtained by using a newly developed tack coat. In addition, the structural integrity of the surface course can be ensured by introducing a thick lift construction procedure.
08023 Longitudinal Joint Construction Techniques for Asphalt Pavements
P. Kandhal, R. Mallick

Thirty hot mix asphalt (HMA) test sections were constructed in Michigan (1992), Wisconsin (1992), Colorado (1994), and Pennsylvania (1995) to evaluate the effectiveness of twelve different longitudinal joint construction techniques. The performance of these test sections was evaluated in 1996 after one to four years in service.

The joints with high densities generally show better performance than those with relatively low densities. The Michigan joint technique (12.5 mm vertical offset and 12:1 taper) appears to have the best potential of obtaining a satisfactory longitudinal joint. The cutting wheel and the edge restraining device techniques have good potential but are too much operator dependent to obtain consistent results. Among the three different joint rolling techniques used in all four projects, rolling the joint from hot side generally gave the best performance followed by rolling from hot side 152 mm away from the joint. Paver manufacturers should consider modifying the paver design to obtain a Michigan type, high density unconfined wedge in the lane paved first. Highway agencies should specify minimum compaction levels to be achieved at the longitudinal joint
08024 Development of Performance-Related Specifications for Porous Pavements in Oregon
K. Dunn, J. Gray, R. Hicks, J. Gower

The State of Oregon has employed the use of porous asphalt concrete surfaces (E and F-mixes) since the 1970s. The use of porous mixes has increased substantially in the past five years. Previously, no work had been done to evaluate whether the quality control/quality assurance (QC/QA) procedures used for dense-graded mixes were appropriate for open-graded mixes. This study consisted of a literature review, expert survey, and field survey of selected projects to determine the relative importance of the constituents (e.g., asphalt content, gradation, voids, moisture content) on the long-term performance of the pavement. The overall objective achieved by this study was the development of a basis for an improved QC/QA specification for porous pavements in Oregon. Specific objectives achieved include: 1) evaluation of experiences of others to control quality of open-graded mixes, 2) conducted a field survey of selected projects in Oregon to determine what factors most affect pavement performance, 3) recommended modifications to existing specifications which would include pay adjustments, and 4) developed a plan for implementing the resulting recommendations. This study found that the factors to be controlled during the production of porous pavements include asphalt content, gradation, and moisture content.
08025 Quantifying the Impact of Construction Specifications on Asphalt Pavement Performance Life
A. Noureldin

Asphalt content, aggregate characteristics, pavement layers thicknesses and their degree of compaction, and initial pavement smoothness are key quality control aspects in asphalt pavement construction. These measurable items are routinely checked during the constmction process.

The overall pavement performance life may be significantly affected when the specified values of those items are not achieved in situ. Quantification of their impact on pavement performance is essential for quality roadway construction, and rational pay adjustment factors.

This paper presents an approach to estimate the expected loss (or gain) in pavement performance life resulting from any in situ deviation in the above performance related characteristics from the specified values.
08026 Field Management of Hot Mix Asphalt Mixtures
J. Scherocman, D. Decker

The purpose of this report is to discuss the factors that contribute to the differences that occur in the properties of a Hot Mix Asphalt (HMA) mix designed in the laboratory and the properties of the "same" mix produced in an asphalt batch or drum mix facility. Emphasis is placed on the causes for the differences in the mix volumetric characteristics between the lab and the field with the understanding that laboratory mix design is only a starting point which must be verified through the HMA plant production. Major areas considered are: aggregate, asphalt binder, plant production process, hot mix storage, and hauling of the mix.

This publication provides a ranking system to prioritize the importance of each factor in contributing to the differences which may exist. Therefore, this document is intended to serve as a reference to assist HMA producers in understanding variables affecting volumetric properties.
08027 Introducing Quality System to Asphalt Mixing Plants – The Israeli Experience
S. Nesichi, I. Choustere, M. Divinsky

Significant increase in the national asphalt hot mix production required development of the quality system in asphalt mising plants. The paper describes the quality system in detail and presents original statistical elaboration with respect to the problem under study. A major component of the quality system is a Quality Mark (QM) characteristic which is a statistical estimation for the quality of the produced asphalt mixture.

Analysis of the actual data evidences that optimal quality characteristic can be derived with provision for the individual quality estimations for the diagnostic parameters such as Bulk Density, Bitumen Content, Filler Content, etc.

The prediction model for the QM characteristic is presented and its advantage and sensitivity are demonstrated.

The results of the analysis allow to distinguish the quality level of the plant production processes on the basis of the QM characteristic as well as prepare its quantitative estimation.

The approach shows essential efficiency. and can be recommended in practical applications of quality estimations for asphalt mixing plant production.
08028 Evaluation of Flexible Pavements in the Middle East
F. Chan, R. Armitage

The paper presents data from a number of sites in the Middle East where detailed pavement evaluation has been performed; generally utilising the FWD, DCP, coring/pitting and, sometimes high-speed ground radar, to determine pavement layer thickness and condition. This data has enabled both empirical and mechanistic design methodologies to be used and compared. Emphasis is made to one particular project in Qatar, where over 3000 FWD test points were analysed and relationships between deflection levels, stiffnesses, predicted lives and Modified Structural Number were developed. Data from the detailed assessment of a heavily trafficked pavement in the United Arab Emirates (U.A.E) is also given to illustrate the importance of material characterisation when developing maintenance measures. The results from the FWD were used in conjunction with performance related laboratory test results, predominantly using the Nottingham Asphalt Tester, NAT. The NAT enables stiffness, deformation resistance and fatigue cracking resistance properties of bituminous materials to be determined.
08029 Pavement Response Due to Dynamic Axle Loads
M. Huhtala, J. Pihlajamaki, P. Halonen

This paper describes the results of primary response measurements carried out to study the effects of dynamic loadings of vehicles on pavements. The measurements were made at the Virttaa test site in Finland as part of the OECD/DIVINE project. Two instrumented pavements and two artificial bumps were used to excite body bounce and axle hop. Instrumented vehicles were from Canada, the United Kingdom and Finland. The strains at the bottom of the bituminous courses were in almost direct proportion to the dynamic wheel loads on thick bituminous pavement. They were similar if there were air or steel suspensions or if the dynamic load was caused by body bounce or axle hop. On thin bituminous pavement the size of the changing tire imprint plays an important role and dynamic wheel loads have only a slight effect on the strains.
08030 The C-SHRP Lamont Test Road: Five Years of Performance Monitoring
L. Dunn, J. Gavin

As part of the Canadian Strategic Highway Research Program’s study entitled "Performance Correlation for Quality Paving Asphalts" a full scale test road was constructed in 1991. The Lamont Test Road (LTR) was constructed in order to assess the low temperature transverse cracking performance of seven markedly different asphalt cements. Extensive field and laboratory testing and ongoing performance monitoring was undertaken.

This paper documents: the asphalt cement selection and physical properties; the quality assurance results; the results of subsequent SHRP Superpave laboratory grading of the asphalt cements; the results of the LTR’s performance after five winters of service and; the temperature monitoring during the first three winters and subsequent weather station data for the remaining two winters.
08031 Characterization of Stone Matrix Asphalt Mortars
E. Brown, J. Haddock

Stone Matrix Asphalt has been used for over 20 years in parts of Europe and Scandinavia. Recently, it has gained more recognition in the United States. The mixture has been successful due in part to its durability. This durability is provided by a mortar that consists of asphalt binder, fine aggregate, mineral filler, and a stabilizing additive.

This paper details research aimed at applying the Superpave binder test methods and specifications to SMA mortars. It was found that the use of the Dynamic Shear and Bending Beam Rheometers does seem to be viable with mortars.

Data obtained with the Dynamic Shear and Bending Beam Rheometers suggests that specifications for SMA mortars can be established if the current Superpave binder specifications related to these two pieces of equipment are multiplied by a factor of 5.
08032 The Construction and Performance of Stone Mastic Asphalt Pavements in the United States
J. Scherocman

Stone mastic asphalt (SMA) pavements were first built in the United States in 1991 using technology obtained from Europe. It was determined, however, that significant differences exist in the aggregate properties and mix design methods used. ln addition, differences in the plant production methods and in the laydown and compaction procedures are present. This resulted in a number of problems in constructing the stone mastic asphalt pavements that are discussed. To date, after up to six years of service under traffic, the performance of the SMA pavements has been excellent.
08033 Development of a Stone Mastic Asphalt Design Method for South African Conditions
L. Louw, C. Semmelink, B. Verhaeghe

Thin asphalt layers (of less than 40 mm thickness) are often used for surfacings in South Africa. As these layers are placed on either stiff (cemented) or flexible structures it is important that they be rut resistant, durable and have good fatigue properties. Stone Mastic Asphalt (SMA) has been gaining worldwide acceptance as a stable, durable and fatigue-resistant surfacing mix. The objective of this project was to develop a SMA design method suited for southern African conditions. This paper discusses:
– the recipe mix design methods prescribed by the various road authorities;
– basic principles of volumetric design;
– a theoretical model to determine the volumetric properties of SMA mixes, and
– various compaction methods, including the gyratory compactor and the Marshall impact hammers.

In the design of SMAs the applicability of grading envelopes is compared with volumetric properties. The laboratory results are compared with those obtained from the model. The K-mould apparatus, a dynamic triaxial loading and data acquisition system, was used to determine the rut resistance ie. dynamic creep and effective stiffness (Esec) of the material.
08034 Effect of Surface Seals on Aging of Underlying Asphalt Concrete
J. Button

Asphalt surface seals are defined herein as slurry seals, micro-surfacings, and chip seals (seal coats). The objective of this study is to estimate, by laboratory testing, the relative aging abatement effects of surface seals on the upper 13 mm of an asphalt pavement.

A surface seal can retard oxidative hardening of an underlying asphalt concrete layer by 0 to 2 years, depending on the situation. However, most of the oxidative aging in the upper stratum of an asphalt concrete pavement occurs during the first 4 years after construction. Therefore, in order for a surface seal to significantly delay oxidative hardening of the underlying pavement, it must be placed during the first two years (approximately) of the pavement’s life. Ultraviolet (actinic) light penetrates asphalt cement only a few microns and, therefore, does not contribute materially to hardening of the uppermost 13 mm of an asphalt concrete pavement. For practical purposes, these three surface seals will protect the top 13 mm of an underlying pavement from oxidation as if they were impermeable to air and water.
08035 Study of Maintenance Treatments for Asphalt Pavements
D. Morian, S. Gibson, J. Epps

During the conduct of the Strategic Highway Research Programs (SHRP) on highway operations, flexible and rigid pavement preventive maintenance treatments were placed on pavements in the United States and Canada. The placement and performance monitoring of these Specific Pavement Studies (SPS-3 and SPS-4) has been conducted under the SHRP and Federal Highway Administration (FHWA) Long Term Pavement Performance Program (LTPP). Field performance reviews of the preventive maintenance treatments have also been conducted by Expert Task Groups (ETG) organized by the Pavement Division of the FHWA.

This report summarizes the results of the ETG performance surveys conducted after 5 years of service and the results of the preliminary analysis of LTPP Database data for the SPS-3 experiment.
08036 Full Scale Performance Trials and Accelerated Testing of Hot Mix Recycling in the UK
J. Potter, J. Mercer

This paper reviews the research carried out on the hot-mix recycling of bituminous materials over more than a decade in the UK. Results from trials on public roads and full-scale accelerated load testing of recycled roadbase in the TRL Pavement Test Facility are summarised and discussed. Hot rolled asphalt wearing course has been recycled in-situ using the Remix method with up to 80 per cent of the original surfacing material in the mix. In off-site mixing plants, recycled bituminous roadbase has been produced with up to 60 per cent of reclaimed material in the mix. Their performance in the road has been assessed by measuring longitudinal profile, transient deflection, depth of rutting, surface texture and resistance to skidding. Performance-related laboratory tests have also been carried out. In general, the trials indicate that the performance of recycled materials is as good as that of equivalent conventional materials. The results of the research have been implemented in the UK Specifications.
08037 Progress in Hot-ln-Place Recycling Technology
R. Terrel, J. Epps, M. Joharifard, P. Wiley

The concept of recycling asphalt pavements has been attempted using a range of methods for more than eighty years. Starting with simple concepts of crushing old pavements for use in highway fill, the technology has progressed through numerous phases. The most recent began in the mid 1970s when both central plant and in-place methods were initiated. Hot central plant recycling and cold in-place recycling (CIR) has gained general acceptance by many agencies. Hot in-place recycling (HlR) has been used for nearly 50 years but public agencies have been slow to implement the technology. However, recently developed equipment and procedures have made HIR a very viable alternative for pavement rehabilitation.

