Center of Excellence for Airport Pavement Research
B. J. Dempsey,* Director, E. J. Barenberg,* Associate Director, M. R. Thompson,* Associate Director
Federal Aviation Administration, DOT 95-C-001

The Federal Aviation Administration established an Air Transportation Center of Excellence (COE) for Airport Pavement Research in the Department of Civil and Environmental Engineering at the University of Illinois at Urbana-Champaign on April 12, 1995. Northwestern University is a cooperative partner in the research program.The universities have developed a strong working partnership with the FAA in providing pavement design for the next generation of aircraft. An experienced research team has been assembled for conducting basic research in airport pavement technology, including modeling of airport pavement structures, constitutive behavior of pavement materials, material characterizations, and advancement in the art of pavement evaluation.The COE is conducting research in 13 project areas (11 projects at the U of I and 2 projects at NU) relating to pavement structural modeling, materials, subgrades and base courses, nondestructive evaluation, design, and management. New technology from the studies is being coupled with existing Best Demonstrated Available Technology (BDAT) to support the development of pavement designs adequate for accommodating the new generation of larger aircraft like the Boeing 777-300. The new COE technology and BDAT are being provided to the FAA for supporting/enhancing/refining its recently developed LEDFAA pavement design procedure. As activities progress, the center is providing information to (and cooperating with) FAA staff to support the development of an alternative mechanistic-based design system for the economical and reliable design of new pavements and overlay design for existing pavements. These pavements will be constructed with a wide variety of paving materials (traditional and/or new) and layer configurations/arrangements; will include new design features (such as improved load transfer devices in concrete pavements); and will accommodate a broad range of aircraft loadings. Numerous publications have been prepared from COE research activities since it was established in 1995. Many of the publications can be obtained from the COE website at http://uiairpave.ce.uiuc.edu.Most of the center's projects at Urbana follow. A few more are in other sections of the Civil and Environmental Engineering summary.

Mechanistic-based Airport Pavement Design Concepts
E. J. Barenberg,* M. R. Thompson,* E. Tutumluer, N. Garg, H. Ceylan, F. Gomez-Ramirez
FAA Center of Excellence for Airport Pavement Research

Current FAA design procedures were developed over an extended period of time using a combination of pavement analysis procedures and experience with performance of pavements in service. The accelerating pace at which new generation aircraft and materials are developing makes this approach inadequate. The primary objectives of this study are to identify, review, and evaluate the most current, emerging, and new technologies that relate to airport pavement design processes. The approach proposed will facilitate the development and maintenance of the best demonstrated available technology for M-B airport pavement design procedures.

Fatigue Characteristics of Steel Railroad Ties
E. J. Barenberg,* K. BaRaKa
Tie and Track Systems, Inc.

Steel ties are being tested under varying magnitudes of cyclic loading to determine their fatigue characteristics. Ties are being loaded to five million cycles of repeated loading or until failure, whichever occurs first. Various combinations of systems for fastening rails to the ties and various tie dimensions are being evaluated.

Affiliated Laboratory for Railroad Engineering
E. J. Barenberg,* C. Barkan
Association of American Railroads

The AAR Affiliated Laboratory Program is intended to (1) attract faculty and students to work in areas of interest to the railroad engineering profession; (2) assist the railroad industry in the solution of technical problems related to the railroad operation and related industries; (3) develop a pool of experts familiar with railroad engineering problems and assist the industry in the solution of their problems; and (4) develop courses and research programs to entice highly qualified students to work and study in areas related to railroad engineering. Most of these objectives will be accomplished by expanded programs of research on engineering problems related to the railroad industry.Funding for the laboratory is under three categories: general, core, and project. General category funds are used for program coordination and administration plus any research activities elected by the program director. Core projects are selected by a technical advisory committee, and projects are funded by the various divisions of AAR as funds permit. The current projects under the core and project funding are described in the subsequent statements.In 1998, this program supported a number of projects conducted by faculty in the Departments of Civil and Environmental Engineering, Forestry, Materials Science and Engineering, and Mechanical and Industrial Engineering.Detailed summaries of the projects are given in the principal investigators' departmental sections of this book. The project outside of the College of Engineering is:Fatigue Life of Wood Bridge Stringers, P. Chow, Wood Science, Forestry.

