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The methodology behind the current mechanistic-empirical design of jointed concrete pavements (JCP) is not very sensitive to the properties of the foundation layers of a pavement system. For this r...

Low volume road (LVR) flexible pavements have thin asphalt concrete surfaces and they show considerable sensitivity to the quality (shear strength, moisture sensitivity) of granular base/subbase layers and the subgrade support conditions. The Illinois DOT (IDOT) Mechanistic-Empirical (M-E) flexible pavement design procedures consider seasonal subgrade effects. Mn/ROAD data/information have been used to evaluate/verify the IDOT procedures. For Mn/ROAD subgrade soils, extensive FWD (Falling Weight Deflectometer) and laboratory testing data are available. FWD deflections and estimated subgrade stress ratios (SSR = deviator stress/unconfined compressive strength) were used to study the effect of subgrade type (sand/cohesive) and moisture/temperature effects on pavement structural response and performance. The IDOT "critical period" concept for sub-grade characterization is presented and discussed. The study showed that proper subgrade characterization is very important for adequate design of pavement structure. For the covering abstract see ITRD E118503.

This study aimed to investigate the effect of aircraft ground manoeuvring operations on shear failure potential of airfield asphalt pavements using the multi-axial stress state criteria. A numerical modelling study was conducted to characterise the stress state in the asphalt layer using an advanced three-dimensional (3-D) finite element (FE) model that has been validated in previous studies. The complex tyre–pavement interactions were characterised with non-uniform distributions of tyre–pavement contact stresses at vertical and tangential directions. Different tyre rolling conditions caused by aircraft ground manoeuvring during landing were simulated including free rolling, full-braking, and turning. The effects of takeoff weight and operating speed were also considered in the analysis. The multi-axial stress states in the bulk asphalt material and at the asphalt layer interface were analysed by means of the Mohr–Coulomb failure criteria in a normal-shear stress plane. The results emphasised the importan...

This paper investigates airfield flexible pavement responses under heavy aircraft and high tire pressure loading considering the realistic aircraft tire–pavement interaction. An advanced three-dimensional finite element model was developed; it characterized the hot-mix asphalt layer as a viscoelastic material and used implicit dynamic analysis to predict time-and temperature-dependent pavement responses under various loading conditions. The tire loadings were simulated as moving loads having uniform and nonuniform contact stress distributions. To illustrate the effect of moving load, stationary loading analysis was conducted with the equivalent modulus determined from the middepth pulse time under moving loading. Two temperature profiles were considered in the analysis, as compared with the constant temperature profile using the average temperature. The pavement responses in the asphalt layer (tensile, compressive, and shear strains) under different loading conditions were calculated and analyzed in terms of pavement failure mechanisms. The results emphasized the importance of considering nonuniform contact stresses and moving load in airfield pavement analysis. On the contrary, applying the average temperature profile in summer was a conservative approach for predicting fatigue cracking potential but underestimated rutting or near-surface cracking potential in the airfield pavement. The rut depths in the asphalt layer were predicted by using mechanistic–empirical performance models and compared with the measurements from the full-scale test. The results suggested that specific calibration parameters should be developed to provide accurate prediction of rut depth for airfield pavements.

Six flexible pavements were constructed for construction cycle 7 (CC7) at the Federal Aviation Administration (FAA) National Airport Pavement Test Facility in Atlantic City, New Jersey. Four test sections on the north side measure 200 mm (LFP-4), 250 mm (LFP-3), 300 mm (LFP-2), and 375 mm (LFP-1) that are made of hot mix asphalt (HMA) over an aggregate subbase (thickness varying between 850 and 1,025 mm) resting on a subgrade with a California bearing ratio of 5.5. The fifth test section, LFC-5, is conventional flexible pavement with 125 mm of HMA over aggregate base and subbase, and the LFC-6 structure is the same as LFC-5 except that the crushed stone base layer is replaced with asphalt-stabilized drainable base. The objective of CC7 tests is to develop perpetual pavement design criterion and to validate or refine the fatigue model for HMA in airport pavement thickness design software FAARFIELD. The HMA fatigue model is based on the ratio of dissipated energy change (RDEC). Four fiber optic strain plates were installed to measure transverse and vertical strains at top and transverse strains at bottom within the HMA layer. Full-scale accelerated pavement tests were performed. Traffic test load parameters were six-wheel gear, 245-kN wheel load (gear load 1,470 kN), and 4-kmph speed. Pavement performance was monitored using crack maps, straight edge rut depth, and surface profile measurements. LFC-5 and LFP-4 showed significant fatigue cracks and rutting. LFP-1 and LFP-2 performed well with no signs of cracking. This article presents a discussion on the RDEC fatigue model, pavement thickness design, pavement material characterization test results, pavement instrumentation, accelerated pavement tests under heavy aircraft gear loads, and pavement responses measured using embedded sensors. The test section performance shows that, under loading conditions used in the study, by increasing HMA thickness from 25.4 to 30.5 cm, fatigue cracking was eliminated for the duration of testing (38,000 passes).