HlR methods began with various equipment that used flames which impinged directly on the pavement surface then progressed through several evolutions of heating methods including infrared. The current state-of-the-art is a hot-air system that overcomes the previous limitations of shallow depth of heating, burning of the surface, and creation of objectionable smoke.

This paper includes a technical description of HIR equipment and methods and test results from early projects using the more modern, efficient equipment. The data and early performance evaluation show that the 100% recycled asphalt concrete was aged insignificantly and had laboratory test properties equivalent to virgin hot mix.
08038 A Theoretical Model of Long Term Flexible Pavement Performance
A. Collop, D. Cebon

A new ‘whole-life’ pavement performance model (WLPPM) has been developed that is capable of making deterministic pavement damage predictions due to realistic traffic and environmental loading. The WLPPM is divided into three main areas: (i) dynamic vehicle simulation, (ii) pavement primary response (stresses, strains etc) model, and (iii) material damage (surface rutting and fatigue cracking) model.

The WLPPM is used to investigate the relationships between ‘hot spots’ (due to peak dynamic tyre forces), and ‘weak spots’ (due to initial pavement stiffness variations) and long-term flexible pavement damage. The effects of spatially repeatable patterns of loading on long-term flexible pavement performance are also investigated. A method is described for simulating vehicle fleets with varying degrees of ‘spatial repeatability’ of dynamic tyre forces using a small number of dynamic tyre force histories. Results indicate that thinner pavements are most sensitive to the level of spatial repeatability exhibited by the vehicle fleet. Pavement damage predictions made without assuming an appropriate level of spatial repeatability can be in error by 20-150%, the higher values being for thinner pavements that fail by fatigue damage.
08039 Resin Modified Pavement: A Composite Paving Material
G. Anderton, R. Ahlrich

Resin modified pavement (RMP) is a composite pavement surfacing that uses a unique combination of asphalt concrete and Portland cement concrete materials in the same layer. The RMP material is generally described as an open-graded asphalt concrete mixture containing 25 to 35-percent air voids which are filled with a resin modified portland cement grout.

The RMP process was developed in France in the 1960s under the trade name "Salviacim" as a fuel and abrasion resistant surfacing material. RMP was introduced into the United States pavements industry by researchers at the U.S. Army Engineer Waterways Experiment Station (WES) beginning in 1987. WES researchers were hoping to develop a cost effective and easily-constructed alternative to portland cement concrete. Numerous full-scale field applications have since followed.

This paper gives a general description of the RMP process, including discussions of structural and material designs as well as construction techniques. Performance of significant field applications and the projected future of RMP are also discussed.
08040 Calibrating Mechanistic Flexible Pavement Rutting Models from Full Scale Accelerated Tests
W. Kenis, W. Wang

This paper summarizes research conducted at the Federal Highway Administration (FHWA) to validate and calibrate two different flexible pavement mechanistic permanent deformation models. The research uses internal calibration method and demonstrates applications of the method using rutting performance data generated from selected full scale accelerated pavement tests.

Since 1970, the FHWA has sponsored research both nationally and internationally on a wide variety of topics dealing with flexible pavement performance modeling. Some of these efforts led to the development of the VESYS mechanistic flexible pavement analysis system. This system is capable of performing pavement primary response analysis and performance prediction. A recent version, VESYS 5, includes two flexible pavement rutting models, "system rutting" and "layer rutting" models, along with other pavement performance models to predict pavement performance for different pavement materials under daily traffic loading and under different climatic seasons. Also under the FHWA sponsored programs, several full-scale pavement testing programs have been developed to better understand and quantify pavement performance under controlled tragic loads. Among those full-scale testing programs, a permanent, outdoor Accelerated Loading Facility (ALF) was constructed at FHWA and has been in operation since 1986. The ALF tests are conducted under controlled conditions, therefore, it provides a valuable source of data for validating, calibrating and improving currently used flexible pavement performance models.

In this study, selected sets of field performance data from FHWA’s ALF testing program were used to validate and calibrate the two flexible pavement rutting models used in VESYS 5. A procedure for mechanistic model calibrations using of full-scale test data was established. It was further shown that the calibrated rutting model can be used to predict the rutting performance of other flexible pavements.
08041 Finite Element Simulation of Damage Development in Asphalt Concrete Pavements
A Scarpas, R. Al-Khoury, C. van Gurp, S. Erkens

An extensive experimental and analytical investigation is being currently carried out on the mechanisms leading to the initiation and propagation of fatigue damage in the top layers of asphalt concrete pavements when subjected to various types of loading. One of the major goals of the investigation is the development and finite element implementation of a triaxial, strain rate sensitive, history and temperature dependent constitutive model for asphalt concrete under arbitrary states of stress.

Because of the hierarchical formulation of the model, the analyst can activate, at will, those features of the model which he considers relevant to his specific interests. Explicit procedures are suggested for the experimental determination of the parameters. As a minimum, only uniaxial test results are needed for determination of the basic parameters. An actual example of such a procedure is presented.

In its current, prototype formulation, the model has been implemented in the finite element code CAPA3D. Results of the utilization of CAPA-3D for the investigation of the dynamic non-linear response of asphalt concrete pavements are reviewed in the last part of this contribution.
08042 Theory, Validation and Application of the Visco-Elastic Multilayer Program VEROAD
P. Hopman, R. Nilsson, A. Pronk

VEROAD is a linear visco-elastic multilayer program. The acronym VEROAD stands for Visco-Elastic Road Analysis Delft. The program takes fully account for both the viso-elasticity of the asphalt material and the movement of the wheel. Thus the actual time dependent displacements, stresses and strains and the permanent deformation are obtained, fully three-dimensionally. From these quantities others can be derived: the dissipated energy due to the passage of a wheel, the effect of lateral wandering on permanent deformation, the principal stresses, the rotation of the principal stresses, etc.

The underlying theory is described shortly. The program has been validated by comparing the longitudinal and transversal strains measured in full scale tests with those calculated by using VEROAD. The agreement can be called excellent. The field of application is obvious. It ranges from analyzing full scale test results to pavement design, from mix design to analysis of the damaging effects of different wheel configurations. In the article also attention is paid to the experimental determination of the material parameters to be used in VEROAD.
08043 Bimodular Analysis of Asphalt Pavements
M. Mamlouk, P. Khanal

When wheel loads are applied on the pavement surface, both tension and compression are developed in the asphalt concrete layer. Laboratory tests were conducted on asphalt concrete specimens under different dynamic loading and temperature conditions. Largely different tensile and compressive moduli were obtained, especially at high temperatures.

A nonlinear finite element multi-layer program that can account for the bimodular nature of asphalt concrete (BIMODPAV) was developed. The program applies traffic loads in increments, checks the stress state at each element, and selects the appropriate modulus accordingly using the modulus values obtained from the lab tests. The BIMODPAV program was further used to analyze stresses, strains and displacements in typical pavement sections under different conditions. The results indicate that pavement response parameters calculated by the bimodular analysis are significantly different from those calculated by assuming a single modulus value. Using single-modulus analyses erroneously over-predict fatigue and rutting pavement lives as compared to those obtained from the bimodular analysis. The effect of bimodularity is most significant for pavements with a thick asphalt layer and/or at high temperatures. The mechanistic analysis technique developed in this study allows pavement to be designed in a more scientifically-based manner.
08044 Finite-Element Dynamic Analysis of Distressed Asphalt Pavements
W. Uddin, Z. Pan, P. Noppakunwijai, C. Plaxico, R. Hackett

Three-dimensional finite-element pavement-subgrade models are developed in this study to simulate falling weight deflectometer (FWD) loading on highway pavements. Reasonably good agreement is found between FWD deflections measured on selected pavements and computed dynamic deflections for pavement models subjected to the FWD load pulse and contact simulation. Effects of loading force-time history and pavement cracking on the surface deflections response of an asphalt pavement are also presented. The creep modulus of asphalt mix is predicted using a micromechanical model which calculates the viscoelastic response from creep compliance test results of the binder and elastic properties of the aggregates.
08045 Evaluation of the Interaction Between the Asphalt Concrete Layers by a New Dynamic Test
M. Crispino, B. Festa, P. Giannattasio, V. Nicolosi

To study the dynamic interaction between flexible pavement layers a special equipment was designed and built and a testing methodology was also developed. Theoretical analysis and initial testing have demonstrated qualitative aspects of the phenomenon. On such basis it was suggested to represent the horizontal interaction between flexible pavement layers as a structural restraint following Kelvin’s model. The representing parameter has been defined by the authors as: Interlayer Reaction Complex Modulus Kl*. The statistical characteristics of the test developed were evaluated, together with the values of the norm (absolute value) and of the phase angle (between load and deformation) of the vector KI* at two different temperatures. Statistical analysis has shown that test reliability is adequate for research purposes but still low for normalization. The test and the parameter KI* appear to be suitable for the representation and evaluation of the interaction between asphalt concrete layers for flexible pavements.
08046 Modelling of Granular Materials Using the Discrete Element Method
P. Ullidtz

With the Discrete Element method it is possible to model materials that consists of individual particles where a particle may roll or slide on other particles. This is interesting because most of the deformation of granular materials is due to rolling or sliding rather than compression of the grains. This is true even of the resilient (or reversible) deformations. It is also interesting because the Discrete Element method models resilient and plastic deformations as well as failure in a single process.

The paper describes two types of calculations. One on a small sample of angular elements subjected to a pulsating (repeated) biaxial loading and another of a larger sample of circular elements subjected to a plate load. Both cases are two dimensional i.e. plane strain.

The repeated biaxial loading showed a large increase in plastic strain for the first load pulse at a given load level. Additional load pulses at the same load level gave decreasing plastic strain rate, in agreement with what is normally observed on granular materials. The resilient modulus was much lower than the stiffness of the elements and was decreasing with increasing deviator stress. At high deviator stresses the stiffness of the assembly of elements was less than one percent of the stiffness of the elements. This is also in good agreement with observations on granular materials.

Plate loading showed a distribution of vertical stress that was close to the stress in an elastic continuum. Very little stress concentration was observed, but this might change if angular elements were used. The horizontal stresses on the other hand were quite different from the horizontal stresses in an elastic continuum. Modulus and Poisson’s ratio calculated at different points of the particulate medium, from the stresses and strains, showed large variations. Dilation of the material was frequent.
08047 Mechanical Properties of Unbound Base Course
J. Belt, T. Ryynanen, E. Ehrola

A laboratory-scale pavement testing facility with a moving vehicle load can be used to simulate reliably the stresses caused by traffic in the road structure and is therefore well suited to the testing of materials and structures. The measuring system developed here can be used to determine reliably both elastic and permanent deformations within the structure, which, in turn, can be used to determine relative strains.

The mechanical properties of the unbound base course and their significance for the performance of the whole road structure depend on the thickness of the bound layer and the quality of the material. When the asphalt concrete (AC) layer is thin, it would be good to have grading with Fuller’s "n" value equal to 0.4 or 0.5 in the unbound base course. When the bound layer consists of very soft asphalt, in turn, it would be good to aim at a grading curve with "n" = 0.5. A large maximum grain size in the base course minimizes both permanent and elastic strains.

Compaction of the unbound layers also has a distinct effect on the mechanical properties of the layer. A high degree of compaction minimizes permanent strains. Effective compaction, however, results in grinding of the materials. The compaction of unbound rough materials and their grinding during compaction can be evaluated with the Intensive Compaction Tester gyratory compactor both quickly and inexpensively.
08048 A Comprehensive Constitutive Model for Granular Materials in Flexible Pavement Structures
R. Bonaquist, M. Witczak

This paper summarizes research leading to the development of a comprehensive constitutive modeling approach for granular bases, subbases, and subgrade soils. The model that was developed is based on the flow theory of plasticity. It rationally considers both the resilient and permanent deformation response, and accounts for the effects of repeated loading and saturation and drainage conditions. The model can be used to predict pavement performance, to select pavement layer thicknesses to resist permanent deformations, and to select material properties to assure adequate performance. This paper describes the conceptual model development. It also presents results from a laboratory evaluation of the constitutive model using three materials covering the range of materials typically classified as granular in pavement construction. Finally, the modeling concepts are applied to practical pavement design problems.
08049 Assessing Seasonal Variations in Cohesive Subgrade Soils
W. Khogali, K. Anderson

In 1990, an investigation was initiated to measure seasonal variations in subgrade stiffness of cohesive soils in Alberta. The main objective of this study was to identify and select suitable strength indices for measuring seasonal variations in pavement response.