Crack Propagation and Failure of Plain and Fibrous Concrete under Repeated Loading
E. J. Barenberg,* D. Lange, N. Hawkins, J. Roesler
University of Illinois

Fatigue behavior of plain and fibrous concrete is being investigated. Special attention is given to crack propagation under repeated loading and how the cracks propagate in different types of specimens under different loading conditions. Effect of specimen size is one of the aspects under investigation.

Investigation of D-Cracking of Concrete Pavements at Willard Airport
E. J. Barenberg,* B. J. Dempsey
University of Illinois

D-cracking of concrete pavements at Willard Airport is being investigated. Rate of development, extent, and methods for mitigation are being investigated. Both laboratory and field testing are being used to evaluate the alternate repair methods and procedures for mitigating propagation of D-cracking.

Lateral Stability and Buckling of Rails
E. J. Barenberg,* Y. Bao
Association of American Railroads

Continuously welded rails are used to eliminate the maintenance problems caused by joints in rails. If the rails are welded at too high a temperature, they tend to pull apart at low temperatures. If the rails are welded at too low a temperature, they tend to buckle or "sun-kink" at times of high temperature. This study examines the factors that influence the buckling temperature and ways to reduce the tendency to buckle. A track buckling model called "ILLIBUCKLE" has been developed using the finite elements in ABAQUS. This model is being used to evaluate procedures for increasing lateral track stability. For CRW with a high degree of curvature, the track may not buckle but may move laterally with temperature changes.

Models to Analyze the Lateral Stability of Ladder Sleeper Track Systems
E. J. Barenberg,* Y. Bao, J. Min
Railway Technical Research Institute, Japan

The Japan Railway Technical Research Institute has developed a track system of longitudinal ties with cross connections to be used in lieu of the conventional cross tie track system. This system is referred to as a ''ladder sleeper track system.'' The purpose of this research is to modify computer models developed at the University of Illinois to evaluate the lateral stability of conventional cross tie track systems for use on the new ladder sleeper track system. The models will then be used to evaluate the lateral stability of the new system and to make recommendations for modifications in the systems to enhance its lateral stability.

Technology Transfer Models for FAA Center of Excellence
R. F. Benekohal,* F. Colemen III,* E. Shim
FAA Center of Excellence for Airport Pavement Research

The project will develop a framework for airport pavement technology transfer. The primary objectives of this study are identifying, reviewing, and evaluating the most current, emerging, and new technology transfer techniques appropriate for the Center of Excellence; recommending viable options to the FAA for accomplishing the technology transfer; and preparing at least one demonstration package to illustrate the most viable option(s). A WWW site is being developed to become an integral component of an on-going technology transfer mechanism for the center.

Evaluation of Automatic Vehicle Identification in a Weigh-in-Motion System for CVO
R. F. Benekohal,* J. Barnett, Y. El-Zohairy, C. Tirums
Illinois Department of Transportation

This study evaluates the performance of an automatic vehicle identification (AVI) and a high-speed weigh-in-motion (WIM) system to preclear trucks around the weigh stations. This project includes the following studies: travel time and flow interruption, overall performance of the system, users' opinions survey, comparison of WIM and static scales data, and traffic safety and accidents around weigh stations. The AVI system will be installed on commercial vehicles, and the WIM will be at the mainline speed of vehicles.

Development of Signal Coordination Models for Congested Networks
R. F. Benekohal,* G. Abu-Lebdeh
Federal Highway Administration (Eisenhower Fellowship)

This study investigates the current signal coordination procedures and develops a methodology for handling coordination of congested intersections. The current signal coordination models rely primarily on delay as the measure of effectiveness. However, the delay model used in these procedures is not developed for congested conditions, thus the coordination plans are not very accurate or effective. Other measures of effectiveness are examined to optimize traffic flow through a congested network of intersections.

Multilevel Analysis of Highway Accidents
R. F. Benekohal,* E. Shim
University of Illinois

The objectives of this study are to conduct multilevel analyses of highway traffic accidents. The relationships between accident frequency and geometry, traffic composition, and capacity of highways are examined. Accident data are grouped into different levels, and correlations among different levels and variables are examined. Furthermore, longitudinal and cross-sectional analyses are made to determine the temporal and spatial effects of variables on accidents.

