Advancing Airfield Pavements

Results are described from asphalt strain gage measurements made during pavement response tests on the flexible pavement test items at the National Airport Pavement Test Facility (NAPTF). Tests were run at speeds of 0.08, 0.15, 0.23, 0.3, 0.6, 1.5, and 2.2 m/sec (0.25, 0.5, 0.75, 1.0, 2.0, 5.0, and 7.33 feet/sec) with dual-wheel configurations at wheel loads of 106.8, 133.5, and 160.2 kN (24,000, 30,000, and 36,000 pounds) and tire pressures of 1378 kPa (200 psi). The strain gages were located at the bottom of the 125-mm- (5-inch)-thick surface asphalt layer of the conventional and stabilized-base test items and additionally at the bottom of the 125-mm- (5-inch)-thick stabilized-base asphalt layer of the stabilized-base test items. Gages were oriented along the travel direction and transverse to the travel direction. Measurements were made at asphalt temperatures of 11.1°C (52°F) and 22.2°C (72°F). Significant permanent deformations were found in the measurements, particularly in the transverse direction. The measured strains were found to vary strongly with temperature and test speed, spanning the range of 300 to 2,000 microstrains. The upper range of these values is much larger than was anticipated, and the strains are 2 to 3 times higher than layered elastic computer program predictions of asphalt strain responses for the structural and load conditions existing during the tests. Longer duration of loading results in reduced asphalt stiffness. However, the longer duration of loading at slow speeds increases the amount of viscous flow and leads to significant increases in the total strain within the asphalt mix as speed decreases.

During the testing period from the summer to the winter of 1999, heavy weight deflectometer (HWD) tests were routinely conducted on the three Portland Cement Concrete (PCC) test items at the Federal Aviation Administration's (FAA) National Airport Pavement Testing Facility (NAPTF). Analysis of the HWD data indicated that the measured deflections at the center of the PCC slabs remained almost the same over time, but at the joints and corners the measurements varied significantly over time. In wintertime, the deflections at the joints and corners were significantly larger than those measured in the summer. In addition, the joint load transfer capability by deflection (LTD), defined by the ratio between the unloaded and loaded side deflections, was lower in winter. Also, the dummy joints received lower values than the doweled joints. A strongly nonlinear relationship between corner deflections and loads was also observed in the wintertime. The analysis indicates that the slab shapes varied all the time but were always curled up; The curling was more significant for slabs resting on a stronger subgrade in wintertime. It has been found from the HWD data that the calculated LTDs can be very different when the HWD loading is applied on both sides of the joints, indicating that LTD may be sensitive to traffic direction. However, the sum of the above two deflections (SD) remains almost the same for both traffic directions. In the NAPTF test items, the SDs varied significantly from the summer to the winter, indicating that it is sensitive to the curling state of the slab. Therefore, although the parameter SD has not been used often in engineering practice, it may be a good indicator of the curling state of a pavement.

Airport pavement thickness design procedures predict a significant amount of interaction between the loads from multiple-wheel and closely spaced multiple-truck landing gear configurations. But the true degree of interaction is not known, and measurements from full-scale tests are required to determine how closely wheels and trucks can be spaced without significant load interaction. As a supplement to traffic tests run to failure at a later date, pavement response tests were performed to study the wheel load interaction effects. Pavement responses (stresses, strains, deflections, etc.) were measured at various depths in each of the nine pavement test items at the National Airport Pavement Test Facility (NAPTF) for different combinations of wheel configurations, truck configurations, and load levels. Moving loads were applied at a speed of 0.15 m/sec (0.5 feet/second). A total of 522 tests were performed on six flexible pavement test items and 108 tests were performed on three rigid pavement test items. This paper describes the response test objectives and test procedures. Some typical pavement responses are presented. Data from the response tests is being analyzed at the FAA Center of Excellence for Airport Technology at the University of Illinois. The raw data is also available from the FAA for independent analysis.