The study consisted of two phases: a field investigation phase and a laboratory testing program. The field phase involved instrumenting an in-service pavement section in Alberta with thermal conductivity sensors to measure temperature and soil suction. This data coupled with Falling Weight Deflectometer deflection tests performed within the instrumented section were used to accomplish the research goals.

The laboratory program consisted of extensive repeated load testing on remolded samples of the subgrade material taken from the instrumented site. Results obtained from these tests were used to develop predictive resilient moduli relationships.

Both field and laboratory phases produced novel and practical approaches for quantifying the influence of seasonal variations on subgrade strength.
08050 Mechanical Behaviour of Soils and Unbound Granular Materials, Modelling of Flexible Pavements – Recent Advances
J. Balay, A. Gomes Correia, P. Jouve, P. Hornych, J-L. Paute

Different European Laboratories (Administration, Universities) were awarded a laboratory twining project between 1990 and 1993, under the "Science" programme, which closure has taken place with Euroflex ’93 Symposium (Lisbon, 1993). This research aims to harmonise and develop rational procedures to take into account the mechanical characteristics of soils and unbound granular materials, to apply into the design of flexible pavement structures.

A round-robin test programme for unbound granular materials carried out by different laboratories enable to establish reliable test procedures for characterisation of elastic and plastic behaviours of these materials. The procedure for elastic behaviour is summarised in this paper. Concerning the modelling of flexible pavements structures, the behaviour of unbound granular materials was described by a non linear elastic constitutive law (Boyce), with which a classic plasticity criterion was added (Drucker-Prager) in order to give a stress field in the material compatible with its strength.

This model was implemented in FEM codes: CESAR LCPC-2D and 3D, and Noel 8-2D of University of Nantes. The results of FEM-2D (single wheel) and FEM- 3D (dual wheel) calculations realised for most representative flexible pavement structures are presented.
08051 Pavement Subgrade Performance Study in the Danish Road Testing Machine
H. Ertman Larsen, P. Ullidtz

Most existing pavement subgrade criteria are based on the AASHO Road Test, where only one material was tested and for only one climatic condition. To study the validity of this criteria and to refine the criteria a co-operative research program entitled the "International Pavement Subgrade Performance Study’ was sponsored by the FHWA with American, Finnish and Danish partners.This paper describes the first test series which was carried out in the Danish Road Testing Machine (RTM).

The first step in this program is a full scale test on an instrumented pavement in the Danish Road Testing Machine. Pressure gauges and strain cells were installed in the upper part of the subgrade, for measuring stresses and strains in all three directions. During and after construction FWD testing was carried out to evaluate the elastic parameters of the materials. These parameters were then used with the theory of elasticity to calculate the stresses and strains at the position of the gauges and to compare these values to the stresses and strains recorded under the rolling wheel load.

Plastic strains resulting from 50,000 applications of each of two load levels (20 kN and 40 kN) were recorded, as well as the permanent deformation of the pavement surface. A simple model describing the plastic strain bas been developed.

The test showed that currently used subgrade strain criteria are conservative if used with the measured strains in the subgrade. If used with strains calculated from FWD tests using linear elastic theory, however, the strain criteria seem to give a reasonably good prediction of the bearing capacity of the pavement. The differences between measured and theoretical values appear to be due to inhomogeneities in the pavement, to the non-linear elastic subgrade modulus, and to a modulus gradient in the subgrade.
08052 A Regression Model for Better Characterization of Resilient Properties of Subgrade Soils
A. Puppala, L. Mohammad

Subgrade soil characterization in flexible pavement design is necessary for estimating the structural capacity of flexible pavements and then determining tbe pavement layer thicknesses. Several non-linear and linear models have been used to characterize the subgrade soils. The current bulk and deviatoric stress models have limited applications since they are essentially developed for a particular soil type. Few other models are restricted by the multiple collinearity problems in the regression analysis. A regression model with confining and deviatoric stresses as attributes is adopted in this paper to analyze the repeated load triaxial test results. This model is simple, easy to analyze the repeated load triaixial test results and does not have any structural type collinearity problems. This paper presents the regression model analysis results on different subgrade soils including mixed soil types. The repeated load triaxial tests conducted on granular, cohesive and mixed soil types at various moisture content levels are first analyzed to determine the model constants. The model constants are then correlated with the basic soil properties. The correlations are evaluated in their reliability in predicting the resilient properties of the same subgrade soils. This evaluation, which is fairly successful, showed that this approach can be used to predict the resilient properties of similar type soils. This approach will save significant project costs since core sampling and resilient modulus testing tasks can be averted.
08053 Specimen Preparation and Repeated Load Triaxial Testing of Subgrade Soils
S. Baltzer, L. Irwin

This paper presents part of the research work being performed under the "International Subgrade Performance Study" sponsored by the Federal Highway Administration (FHWA). The objective of the subgrade study is to define one or more predictive models that will relate rutting to soil type, stress/strain level, and soil moisture conditions. Full-scale instrumented flexible test pavements will be constructed in the Frost Effects Research Facility at the U.S. Army Corps of Engineers Cold Regions Research and Engineering Laboratory (CRREL) and at the Danish Road Institute (DRI). Accelerated loading will be used to simulate traffic, and pavement performance will be measured. As part of the research work, repeated-load triaxial testing of both resilient and plastic properties of the subgrade soils will be performed. Characterization of resilient properties is being done at Cornell University. Special testing equipment and procedures for specimen preparation have been developed. The procedure produces specimens with a uniform density and moisture gradient. The test plan for repeated-load triaxial testing of resilient modulus, and plans for model building from the results are described.
08054 Asphalt Mix Fatigue Behavior Experimental Structures and Modeling
H. Odeon, J-C. Gramsammer, C. Caroff

An extensive research program on asphalt mix fatigue was conducted jointly by the LCPC (French transportation research laboratories) and Scetauroute (French highway engineering agency) between 1990 and 1994. The program included tests on the LCPC circular fatigue test track and a theoretical analysis of the hehavior of structures. This article looks into the parts of the program dealing with the fatigue tests and modeling. The aim of this program was to clarify the behavior in the laboratory and on pavements of asphalt mixes differing only in the type of asphalt. Additionally, it involved adding constituents to improve the design method in the case of high-modulus asphalts. On the fatigue test track more than 7 IO^6 load sequences were applied to twelve structures over the course of three experiments. The experimental pavements revealed similar behavior in asphalt concrete of the same thickness, and the good performance of high-modulus materials whenever proper thicknesses were used. The model made it possible to determine a correlection coefficient in connection with rigid materials for the French pavement design method and brought out the value of controlled-force tests.
08055 Fatigue Behavior of Asphalt Mixes: Influence of Laboratory Test Procedures on Fatigue Performances
C. de La Roche, N. Riviere

Since 1990, the LCPC carried out three "semi-scale" experiments on its test track aimed at studying the fatigue behavior of asphalt mixes in the aspect of the influence of the nature of asphalt.

The large amount of laboratory tests carried out on the six different tested materials show that, if the modulus is a value relatively independent of the measurement method, the fatigue behavior in the laboratory strongly depends on the test procedure (frequency, temperature, two or three points bending, controlled force or displacement, with or without rest period). The results obtained don’t allow to choose one type of fatigue test as more relevant than another one in all cases.

A systematic study carried out in laboratory in order to better define the data obtained from the fatigue tests highlights the energy dissipated in the form of heat during the continuous tests. It also points out that the differences in the results between the continuous and discontinuous tests are probably not attributable to an actual healing of the material during the rest periods.
08056 Comparison of Fatigue Criteria for Flexible and Semi-Rigid Pavements
J. Judycki

The paper presents comparison of fatigue criteria which are used in mechanistic methods of pavement design. The following criteria were considered: (a) for fatigue cracking of asphalt layers and structural rutting (subgrade strain): LCPC and SETRA (France), Nottingham University (United Kingdom), Road Research Centre in Belgium, Shell and The Asphalt Institute (USA) and (b) for fatigue cracking of bases treated with hydraulic binders: CSIR (South Africa), Road Research Centre in Belgium, University of Illinois (USA). The aim of the comparison was to select suitable fatigue criteria for the revision of the 20-year old Polish catalogue of typical pavements which was required due to significant increase in traffic volume and in axle loads.

In the paper the fatigue formulas for all the considered criteria were given and fatigue curves were compared. Pavement structures with different base courses were designed for a range of traffic volumes with regard to various fatigue criteria and Polish design considerations. The designed structures were compared with pavement structures included in the old Polish catalogue of typical pavements which performance can be evaluated as acceptable. On this basis the following criteria were selected as suitable for Polish conditions: (a) for fatigue cracking of asphalt layers and structural rutting (subgrade strain) – The Asphalt Institute (USA), and (b) for fatigue cracking of cement treated bases – CSIR (South Africa), Road Research Centre in Belgium, University of Illinois (USA). New typical pavements structures were designed according to the selected fatigue criteria.
08057 Possibilities of a Semi-Circular Bending Test
M. van de Ven, A. de Fortier Smit, R. Krans

The possibilities of a Semi-Circular Bending (SCB) test on semi-cylindrical specimens is investigated as an alternative to the Indirect Tensile Test (ITT) to determine the flexural strength, stiffness and fatigue behaviour of asphalt concrete. Finite element analysis relations for the stresses and deformations under SCB have been derived. Based on these relations the tensile strength and fatigue behaviour of two asphalt mixes were determined with laboratory tests. These results have been compared with ITT results on the same mixes.

It can be concluded that the SCB gives results comparable with ITT for the tensile strength. The determination of stiffness requires accurate measurement of the relatively small vertical deformations under loading. Fatigue tests can also be carried out. The SCB test can be used as a mix design test for performance related specifications and a reliable quality control test for mix production and road construction. A standard test set-up is proposed.
08058 Stiffness and Fatigue Characteristics of Some Asphalt Wearing Courses Used in South Africa
N. Kong Kam Wa, H. Theyse, B. Verhaeghe, E. Knottenbelt

This paper deals with an extensive research program into the upgrading of the fatigue transfer functions of asphalt mixes in use in South Africa. Parts of the program have recently been completed and the aim of the paper is to summarise and discuss the results obtained to date. Two stages of the program are discussed in this paper: a comparison of stiffnesses of asphalt mixes obtained from different sources, and the evaluation of the fatigue life of laboratory asphalt mixes and development of laboratory fatigue regression models.

In the first of the above-mentioned stages, stiffnesses of asphalt mixes were determined in the laboratory (using the Indirect Tensile Test) and from two theoretical stiffness prediction models (Shell method and Asphalt Institute method). Attempts were also made to backcalculate field stiffness using the Multi-Depth Deflectometer (MDD) results of four Heavy Vehicle Simulator (HVS) field tests. In the second stage fatigue tests were undertaken in the third- point beam fatigue test apparatus in the constant strain mode at various strain levels. Regression models were developed for the following independent variables: strain, temperature, initial flexural stiffness, load frequency, aggregate grading and binder type.

The findings indicate that the Shell BANDS- program and the Asphalt Institute’s equation (AI) can be used for an approximate determination of asphalt stiffness, provided that the methods are used correctly. There is also some indication that there is a correlation between the resilient modulus obtained in the Indirect Tensile Test and the actual effective field stiffness, but this has to be verified by further studies. In the second part of the investigation it was found that the fatigue regression models obtained from this study gave a higher life than other models such as those of the Asphalt Institute, TRRL and NCHRP. The coefficients of determination obtained were, however, very good.
08059 Fatigue Analysis of Asphalt Pavements with Thick Asphalt Mixture Layer
T. Nishizawa, S. Shimeno, M. Sekiguchi

In the prevailing structural design of asphalt pavements, fatigue cracking at the bottom of asphalt mixture layer is considered to be a major failure mode of the pavement structure. In Japan, however, such failure has rarely been observed in the asphalt pavements with thick asphalt mixture layer including asphalt stabilized base course which has been in service for more than 20 years. Failure modes of the asphalt pavements are rutting and surface cracking. The asphalt stabilized base courses in such pavements have been alive without major repairing. Therefore, the concept of the structural design should be reconsidered in terms of the fatigue cracking.