Platooning Effects on Delay at Signalized Intersections
R. F. Benekohal,* Y. El-Zohairy
University of Illinois

This study is developing delay models that directly consider the platooning characteristics of vehicles at signalized intersections. The Highway Capacity Manual (HCM) delay models use an adjustment factor to account for the platooning effects. The 94 HCM uses a delay adjustment factor, DF, that can increase the uniform delay by 256% or reduce it by more than 70%. The new models eliminate the need for applying delay adjustment factors. Delay models are developed that consider the platooning characteristics as a part of the model derivation. The effects of platoon size and platoon density are formulated on the intersection delay.

Modeling Platooning and Headway Characteristics of Vehicles
R. F. Benekohal,* S. Sadeghhosseini
University of Illinois

This study examines the platooning and headway characteristics of vehicles at different traffic volumes. Models for platoon size distributions are developed, and the relationships between platoon size and platoon headway are studied. Spacing, speed, and safe following distances are determined, and potential safety impact of each is examined. A significant portion of vehicles platoon even at relatively low-volume conditions. Understanding the platooning characteristics of vehicles would help to utilize the ITS technologies that would increase the traffic throughput and would improve traffic safety.

Traffic Flow Simulation Models for Unsignalized Intersections
R. F. Benekohal,* M. F. Aycin
University of Illinois

Traffic flow characteristics at unsignalized intersections influenced by the adjacent signalized intersections are modeled. The flow behavior at microscopic level is studied and mathematical models are developed to describe it. Car-following models are developed for the signalized and unsignalized intersections. A computer program has been written and debugged. Calibration and model validation are in progress. Effects of platooning on delay at unsignalized intersections will be studied using this model.

Interconnected Rail-Highway Intersection Signal System Simulator
R. F. Benekohal,* R. Morocoima
Partnership Illinois Funds; University of Illinois

This project will provide hands-on education and training opportunities on the use of complex railroad-highway interconnect signal systems. A simulation model for an interconnected rail-highway intersection signal system simulator (IRISSS) will be developed. It will be used to educate and train municipal and state officials on safe and effective use of these systems. IRISSS not only will be an educational tool, but also will be used to showcase the potentials for future partnerships with private and public agencies.

Evaluation of Pilot Study of Advisory On-Board Vehicle Warning Systems at Railroad Grade Crossings
R. F. Benekohal,* E. Forrler, M. Aycin
Illinois Department of Transportation

This study will evaluate the effectiveness of advisory on-board vehicle warning systems at five railroad grade crossings. Approximately 300 commercial vehicles will be outfitted with the on-board system. The vehicles will be provided with supplementary on-board warning messages to advise them of a train approaching or occupying the crossings. Four drivers' opinion surveys will be conducted before the modality is switched. Emphasis will be placed on the reaction/perception of drivers to the information provided and understandability of them. The system reliability and effectiveness will also be determined.

Enhancements to IDOT Traffic Management Algorithms
R. F. Benekohal,* A. Butzek, M. Girianni
Illinois Department of Transportation

The IDOT maintains travel time information obtained from its traffic sensors for freeway segments in the NE Illinois region. These are used to inform motorists of expected travel times by way of radio and television station traffic reports, World Wide Web traffic maps, and changeable message signs. This research is to incorporate travel time information taken from electronic toll collection records to give the IDOT complete travel time information for all tollways in addition to freeways in NE Illinois. Algorithms are being designed, calibrated, and validated to provide estimates of tollway segment travel times based on real-time toll transaction information.

Micromechanical Analysis of Asphalt-Filler Mastics
W. G. Buttlar,* A. Waldhoff
National Highway Institute

The stiffening effects of mineral fillers, when combined with asphalt binders, are being studied using micromechanical models for particulate composites. Theoretical results will be validated through tests on asphalt-filler mastics using dynamic shear and bending beam rheometers. The intent of the work is twofold: (1) to evaluate applicability of particulate micromechanics models to predict mastic stiffness and (2) to use the models to evaluate and quantify physicochemical stiffening effects, which are influenced by particle size, distribution, and surface charge. These concepts are being used in a forensic investigation of premature crack development on portions of two Interstate pavements in Illinois.

