FAA Research Projects - 2005

Subgrade Support and Stabilization

The Subgrade and Pavements research project sponsored by the FAA includes four specialized areas of research. Each area of the research is led by a faculty investigator.

Moisture Curling of Concrete Slabs for Airfield Applications

Faculty Investigators: David Lange and Jeffrey Roesler

Overview:

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:

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.

Proposed activity for FY2005

Experimental

• Complete thin plate tests to discern material properties
• Complete prism and dogbone tests for bulk property of high fly ash concrete

Material property modeling

• Determine model for RH-shrinkage relationship

Structural modeling

• Address gravity, Poisson’s ratio, drying creep and sparse solver issues
• Validate model: Use structural model to “predict” NAPTF results

Application

• Use model to learn about role of material in slab curling problem

Raw Materials

Faculty Investigator: Leslie Struble

Overview and Objectives:

The objective of this project is to survey and test the suitability of local materials (coarse aggregate, sand, cement, and admixtures) for use in portland cement concrete. This project will interact closely with the project on portland cement concrete mix design. Particularly important is the potential for concrete deterioration due to reactions involving the aggregate (alkali-silica reaction, alkali-carbonate reaction, and freeze-thaw cycles). The project will provide a database of aggregate and sand properties and recommendations concerning aggregates, cements, and admixtures.

The Illinois Department of Transportion (IDOT) is an important resource of information for this project. Immediately available data will be a useful starting point for identifying preferred aggregate sources from the 250 quarries currently serving the State of Illinois. For example, IDOT maintains a testing program for coarse aggregates produced in the Illinois marketplace, and publishes results listing results by quarry here. The list currently includes about 20 quarries serving IDOT District 1 with crushed coarse aggregate meeting their highest quality “40 Design Life” rating. These are generally crushed dolomitic limestone aggregate sources that IDOT believes to have not only excellent freeze-thaw durability but also high ASR resistance. Further evaluation of the most attractive aggregate sources is a core component of this project. The proposed work includes a physical testing program that will provide substantial and detailed knowledge of the performance and variability of fine and coarse aggregates from different sources, as well as consideration of cements and admixtures available to OMP.

Experimental Work:

In previous work at UIUC for IDOT, we have identified siliceous fine aggregates in Illinois that caused damaging expansion in concrete pavements due to alkali-silica reaction in concrete. The primary reactive component is chert. Therefore sands will be examined for the presence of chert and for reactivity using standard tests.

Through testing at IDOT, experience has been gained in the identification of limestone coarse aggregate that causes damaging expansion and cracking in concrete pavements due to freeze-thaw cycles (the so-called D-cracking). Based on IDOT testing results, aggregate sources will be recommended that show only very good freeze-thaw resistance.

With limestone aggregate, hardness is always a concern. Aggregate that is too soft produces concrete with poor abrasion resistance. Aggregate hardenss will be measured using standard tests.

Other aggregate properties required for concrete mix proportioning will be measured, such as gradation and moisture content.

Aggregate sampling will be done in consultation with quarry management and IDOT personnel to assure that test results are representative of the range of aggregate materials likely to be encountered during concrete production.

The soil and groundwater associated with the OMP will be tested for sulfate content to determine the potential for expansion and cracking of the concrete due to sulfate reaction.

If testing indicates that any of these deterioration processes is likely, recommendations will be made for mitigating damage through the cementitious materials (portland cement and mineral admixtures).

Wherever possible, standard ASTM tests will be utilized.

In previous ACBM research, UIUC has gained experience in testing rheology of cement paste to detect combinations of cement and high-range water-reducing admixture that produce slump loss in concrete. If the project on PCC mix proportioning indicates that such chemical admixtures will be used, then specific cement-admixture combinations will be tested for rheological behavior.

PCC Mix Designs

Faculty Investigators: Jeffery Roesler and David Lange

Overview:

The concrete materials selected for airfield concrete pavements have a large impact on its structural and functional performance. The concrete materials must be optimized to produce a mix that can be easily mixed, placed, cured, and resist the environmental and mechanical loading that will be applied over its service life. The concrete mix design must accommodate volumetric changes at early-ages without premature cracking, limit the amount of thermal and moisture curling, and minimize the long-term contraction-expansion movements which lead to poor joint performance.