We conducted fatigue analysis for various asphalt pavements with thick asphalt mixture layer in Japan. Radial strains at the bottom of asphalt mixture layer and vertical strains at the top of subgrade were calculated. Then, fatigue damages were estimated by applying the calculated strains to fatigue curves presented in the manual. In the analysis, wheel load distributions were taken into account by employing the Miner’s law. The results of the fatigue analysis showed that the fatigue crack at the bottom would occur in the asphalt pavements with thick asphalt mixture layer in less than 10 years. The results do not agree with our field experiences mentioned above.

We made an assumption that, at the strain level of less than 200 micro, asphalt mixture would not fatigue because of the healing effect. Being based on the assumption, we conducted the fatigue analysis again. The results of the analysis seemed to be quite reasonable and agree with our experiences in Japan.
08060 Variability in Roadbase Layer Properties Conducting Indirect Tensile Test
S. Said

Knowledge of variabilities in the properties of asphalt pavement layers is valuable in the structural evaluation of pavements. Mix composition and construction procedure influence the mechanical properties of bituminous layers. Fatigue and stiffness characteristics are two of the most important parameters in input data to pavement evaluation models. In this study, more than 300 cores from 15 test sections were drilled from roadbase layers for determining mix composition, fatigue and stiffness properties. These cores have been tested at different temperatures when conducting the Indirect Tensile Test (ITT). The ITT, which is probably most suitable for examining specimens from pavement layers, has proved to be sufficiently accurate for routine use, such as determination of mix properties, and also in quality control. A good correlation has been found between laboratory based and field based fatigue curves for the roadbase mix.

Statistical fatigue relationships based on the laboratory measurements are also presented and the effects of the variabilities in the mix properties are illustrated. It is hoped that knowledge of the characteristics of bituminous pavement layers with their variations and the use of ITT in routine measurements may contribute to further utilization of pavement evaluation models by road engineers.
08061 Comparison of 2 and 4 Point Fatigue Tests and Healing in 4 Point Dynamic Bending Test Based on the Dissipated Energy Concept
A. Pronk

At the 4th Eurobitume Symposium a fatigue life definition was introduced, which was based on the dissipated energy concept (Hopman et al, (1989)). This new definition is based on a change in a material related aspect (dissipated energy per cycle) instead of a specimen property. It was shown that, using the dissipated energy law and this new fatigue life definition, the results were exchangeable for strain and stress controlled fatigue tests even at different frequencies. These experiments were only carried out in a 4 point dynamic bending test. In this paper the results are presented of a comparison of fatigue lives measured in 2 and 4 point dynamic bending tests. In spite of the new fatigue life definition, the results are not comparable for both tests. This may be due to the composition of the mix at issue and the small dimensions of the specimen in the 2 point bending test.

Also the healing phenomenon is studied in the 4 point bending test. Rest periods between loadings ought to enlarge the fatigue life considerably. After a resting period the stiffness modulus is largely restored. If instead of resting periods (with zero loading), load blocks are used with a smaller load amplitude, it is shown that during these pseudo rest periods the stiffness modulus will increase. Depending on the duration of the pseudo rest period and the amplitudes of the loadings, this increase will be followed by a decrease in stiffness modulus. These findings confirm the opinion that healing already takes place during the fatigue process and should be taken into account in the interpretation of the fatigue measurements and the characterization of the fatigue properties. Based on the dissipated energy concept a model is proposed taking into account the healing phenomenon. This model should enable a more fundamental description of the asphalt fatigue properties including healing.
08062 Development of Performance Prediction Models for Dry-No Freeze and Dry-Freeze Zones Using LTPP Data
K. Senn, D. Frith, M. Yapp, L. Scofield

The Long Term Pavement Performance (LTPP) program is currently in the eighth year of a twenty year project to monitor and collect pavement data on approximately 800 general pavement studies (GPS) sections across the United States and Canada. This paper focuses on GPS 1 sections (asphalt surfacing on a granular base) located in the Dry-Freeze and the Dry-No Freeze zones of the Western United States. Approximately 50 sites were selected from these two zones.

Using data collected from the LTPP sites, this paper presents the analyses used to develop pavement performance prediction models. Performance is measured in terms of individual distress types, such as roughness and fatigue cracking. A discussion of the problems inherent in such a process is also included.

The authors concluded that although it was possible to recognize performance trends, developing meaningful prediction models was not feasible for GPS sections. It was recommended that future analysis along similar lines focus on specific pavement study (SPS) sections.
08063 Development of Deterioration Models for Cold Climate Using Long-Term Pavement Field Data
H. Jamsa, H. Spoof, L-G. Wagberg, N-G. Goransson, W. Hudson

The paper describes the results of the Long-Term Pavement Performance (LTPP) study carried out in Finland and Sweden on the GPS-1 experiment (asphalt concrete on granular base). The main results include new pavement deterioration models which are based on a failure time approach using censored data on 64 test sections. A large number of independent variables were examined to identify factors which explain most of the pavement deterioration on wheel paths (traffic related distress) and on a whole pavement surface (traffic and climate related distress). The most important factors explaining deterioration included tensile strain at the bottom of the asphalt layer, or the surface curvature index calculated from FWD measurements and the freezing index. In addition to deterioration models, a new neural network approach to calculate tensile strains on the basis of measured deflection bowl and asphalt layer thickness is introduced.
08064 Comparison of Accelerated Pavement Test Results with Long Term Pavement Behaviour and Performance
F. Jooste, S. Kekwick, E. Sadzik, G. Rohde

A comparison was made of pavement behaviour and performance as measured during an accelerated pavement test conducted by the Heavy Vehicle Simulator (HVS) in 1980, and actual behaviour and performance of the same pavement section measured in 1996. Behavioural aspects such as deflection, Dynamic Cone Penetrometer shear strength, moisture and density were found to correlate reasonably well with measurements made during the accelerated pavement test 16 years earlier. Rutting measured in 1996 compared well with rut depths measured during the accelerated pavement test at a similar number of equivalent standard axles. Rut development as measured during the accelerated pavement test also compared well with predictions made with the World Bank’s Highway Design and Maintenance Program (HDM). Results obtained indicate that, for the pavement section studied, environmental effects did not significantly change the behaviour and performance of the pavement.
08065 Performance Prediction of Accelerated Loading Facility (ALF) Trials Using Elastic, Visco-Elastic and Elasto-Plastic Analysis
W. Yandell, G. Behzadi

Most current methods of flexible pavement design take only the stiffness of materials into account in terms of the resilient modulus and the theory of linearized elasticity is utilzed to determinee the principal criieria of rutting and fatigue life. The need to incorporate elastic and vlsco-elastic or plastic models into practical flexible pavement design procedure is now well founded. The main purpose of this research is to demonstrate the importance of plastic parameters and their attendant residual stresses and strains on pavement life.

The elastic and plastic behaviour of materials from three Accelerated Loading Facility (ALF) sections were characterized using a repeated load triaxial apparatus. The Mechano-Lattice (ML) elasto-plastic, Visco-elastic (VESYS) and linear elastic (adapted CIRCLY) analysis were used to predict the performance of three ALF trials. It was found that the predicted rutting by Mechano-Lattice in all cases was close to the field and was superior to VESYS and adapted CIRCLY methods. VESYS and Mechano-Lattice analysis have shown that in Somersby section no cracking should occur before 7.3 x 10^5 repetitions of 80 kN load. This is supported by ALF test results. The CIRCLY analysis has shown that cracks will happen before the above repetitions. By ML analysis it is observed that if residual stress accumulation was ignored, bottom lateral cracks would commence according to CIRCLY predictions, but residual compression stress cause the transient stresses to reduce as passes continued.
08066 CALTRANS Accelerated Pavement Testing (CAL/APT) Program – Test Results 1993-1996
W. Nokes, J. Harvey, L. du Plessis, F. Long, P. Stolarski

Results to date (Fall 1996) from the Caltrans Accelerated Pavement Testing (CAL/APT) Program are discussed and include those for the Phase I program and initial results from the Phase II program.

The Phase I program involved a study of the comparative performance under Heavy-Vehicle-Simulator (HVS) loading of Caltrans dense-graded asphalt concrete (DGAC) and asphalt-rubber, hot mix, gap-graded (ARHM-GG) as overlays on a fatigue-cracked asphalt pavement and an evaluation of pavement rutting from channelized traffic resulting from simulated Automated Vehicle Control Systems (AVCS).

The initial part of the Phase II program includes an evaluation, under HVS-loading, of the performance of two pavements, one containing an asphalt-treated permeable base (ATPB) and the other an aggregate base (AB), designed and constructed according to Caltrans procedures. The HVS testing of pavements for the Phase I program was performed in South Africa while the Phase II program is being conducted at the University of California at Berkeley (UCB) Richmond Field Station.

Laboratory tests have been performed for both phases at UCB involving evaluations of the stiffness and permanent deformation characteristics of the various pavement components and fatigue characteristics of the asphalt mixes. These results have been used to analyze the performance of the HVS-loaded pavements.

By combining the results of both the HVS and laboratory tests, interpretations of pavement performance are described and recommendations for pavement design and construction have been made to Caltrans.
08067 The Impact of the Heavy Vehicle Simulator (HVS) Test Programme on Road Pavement Technology and Management
F. Rust, S. Kekwick, E. Kleyn, E. Sadzik

The political and socio-economic changes in South Africa over the past five years have had a significant influence on the South African HVS programme. From a fleet of three production machines operating solely in South Africa since 1978, only one now remains in the country, while the other two are used in the CalAPT programme in California. Nevertheless, the SA HVS programme has, in turn, had a marked impact on the development of pavement engineering technology in South Africa and has demonstrably effected significant savings to the country. In particular, the focus of the programme has been redirected to address the issues currently facing the South African road building industry.

This Paper gives an overview of the history and current status of the SA HVS programme and highlights the impact of the programme on both technological advances in pavement engineering and cost savings to the industry.
08068 Mechanistic Evaluation of Fatigue Damage Growth and Healing of Asphalt Concrete: Laboratory and Field Experiments
Y R. Kim, H-J. Lee, Y. Kim, D. Little

Fatigue damage growth and healing of asphalt concrete are studied in this paper using laboratory and field experiments. The field study was performed using the stress wave technique on asphalt pavement sections with varying degrees of damage. The elastic modulus of an asphalt concrete layer is calculated from the stress wave data using the dispersion analysis based on Short Kernel Method. The laboratory study employs two fundamentally different approaches to modeling the mixture fatigue behavior; continuum approach and micromechanical approach.

The continuum approach applies the elastic-viscoelastic correspondence principle to eliminate the time-dependence from the hysteretic behavior of asphalt concrete under cyclic loading. Pseudo stiffness, stiffness after the application of the elastic-viscoelastic correspondence principle, decreases following a characteristic S-shape curve due to the fatigue damage growth when plotted against number of loading cycles. This curve is vertically shifted when rest periods are introduced, resulting in a longer fatigue life. The same trend is observed from the field study between the elastic modulus and the number of loading cycles.

Work potential theory, a continuum damage theory based on thermodynamics of irreversible process, is then applied to the laboratory data to model the changes in pseudo stiffness due to fatigue damage growth and microdamage healing. The resulting model is found to be mode-of-loading independent and capable of predicting the changes in stress-strain behavior under compound loading histories with multi-level loading and varying durations of rest. A validation study is performed on the fatigue performance prediction model using the data obtained from uniaxial fatigue testing of AAD and AAM mixtures under constant stress/strain amplitude cyclic loading histories with and without rest periods.

