CEAT-FAA Projects 2006


Moisture Curling of Concrete Slabs for Airfield Applications

Faculty Investigator(s): David Lange and Jeffrey Roesler

Graduate Student(s): Chang Joon Lee and Yi-Shi Liu

Overview of Project:

Slab curling is a well-known phenomenon that plagues concrete pavements subject to cyclical temperature and moisture variation. Slab curling occurs when a gradient of thermal or drying shrinkage stresses exists through the thickness of a concrete slab. Higher tensile stress at the top of the slab can be caused by cooling or drying of the top surface. The edges and corners of the slab will lift when the tensile stress is sufficient to overcome the self-weight of the concrete slab. When portions of the slab lift off the subgrade, the slab is vulnerable to corner cracking as loads are applied to the slab.

The proposed project is the third year of a project intended to be a three-year project. The project includes analysis of NAPTF data, new laboratory tests, and development of a computer model of slab behavior. The project considers concrete with high fly ash concrete that promises cost-savings and improved volume stability.

In the first two years, we have analyzed data from NAPTF related to corner cracking of concrete slabs. In addition, we have conducted lab tests and developed a computer model of the slab curling behavior. The unique features of the model include ability to handle time-dependent and stress-dependent material properties, driven by internal stresses associated with gradient moisture and temperature gradients. The lab experiments and NAPTF data analyis are critical components of the computer modeling effort insofar as they provide the required input properties and a basis for calibration of the model.

Objectives of Project:

The goal of this project is to further our understanding of slab curling and behavior of high fly ash concretes for airport pavements. In addition, the project will deliver a computer model that can be used to analyze the full range of material properties, environmental conditions, slab configurations, and other factors that contribute to the curling problem.

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Fatigue and Fracture Behavior of Airfield Concrete Slabs

Faculty Investigator(s): S. Shah, Northwestern University and Jeffrey Roesler

Graduate Student(s): David Ey (Northwestern U) and Cristian Gaedicke

Overview of Project:

The long-term mechanical behavior of concrete subjected to cyclic fatigue loads is an important factor in the design and analysis of airport concrete pavement structures. Previous research for the 2-D loading case found that the static load response could be visualized as a failure envelope curve, where each point in the post-peak region was an equilibrium point representing the maximum load that could be supported for a given level of damage. The favorable comparison between the percentage increase/decrease in compliance/stiffness or crack length in fatigue and static post-peak load indicates that the damage level is comparable for the two loadings. UIUC tests showed the static and fatigue failure of fully-supported concrete slabs was a result of a single crack initiation and propagation which has allowed for the implementation of the static failure envelope for fatigue crack growth prediction.

Objectives of Project:

The objective of the proposed research is to characterize the fatigue response of concrete pavement under three-dimensional tensile/compressive loading and predict fatigue cracking in concrete slabs using the principles of fracture mechanics instead of S-N curves. This will enable a more fundamental understanding of the effects of load pulse type on fatigue crack growth rates and failure. In FY2004, the stress intensity factors and compliance values for edge-notched slab were developed for several initial notch lengths. The slab test data was re-organized in terms of compliance in order to predict the length of crack versus load cycles for both single and tridem loading pusles. Monotonic edge-notch slab tests will also be completed to create the static failure envelope for this concrete. This will be used to calibrate the two proposed stage crack growth model: acceleration (R-curve approach) and deceleration (Paris Law approach). Fully-supported beam tests will also be tested under static and cyclic loading to confirm that the static failure envelope under full support conditions can predict the fatigue crack growth for the same specimen configuration.

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Materials Testing and Permanent Deformation

Faculty Investigator(s): Erol Tutumluer

Graduate Student(s): Deniz Tursun, Tongyan Pan and In Tai Kim

Overview of Project:

The low and medium strength flexible sections tested at the National Airport Pavement Test Facility (NAPTF) failed with up to 4-in. surface ruts. Highest contributions to permanent deformations were often from the 8 to 30 in. thick P209 base and the 12 to 36 in. thick P154 subbase layers until subgrade failure was realized with increased wheel loads. Knowledge is required of the relative contribution of the aggregate layers to the total permanent deformation of the airport pavement structure.

Objectives of Project:

The objective in this ongoing/continuing research has been to develop permanent deformation test procedures for the aggregate base/subbase materials from advanced repeated load triaxial tests, determine most damaging field stress states for the heavier and moving nature of aircraft wheel loads, and as a result, develop realistic rutting prediction models validated with the NAPTF P209/P154 performances.

For the 2005 fiscal year, efforts will focus on validating and finalizing the developed permanent deformation prediction models using the measured ruts recorded in the NAPTF P209/P154 granular base/subbase layers. Such validation will require a thorough investigation of the impacts of moving wheel loading, i.e., extension-compression-extension type multiple path stress tests, on rut accumulation by considering the effects of: [1] NAPTF previous loading stress history (related to observed behavior of virgin and conditioned specimens in laboratory testing), [2] NAPTF trafficking travel speeds (related to load durations in laboratory testing), [3] traffic wander and application direction, and finally, [4] realistic multiple wheel loading of the dual-tandem and dual-tridem gear configurations.