Evaluation of Reflective Crack Control Policy
W. G. Buttlar,* D. Bozkurt
IDOT Illinois Transportation Research Center

Reflective cracking in asphaltic pavement overlays is a widespread and costly phenomenon caused by movements of cracks and joints in original, overlain pavement layers. Current IDOT policy allows a choice among three reflective crack control treatments, each designed to retard reflective cracking by restricting movements at joints and cracks and/or providing base isolation. While the currently allowed treatments are thought to delay the initial appearance of reflective cracks, the cost-effectiveness of these systems has never been investigated. Cost-effectiveness will be determined by studying the costs and performance benefits of a number of overlay projects conducted by IDOT, both with and without crack control treatments.

Development of a Hollow-Cylinder Tensile Tester for Asphalt Mixtures
W. G. Buttlar,* G. Al-Khateeb
University of Illinois

The Strategic Highway Research Program (SHRP) was a $50-million research effort that led to the development of performance-based tests and prediction models for the design of asphaltic paving mixtures. However, there are many obstacles standing in the path of full implementation of the new methodologies, particularly the cost and complexity of the new test devices. A hollow-cylinder tensile test device is being developed to serve as a low-cost, easy-to-operate device for the control of low-temperature cracking of asphalt pavements. Viscoelastic and fracture-related properties of standard laboratory cylinders will be determined at low temperatures using the new device.

Characterization of Asphalt Concrete for Airport Pavement Design
S. H. Carpenter,* K. Ghuzlan
FAA Center of Excellence for Airport Pavement Research

New aircraft are producing loading conditions that have not been present before. This project will examine the impact of these new loading conditions on the performance and characterization of the asphalt concrete to develop appropriate testing methodology for use in new pavement design methodologies. Beam fatigue evaluations will illustrate the effect of the load pulse duration and shape on the fatigue life of asphalt concrete, which may change for different pavement structures. Viscoelastic characterization will be required to account for the duration of the load pulses for stiffness determinations. Constitutive testing technology developed for asphalt concrete in highway applications will be evaluated for adaptation to airport conditions.

SHRP Asphalt Testing for Performance-related Specifications
S. H. Carpenter,* B. Vavrik, R. Fries, J. Kern
Illinois Department of Transportation

The Strategic Highway Research Program (SHRP) has developed a new sequence of tests and specifications for asphalt cements and mixes to enhance the ability of specifications to provide a level of service in the constructed pavement. These new procedures require the use of new equipment and methods not normally used in the transportation industry. The objectives of this study are to install the new equipment, perform shakedown testing to establish operational characteristics, and then perform characterization testing of typical Illinois materials. This will include evaluating the suitability of asphalt cements and mixtures currently available to determine if modification will be required to satisfy the new Superpave specifications for Illinois climate, traffic, and materials.

Development of a Self-contained Portable Device for Superpave Binder Testing - Field QC/QA Testing with the Duomorph
S. H. Carpenter,* J. Mallela
National Highway Cooperative Research Program

The Duomorph is a piezoelectric disk assembly that induces precisely controlled deformations into a surrounding medium and senses the resistance to these deformations, allowing the dynamic properties of the viscoelastic medium to be determined. This project will document the capabilities of the Duomorph to function as a Superpave asphalt binder test device. The Duomorph can potentially replace the three mechanically complex Superpave test devices, providing dynamic and creep testing at all temperatures, while at the same time providing testing capabilities for a broader range of materials in a more durable low-cost device. The second phase is now developing a field-ready prototype device.

Compaction Characteristics of Hot Mix Asphalt Concrete
S. H. Carpenter,* W. R. Vavrik
Caterpillar Inc.

The characterization of deformation properties of hot mix asphalt concrete at temperatures and void levels representative of those encountered during paving have not been identified in a manner that would provide for optimization of construction equipment. With the new Superpave mixtures, the operation of pavers and rollers is even more crucial to attaining proper density prior to opening to traffic. This project will conduct specific stress path testing at air void levels up to 15% and temperature regimes up to 136°C to characterize the deformation properties of one typical hot mix asphalt concrete mixture to demonstrate equipment capabilities and data quality.