Finally, a micromechanical approach is presented which describes a fracture process as a balance between the energy imparted to the system and the energy taken up by the newly created crack surfaces. Different microdamage healing behavior of AAD and AAM mixtures described by the coefficients in the continuum damage model is explained by the difference in micromechanical properties between the two binders, such as total cohesive surface energy and different proportions of the Lifschitz-Van der Waals and the acid-base components in the surface energy.
08069 Fatigue Life Prediction Using Visco-Elastic Analysis
G. Rowe, S. Brown

Several pavements were tested with a wheel tracking device to determine the fatigue performance. The use of the visco-elastic method (with a dissipated energy criteria) was compared to elastic analysis for those pavements tested. Strains measured in test tracks show that, in the longitudinal direction, compressive strains occur which are followed by a tensile peak and then compressive strains again, whereas, in the transverse direction, the strain is all tensile. If a visco-elastic model is employed, non-symmetrical stress/strain responses can be calculated. Further analysis illustrates that using asphalt material properties associated with a visco-elastic model the effect of multiple wheel passes on the strain response could be explained with reasonable accuracy. Analysis of pavements produced a similar ranking to the performance obtained in the test pavements and indicated that as temperature is increased, life decreases, consistent with fatigue calculations by other techniques.
08070 Using Paris’ Law to Determine Fatigue Characteristics – Discussion
S. Erkens, J. Moraal, A. Molenaar, J. Groenendijk, M. Jacobs

This paper consists of three parts, which are related to a new fatigue characterisation method that was developed at the Road & Railroad Research Laboratory (RRRL) of the Delft University of Technology. The basic idea behind this method is the use of Paris’ law to determine the fatigue properties of an asphalt mix. In the first part of the paper the background of this method will be discussed. In this section a theoretical justification of the use of Paris’ law to describe fatigue cracking will be presented, as well as experimental data to support that justification. In the second part of the paper this method will be described. An overview of the types of tests as well as the data processing procedure will be presented. For a more elaborate presentation of the complete method, the reader is referred to Jacobs (1995), Erkens et al. (1995) and Sabha et al. (1995). In the third section the modifications that resulted from additional research at the RRRL, intended to modify the procedure for application on another asphalt mix are discussed. From this paper it can be concluded that crack growth covers a major part of the fatigue process. Thus, Paris’ crack growth law provides an approximation of the overall fatigue life. Furthermore, it is shown that the parameters in the crack growth law can be determined using simple tests. The fatigue characteristics that were predicted using this approach, agreed well with actual fatigue data.
08071 The Rehabilitation of the N1 Freeway Between Cape Town and Paarl
M. White, J. van der Walt, C. van der Merwe, E. Pretorius

This paper describes the rehabilitation of three different pavement types existing within a 35 km section of a heavily trafficked dual carriageway freeway between Cape Town and Paarl, South Africa. This freeway was originally constructed between 1968 and 1973 and the first stage of the rehabilitation was carried out in 1985. A further detailed investigation of the structural and functional condition of these pavements using the South African mechanistic pavement design approach was carried out in 1993.

Various rehabilitation measures were selected to best suit the three different pavement types and the second stage of the rehabilitation was carried out in 1995 within a limited budget. The freeway pavement should now be able to carry the projected twenty year design traffic loading of 6.5 x 10^6 equivalent 80 kN axle loads. A rut resistant, continuously graded asphalt surfacing was used and rolled in, precoated stone chips were added to provide a skid resistant surface.
08072 Design of (Reinforced) Asphaltic Overlays
A. de Bondt, A. Scarpas

In the field a designer faces a lot of problems when the effectiveness values of overlay alternatives have to be assessed; especially if the existing pavement is cracked or jointed. Since the effectiveness of alternatives such as applying modified bitumen, fibres, stress-relieving systems or reinforcing systems is site dependent, designers have to consider more than one alternative in their analysis and implement the optimum one. In the paper a design methodology is presented which focusses on the reflection of cracks from an old surface into and through an overlay. It is the result of a six-years project at Delft University of Technology encompassing field measurements, laboratory testing, theoretical development and numerical simulations. Within the methodology the evaluation phase is build-up in such a way that its results can be used directly for the design phase.
08073 Thin Asphalt and Double Seal Rehabilitated Lightly Cemented Pavements: Evaluation of Structural Behaviour and Life Cycle Costs
W. vdM Steyn, M. de Beer, A. Visser

A multi-year Accelerated Pavement Testing research programme was initiated to study the behaviour of rehabilitated Lightly Cemented Pavement (LCP) structures. The aim of this work was to quantify the structural behaviour of these rehabilitated pavements, and to optimise the life-cycle cost for the road agency.

The main findings were that the rehabilitated LCPs tested in the study only failed in terms of permanent deformation due to pumping of fines in the wet condition (G1 crushed stone and thin (< 50 mm) asphalt rehabilitation options) and bleeding of the double seal (double seal rehabilitation option).

The economic analysis of these rehabilitated LCPs, indicated that the double seal rehabilitation option is the most economical option for traffic classes with equivalent traffic demands less than or equal to 10 million equivalent standard axles, while the G1 crushed stone rehabilitation option was the most economical option for 10 to 30 million equivalent standard axles.
08074 Testing and Analysis of the TxMLS Test Pads at Victoria, Texas
D-H. Chen, M. Murphy, C. Pilson, W. Hudson

Hundreds of Falling Weight Deflectometer (FWD) tests were conducted to characterize the material properties of the test pad under accelerated trafficking. Cores were obtained to verify pavement thickness and to determine material properties in the laboratory. In addition, FWD tests were performed on an instrumented pavement section, and pressure cell and MDD data were simultaneously collected. Structural analysis of the pavement was performed by examining results from numerous sets of layer moduli. FWD deflections were used to determine layer moduli through backcalculation. Theoretical stress and strain were then computed using multi-layered elasticity based programs. The theoretical stress and strain were then compared to the measured pressure and strain. Furthermore, pavement life was computed using distress models suggested by the Asphalt Institute and then compared with the actual termination life determined in the field. The findings are presented in the paper.
08075 A Rational Evaluation of Pavement Performance Using the Texas Mobile Load Simulator (TxMLS)
F. Hugo, T. Scullion, N-K. Lee, K. Fults, T. Visser

The paper gives an overview of findings from the first three MLS test pads. Distress occurred as both rutting and cracking. However, the extent of each distress type varied between the test pads. This was unexpected since they had similar structural compositions. Changes in pavement response and material characteristics were monitored during testing using NDT. Tools used for measuring performance included a profilometer and a procedure for capturing and monitoring cracks. A diagnostic evaluation showed that the differences were probably related to varying subgrade strength, and poor performance of the lime treated limestone river gravel base and the asphalt surfacing due to water ingress and aging.
08076 Validation of Some Superpave Design Parameters by Wheel Testing with the Scale Model Mobile Load Simulator
M. van de Ven, A. de Fortier Smit, R. Lorio, R. McGennis

The validation of SUPERPAVE has become an important issue. The SUPERPAVE parameters selected for validation were aggregate grading and Fine Aggregate Angularity.

The Model Mobile Load Simulator (MMLS) and a Simple Shear Tester (SST) were used for the validation. The results of these tests are compared with South African specification tests.

It was concluded that it is difftcult to design a fine aggregate mix which satisfies the SUPERPAVE level 1 requirements for low design traffic. Small variations in the nominal maximum aggregate size of a mix may change the restricted zone of that mix. The result of this for a particular mix tested was that it passed through the restricted zone but performed well nonetheless. Fine Aggregate Angularity had a significant effect on the rutting susceptibility of a mix tested. This effect, while apparent under MMLS loading, was less apparent in the results of dynamic creep and SST testing. The dynamic creep and SST tests were found to be performance indicators. These tests, however, should be supported by actual performance tests, such as the MMLS test.
08077 Long Term Ageing of Pure and Modified Bitumen: Influence on the Rheological Properties and Relation with the Mechanical Performance of Asphalt Mixtures
L. Francken, A. Vanelstraete, A. Verhasselt

This paper presents a study of the behaviour of eight road binders (one reference bitumen and 7 modified bitumens) used in porous asphalt wearing courses of an experimental road built in 1985. The complex moduli as well as different other characteristics of the binders were determined on the original binders and mixtures. A relationship between the complex modulus of binders and that of the corresponding mixtures has been validated for the case of modified bitumens. The complex moduli as well as different other characteristics of the binders were determined after different exposure times in a laboratory simulated long term ageing test. For some of the binders, these results were compared with the results obtained on tbe binders extracted from cores on the mixes, in service for 12 years. It was investigated whether the complex moduli of the aged mixes could be estimated on the basis of that of the aged binder, with the help of the relationship between the complex modulus of the binders and mixtures.
08078 Do Superpave Binder Tests Reflect Long Term Pavement Performance Better Than Traditional Tests?
M. Partl, H. Fritz

Recovered binders from a Swiss long term pavement performance (LTPP) study have been investigated with dynamic shear and bending beam rheometer to evaluate whether superpave binder tests reflect LTPP better than traditional tests. In addition, tests were performed to quantify changes that may occur due to long-term storage at room temperature. The results show that the new superpave binder tests are valuable tools to assess binders from old pavements but should be further analyzed, for example, by master curves and Black diagrams. It was found that on a large scale basis superpave binder tests lead to a ranking similar to traditional tests, especially for warm temperature characteristics. As, on the other hand, traditional tests are often the only link to original pavement data, this type of tests should still be performed in parallel for LTPP studies. Finally, it was found that long-term storage may reduce the penetration considerably.
08079 Effect of Polymer Modifiers on Dense-Graded, Heavy Duty Pavement Mixtures
R. Freeman, J. Newman, R. Ahlrich

This study was initiated to investigate some potential benefits of polymer modification on dense-graded, heavy- duty pavement mixtures, The following polymers were used to modify asphalt binders and mixtures: an ethyl vinyl acetate (EVA), a low-density polyethylene (LDPE), a styrene butadiene styrene (SBS), an hydrogenated SBS, and a finely ground tire rubber. Each of the polymers was blended with one or more of the following asphalt cements: an AC-10 and three sources of AC-20. Both conventional and recently-developed test methods were performed on the binders and mixtures to study the effects of the polymer modifiers at both low temperatures and high temperatures. Standard Marshall mixture design procedures did not optimize the mixtures containing tire rubber and dense-graded crushed limestone. The effect of polymers on low-temperature properties was dependent on the modifier/polymer combination. Ground tire rubber was particularly effective at these low temperatures. The high-temperature performance of an AC-20 mixture, produced with crushed gravel, was improved by modification with an SBS.
08080 Evaluation of Design and Construction Effects on Asphalt Pavements Performance Through a Portable In-Situ Shear Test Device
A. El Halim, I. Rickards, R. Haas, R. Abdel Nabi

One of the main objectives of SHRP has been the development of more reliable testing methods for assessing the field performance of asphalt pavements. The methods and equipment developed by SHRP indirectly evalute field performance and mechanical properties by the laboratory testing of samples. A concentrated research effort was directed to extending the SHRP methodology by developing a portable, in-situ shear strength test device. This device was designed and fabricated at Carleton University, and is known as the Carleton In-Situ Shear Strength Test device (CISSST).

This paper presents a description of the development and details of the device, its use in the field and the results of a variety of field situations. The results show the profound effect of road geometry (in-situ shear strength of up to 60% higher on a straight line as compared to curved sections), the effect of taking cores to the laboratory for testing (in-situ shear strengths can range up to 300% higher), and the effect of traffic on the in-situ shear strength.
08081 Volumetric Considerations in Testing, Construction, and Performance of HMA Pavements
M. Stroup-Gardiner, D. Newcomb, R. DeSombre, R. Olson

Volumetrics describe the relationship between the mass of matter and the volume it occupies. Density, a quotient of mass to volume, is the most commonly used parameter for HMA mix design, quality assurance, and quality acceptance. The proper use of density measurements depends strongly upon the ability to accurately and precisely measure both the desired volume and mass of the mixture. Three independent studies were conducted to investigate the variability of density measurements (i.e., various measurements of bulk specific gravities), control of volumetric proportions during construction, and the influence of in-place densities on pavement performance.
08082 Asphalt Content by the Ignition Method: Virginia’s Experience
B. Prowell, R. Schreck

In 1995, the Virginia Department of Transportation (VDOT) adopted the ignition method as an alternative to chlorinated solvent extraction for quality control and acceptance of hot-mix asphalt. The production of trichloroethane was outlawed in the United States on December 31, 1995, as part of the 1990 Clean Air Act Amendments.

Implementation of the ignition method was accomplished through a training program jointly sponsored by VDOT and the industry. Approximately 75% of the industry began using the method in 1995.

Field data from four standard VDOT mixes were evaluated. The mixes were produced at different plants and contained different types of aggregate from different sources. Test data from the ignition furnace, solvent extraction, and nuclear asphalt contents are provided.

As a result of VDOT’s favorable experience with the ignition method, this method is mandatory for all VDOT QC/QA.
08083 The Retained Thickness Index: A Quick Tool for Network Evaluation
W. Hoyinck, C. van Gurp, M. Jacobs, J. Hiemstra

This paper presents the approach of the Retained Thickness Index (RTI) for the assessment of the residual structural integrity of asphalt pavements on the network level. Lacroix Deflectograph deflections and distress identification served as major input variables. The procedure makes use of the whole deflection basin and is not restricted to application of the maximum deflection only. The approach provides additional data on cracking origin (top-down or bottom-up) and crack propagation, and can be used in combination with the commonly used analysis methods.