For model validation purposes, more detailed rutting data for the canalized trafficking scenarios will be gathered from the 3rd round of NAPTF testing of the variable thickness P154 subbase course flexible pavement test sections built over the low strength subgrade. Results of trench studies and forensic type analyses will also be useful for evaluating layer ruts and post-failure material properties in these failed sections.

With the successful completion of this research effort, a comprehensive report will be written on the project findings; a permanent deformation test procedure will be drafted to specifically address the heavier airport pavement wheel loading of aggregate materials; and finally, a methodology will be devised to predict rutting potentials of the airport the P209/P154 granular base/subbase layers in newly constructed and rehabilitated airport pavements. Recommendations based on limiting stress criteria will also be made for the development of specifications for field construction and compaction of these unbound granular layers.

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Energy Based Fatigue in Airport Pavements

Faculty Investigator(s): Sam Carpenter

Graduate Student(s): Shihui Shen

Overview of Project:

Current technology cannot address the damage caused by rest periods between load applications, nor does it account for the behavior of pavements designed for extremely low strain levels. Previous research at the FAA Center of Excellence by Ghuzlan and Carpenter has developed a dissipated energy approach that has the potential to be a pavement design criteria in the future when viscoelastic analysis programs are utilized. Continued work by Carpenter and Shen clearly establish the nature of dissipated energy across the entire spectrum of loads, and has provided insight into the energy based nature of healing in an HMA when loads are spaced out by periods as short as 2 to 10 seconds. The dissipated energy change analysis has clearly established a unique energy level below which damage does not occur which for the first time provides analysis tool to examine the fundamental behavior difference in polymer modified binders. All mixtures behave exactly the same at the same dissipated energy value, thus the fundamental differences induced by binder properties can be studied. Additionally, the dissipated energy analysis accounts for different fatigue load modes such as constant stress, important to airport HMA behavior.

The work during the past year by Shen has clearly indicated the healing effect on one unmodified binder. This healing produced by applying a rest period between load cycles increases the fatigue life by a factor of 10 for a 5 second rest period. This process goes a long way toward explaining the extended fatigue life noted on airport HMA pavements compared to highway loadings. When this healing process is validated on other mixtures and modified binders, in conjunction with viscoelastic pavement response programs airport traffic can be evaluated and included in the HMA thickness design process in a mechanistic manner.

Objectives of Project:

Work for the next fiscal year will include extension of the healing process to more mixtures including polymer modified binders typical to airport HMA pavements. This testing will establish life extensions as a function of rest period. Testing a variety of different binders will demonstrate binder effects and show if there is a consistent energy recovery associated with a time of rest. Combining this energy recovery with energy damage from a load allows a mechanistic based damage approach to be prepared and integrated into a thickness design procedure that accounts for different materials.

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Design of Flexible Overlay Systems for Airport Pavements

Faculty Investigator(s): Bill Buttlar

Graduate Student(s): Hyunwook Kim

Overview of Project:

The primary objective of this project is to evaluate current flexible overlay design assumptions utilizing the versatile 2-D and 3-D nonlinear finite element analysis (FEA) tool and advanced material models. The present scope of the work is focused on the analysis of flexible (asphaltic) overlays placed on rigid bases. The proposed analysis will also permit the modeling of interlayer fabrics, grids, and base-isolating mixtures. The long-term goal is to develop tools that can inform and evaluate the current FAA overlay design procedures, design assumptions, typical values, etc.

Objectives of Project:

Most of the efforts of the past quarter were concentrated on the literature review in finalizing the new project scope and in modifying and beginning to analyze the existing models. The project highlights over the past quarter can be summarized as follows:

  • A review of recent literature was conducted to assist in the development of a revised modeling plan to extend the parametric work of Ms. Fang-Ju Chou.
  • The movement of all models to a new computing platform is now complete.
  • A number of the existing models have been modified to meet the new project goals. The new simulations are underway.
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Development of a Radar-based Bird Strike Advisory System and Workshops for Radar Development

Faculty Investigator(s): Ed Herricks

Graduate Student(s): Amy Marcinkevage and Jamie Rose

Overview and Objectives of Project:

The objectives of this research are to:

  • Support for the development of a basic radar system for bird detection and recognition
  • Continue development of Airport Birdstrike Hazard Advisory System based on GIS technology and radar tracking of bird movement
  • Provide support for AAR 410 wildlife management technology evaluations

Objective 1: Support for the development of a basic radar system for bird detection and recognition.

Objective 1a: Support the continued field testing of the basic bird radar.

With completion of the demonstration of the basic bird radar at DFW airport, the basic elements of a bird hazard radar will be assembled. The Center will work with FAA and USAF staff, and Waveband personnel to advance the demonstrated capabilities of the basic bird radar. These advanced capabilities will include placement of radar in an AOA to optimize radar utility, visualization of radar coverage in relation to landscape features, integration of radar operations with known wildlife hazards and normal airport operations, and demonstration of real-time, or near real-time, data collection and analysis capabilities in support of bird strike hazard management.