Highway Problems - Illinois Cooperative Highway and Transportation Research Program
S. H. Carpenter*
Illinois Department of Transportation

Nine separate projects were included in the Illinois Cooperative Highway Research Program in 1998. They range in subject from the development of pavement design procedures to concrete column rehabilitation.IHR-2 provides support for initial investigations of new cooperative research with the Illinois Department of Transportation (IDOT). During this year, the project funded studies related to skid trailer instrumentation, testing equipment, alkali-silica reactivity, accelerated pavement testing, thermal cracking of asphalt pavement, and rehabilitation of deteriorated concrete columns.

Evaluation of Potential Applications of End-Result and Performance-related Specifications
S. H. Carpenter,* W. G. Buttlar,* D. Lange,* M. Harrell, R. Clinton
Illinois Department of Transportation

Material and construction specifications are typically grouped as: (1) method, (2) end-result, or (3) performance-related. Illinois Department of Transportation (IDOT) specifications for asphalt concrete paving (ACP), portland cement concrete paving (PCCP), and structural concrete for substructures and bridge decks (SC) contain elements of all three. IDOT has developed a quality control/quality assurance (QC/QA) program for ACP that is extensively used. IDOT's PCCP QC/QA program is still evolving, and IDOT does not have a QC/QA program for SC. The primary objective of this research project is to evaluate the potential applications of end-result and performance-related specifications to ACP, PCCP, and SC.

Human Factors and Hardware Reliability Analysis of a Vehicle-arresting Barrier (VAB) at Proposed High-Speed Passenger Train At-Grade Crossings
F. Coleman III,* Y.-J. Moon, H.-J. Ham
Illinois Department of Transportation

Guidelines prepared by the Federal Railroad Administration (FRA) for high-speed passenger trains that are expected to travel at speeds between 110 mph and 125 mph require that at-grade crossings be blocked from vehicle entry. IDOT's proposal to the FRA to test a vehicle-arresting barrier has been accepted for three sites along the proposed high-speed passenger train corridor. The objective is to fully document the demonstration of this new technology and to determine the operating requirements necessary for successful implementation.

Theory and Proof of a Dynamic Dilemma Zone at Highway-Rail Intersections Leading to Retiming of Warning Signals
F. Coleman III,* Y.-J. Moon
Illinois Department of Transportation

Operating times of existing warning signals are based on a fixed dilemma zone which assumes uniform vehicle approach speed at highway-rail intersections. Actual vehicle speed profiles are found to be nonuniform and generally decelerating, suggesting a dynamic dilemma zone (DDZ) is created on approach to these intersections. Analytical modeling is employed to prove the existence of a DDZ. Stochastic simulation modeling of speed profiles and driver behavior is used to establish the extent of the DDZ and establish new warning signal operation times to increase the likelihood of driver warning signal recognition and ability to stop prior to the intersection.

Simulation and Validation of Four-Quadrant Gate Operating Parameters at Highway-Rail Intersections
F. Coleman III,* Y.-J. Moon
University of Illinois

High-speed rail service at speeds between 80 to 110 mph requires one or more countermeasures to prevent accidents between vehicles and trains, such as grade separation, constant warning time devices, four-quadrant gates, and active advance warning systems. A nonsite-specific stochastic simulation model incorporating human factors, vehicle kinematics, vehicular volumes, and train operations is formulated to determine four-quadrant gate operation values. Validation of simulation-based gate operation values is determined from video-based heuristic gate operation values from an existing site in North Carolina.

Effects of Traffic Signal Coordination on Accident Rates
F. Coleman III,* Y.-J. Moon, C. Espindola
IDOT Illinois Transportation Research Center

Signal coordination on higher volume roadways is a practice instituted to allow more efficient traffic movement on major streets. This has led to changes in driver behavior on the major and minor streets and affects pedestrians ability to cross streets safely. Preliminary accidents analysis suggests a change in number and types of accidents related to driver and/or pedestrain behavior on roadways with signal coordination. This research will explore and identify if there is a correlation between signal coordination and a change in accident patterns along major corridors.