Current mechanistic-based design methods for the design of airport flexible pavements use vertical strain criteria to consider pavement rutting. Variations in subgrade strength, and aircraft traffic are considered based on cumulative damage according to Miner's hypothesis. Cumulative damage is calculated as the ratio of the number of load applications to the number of allowable load applications to failure. The total cumulative damage factor can not exceed one. New design procedures based on Subgrade Stress Ratio (SSR= ratio of deviator stress to unconfined compressive strength) have emerged for better considering subgrade rutting in airport flexible pavements. To consider the effect of traffic mix loading and sequence (stress history) and variations of subgrade strength on the rutting performance of subgrades, analyses of laboratory data and computed subgrade stress distributions were conducted. The permanent deformation laboratory data indicate that if a soil is subjected to an increased or decreased repeated stress sequence, the highest applied stress produces most of the permanent deformation with lower repeated stress level having little contribution on permanent deformation. Analyses of stress distributions based on aircraft type, aircraft wander, pavement thickness, and subgrade strength show that the distribution of high stress levels (above 85% of the allowable SSR) have a significant influence on the rutting performance of airport flexible pavements. This paper presents a subgrade damage approach that supports design procedures that use subgrade stress ratio or subgrade stresses for limiting subgrade rutting. The approach is based on an extensive literature review of current damage concepts included in current mechanistic-based design procedures, soil permanent deformation laboratory data, and airport traffic conditions. The research included in this paper was conducted at the FAA's Center of Excellence for Airport Pavement Research located at the University of Illinois at Urbana-Champaign.

This paper describes an analytical pavement design for a new Taxiway at the Airport on Jersey, one of the Channel Islands, Great Britain. Jersey, being an island, has limited aggregate resources and high harbour dues (import tax) making the importation of materials and specialised plant expensive. Therefore optimising the pavement design and the performance of locally available materials were key to achieving best value within the Project. The Client also wanted to ensure the construction Contractor could adopt and manage the ground condition risks under a construction contract. A comprehensive ground investigation including trial pitting, laboratory testing of soil samples, in situ Dynamic Plate Bearing (DPB) and Dynamic Cone Penetrometer (DCP) tests were performed along the alignment of the new Taxiway, in order to predict the appropriate subgrade stiffness for the design. A design stiffness of 80 MPa was calculated from the DPB measured stiffnesses, using Brown's model to account for pavement confinement and the stress sensitive nature of the material under actual design aircraft loading. A laboratory test programme and site trials were carried out using local aggregates, to assess the mechanical properties of potential cement bound, bituminous and pavement quality concrete materials for use in the lower and upper pavement structure respectively. Since the designs were based on an analytical approach, the materials were specified in terms of performance rather than recipe. End product performance related testing of capping (subgrade improvement) was adopted to monitor and approve the pavement foundation during construction. The development work achieved considerable improvements in the pavement value for money and allowed the utilisation of more sustainable pavement materials with associated environmental benefits.

The main objective of this study is to develop a new thickness design program for rigid airfield pavements in attempts to accommodate the new Boeing 777 airplanes based on the plate theory approach. The differences of the conventional FAA design method and the newly developed LEDFAA design methodology are investigated. The original concept of pass-to-coverage ratio is reevaluated. The prediction models developed by Lee, et al. are utilized for the estimation of critical edge stresses. The concept of cumulative damage factor is used to account for the combined damages of different aircraft types and departures. Structural deterioration relationships are compared and tentative modification alternatives are investigated. An equivalent stress factor and an alternative structural deterioration model are proposed. The proposed approach has been implemented in a user-friendly computer program (TKUAPAV) and a case study is presented for practical trial applications.

In Copenhagen Airport, extensive developments in the field of Semi-Flexible pavement structures have demonstrated high potentials for very heavy loads and static loads in particular. The experience of the Semi-Flexible Pavement (SFP) concept dates back 25 years. However, during the late eighties, a new generation of this special product emerged which brought about further development towards high quality pavements exhibiting very high strength and durability. Today, it is possible to design Semi-Flexible Pavements for type E aircrafts in regard of aprons, stand gates, de-icing stands, start-up pads, taxiways and other heavy loaded areas. More than 300,000m² has been applied in Copenhagen Airport. Of this area, 165,000m² are constructed from 1988 through 2000 utilizing the enhanced second generation technique. The general SFP concept consists of a joint less wearing course composed of an open-graded asphalt concrete filled with a special slurry grout. The underlying bituminous layers are designed for high strength and high load-bearing capacity. The Semi-Flexible wearing course will not develop cracks due to shrinkage, nor will it show any plastic flow. The joint less SFP have provided Copenhagen Airport with a high performing pavement with a minimum of maintenance. The better economy and advantageous technology offered by the SFP have been desirable compared to concrete slab pavements. The new enhanced Heavy-Duty Semi-Flexible Pavement structures are expected to be the desired solution for pavements designed for heavy loads.