Over the past five years, the UIUC concrete pavement and materials research group has been actively involved in experimental research of airfield concrete pavement that specifically addresses concrete shrinkage, creep, and stress development; concrete fatigue, characterizing and design of concrete pavements; curling of concrete slabs; joint design; and fiber-reinforced concrete materials (1-13).

Overview:

The objective of this research proposal is to investigate concrete material properties required to achieve long-term performance at the Chicago O’Hare International Airport (ORD) and then to develop material constituents and proportions to assure the desired material properties will be met. The project will include analysis of the existing concrete mix designs used for airfield applications, available materials suitable for the proposed mix designs, laboratory tests to determine the shrinkage, creep, and strength of proposed mixes, consideration of mix designs to produce optimal joint types and spacing, and review of fiber-reinforced concrete materials for airfield applications. Appropriate modeling of the results will be completed to extend the understanding of materials not included in the laboratory-testing program. It is expected that the following work plan will take approximately two years to complete with the time critical tasks to be completed first.

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Wildlife Issues Research Project

Development of a Wildlife Hazard Information Prototype for WHAS

Faculty Investigator: Ed Herricks

Research Assistant: K. Marcinkevage

CEAT has developed a research approach based on an understanding of FAA needs and requirements and an awareness of advanced techniques in wildlife management, risk assessment, monitoring, and computer systems. This approach recognizes the major role the FAA plays in supporting all aspects of airport operations and aircraft movement. Although each airport may present a singular set of issues to challenge wildlife hazard abatement, there are sufficient similarities associated with airport/aircraft operation, wildlife behavior, and abatement technologies to encourage a systematic approach to wildlife hazard abatement. This suggests that a WHAS, developed to provide a systematic approach, is a critical component of future airport safety technology. As a part of continuing development of WHAS components, this research will advance the Wildlife Hazard Information component of WHAS, a GIS-based consolidation of wildlife and airport operations information.

Review and Assessment of Radar/Sensor Application in WHAS

Faculty Investigator: Ed Herricks

Research Assistant: E. Woodworth

A critical need in WHAS development is the identification of wildlife sensing and warning technologies that can be used in the airport setting (approximately 6 miles from the airport to an altitude of 3000 ft agl). This project evaluates and prioritizes FAA/WHAS radar/sensor requirements for avoiding collisions of civilian aircraft with birds in the airport vicinity. In addition, this project identifies existing radar installations, radar systems, and other sensors potentially useful in meeting radar/sensor requirements for avoiding collisions of civilian aircraft with wildlife in the airport vicinity.

Development of WHAS Support for Evaluation of Radar Detection/Recognition of Wildlife Hazards at DFW Airport

Faculty Investigator: Ed Herricks

Research Assistant: J. Fisher

This research is conducted in support of a continuing FAA program of research and development directed to airport safety technologies that will decrease aircraft damage and the risk of human fatalities or injuries by reducing bird and wildlife strikes near airports. The longer term gails of that research area include the development of FAA Wildlife Hazard Abatement System (WHAS) elements for airports and national aircraft movement that is specific to FAA needs for civilian aircraft. The WHAS is envisioned as a real-time, or near real-time, warning system, which is risked-based, and is applicable to the site-specific needs of airports as well as the needs of civilian aircraft transiting large areas where wildlife hazards must be abated

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Anti-icing Research Project

Anti-icing Coating Self Cleaning Properties and Wearing Characteristics Study at ORD

Faculty Investigator: Barry Dempsey

New technological advances promise safer aircraft ground operations during winter storm conditions, less-costly environmental compliance with US EPA storm water runoff regulations, and faster reopening of closed runways and taxiways due to winter storms.

Recent advances in pavement texturing processes promise reduced reliance on anti-icing chemicals that pose cost and environmental concerns. A new texture aggregate coating technology is being evaluated at O'Hare to determine its ability to retain anti-icing properties over a series of winter storm events and the durability of these surfaces under controlled traffic and snow removal operations. Previous research includes lab studies and construction of a larger field observation bed at O'Hare in 2003. The current project is a more comprehensive effort to evaluate performance of the test bed under more controlled conditions and more frequent data collection.

The durability, surface friction characteristics, and anti-icing effectiveness of the new textured aggregate coating will be assessed, and compared to alternative anti-icing techniques.

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