Development and Evaluation of VFR Lighted Flyways in the Chicago TCA Environment
B. J. Dempsey,* P. Hongschaovalit
IDOT Illinois Transportation Research Center

The purpose of this research is to develop a series of ground markers for visual flight rules (VFR) aircraft navigation around the O'Hare International Airport Class B airspace. This study includes the development, fabrication, and evaluation of the VFR marker. A unique flashing strobe was developed for nighttime navigation. The prototype VFR marker has been successfully evaluated in the Chicago Terminal Control Area (TCA). A draft final report for the project has been completed.

Evaluation/Characterization of Airport Pavements Using the Impact-Echo and Spectral Analysis of Surface Waves
H. L. M. dos Reis* (General Engr.), A. Habboub
FAA Center of Excellence for Airport Pavement Research

The development of nondestructive evaluation techniques for nonmetallic, heterogeneous materials such as concrete has lagged behind the progress made for relatively homogeneous materials like metals and ceramics. Difficulty in evaluating concrete pavements is further increased because the presence of some macroscopic defects in concrete is not detrimental to performance. By using impulse-echo, spectral analysis of surface waves, pulse velocity, and acousto-ultrasonics, this reserach project aims to develop an instrument capable of scanning airport pavements to evaluate layer thicknesses, material properties, damage accumulation, and other defects such as delaminations. The output of this instrument should include a color-coded feature pavement scan.

Nondestructive Evaluation of Segregation in Hot-Mix Asphalt Pavements
H. L. M. dos Reis* (General Engr.), S. H. Carpenter, A. Habboub
FAA Center of Excellence for Airport Pavement Research

Segregation is the separation of the coarse and fine aggregate particles from a mass containing a variety of particle sizes. Current methods of detecting and evaluating segregation are basically qualitative and strongly operator dependent. The purpose of this project is to develop a nondestructive testing and evaluation method to quantitatively evaluate/characterize porosity and segregation in asphalt concrete.

Nondestructive Evaluation of Airport Pavements Using Stress Wave Methods
H. L. M. dos Reis* (General Engr.), A. Habboub
FAA Center of Excellence for Airport Pavement Research

Using impulse-echo, spectral analysis of surface wave, pulse velocity, and acousto-ultrasonics, the purpose of this project is to develop an instrument capable of scanning airport pavements to evaluate layer thickness, material properties, and defects such as damage accumulation and delaminations. The output of this instrument should include a color-coded feature pavement scan.

Load Transfer between Slabs in PCC Pavements
N. M. Hawkins,* E. J. Barenberg,* D. A. Lange,* M. Abdul-Maksoud, S. Wattar
FAA Center of Excellence for Airport Pavement Research

A fundamental understanding of the behavior of joint systems in PCC pavements is being sought. The project efforts are directed toward the performance of different joint systems and to determine how their behavior and performance vary with time. New joint systems and new methods of load transfer are being examined and evaluated for behavior and performance. Numerical models (both currently available and newly developed) are being used to evaluate the behavior and performance of joint systems. Initial evaluation of shear performance of a variety of joint systems is being made using laboratory bench samples. The performance of the most promising joint systems will be validated using large slabs under repeated loading in the laboratory.

Structural Behavior and Modeling of Airport Pavement Systems
K. D. Hjelmstad,* I. D. Parsons,* E. Taciroglu, I.-S. Eom, J. Kim
FAA Center of Excellence for Airport Pavement Research

The analytical modeling of pavements using 3-D finite-element analysis will be essential to understanding the fundamental behavior of pavements. The problems of modeling cracked slabs, reinforced and unreinforced joints, interfaces between layers of material, and materials with complex constitutive behavior are intimately coupled with questions concerning the 3-D aspects of the response of pavements, loading rate effects, and correlation with field tests. The current thrusts of the project include: (1) 3-D elastic analysis of wheel load interactions, (2) finite-element analysis of through-cracks and joints in rigid pavements, and (3) development of computational tools for large-scale 3-D problems.

High-Performance Concrete for Airport Pavements
D. A. Lange,* J. F. Young,* L. Struble,* H. Shin
FAA Center of Excellence for Airport Pavement Research

Low-porosity concretes are being evaluated for use as overlays on existing airport pavements. These materials contain high additions of silica fume and superplasticizers to provide dense concretes of low permeability, good bonding characteristics, and improved wear resistance. However, cracking caused by thermal and drying shrinkage is a concern. This project examines the properties of these concretes experimentally and models their cracking tendencies. Development of bond with the existing pavement will also be considered.