Airport managers are often faced with the dilemma of selecting a single rehabilitation project among many candidate projects that are in need of rehabilitation. Another scenario requires that the airport manager select multiple projects to be completed within a specified time period, such as 5 years, given a certain amount of available funding. Often, these decisions must be made with little or no real operational, engineering, or economic justification. This paper describes an approach for the prioritization of rehabilitation projects as part of the development of a Capital Improvement Program (CIP). This approach combines detailed engineering and economic analysis with practical concerns to limit operational issues and safety concerns. The following considerations are addressed in this approach: A) Operational issues; 1) Safety issues, 2) Functional considerations, 3) Airline's operational issues, 4) Importance of facility to overall operations, 5) Pavement classification, and 6) Allowable closures. B) Engineering analysis; 1) Pavement condition index (PCI), 2) Pavement structural capacity, 3) Structural remaining life, 4) Functional remaining life, 5) Aircraft and pavement classification numbers (ACN/PCN), and 6) Pavement load limits. C) Economic analysis; 1) Available funding, 2) Funding sources, and 3) Life cycle cost analysis. The approach presented in this paper has been employed in the development of CIPs for major commercial airports both in the United States and around the world. It has proven to be an effective tool for developing a workable CIP and for maintaining pavements in good condition. Airport managers have been able to apply the results to make the best use of available funds, and in some cases to provide justification for increased funding levels.

The International Falls-Koochiching County Airport in Minnesota is located in one of the most severe climates in the U.S. The average annual air temperature is 0°C (32°F), with temperatures reaching 38°C (100°F) in the summer and exceeding — 40°C (–40°F) in the winter. Low temperature cracking has been a continual problem, with numerous 25mm to 100mm wide transverse cracks along the airport runway. Excessive stresses from the harsh environment have also caused significant secondary longitudinal and transverse cracking in the pavement. To address the demands of this environment, transverse contraction joints had been installed at approximately 15 meter intervals. When it came time to resurface the runway, the Koochiching County Commission and the consulting engineering firm of Short Elliott Hendrickson, Inc. (SEH) decided to use both FAA engineering recommendations and the technology developed by SHRP (the Strategic Highway Research Program) to select an asphalt binder designed for this difficult climate. SEH proposed the newly developed SHRP specifications as an alternate bid for the project. The Federal Aviation Administration (FAA) reviewed and approved the alternate proposal, which provided funding to allow the innovative technology.

The arrival of "New Generation Aircraft" (NGA) landing gear configurations, such as Boeing's 777 Dual-Tridem gears, has generated wide-spread concern about the effects of Multiple Wheel Load Interaction (MWLI) on airport flexible pavement response and performance. In mechanistic-empirical design, pavement responses (stresses, strains and deflections) are used to estimate the development of pavement distress (rutting and asphalt concrete fatigue cracking). Various standardized methods (FAA and ICAO), based on the CBR approach, do not provide a realistic representation of MWLI effects on pavement responses (deflection, stresses and strains). It is believed that more advanced structural models are capable of better representing the response interaction from NGA landing gears, but these have not yet been verified with field data. In 1999 the FAA's National Airport Pavement Test Facility (NAPTF) initiated full-scale testing to establish design criteria for the current trend in NGA gears. Typical flexible airport pavement sections were constructed over 3 different subgrade support levels (Low, Medium and High). Sensor installation includes Multi-Depth Deflectometers (MDDs) and Pressure Cells (PCs) to capture critical pavement responses under Dual, Dual-Tandem or Dual-Tridem gears. This paper presents an analysis of the flexible pavement response data for slow-rolling gears (0.34 mph), gathered at the NAPTF. The data can be used to quantify the degree of MWLI. Responses were obtained for various longitudinal and transverse gear offsets from the specific sensor (MDD and PC) for 3 different wheel load levels (24, 30 and 36 kips). Additional analyses of the NAPTF response test results are currently in progress at the University of Illinois Center Of Excellence for Airport Technology (UofILCOE). One of the primary objectives of this on-going study is to validate the principle of superposition for flexible airport pavements. Chou and Ledbetter conducted a re-analysis of the 1971 US Corps of Engineers Multiple Wheel Heavy Gear Load Tests (MWHGL) where they concluded that multiple wheel gear responses can be reasonably approximated by superposing single wheel responses provided that the single wheel responses were accurately measured or computed. Therefore, an accurate structural model of a single wheel load can be used to determine pavement responses for multiple wheel gears. These results will serve to quantify MWLI, validate/calibrate flexible pavement structural response models, and, hence, aid in the development of better tools for the design/evaluation of airport pavement systems subjected to NGA gear loads.