Hot mix asphalt (HMA) design for commercial airports in the USA is performed in accordance with the Federal Aviation Administration Advisory Circular 150/5370-10E, ‘Standards for Specifying Construction of Airports’, Item P-401 – Plant Mix Bituminous Pavements (2009). HMA for airports in France is designed in accordance with ‘Bituminous mixtures and surface dressings for airport pavements – Guide to the application of standards’ developed by French Civil Aviation Center (STAC). This paper presents test results from the laboratory characterisation of HMA used in USA and French airport pavements.

Asphalt pavement distresses like surface shoving and slippage cracking can be found at airports in areas where aircraft brake and turn, such as high-speed exits, as a result of the high surface-shear forces. Slippage failure is typically caused by the deterioration of bonding between asphalt layers (delamination), or a lack of shear resistivity within the surface-layer asphalt mix. High pavement temperatures have also been shown to contribute to slippage failures in asphalt concrete pavements. At the intersection of Runway 4 R-22 L and High-Speed Taxiway N (HST-N) at Newark Liberty International Airport (EWR), interlayer delamination was determined to be the cause of shoving and slippage cracking on the pavement surface. In 2012, asphalt strain gauges were installed during a scheduled repaving of the runway and taxiway. This paper details the components of an asphalt strain gauge instrumentation system, and analyzes the strain responses collected from the gauges installed at EWR. By identifying la...

Four flexible pavements were constructed on the north side for Construction Cycle 7 (CC7) at the Federal Aviation Administration’s (FAA) National Airport Pavement Test Facility (NAPTF) to develop flexible perpetual pavement design criterion and validate/refine/modify the fatigue model for asphalt concrete (AC). H-Bar asphalt strain gauges (ASG) were installed in four test sections to measure transversal and longitudinal strain at the bottom of the AC layer. Fiber optic strain gauges (FOSG) were also installed in one of the test sections (8-inch thick asphalt concrete layer). Full-scale tests were performed on these pavement test sections under heavy aircraft gear loads using the National Airport Pavement Test Vehicle (NAPTV). Three traffic speeds, four gear configurations and three wheel loads were used to evaluate the mechanical response of the AC layer. It was found that response of fiber optic strain gauges is comparable to the asphalt strain gauge. The effects of traffic speed, gear configuration, and wheel load on the asphalt concrete strain were investigated. Strain basins were established based on five wander positions.

Accelerated Pavement Test Facilities are not a common type of facility for Architecture and Engineering (A/E) firms to have experience with. The Federal Aviation Administration (FAA) commissioned the design of their APT Facility, the National Airport Pavement and Materials Research Center (NAPMRC) in 2012. Personnel from the FAA’s National Airport Pavement Test Facility near Atlantic City, NJ USA worked with an A/E firm to develop a facility to utilize the FAA’s Heavy Vehicle Simulator for Airfields (HVS-A). The HVS-A commissioned by the FAA and built by Dynatest Corporation is the largest HVS ever constructed by Dynatest. Challenges were encountered in working with designers to build pavements “designed to fail” and to gather information from those pavements as they fail. This included educating the designers to the build, test, fail and repeat concept of accelerated pavement testing. The NAPMRC encompasses both indoor and outdoor test pavements. Electric power required to run the HVS-A needed to be provided throughout the facility to make full use of the six lanes of test pavement being constructed. Data collection and communications networks that could deliver pavement sensor information were designed with flexibility to handle a variety of sensor for the original and future test pavement builds.

Pavement distresses are external indicators of pavement deterioration caused by loading, environmental factors, construction deficiencies, or combinations thereof. The Hot Mix Asphalt (HMA) design for commercial airports in United States of America (USA) is performed as per Federal Aviation Administration (FAA) Advisory Circular AC 150/5370-10G “Standards for Specifying Construction of Airports”, Item P401—Plant Mix Bituminous Pavements (2014). According to FAA study “Operational Life of Airport Pavements”, pavements that meet FAA standards and specification (for design, and construction) generally performed well over their design life. However, recently cases of debonding and slippage have been observed at airports in USA, and other countries. This distress was also observed in the full-scale accelerated pavement tests during flexible pavement construction cycles 1 and 3 at the FAA’s National Airport Pavement Test Facility (NAPTF) and was attributed to tack coat and environmental factors. Asphalt strain gages were installed at the top of milled HMA surface and bottom of HMA overlay at Runway 4R-22L at Newark Liberty International airport (EWR) to study the debonding and slippage distress. Sensor responses were used to detect the onset of debonding and subsequent slippage in the HMA overlay. This paper summarizes the results from two case studies—HMA behavior under full-scale accelerated pavement tests at NAPTF, and the pavement instrumentation project at EWR airport.