Subgrade Evaluation for Airport Pavement Design
M. R. Thompson,* E. Tutumluer, M. Bejarano, N. Garg, U. Seyhan
FAA Center of Excellence for Airport Pavement Research

Subgrade soil and granular base/subbase evaluation is an important part of airport pavement design. Moduli and strength are of major concern. The objectives of this research are to (1) develop improved/new procedures and methodologies for establishing subgrade soils and granular base/subbase modulus/strength inputs (including subgrade design criteria) for mechanistic-based airport pavement design, and (2) establish concepts and procedures for effectively considering "subgrade stability" in airport pavement construction operations.

Stabilized Base Materials
M. R. Thompson,* D. Arellano
FAA Center of Excellence for Airport Pavement Research

Current FAA airport pavement design procedures and policies require stabilized base and subbase for new pavements designed to accommodate aircraft weighing over 100 kips. The primary objectives of this study are to identify, review, and evaluate the most current, emerging, and new technologies that relate to stabilized-base material utilization in airport pavements. The project will facilitate the development and maintenance of the best demonstrated available technology for stabilized-base materials.

Mechanistic Design Implementation and Monitoring
M. R. Thompson,* E. J. Barenberg,* F. Gomez-Ramirez
Illinois Department of Transportation

Mechanistic-based thickness design concepts and procedures for rigid and flexible pavements were developed by the U of I in previous IDOT-sponsored projects. IDOT implementation activities are completed for jointed concrete and full-depth asphalt concrete (AC) pavements. Implementation activities for continuously reinforced concrete, conventional flexible (AC granular base), and AC high-strength stabilized base pavements are in progress. Selected rigid and flexible pavements are being monitored to develop data for future refinements and/or modifications to the mechanistic-based procedures. This project is to provide technical support to and to cooperate with IDOT in implementation and monitoring activities associated with the mechanistic-based design of flexible and rigid pavements.

Cooperative Evaluation of Minnesota Road Test Results to Illinois Conditions
M. R. Thompson,* E. J. Barenberg,* J. Roesler, N. Garg, C. Alvarez
Illinois Department of Transportation

This study is a cooperative effort between the Minnesota Department of Transportation, the U of I Department of Civil and Environmental Engineering, and the Illinois Department of Transportation (IDOT) to provide broad utilization of the data obtained from the Minnesota Road Research Project, the most comprehensive "full-scale" road test constructed since the AASHO Road Test. It includes 40 pavement sections (both concrete and flexible-type construction) for high-volume truck traffic and low-volume roads. It is the most extensively "instrumented" series of pavements ever constructed in the U.S. Results obtained from the cooperative efforts will be particularly helpful in verifying, refining, and modifying IDOT's flexible and rigid pavement analyis and design concepts and procedures.

Video Analysis of Aggregates
E. Tutumluer,* J. Stefanski
Federal Highway Administration

Aggregate particle shape, size, and gradation can impact the performance of asphalt concrete (AC) pavements. The Strategic Highway Research Program (SHRP) has developed a set of consensus properties to identify proper aggregates for AC mix designs. The efforts in this project are focused mainly on comparing results of different video-imaging systems for flat and elongated particles, coarse aggregate angularity, and gradation. Both the precision and accuracy of results for each property will be studied. The project will also facilitate the development of an image analysis system for automating the determination of the aforementioned high-priority aggregate properties.

Laboratory Determination of Anisotropic Properties of Granular Materials
E. Tutumluer,* U. Seyhan
University of Illinois

Unbound aggregates essentially of a particulate nature are extensively used in the unstabilized bases/subbases of flexible highway and airport pavements. These granular layers loaded under anisotropic conditions typically exhibit a directional dependency of material properties. As the material stiffens, the deformability decreases with a higher modulus attained in the vertical loading direction. A new repeated load triaxial testing device, named FastCell, has been custom-designed to independently pulse either vertical or radial loading/confining pressures. Anisotropic properties of aggregates will be determined in the laboratory from the measured vertical and radial specimen deformations. Significant improvements will be achieved in material characterization of aggregates.