Currently, there is no universally accepted procedure or approach to performing remaining life analyses for airfield pavements. However, there are several methods that have been employed to estimate the remaining life of airfield pavements, each with advantages and limitations. Airport managers and engineers understand the importance and significance of this concept, and are increasingly interested in seeing reported some measure of remaining life as a part of pavement management and evaluation projects. This paper describes in detail several different approaches that are used to estimate the remaining life of airfield pavements (both bituminous- and concrete-surfaced). These include a design-based or traffic-based approach, a PCI approach, and a mechanistic-empirical analysis approach. The advantages and disadvantages of each approach are discussed. Although it is acknowledged that estimating remaining life is not an exact science, and that the chances of obtaining the same result from different approaches is slight, the information obtained from such analyses is extremely useful as part of an overall evaluation of an airport's pavements, as well as in planning and programming pavement rehabilitation activities.

In Illinois, asphalt mixtures have been used for paving general aviation (GA) airport pavements for nearly 70 years. Originally, these pavements were constructed as an all-weather coating that covered the turf facilities; over time they developed into a designed pavement structure. A comprehensive analysis of the asphalt pavement distress in the early 1990's showed that environmental distresses are very prominent in the GA airport pavements in Illinois, while very little load-related distress was observed. A method to mitigate this problem lies in the improved design of the mix components to provide a durable surface that will resist thermal and block cracking while providing adequate load carrying capacity. The Superpave system could provide the tools necessary to design superior performing asphalt pavements for airport applications, however there has not been a translation of the Superpave system into airport applications, especially in GA airports. The is a need to transition the design method for airfield pavements to one based on the Superpave Gyratory Compactor (SGC). This necessity comes from the widespread implementation of the Superpave system in highway applications. This new mix design and control method would then be termed a "Superpave-Gyratory" design, where the SGC is used in the design and field control of the mixture while maintaining the characteristics of the FAA specified mixture, P-401. This paper describes the new technologies given in Superpave and their relation to GA airport pavements in Illinois. The history of asphalt mixture design is examined, and the current mixture design philosophy that is used to ensure the durability of the asphalt pavement is presented. The paper outlines the issues involved in the transition to Superpave Gyratory asphalt mixture design, including performance graded asphalt binders, design compactive effort (N_des), and quality control/quality assurance procedures. Recommendations are made, based on evaluation of current materials, for determining the appropriate performance graded binder and design compactive effort. An implementation plan is presented for the transition to Superpave-Gyratory mixture design for GA airport pavements. This plan includes a new mixture design philosophy that will govern the selection of aggregates and asphalt binder, volumetric mixture design, and field quality control. This improved mixture design procedure should help lower the cost of asphalt pavement construction by using similar technology to the highway industry in the design and control of asphalt mixtures.

This paper presents a study of wander patterns for three different commercial aircraft (B-777, B-727, and DC-10) operated at Denver International Airport. Environmental and dynamic sensors (including two rows of position sensors) are present in runway 34R-16L. This study analyzed data collected by the position sensors in order to determine the aircraft gear path along the instrumented section. Wander pattern histograms were obtained using an automated system developed to calculate the aircraft gear lateral distribution at any longitudinal location between the two rows of position sensors. Wander patterns obtained from this airport for the B-727 and DC-10 were similar to previously published data. The wander pattern of the B-777 was found to be similar to the DC-10 in terms of mean position and standard deviation. Analysis of the wander patterns relative to the slab geometry shows that B-777 and DC-10 track the longitudinal construction joint, whereas the B-727 traverses down the middle of the slab.

The TAKEOFF computer program of APR Consultants Inc. has been verified with two full scale field problems (Case 1 and Case 2) and one theoretical experience (Case 3). The results show a promising simulation and correlation between the pilot experiences by means of presented Tripreports and the calculated data. From the experiences described below it is possible to make conclusions and recommendations concerning Runway Roughness Criteria. The so called Dynamic Main Gear Load Factor is introduced as one of the criteria to look after. These criteria cover a safe boundary, a warning area where a study is recommended to judge the runway longitudinal profile, a maintenance level and an absolute minimum level where it becomes necessary to close the runway. The presented Runway Roughness Criteria are found to be practical and easy to use.