The Retained Thickness Index is based on the flexural rigidity, inferred directly from the deflection bowl, and the occurrence of cracking observed in the wheelpaths. Both input parameters can be collected quite quickly.

Verification of the model was performed in 1996 on some fifty test sections of the SHRP-The Netherlands programme. This paper describes an attempt to fine tune the methodology. To this end some thirty test sections on the county network of Gelderland were made available, which is gratefully acknowledged by the authors. Analysis of Deflectograph testing, cracking surveys and asphalt coring on cracks attributed to establishing the accuracy of the predictive method.
08084 Backcalculation of Pavement Layer Moduli Using Genetic Algorithms
S. Kameyama, K. Himeno, A. Kasahara, T. Maruyama

A new method was developed to backcalculate pavement layer moduli from pavement surface deflection, measured by an FWD, using genetic algorithms, It was found that layer moduli can be accurately estimated by backcalculation using this method, with surface deflection calculated by the theory of elasticity for layer structures as the input condition. This method was also applied to data of asphalt and concrete pavements, measured by the FWD. The results showed that backcalculated moduli could sometimes be estimated even in the case where an appropriate solution could not be obtained by conventional backcalculation methods.
08085 Performance-Based Asphalt Mix Properties in Relation to Preventive Pavement Maintenance
A. Loizos, J. Fatseas

In the present work the major findings concerning the data analysis of a Long Term Pavement Performance study, focusing on the evaluation of the asphalt mix performance in relation to preventive pavement maintenance, are presented and discussed. The performance study comprised laboratory tests for both the original and the in-service bituminous materials, as well as destructive and nondestructive tests on the in-service pavements. The stiffness of the existing asphalt concrete layers was estimated using laboratory mechanical tests, traditional component analysis, as well as backanalysis based on FWD tests. In addition, the fatigue strength of the existing asphalt mixes was estimated. After a longer time period the pavement remaining life predicted through the fatigue analysis was validated by performing FWD tests on the non-maintained pavements, as well as pavement condition distress assessments. The results of the analysis showed that the interpretation of the asphalt mix performance based on FWD tests can give useful information for possible rational pavement preventive maintenance requirements. The laboratory estimated asphalt mix properties are to some extent still necessary for supporting the relevant engineering judgments for the interpretation of the FWD-based backanalysis.
08086 Evaluation of Spring Thaw Load Restriction and Deflection Interpretation Techniques
D. Van Deusen, C. Schrader, G. Johnson

A study was undertaken to evaluate criteria used to predict when to place and remove springtime load restrictions. The objectives were to (1) evaluate current springtime load restriction procedures, (2) investigate pavement strength changes in relation to springtime freeze-thaw events, and (3) suggest a more rational method for determining when to remove the load restrictions.

Mn/DOT load restriction placement and removal dates for a ten year period were tabulated and compared to predictions based on the existing model. Data collected from eight different flexible pavement test sections, including falling-weight deflectometer, resistivity probe, and in situ strain gauge data, were used to assess environmental effects on pavement strength.

It was found that, while the existing procedure works well for predicting the onset of thaw, the predicted thaw durations were higher than field observations. Deflection tests indicated that the period of minimum strength coincides with the approximate time that thawing is complete.
08087 Comparative Studies of Deflectometry with Benkelman Beam and FWD Supported by Mechanistic Analysis and Repeated Load Testing
L. Motta, J. Medina, J. Macedo, C. Albernaz

Deflectometry of two road experiments in Brazil was made using both the Falling Weight Deflectometer (FWD) and the Benkelman beam (BB). Deflection basins measured by these two instruments were compared to computed basins obtained through the finite element method and using resilient moduli results of repeated load testing. Measurements were made in different layers of pavement structures under construction. Noureldin’s simplified procedure for backanalysis was used together with Benkelman beam measurements.
08088 Comparisons Between Laboratory and In Situ Determined Asphalt Concrete Moduli
N. Thom, R. Elliot, L. Cheung

One of the key parameters for analytical design or evaluation of a pavement is the stiffness modulus appropriate to each layer. This paper discusses both the laboratory determination of stiffness modulus, by means of the Indirect Tensile Stiffness Modulus (ITSM) test, and in situ determination, by means of the Falling Weight Deflectometer (FWD). Their complimentary roles are highlighted by means of several examples. The role of ITSM testing in allowing proper temperature correction of FWD data is presented. A comparison of laboratory and in situ moduli is seen to provide information on crack severity, material variability and debonding.

Finally, these stiffness modulus tests are set in the context of a full pavement evaluation and their role in providing vital evidence on overall pavement condition is shown.
08089 Long-Term Performance Study for Asphalt Pavements
L. Sun, X. Liu, Z. Xu

Based on the analysis to the pavement data collected in 5 Districts covering about 12,000 km long highway, a pavement performance equation with a general form has been developed, and with the equation, the effects of the pavement structural component, pavement bearing capacity, traffic and environmental condition on the pavement performance have been analyzed. The study results show that the pavement surface course thickness has a major effect on the pavement performance, the following are ESAL, deflection and base course type, and that in the early stage of performance curve, the surface course thickness plays a dominant role, while in the later stage, the effects of deflection become more significant than in the early stage. The analysis shows that in the 5 Districts mentioned in this paper, the service life difference of pavements due to the climatic condition reaches up to 22%.
08090 The Separate Effects of Traffic Loading and Environment on Rutting and Cracking Trends of Asphalt Pavements
D. Mfinanga, H. Ochiai, N. Yasufuku, H. Yokota

Road pavements deteriorate with traffic loading and environment but the separate effects of these factors are not yet well defined especially with age or environment. This paper aims at finding the separate effects of these two factors on asphalt pavement rutting and cracking. It is believed that this will lead to better modeling of pavement deterioration by clearly understanding and treating the two factors as separate entities. A methodology was devised to separate the two effects, in which pavement age is used to represent the cyclic effect of environmental forces, and analysis was carried out. Results show how each of these factors influence pavement rutting and cracking and provide a further understanding of the influence of some of pavement parameters on pavement rutting.
08091 Pavement Performance Test for Innovative Design Method
V. Rikovsky, I. Gschwendt

In 1987 was published the Catalog of flexible and cement concrete pavements prepared on the base of analytical-empirical design method. This papers deals with an improved design procedure for asphalt pavements on the base of new theoretical knowledge and experiences with modified and new road building materials and result of asphalt pavements behavior on circular test track (CTT VUIS-CESTY Research company Bratislava). The CTT has been used for test on six pavements structures under 11.5 kN axle load. The research program resulted in development on classification of used materials and innovation of design method using fatigue strength as a criterion.
08092 Five-Year Performance Evaluation of Asphalt Pavements at Bibi New Test Road
S. Nakagawa, A. Ogasawara, A. Kasahara

In order to transfer from the conventional and empirical asphalt pavement design method used in Japan to a mechanistic design method, a test road was constructed on National Highway 36 in Hokkaido, in August 1990. The test road, called the Bibi New Test Road has eight different pavement structures. Since its construction, traffic monitoring, and surface distress and deflection surveys have been regularly conducted. Performance data have been obtained regarding surface distress and deflection for up to 6.2 million of equivalent 49kN wheel load. The performance curves in relation to the surface distress were approximated by the exponential function with correlation coefficients of 0.98 and greater. The Structural Suitability Index (SSI), based on fatigue damage to the asphalt mixture, was proposed as an index of structural adequacy. The SSI performance curves were approximated by the exponential function with correlation coefficients of 0.93 and greater.
08093 A Comparative Study of Performance of Different Designs for Flexible Pavements
N. Khosla, N. Kim, S. Satish, Y. R. Kim

This paper describes the results of a comparative study of performance of different pavement designs in North Carolina. Testing was carried out at an instrumented test facility constructed on the US 421 Bypass near Siler City, North Carolina. The experimental stretch was about seven and a half miles long and was composed of 12 pavement section types, two of each type in two directions of traffic (having different expected traffic loads), for a total of 48 sections. Based on field measurements, such as stress, strain, and distress survey analysis, the performance of the various sections were analyzed. Subgrade stabilization was found to provide the maximum assistance to the pavement sections. Sections with asphalt concrete bases performed better than sections with aggregate base courses. Cement- treated base course sections performed the worst. Also, in this study, it was noticed that almost all the rutting was limited to the asphalt concrete layers.
08094 Pavement Performance Modelling using LINTRACK
J. Groenendijk, L. Dohmen, A. Maagdenberg, A. Miradi, A. Molenaar, C. Vogelzang, M. de Beer

Accelerated load testing (ALT) facilities like the LINTRACK are believed to be an essential tool in the development of improved performance models for asphalt pavements. It should however be realized that even such facilities are only capable of modelling real life conditions in a simple way. For that reason ALT studies undertaken in the Netherlands have the primary goal to improve response and damage models, which in turn can be used for performance predictions. This paper first describes the main features of the ALT studies performed in the Netherlands on a thick (150 mm) and thin (70 mm) asphalt pavement on a sand subgrade. These show that the current Dutch design model is unable to fully describe the behaviour of these pavements. Therefore, three suggested improvements to this design model are described:

1) Mix-wise prediction of fatigue characteristics for practical conditions from simple tests.

2) Calculation of strains and stresses using a linear visco-elastic multi-layer approach.

3) Modelling of the wheel load, using a rectangular, non-uniform three-dimensional distribution of contact stresses.
08095 Subgrade Strain Criterion for Limiting Rutting in Asphalt Pavements
B. Pidwerbesky, B. Steven, G. Arnold

The subgrade strain criterion for asphalt pavements was investigated by instrumenting pavement layers and underlying subgrades. Vertical compressive strains under wheel loads were recorded under accelerated and normal rates of loading. Four test pavements in the Canterbury Accelerated Pavement Testing Indoor Facility (CAPTIF), Christchurch, New Zealand, and one in-service pavement were included in the research. The asphalt surfacings were 2.5 mm to 85 mm thick, the subsurface granular layers were 135 mm to 300 mm thick, and the subgrade CBR ranged from 4%to28%.

Vertical compressive strains measured in the unbound granular layers and subgrade of flexible pavements are substantially greater than predicted values. Vertical compressive strains in unbound granular layers under thin asphalt surface layers can be equal in magnitude to the subgrade strains. A new subgrade strain model is developed and presented in this paper, which substantially reduces the required thicknesses of overlays.
08096 Permanent Deformation and Fatigue Properties of Polymer Modified Asphalt Mixes
S. Maccarrone, A. Ky, G. Gnanaseelan

An investigation was undertaken to evaluate permanent deformation and fatigue characteristics of polymer modified asphaltic mixes. The investigation included a laboratory testing program and a field evaluation of performance using an accelerated loading facility (ALF). Binders evaluated included the polymer types commonIy used in Australia for hot mix applications. Mix testing included wheel tracking at 60°C to examine permanent deformation and beam testing for fatigue characterisation.

Results of ALF traffickmg shows the permanent deformation of the polymer modified mixes is lower than conventional mixes both in magnitude and in rate of deformation. Laboratory wheel tracking is shown to correlate weII with ALF results. Compaction has a large influence on both fatigue and elastic properties of asphalt mixes. Using the Shell fatigue relation as an indicator of field fatigue performance of bituminous mixes, relative fatigue multipliers for the various polymer modified binders were estimated. Finally binder parameters which best correlate with permanent deformation and fatigue properties are discussed.
08097 Study of Rutting of Wearing Courses on the L.C.P.C. Test Track
J-F. Corte, Y. Brosseaud, J-R Kerzreho, A. Spernol

In the last years three experiments have been carried out with LCPC accelerated loading facility to investigate the rutting resistance of different wearing courses. As far as asphalt concretes were concerned, attention was paid to the influence of the nature of the binder, keeping the other parameters constant. The reference mix was selected with a given proportion of rounded sand and a 50/70 pen grade pure bitumen. The performance of this material was compared to mixes with polymer modified binders, special bitumen and bitumen with additives. These materials were used in a 8 cm thick surface layer. A comparison was also made with a high modulus asphalt concrete as a bounding layer covered by a very thin bituminous concrete. Depending on the experiments the loading axles were single large wheels or common dual wheels. A heating system was tested to increase the temperature in the pavement upper layers. Data were obtained on the influence of the material type, loadings, and temperature on rutting.
08098 Determination of Viscoelastic Properties from Indirect Tension Test
W. Zhang, A. Drescher, D. Newcomb

This paper presents two test procedures, the constant load and haversine load, for determining the viscoelastic properties of asphalt concrete using the indirect tension (diametral compression) test. Equations for calculating the creep compliance and complex compliance from test result are derived. Locations of change in length measurements are recommended. Details of data reduction algorithms and the pros and cons of the two procedures are discussed. A series of laboratory tests were conducted on two groups of specimens to illustrate the methodology and verify the analysis.
08099 Mechanistic-Empirical Modelling of the Permanent Deformation of Unbound Pavement Layers
H. Theyse

This paper describes recent research the aim of which was to develop permanent deformation design transfer functions for unbound pavement layers from Heavy Vehicle Simulator (HVS) test data. Two types of data generated during an HVS test are used to develop the permanent deformation models on which the design transfer functions are based. These are the in-depth deflection and permanent deformation data obtained from the Multi-Depth Deflectometer (MDD) measurements taken at regular intervals during an HVS test. Test data from a number of HVS tests, selected from the moderate and wet regions in South Africa, were used for the development of the permanent deformation models.