CENTER supported radar testing at Klamath Falls, OR; Huntington Beach, CA; the Salton Sea, CA; along with a major testing effort at DFW airport. The Center developed analysis protocols for the radar data, and carried out extensive analysis and processing.

Objective 1b: Plan and initiate a long term evaluation of the radar at an airport.

Following the demonstration of the general radar capability, the Center will work with FAA staff on the development of a long term evaluation of the radar. The initial activity in the long term evaluation will be the development of a Quality Assurance Program Plan (QAPP) for the evaluation. The QAPP developed by Waveband, Inc. for initial radar testing will provide the foundation for the long term evaluation QAPP. The Center will work with FAA personnel, Waveband staff, and airport personnel to develop a long term evaluation program that will evaluate radar operation and maintenance, and the utility of radar capabilities in airport wildlife management.

A QAPP was developed for Waveband testing and was further refined based on FOD radar testing at JFK. Development of a long term test plan has occurred through participation in FAA/USAF/Waveband meetings and development of ORD test possibilities.

As part of the long term evaluation program, the Center will continue development of new tools for visualization and use of radar data, along with advanced techniques for the use of radar data in hazard models.

The Center has completed multiple elements of new tool development:

GIS

  • Continuing development of DFW GIS, including freeware distribution of GIS for new laptops at DFW
  • Continuing development of JFK GIS w/ tech transfer
  • Development of support for existing GIS at SEATAC, along with improvement and expansion of their GIS
  • Development of ORD GIS
  • Development of rapid GIS implementation strategy
  • Testing of rapid GIS strategy at San Jose, SFO
  • Providing technical training and technical support for end-users of GIS products at airports

PDA Integration

  • Development and application of portable GIS for JFK and DFW
  • Development of data acquisition forms – multiple applications at DFW and JFK, examples for SEATAC!
  • Development of modifications to basic system to improve user-friendliness
  • Integration with GPS technology for improved data acquisition
  • Integration of portable GIS with desktop GIS and data management programs

Data Acquisition, Processing, and Management

  • Developed multiple data forms for DFW in support of radar testing and ongoing wildlife studies
  • Developed multiple data forms for JFK in support of wildlife management and FOD radar testing
  • Developed data forms for SEATAC in support of wildlife management
  • Developed new visualization tools within data forms to improve quality of collected data
  • Center is presently digitizing historic data for SEATAC
  • Developed integration of Center approach with AirMan database format

Objective 1c: Integration of radar data into a real-time, or near real-time, bird strike advisory system.

With the identification and evaluation of radar capabilities, the Center will initiate a full scale integration of radar capabilities with the existing GIS-based wildlife hazard advisory system. It is anticipated that radar data will be incorporated into the GIS-based bird strike advisory system in several ways. First, radar recognition capabilities will be integrated with the GIS platform that will also feature flight path data for the airport. A real-time, or near real-time, GIS base visualization capability will be developed to provide integration of landscape, aircraft flight path, and bird flight path data.

Based on DFW testing, a full integration of radar detection with GIS was completed. Products include animations and full integration of radar detection with airport flight paths. 3D analysis of potential conflicts between wildlife detected with the radar and airport approach paths has been carried out.

Radar operational schemes will be developed to meet the specific challenges of airport operations, for example, the capabilities of the radar will be evaluated to determine optimum locations for radar deployment for bird hazard detection.

GIS capabilities were used to plan and execute bird radar studies, including development of deployment scenes required for testing approvals, and evaluation of deployment issues as testing proceeded.

Integration of the radar in a bird strike hazard advisory system will require several steps. The radar is considered an advanced tool for acquisition of data on the presence and abundance of birds and the characterization of bird movement patterns. Through using the radar to recognize birds and track movements, it will be possible to enhance wildlife observation reporting at the airport, improve the capacity to model bird movement patterns and confirm hazard potentials when other observational methods are ineffective (e.g. at night).

The integration program anticipated by the Center will thus include consideration of radar capabilities identified in Task #1a, the development of procedures to incorporate radar data in existing GIS systems, and the advancement of the visualization capacity of the existing GIS systems to better accommodate 3-dimensional data provided by the radar.

Based on DFW radar trials a number of steps were taken to develop procedures for bird movement characterization.

A model of bird movement was developed and refined for blackbird movement based on DFW observations. Bird movement modeling was integrated with GIS and flight path information to develop a new hazard evaluation tool for WHAS.

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Minority Student Outreach Program

Faculty Investigator(s): David Lange

Overview of Project:

One of the major objectives of CEAT is to educate and train students for airport-related engineering positions with State, Federal, and Private agencies. In addition, the FAA COE program has encouraged outreach to underrepresented minority groups. Since FY2001, CEAT has included a minority outreach program as part of the scope of work. The objective of the minority outreach program is to increase the number of minority students obtaining advanced degrees in Civil Engineering with an emphasis on expertise directly relevant to improving airfield pavement technology. Up to six students every year from FY2001-4 have been involved in summer research at UIUC.

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