During January–March 2000, a Network Level Pavement Management Study (PMS) was conducted at Washington Dulles International Airport (IAD), Washington, D.C. during nighttime closure hours. Due to the increased level of air operations at IAD, specific time-critical maintenance efforts had to be employed, such as quick curing Portland cement concrete (PCC) patches and spall repairs. It was important for the IAD engineering staff to have these site-specific time-critical maintenance activities and costs represented in their MicroPAVER database for programming and budgetary purposes. The majority of the runway and taxiway pavements were originally constructed in 1959. All of the existing airfield pavements are PCC and all future construction is expected to be PCC. In order to keep the airfield pavements operational amid intense air traffic schedules, special time-critical maintenance activities had to be employed. This paper will focus on how these time-critical maintenance activities were incorporated into the MicroPAVER database workplan tables and how they were graphically represented in PAVER-Geographic Information System (GIS) for presentation purposes.

The US Army Corps of Engineers CBR method (Method S77-1) for the design of flexible aircraft pavements was calibrated against full-scale trafficking tests on unbound pavements conducted 30 years ago. The method used single layer analysis so had no direct mechanism for crediting bound layers for their superior load spreading characteristics. Bound layers were increasingly used, however, and were typically accounted for within the empirical design by using layer equivalency factors. The layered elastic method was introduced into regular design practice in the mid-1990's, with the release of the computer program LEDFAA by the U.S. Federal Aviation Administration and also the Australian-developed program APSDS (Airport Pavement Structural Design System). These tools facilitated the treatment of bound layers and eliminated the need for the `layer equivalency' concept. Also, because the effects of the actual aircraft wheel configurations and loads of all aircraft in the design mix could now be quickly computed, the concepts of `equivalent single wheel load' and `design aircraft' were no longer needed. In the case of APSDS, its method for dealing with aircraft wander meant that the `pass-to-coverage ratio' was not required. Until recently the subgrade performance relationship used by APSDS was appropriate only for large multiwheeled aircraft on low strength subgrades. The relationship was derived by direct calibration against Corps' tests that involved large aircraft loadings (B747, C5A and B36) on low strength subgrades. Test data for higher strength subgrades and lighter aircraft was very limited, making a broader direct calibration of APSDS problematic. However, S77-1 has been widely used over many years to design pavements for lighter aircraft and for stronger subgrades. The performance of the pavements has generally been satisfactory, and therefore this experience effectively constitutes an extension to the original empirical test data. On this basis, in this study APSDS has been calibrated against S77-1 to produce a layered elastic design tool that is appropriate for all subgrade strengths. This allows the designer to access the full advantages of the layered elastic method, including treatment of wander, to quickly produce designs for complex aircraft mixes and layered structures that are consistent with S77-1.

The experience of The Port Authority of NY & NJ, with the mixes presented, has been a reduction of plastic deformation. Of course, this is predicated on the assumption that these mixes are not placed on existing asphalt pavements that have been softened with jet fuel and/or hydraulic fluids. These mixes can be made stiffer by adopting the SHRP Level I mix design changes recommended. In addition, polymer modified asphalt with a PG of 76-22 and 82-22 adds to the design life of the pavement. To realize the full benefit of these mix designs a genuine QC/ QA plan is required for batching, loading and placing these mixes. The mixes are more susceptible to segregation and can produce an open surface texture, problems which can be alleviated by following good asphalt batching and placing procedures. Some agencies have specified the use of Re-Mix Pavers and/or Materials Transfer Vehicles to minimize the segregation problem.

This paper mainly demonstrates the importance of identifying the most damaging field loading conditions in a pavement, which often require considering the effects of moving wheel loads in laboratory testing and materials characterization. To account for the combined vertical and horizontal pulsing loads imposed on a pavement element under the moving aircraft, a suite of constant stress path tests were performed on a dense graded granular base material. Six resilient modulus models developed from the test results were then used in a finite element program, GT-PAVE, to solve for the critical pavement responses of typical flexible airport pavement sections under the applied wheel loading of the Boeing 777 aircraft. Models obtained from extension stress states resulted in the most damaging field loading conditions since they produced the lowest modulus distributions throughout the granular layer. As a result, the predicted critical pavement responses increased thus causing a reduction in the pavement performance and/or service lives due to the effects of moving wheel loads.