A multi-dimensional, conceptual model for permanent deformation was developed and calibrated with HVS test data for pavement foundation and structural layers of different material qualities. These models provide permanent deformation design transfer functions at different expected performance reliabilities for unbound pavement layers in South Africa.

The use of these design transfer functions is illustrated by a number of examples. The design approach allows each of the pavement structural layers and the pavement foundation to contribute to the total deformation or surface rut of the pavement structure.
08100 Predicting Ruts Caused by Soft Subgrade
N. Thom

Rut prediction, whether stemming from deformation in asphalt or soil, has always been a particularly difficult area for the pavement engineer. This paper centres around a predictive technique for soils and granular materials and presents two examples where the technique has been used and appears to be a sufllciently accurate tool for achieving meaningful results. One example is of trafficking at a laboratory scale, the other relates to airfield pavement design. The derivation of the model itself is described and the means of obtaining model parameters discussed. Finally its role in pavement design is examined and recommendations made for its use.
08101 Implementation of LAMBS Technology: A Partnership Approach
A. Thomson, B. Nothnagel, P. Myburgh

This paper describes a carefully managed process of introducing new research outputs into practice. Specification of LAMBS (Large Aggregate Mixes for Bases) on five major road construction projects, provided a unique opportunity to structure the implementation process so that this new product could be successfully implemented, and so that the LAMBS technology could be refined as a result of the lessons learned. It demonstrates that significant advantages attach to a cooperative process which forestalls adversarial actions and promotes more cost-effective application of professional skills. The liaison process, which included a diverse group of participants, is outlined, and the achievements of the group are described. These include improvement of the LAMBS technology, development of new contract procedures, and enhancement of asphalt production and paving expertise in the field of large aggregate mixes. The partnership approach used provides a model for successful implementation of new technology.
08102 Framework for the Development of a South African Product Performance Guarantee System for the Asphalt Industry
B. Verhaeghe, J. Maree, G. Rutland, R. Vos

The paper deals with the development and implementation of a Product Performance Guarantee System (PPGS) in the South African asphalt industry. The proposed system comprises the formal management of product performance guarantees, in which acceptance criteria are based on the performance of products rather than on their compliance with current prescribed specifications. The system supports aspects such as innovation in materials and design, conditions for acceptance based on performance indicators, as well as formal quality management systems and their development and implementation in the industry. The development and implementation of PPGS are currently proceeding incrementally.
08103 Comparison of Superpave with Conventional Pavement Design
R. May, R. Anderson, D. Perdomo

This paper contains an evaluation of Superpave Mix Analysis performance modeling for three pavement projects. Test results of the Superpave Shear Tester (SST) and the Indirect Tensile Device (IDT) are presented, along with calculated material properties and performance projections for each section. Pavement performance is estimated in terms of fatigue cracking and permanent deformation.

The asphalt concrete overlay constructed at each site was designed using the Superpave Mix Design procedure with materials selected based on the aggregate and binder criteria included in the Superpave system for the traffic and climate of the location. Material properties were affected by binder content and temperature.

Superpave predictions were compared to the results determined using the Asphalt Institute’s DAMA analysis program and the AASHTO design equation. Although these determinations are based on varying assumptions, behavior and distress modeling, material characteristics, and design parameters, there was agreement in some cases. Specific inconsistencies are discussed.
08104 Use of the K-Mould in Determination and Analysis of the Elastic and Shear Properties of Road Materials for Flexible Pavements
C. Semmelink, F. Jooste, M. de Beer

This paper describes a laboratory test system for the rapid determination of the elastic and shear properties of road building materials, including asphalt. The system includes a dynamic loading and data acquisition system, commonly referred to as the "K-mould". The computer-controlled loading and data acquisition systems are described briefly. Typical material parameters such as stress dependent elastic modulus and Poisson’s ratio, cohesion and friction angle are determined from a single test specimen. Some typical results and their application are discussed in this paper. The paper also discusses methods that were used to validate the laboratory-derived results. This was done by evaluating deflection basins measured by Multi-Depth Deflectometer (MDDs) and also by comparing with Falling Weight Deflectometer (FWD) results.
08105 Effect of Asphalt Mixture Master Compliance Modeling Technique on Thermal Cracking Performance Evaluation Using Superpave
W. Buttlar, R. Roque

One of the main components of the Superpave mixture design and analysis system, originally developed under the Strategic Highway Research Program (SHRP), is a mechanics-based thermal cracking performance prediction model (TCMODEL). Thermal stresses are predicted by TCMODEL based upon a viscoelastic characterization of the asphalt mixture at low temperatures. The sophisticated viscoelastic stress analysis performed carefully tracks the stress history of the mixture, and consequently, mixture properties must be known at very long loading times. The time-temperature superposition principle has been employed to allow the required properties to be obtained from creep tests of relatively short duration. However, the techniques originally used in Superpave to construct the creep compliance master curve have been found to be problematic (Buttlar and Roque, 1996a). New analysis techniques are presented which were found to produce accurate performance predictions with as little as 100 seconds of creep testing and without the need for supplementary binder data.
08106 The International Society for Asphalt Pavements and Its Mandate
R. Haas

It is my pleasure to welcome all of you to this 8th Conference on behalf of the International Society for Asphalt Pavements. Our Society is now 10 years old. It was formed at the time of the 1987 Ann Arbor Conference. As you know, however, these Conferences actually go all the way back to 1962, and even though 1972 was in London, 1982 in Delft, 1992 in Nottingham, 1997 of course in Seattle and 2002 in Copenhagen (which will be described in the closing Plenary Session), we still refer to them colloquially as the Ann Arbor Conferences.

Proceedings of these Conferences represent one of the most extensive repositories of knowledge and information in the asphalt pavement field.

In summary, our basic mandate is to ensure the continuity of these premier international events in the asphalt pavement field, to support other regional or international forums and conferences in the intervening years, and to promote the exchange of information world wide on key issues and technology in the asphalt field. We strive to recognize practical problems facing the industry and to cooperate with national, regional and local groups.
08107 Paving The Gap: Research Into Practice
P. Teng

The Federal Highway Administration’s (FHWA) Pavement Technology Program has the primary goal of developing, delivering, and deploying the improved technologies that will ultimately lead to better performing, more durable, and more cost-effective pavements. The program covers five areas: asphalt; portland cement; analysis, evaluation, and management; advanced research; and long-term pavement performance. The Asphalt Pavement Technology Program is dedicated to unifying and accelerating the evolution of asphalt pavement structural design, asphalt mix design, and performance-related specifications. To roll out these technologies in the next 5-6 years, FHWA is working closely with its State, industry, and academia partners.
08108 Future Issues Facing the Hot Mix Asphalt Industry
M. Acott

This paper will describe some of the critical issues facing the HMA Industry. I have had the benefit of input from the South African Bitumen Association (SABITA) – Piet Myburgh and Rob Vos, the Australian Asphalt Pavement Association (AAPA) – Ray Farrelly and John Bethune, the European Asphalt Pavement Association (EAPA) – Max von Devivere, plus our involvement in many study tours that visit NAPA or tours we have initiated. While I am presenting this international perspective, and may include some personal asides, the thrust of this paper is supported by these associations. The not-so-surprising conclusion is that we have many common issues and approaches. The bottom line is that we are now in an era of significant change for the Hot Mix Asphalt (HMA) Industry. It will go down in the history books!
08109 The Asphalt Global Community
E. Miller

The need exists today more than ever for a strong Asphalt Global Community. Environmental issues, crude supplies, politics and policies, emerging technology, and the impact of rapidly-expanding world communications all drive the demand for an improved international exchange of knowledge in asphalt pavements. Each individual, each country, and each association must take the time to determine where and how they fit into this global community. Whether it be through an improved International Society for Asphalt Pavements or through some other newly-formed Asphalt Global Alliance, a blending of technology and an exchange of scientific information will continue to occur. The problem, if any, is the sporadic nature of the exchange. The Asphalt Institute supports an increased pace in establishing more formal communications bridges via a global networking system and an increased focus on research and marketing to expand the use and improvement of asphalt pavements.
08110 Achievements and Challenges In Asphalt Pavement Engineering
S. Brown

This series of international conferences has facilitated the development of mechanistic methods for the design and structural evaluation of asphalt pavements over the past 35 years. While the record is one of real achievement, stimulated by initiatives such as the U.S. Strategic Highway Research Program, there are still problems to solve and challenges to face including that of implementing the results of research. The major achievements are outlined and the latest developments discussed. These include more realistic theoretical modelling and the availability of higher qdality data from modem testing facilities both in the laboratory and in the field. The need to incorporate the principles of soil mechanics more effectively in the design and evaluation of pavement foundations is identified. The continued extensive use of the CBR concept is questioned and the need for application of more relevant parameters is encouraged. Several other procedures which have long been used are critically reviewed and attention is drawn to innovative ideas including new concepts for modelling asphaltic materials. The theme of "Paving-the-Gap" between research and practice is considered and examples given of success. The importance of structural evaluation is emphasised and the need to develop faster, more convenient data gathering facilities is considered. The concept of "Smart Roads" incorporating appropriate low cost instrumentation could help in this context.
08111 Charge to the Conference
J. Maree

The theme of this conference, Paving the Gap – between theory and practice, is an issue with which ISAP conferences have grappled for at least the past decade. While considerable progress has been made to close this gap on several fronts, it can safely be said that we have not been entirely successful in coordinating the ideas and work of those who seek constantly to improve asphalt technology and pavement engineering with the needs and operations of the implementers and users, and hence this theme remains relevant and deserving of closer scrutiny. The aim of this paper is to raise some questions related to the gap which may still exist between theory and practice in the hope that, in attempting to find answers to the questions raised, this conference will come closer to bridging the divide.
08112 Industry Issues for the 21st Century – An International Perspective on Asphalt (Bitumen) Supply
A. Gilmour

In most of the world, the bitumen industry is set to undergo some substantial changes because of increasing pressures coming from within the oil industry, from governments and from the road industry. There is little doubt that the oil and bitumen industries will be able to respond effectively to ensure that the needs of governments and the roads industry for a wide range of competitively priced bitumens are met. Some of the R & D necessary to achieve this has already been successfully carried out but much remains to be done and continued efforts will be needed over the next five years to generate the most efficient solutions for the next century.

It is important to remember that a large majority of the bitumen used in the world is produced in refineries where bitumen represents less than 10% of the total product output. This is unlikely to change substantially in the future as it normally represents the lowest cost method of producing quality bitumen feedstocks.
08113 European Perspective on Aggregate Issues
H. Gormsen

European perspective on aggregate issues is a difficult subject for one main reason: Europe is not one single country, but consists of many countries with individual traditions, experiences and aggregate specifications. And on top of that as all over, the geology differs from place to place. It must be said, that aggregate specifications will be harmonized as part of the general harmonization program in Europe, which is going on to prevent barriers to trade among the member countries of the European Union.

In general I believe, that seen not only in an European perspective but also in a global perspective there are two overall issues:

– The need for high performing infrastructure
– Protection of the environment
08114 Contracting Opportunities in the Twenty-First Century
C. Potts

I am pleased to have this opportunity to speak to you. I will tell you a little bit before I start so you can see as where I am coming from. APAC is a large Hot Mix Asphalt (HMA) producer, actually the largest HMA producer in the United States. We are also the largest concrete paving company in this country as well as being a large aggregate producer. So we have a vested interest in every side of the business.