Various rejuvenating materials were applied on different airfield pavements. With correct application rates and in some instances the use of sand, a rejuvenated pavement can generally provide satisfactory levels of skid resistance.

The first ultra-thin whitetopping (UTW) project on a general aviation (GA) airport in the U.S. was constructed in April 2000 at the Savannah-Hardin County Airport (SNH), Tennessee. This paper provides field evaluation details and summarizes the procedure used for determining the UTW thickness. The existing asphalt concrete (AC) surface was aged and had experienced significant fatigue and thermal cracking. Existing surface conditions were assessed using the concepts of pavement condition index (PCI), and the structural capacity was estimated using the falling weight deflectometer (FWD) and the dynamic cone penetrometer (DCP). Current pavement conditions, structural capacity, and subsurface soil conditions were evaluated to determine pavement design parameters and to make design recommendations. A 2-D finite element code (ILLI-SLAB) was used to calculate deflections and stresses in the UTW. The maximum bending stresses were subsequently used in the Portland Cement Association (PCA) fatigue law to determine the allowable number of load repetitions. A 100-mm thick UTW on top of the existing AC surface with a joint spacing of 1020 mm was recommended based on design calculations. Adequate bond between UTW and the existing AC pavement is essential for satisfactory UTW performance. Strain gages were installed near the surface and bottom of the PCC, and on the top of the milled AC surface to determine if the UTW is completely bonded, completely unbonded or partially bonded to the milled AC surface. The summer season data collected in June 2000 indicated a good bond between UTW and milled AC surface. The next round of data collection (winter season) and analysis is planned for February 2001.

Some 40 commercial and military airports are presently using interlocking concrete pavements. As with conventional pavements, technical knowledge and experience with interlocking concrete pavements have developed through testing, trial and error to accepted design methods, specifications, and construction practices, with concrete payers now being used successfully world wide as aircraft pavements. The components of interlocking concrete pavements are presented with a history of design and construction practices. Selected projects benchmark development of accepted practices. A substantial cost savings from this pavement system provides an incentive for agencies, airport owners, and engineers to compare its cost-effectiveness to asphalt and concrete. As future steps in development, the US Federal Aviation Administration may consider full-scale testing at the National Airport Pavement Test Facility to more accurately quantify the structural contribution of concrete pavers to airfield pavements. In addition, it may consider developing an Advisory Circular to synthesize the literature and experience by other federal agencies, airport authorities, and airfield pavement engineers.

Nondestructive tests (NDT) were performed at various times on flexible pavement test items at the Federal Aviation Administration's (FAA) National Airport Pavement Test Facility (NAPTF) located at the William J. Hughes Technical Center, Atlantic City International Airport, New Jersey. The NDTs were performed with both falling weight deflectometer (FWD) and heavy falling weight deflectometer(HWD) equipment to document the uniformity of pavement and subgrade construction, as well as to acquire data on pavement response over time and increasing numbers of full-scale load repetitions. Since the pavements and subgrades were constructed to exacting standards of uniformity and the NDTs were performed on pavements of known and uniform thicknesses, this enabled the backcalculated subgrade moduli under flexible pavements to be correlated against conventional test results. The FAA's new backcalculation software, FAABACKCAL, was used to process the NAPTF NDT data. This paper discusses the evaluation of the NDT and other test data with respect to: 1) Description of the FAA's new backcalculation software, FAABACKCAL, 2) Linearity in pavement response and backcalculated subgrade modulus with applied HWD force, 3) Comparison of the stiffnesses of conventional and stabilized-base pavements on the same subgrade and like pavements on different subgrades, 4) Relationship between in situ California Bearing Ratio (CBR) and backcalculated subgrade modulus for low-, medium-, and high-strength subgrade, and 5) The effect of the stiffness of underlying layers on backcalculated subgrade modulus.

Extensive works have been conducted to develop a nondestructive structural evaluation system for airport pavements with Falling Weight Deflectometer (FWD). As a result, the system for both asphalt pavements and concrete pavements was built and has been utilized as a practical measure in Japan.

Within the FAA Integrated Airport System airfield infrastructure and the U.S. Defense Department airfield inventory, there are more than 100 million square yards of heavy load concrete airfield pavements greater than 13 inches in thickness and more than 35 years old. These pavements will need major rehabilitation within the next 10 years. Traditionally, concrete pavement restoration (CPR) procedures (including techniques such as sub-sealing, full-depth patching, partial-depth patching, load transfer reconstruction, diamond grinding, and joint sealing) have been employed to maintain these pavements in a fair to good condition. These CPR procedures are becoming less effective today as the present pavement condition ratings are reaching a critical point where major rehabilitation is required. Rubblizing concrete pavement is becoming the paramount concrete pavement rehabilitating technique adopted by state highway agencies for heavy load highway pavements. From 1994 to 1998, states in the northeast, south and Midwest United States have rubblized concrete pavement and placed Hot Mix Asphalt (HMA) overlay over more than 20 million square yards of highways. An additional 25 million square yards of pavement were rubblized in 1999–2000 and overlaid with HMA (primarily Superpave). Most experience with the proven rubblization technique has been with concrete pavements of thickness between 7–10 inches. However, new concepts were employed to successfully demonstrate the rubblization technique on 14 inches of heavy load concrete airfield pavement at the Memphis International Airport, in July 1999. Information acquired during the demonstration at Memphis provided criteria to develop prototype resonant breaker equipment for heavy load concrete airfield pavement (in the 16 inches range). This paper presents the concepts associated with design, construction, and performance of hot mix asphalt (HMA) overlays placed on rubblized heavy load concrete pavements. Emphasis is placed on: 1) Side drains to insure free drainage; 2) Description of rubblization equipment and construction procedures; and 3) Design considerations for rubblization of concrete pavements.

Grant County International Airport in Moses Lake, Washington was restricted from using Runway 4/22 due to the poor condition of the concrete pavement, that was constructed in 1942. The concrete pavement was rubblized in place to provide a base course for an asphalt concrete pavement. A portion of the concrete pavement section was removed and replaced to address a conflict with the Federal Aviation Administration required line of sight criteria.

With air traffic increasing at international airports worldwide there is a corresponding demand to increase the efficiency and capacity of airport infrastructure. The key objective of any airport however, is to maximize the safety of the travelling public regardless of any future expansion objectives. The Greater Toronto Airports Authority (GTAA) over the past 6 years has embarked on an extremely ambitious plan to increase the capacity of Lester B. Pearson International Airport (LBPIA) by almost 100%. In undertaking this development the GTAA has developed extensive methodologies to manage construction contracts while mitigating potential impact to operational throughput and public safety. Proper identification, coordination and implementation of an operational plan is required in order to achieve success when dealing with simultaneous construction of multiple projects. In a constantly changing airport environment a plan must be developed that has the required degree of flexibility to account for unexpected changes to operational requirements as well as the unforeseeable potential for abnormal weather and labor disputes. To mitigate the impact of changing circumstances the GTAA has developed procedures which insure effective and immediate communication of the change to all parties affected and rapid resolution with respect to additional measures for security and safety that may be required. Operational plans need to be developed which focus on the specific problems associated with airside work such as security escort requirements, night work, short closures, segmenting of work, provision of barricades and fencing, maintaining operational surfaces free of FOD, maintaining operational surface zoning requirements and protecting workers from jet blast. At the same time an operational plan must also consider the effect of closures arranged for other projects occurring simultaneously while still satisfying the operational need for capacity and flow. From a contract management position, adequate measures need to be employed to ensure the contractor faces liquidated damages if violations of the operational plan result in operational delays or increased risk to public safety. Many airports across North America are in the midst of moderate to major airside expansion projects. At the GTAA we have developed procedures for dealing with construction while maintaining airport operations. These methods have been developed through careful planning as well as through lessons learned when methods developed have unfavorable or unexpected results. Through this presentation the GTAA hopes to increase awareness of the methods and procedures which have been used with success at LBPIA to aid project managers and airport operational staff who may be embarking on similar development programs. In a busy airport environment it is critical that a well thought out operational plan be developed well in advance, communicated to all parties and implemented. Through careful operational planning and a clear definition of all parties roles and responsibilities with respect to `the plan', safety and security can be achieved at the busiest of airports even during major redevelopment.