We are a wholly-owned subsidiary of Ashland, Inc. which is a large energy company. So we have a big investment in the liquid asphalt and the petroleum side of the business. In this presentation, I have been asked to give a vision of the future of what I see the industry, especially from the contracting standpoint.

It’s a great opportunity because you are just asked to give your opinion, and you don’t have to worry about documenting a lot of facts and giving a technical presentation. I heard some presentations yesterday, and people wanted to see the data, to see the tables, to see the proof. I don’t need to give you any proof. All I have to do is tell you what I think. You can agree with me, or you can disagree with me. It really doesn’t matter one way or the other. I am just giving you my opinion. Everyone in here has an opinion of what the future is going to be in the paving industry. Any of you could stand up and make this presentation.
08115 Cost Effectiveness of Asphalt Pavement Preservation and Maintenance for Reduced Life-Cycle Costs: An International Perspective
G. Kennepohl, J. Bethune, J. Maree

Rapid loss of useful pavement service life, loss of asset value and the need for funding to reconstruct has become a serious concern and challenge, which is addressed in this presentation. Described are the status of asphalt pavement preservation and maintenance strategies as well as a critical assessment of measures to reduce life-cycle costs through preventive maintenance and pavement preservation.

The review of the evolution of maintenance strategies from routine corrective measures to managed pavement distress prevention and preservation has shown that substantial user cost reductions can be achieved. The authors demonstrate, on hand, of case histories from Australia, North America and South Africa, the cost-effectiveness of advanced pavement maintenance strategies, new development and innovations as well as needs and trends for implementing pavement preservation.
08116 Optimized Pavement Structure
H. Goacolu, J. Gramsammer

Most road structures have traditionally been built with layers whose mechanical performance decrease with depth. In the case of treated materials, the structure bends and as a result the upper and lower parts are under the greatest stress. The durability of the structure depends mostly on the characteristics of the material used for the lower part, i.e. the lowest performance material.
The original design of the structure is intended to optimise the use of materials by putting the highest performance materials in the areas which receive the greatest stress.

This road structure is a three layers complex including:
– in the centre, an economical material with modest but sufficient mechanical performance,
– a thin layer of several centimetres on either face made of high performance materials which protect the structure from fatigue.
The article describes the theoretical functioning of this structure and its evaluation using the fatigue test track at the Central Laboratory of Ponts et Chaussees (LCPC).
08117 Recent Development on Recycling Asphalt Pavements In Japan
T. Ikeda, M. Kimura

The Government of Japan has intensively developed the technology to reduce and reuse construction by-products. As for asphalt pavement, the study and trials dated back to 1950s and technical guidelines for recycling asphalt pavement were published in the middle of 1980s. This paper presents current policy on waste management of the Japanese Government and revision of the technical guidelines based on data obtained from test pavements. This paper also mentions data on new issues, re-recycling and recycling modified asphalt.
08118 PARIS: A Collaborative European Approach to Pavement Performance Measurement and Analysis
G. Sweer, H. Jamsa, L. Dohmen, H. Spoof, J. Potter

The PARIS project is a collaborative European research effort aimed at development of pavement deterioration models for use in pavement management systems. The models to be developed will be based on data on the observed long term performance of over 800 test sections in 15 European countries. These field data will be augmented by data from Accelerated Loading Tests in three of the participating countries. This paper gives an overview of the project. Details are presented on the test sections involved, on the normalisation of local distress data to a common European format, on the database used for storage of the data and on the analysis system to be applied.
08119 Roughness Characteristics of GPS Flexible Pavements in the LTPP Program
R. Perera, C. Byrum, S. Kohn, C. Richter

The Long Term Pavement Performance (LTPP) program in the United States was designed as a 20 year study of pavement performance. One aspect of the LTPP program is the monitoring of over 800 General Pavement Study (GPS) test sections that were established on in-service pavements in all fifty states of the United Sates and in Canada. A major data collection effort at the GPS sections is the collection of profile data that is performed annually. This paper presents the results of a study conducted to investigate the changes in roughness on:

(i) GPS-1 experiment sections, which studies asphalt concrete pavements on granular base, and

(ii) GPS-6B experiment sections, which studies asphalt concrete overlays of flexible pavements.

The changes in roughness at test sections was investigated by using the International Roughness Index (IRI) as the roughness parameter. The test sections were classified according to environmental zones and the IRI trends for the group of test sections included in each zone were studied. Correlation analysis was conducted for GPS-1 sections in the dry freeze and the wet freeze zone between IRI and the factors that have an influence on roughness development. This paper presents a model that was developed to predict IRI for GPS-1 sections in the dry freeze zone. For the GPS-6B sections, the reduction in IRI due to the overlay was examined.
08120 WesTrack Full-Scale test Track: Interim Findings
J. Epps, S. Seeds, C. Monismith, S. Ashmore, T. Mitchell

A federally-funded multi-million dollar hot-mix asphalt (HMA) pavement research project is currently underway to further the development of performance related specifications (PRS) technology and to provide early field verification for the latest Superpave asphalt mixture design procedure. WesTrack refers to a full-scale road test experiment in which various asphalt mixes are being loaded in an accelerated fashion to determine the effect on field performance of "off-target" mix properties. The track is located near Reno, Nevada, and the experiment is being carried out by a team made up of consulting firms, universities and road contractors.

This paper provides background for the project including the nature of the experiment, the experimental factors, structural and mix design, track construction, vehicle loading, driverless vehicle technology, performance monitoring and laboratory testing. It also presents information on the interim performance of the test sections, summarizes the planned approach to developing the pavement performance prediction models and describes the anticipated performance related specification system.
08121 Warranteed Hot Mix Asphalt Pavements: A Cooperative Solution for Agencies and Industry in the United States
G. Huber, J. Sorensen

The use of warranties as applied to hot mix asphalt pavements is just beginning in the United States. Whereas manufacturers of most products offer warranties against defects that affect performance of the product, the application of warranties to paving materials in the United States is not yet commonplace. Introduction of warranties has been hampered for both technical reasons and administrational reasons. Technically, the link between manufactured material and performance on the road is not well understood. It was believed that costs would be lowest if the owner agency carried the risk of performance. Therefore, contractors have been content to use method specifications and leave the risk with the owner. Administrative rules have generally prevented warranties on federally funded projects.

Administrative barriers have been removed and recently the attitude towards warranties in the USA has been changing. Visits to Europe have investigated methods used to warrant pavements and potential benefits to transportation agencies and the industry have been identified. Technically, the effect on pavement performance of asphalt mixture design, materials and workmanship as well as construction is better understood.

This paper discusses recent experiences with the implementation of asphalt pavement warranties in the United States including warranties, performance, asphalt pavement, and innovative contracting.
08122 Superpave Support and Performance Models Management: Evaluation of the SHRP Performance Models System
M. Witczak, H. von Quintus, C. Schwartz

A principal result of the Strategic Highway Research Program was a set of pavement performance models for predicting low temperature thermal cracking, fatigue cracking, and permanent deformation in asphalt pavements under environmental and traffic loadings. The Federal Highway Administration, as part of its Superpave implementation plan, awarded a contract to the University of Maryland and a team of subcontractors to provide a comprehensive and unbiased evaluation of the original SHRP pavement performance models. The principal conclusions from this evaluation are:

(a) the SHRP Superpave system provides an excellent framework for firture modifications and enhancements to the models;

(b) the existing non- load related thermal fracture model predicts field behavior reasonably well, although some minor modifications and enhancements to the model are necessary;

(c) the performance prediction models for load related fatigue fracture and permanent deformation perform poorly, and substantial corrections and enhancements to these models are imperative if they are to be sufficiently reliable for acceptance and use by industry;

(d) although some of the problems in the load related distress models are the consequence of technical and other constraints during the original SHRP research effort, many are the direct result of problems in the asphalt material characterization models and associated test procedures; and

(e) the necessary corrections, modifications, and enhancements to the models will mandate new field calibration and validation.

Detailed evaluation findings supporting these conclusions are presented in the paper. Future plans for the enhancement and implementation of the Superpave performance models are also briefly described.
08123 Addendum to Pavement Performance Modelling Using Lintrack
J. Groenendijk, A. Molenaar

Volume 2, page 1517: The caption for Figure 20 should be:
Vertical Contact Stresses, New R164BZ tyre, 100 kN, 700 kPa (instead of … Longitudinal…)

Volume 2, page 1518: The caption for Figure 22 should be:
Longitudinal Contact Stresses, New R164BZ tyre, 100 kN, 700 kPa (instead of… Vertical…)

Volume 2, page 1523: 2nd column, first line should be:
XminCe = -30.4 -1.55*F + 8.68*10^4 * F*p -2.02 * V = 0.470 (instead of … -8.68*10^4…)
08124 Addendum to Field Management of Hot Mix Asphalt
J. Scherocman, D. Decker

The attached figures provide a snapshot of recommendations and observations made by the National Center for Asphalt Technology (NCAT) based on an analysis of data collected in the Federal Highway Administration’s Demonstration Project Number 74. Demo Project 74’s objective was to compare volumetric properties of field-produced mixtures with laboratory-design values.
08125 Best Paper and Poster Awards
R. Terrel

The co-chairs of the Conference appointed an awards panel to select the best papers and posters. The papers were evaluated based on their technical merit and quality of writing. An additional consideration was how timely and appropriate the subject was for the Conference theme. The oral presentation was not a part of the evaluation, since all panel members could not be present at all sessions. Session chairs had the opportunity to read the papers carefully, and were invited to nominate the best paper in their respective session. In addition, each member of the awards panel was offered the same opportunity to nominate papers from any or all sessions.

All posters were viewed by each panel member, and each selected three or four nominations for best poster. The composite list of nominees was reviewed and pared to those thought to have merit by a majority. Each panel member then again visited each of the nominated posters and evaluated them on the basis of overall appearance, ability to convey the story on its own without an author present, and how well the poster relates to the paper it represented. A further joint analysis and discussion resulted in selection of the top quality posters.
08126 The 9th International Conference on Asphalt Pavements in Copenhagen 2002
H. Larsen

The 9th International Conference on Asphalt Pavements will be held in Copenhagen, Denmark in August 2002. The Road Directorate in Denmark will be the official host for the 2002 Conference and Mr. Hans Ertman Larsen, Deputy Director of the Danish Road Institute – the research centre of the Danish Road Institute – has been appointed Chairman of the Conference and he gave a presentation of the environment for the event. This presentation was in two parts, an oral welcome to the Conference and a video presentation of the venue and sites to visit. In the following you find Mr. Hans Ertman Larsen’s welcome speech and the words linked to the video presentation.
08127 Future ISAP Conferences and Activities
R. Haas

My role in this closing session is to tell you briefly about the future conferences our Society will be participating in, and to tell you also very briefly about some of our future activities. In general, we intend to continue a focus on the future prospects for the paving industry, its nature, its competitiveness, the key issues and the opportunities. We also intend to build better bridges and communication links with all players in the asphalt industry. More specifically, we intend to: . . .
08128 Conference Wrap-Up
R. Hicks

Paving the gap between design and practice. Are we making progress? Is the gap technological or is there simply a need for better communication between all parties involved in order to produce better asphalt pavements? In the opening session, Steve Brown and Hoffee Marree provided us with an excellent foundation for assessing the current state of practice as well as challenges to implementing the latest technology. We need to continue to develop partnerships between researchers and practitioners to ensure full implementation of new technology. Appropriate training is an important element of the implementation package. In planning for the 9th Conference, we must . . .
08129 Technical Advisory Committee Summary of Activities
R. Hicks, J. Mahoney

Planning for the 8th International Conference on Asphalt Pavements, held in Seattle, Washington, began in 1993, almost four years prior to the conference date. Numerous meetings were held with a technical advisory committee to develop the conference format, the technical program, and the social activities for the conference. This brief report highlights the key events in the planning, execution, and closedown of the conference activities. It also provides a summary of the evaluation of the conference obtained through a survey of attendees. It is hoped this will be of assistance to those planning the 9th Conference to be held in Copenhagen in August 2002.
08130 List of Participants

Registered attendees are listed, together with their organizational affiliations and contact details.
08131 Author Index

An alphabetical index of authors, cross referenced to the page numbers in the Proceedings where their papers appear.