A demonstration project involving researchers at the University of Illinois at Urbana-Champaign and Illinois Division of Aeronautics IDOA was developed to investigate innovative construction techniques and materials for the rehabilitation of general aviation airports (GA) to prevent reflective cracking. These techniques involved: pavement rubblization using coarse, medium, and fine breaking patterns; the saw and seal technique; polymer-modified mixtures; and the use of an interlayer stress absorbing composite (ISAC). Besides providing full-scale field trials for the aforementioned rehabilitation techniques, a second objective of the project was to collect response and performance data that will be used in the development of mechanistic overlay design procedures. To this end, a variety of pavement sensors were installed to measure the response of the pavement to applied loads and to environmental changes. This paper presents a summary of the experimental sections, materials, construction, instrumentation and preliminary measurements from the Rantoul National Aviation Center (RNAC) demonstration project. Using the Superpave Indirect Tensile Tester (IDT), the polymer-modified mixture used in the project was predicted to significantly outperform the conventional mixture with respect to thermal cracking resistance in the rubblized sections. Preliminary analyses suggest that accurate measures of temperature, joint deflection, and strain are being collected by RNAC test pavement sensors, and typical sensor measurements are presented. The information presented in this paper is intended to benefit both the practitioner and researcher, by presenting innovative methods, materials, and tools for the design of asphalt overlays to resist reflective cracking.

Serving more than 45 flights a day, apron Taxilane Lima-Alpha is a vital link to 12 gates between Terminals 2 and 3 at JFK International Airport. The asphalt concrete portions of the taxilane were severely distressed, including block cracking and fatigue cracking. Portland cement concrete portions of the surrounding apron consisted of shattered and severely spalled slabs. Debris caused by pavement failure of both materials was routinely found and removed from the area. Between November 16 and December 22, 1998, Phase I of the reconstruction of the taxilane was completed in 20 working nights. The amount of portland cement concrete pavement constructed was 3,047 m² (3,644 sy). After considering several options, the final decision was to use high early strength concrete for the taxilane pavement. In cooperation with the tenant airline, the project was uniquely phased for rapid reconstruction. A complete cycle of demolition, subgrade and base preparation, dowel bar installation, portland cement concrete placement, initial cure, and transition pavement were completed each night. The construction occurred between daily periods of major flight operations. The coordination between construction and airline operations, along with the use of high-performance concrete, allowed a critical portion of apron Taxilane Lima-Alpha to be reconstructed with minimal impact on airline operations. After 2 years, the pavement continues to perform without any sign of distress.

Pavement replacement at any airport is a major undertaking. The more work that is done, the greater the demand on the existing system. When the work to be done is a complete replacement of the existing apron pavement around the operating terminals of one of the busiest airports in the world, the headaches multiply exponentially! Coordination, cooperation, and flexibility become key to a successful project. This paper will take a look at apron replacement at O'Hare International Airport during the 1999 and 2000 construction seasons. It will focus on discussions of the original design for apron replacement, the efforts to start construction, safety considerations, and the actual work undertaken around Concourse G. It will conclude with a look at replacement work started at the end of the 2000 season along the apron inlet lines in the middle of the pavement and recommendations for future coordination to continue the work begun.

The volume of air traffic continues to grow, resulting in an increasing number of aircraft movements. To cope with such growth it is necessary to make optimal use of all available pavements. In order to do this, a planned approach to the maintenance of all pavements is required. This involves a thorough review of the performance of pavements in course of time. Carrying out the right maintenance at the right time will reduce the overall need for maintenance and make any work done more cost effective. To predict maintenance at network level, performance models are required. Performance models in this study were based on data retrieved from the Dutch civil and military airfields. The three models, which have been analyzed, are roughness, surface friction and visual condition. Roughness is only measured when there is an operational reason for checking such. It has as yet proven difficult to produce models for this characteristic. The wetted surface friction is measured annually and an abundance of data is available although limited in their use due to the different pieces of equipment in use as well as differences in set-up. The surface friction is only relevant for Touch-Down areas at busy civil airfields with a high volume of heavy aircraft. A decrease in friction level is derived for these areas related to the number of landings. The visual condition is monitored periodically for most airfields. Performance models based on the Pavement Condition Index have been derived for asphalt as well as concrete surfaced airfield pavements.

A detailed 3D Finite Element (3DFE) Model is developed to examine the nature and magnitude of stresses that develop around dowel bars due to both traffic and thermal loads. The model reveals that under the standard axle load, tensile stresses of magnitudes sufficient to initiate concrete failure may develop in the concrete surrounding the loaded dowels. Compared to the effect of traffic loading, slab distortion due to positive or negative thermal gradient, at no load, does not lead to the development of large stresses around dowels. The effect of the thermal gradient on the stresses induced in concrete around dowel bars was also studied.