Asphalt concrete pavements for commercial airport applications in the USA are constructed according to guidelines in Item P-401, ‘Plant Mix Bituminous Pavements’, Federal Aviation Administration (FAA) Advisory Circular 150/5370-10E. Item P-401 specifies the material characteristics and construction requirements for airport asphalt pavements, but does not currently provide guidance for using the Superpave gyratory compactor (SGC) in the preparation of specimens used in the design of hot mix asphalt (HMA) mixtures. Nearly all state departments of transportation in the USA use the SGC along with the Superpave mix design procedure. Since most HMA mixes are used in roadways, many asphalt contractors no longer maintain expertise and equipment for conducting the Marshall mix design procedure currently used by the FAA. The lack of contractors familiar with the Marshall method may become a significant problem for the FAA in the future. This paper describes a laboratory study of the HMA mix design for airport pavem...

Hot-mix asphalt (HMA) laboratory mix design is intended to determine the proportion of aggregate and binder that, when mixed and compacted under a specified effort, will withstand anticipated loading conditions. Current mix design procedures that use the Superpave® gyratory compactor rely on the engineering properties and volumetrics of the compacted mixture to ensure reliable performance; however, a definitive performance test does not exist. The asphalt pavement analyzer (APA) was evaluated as a tool for assessing HMA mixtures designed to perform under high tire pressure aircraft following FAA specifications. The APA used in this study was specially designed to test simulated high tire pressures of 250 psi, which are becoming more common for aircraft. Thirty-three HMA mixtures were included in the study. Each was designed with the Superpave gyratory compactor, according to preliminary criteria being developed by FAA. The study included some mixtures that contain excessive percentages of natural sand and that do not meet FAA criteria. These mixtures were included to provide relative performance for mixtures expected to exhibit premature rutting. APA testing with the high tire pressure APA resulted in rapid failure of HMA specimens compared with traditional APA testing at lower pressures. Data were analyzed, with a focus on the provision of acceptance recommendations for mixtures to support high tire pressures. A preliminary 10-mm rut depth criterion after 4,000 load cycles is recommended.

Heavy Weight Deflectometer (HWD) tests were regularly conducted at the National Airport Pavement Test Facility (NAPTF) in the two wheel paths and on the pavement test item centerline (non-trafficked area) using the FAA owned and operated KUAB HWD Model 240. The purpose of the tests was to study the effect of traffic tests on the pavement structure. The pavement deflection basin was characterized by measuring deflections at the center of the load plate (D0) and at 30-, 60-, 90-, 120-, and 150-cm offsets (D1, D2, D3, D4, and D5). Pavement surface deflections were measured at three different load levels (53.4, 106.8, and 160.2-kN). A “seating” (or conditioning) drop of 160.2-kN was conducted prior to the measured drops at each test location. The “seating” drop peak deflection data were recorded for all test locations. Analyses of deflection data from the trafficked and non-trafficked areas, including the “seating” drop data, showed that the HWD could be effectively used to evaluate the effect of tra...

Pavement surface deflection basins provide valuable information for the structural evaluation of flexible pavements. Surface deflection measurements are rapid, inexpensive, and nondestructive and are used frequently as an indicator of pavement structural capability and performance potential. In this study, falling weight deflectometer testing results on the conventional flexible pavements (asphalt concrete surface, granular base/subbase) and aggregate-surface/surface-treated test sections in the low-volume road loop at the Minnesota Road Research Project (Mn/ROAD) were analyzed to evaluate the effect of granular material quality on the pavement structural response. Asphalt concrete (AC) modulus and subgrade ``break-point`` modulus were back-calculated using algorithms previously developed at the University of Illinois. The surface deflections were normalized to the same AC modulus and subgrade modulus. The analyses show a limited effect of granular material quality on the pavement deflection response in the case of conventional flexible pavements. Because of higher granular layer stresses, the granular material quality effects on the pavement surface deflection response of surface-treated/aggregate-surface pavements are significant. Increased AC thickness reduces the effect of granular base quality on the pavement deflection response.

Six granular materials were used as base and subbase materials in the flexible pavement test sections for the Minnesota Road Research (Mn/ROAD) project. Crushed/fractured particles are not allowed in aggregate classes CL-1Fsp, CL-1Csp, CL-3sp, and CL-4sp. Ten to 15 percent crushed/fractured particles are required for CL-5sp. One hundred percent crushed/ fractured particles are required for CL-6sp. A comprehensive laboratory testing program was established to determine pertinent engineering properties of the granular materials. Rapid shear tests and repeated-load tests were conducted to determine the shear strength parameters (friction angle and cohesion), resilient modulus, rutting potential, stress history effects on shear strength, and moisture susceptibility. The results from the rapid shear tests and permanent deformation tests show that the rutting potential of a granular material can be characterized from rapid shear test at a confining pressure of 15 psi (103.35 kPa). The rutting parameter A was a function of the shear strength of the granular materials. The shear strength results obtained from rapid shear tests performed at a confining pressure of 15 psi reflect the rutting trends observed in the low-volume road test sections at the Mn/ROAD project. Results from repeated-load tests were used to develop the parameters for K-θ, UT-Austin, and Uzan’s models for evaluating the resilient modulus of granular materials. The axial strain values calculated from the resilient modulus models appear to be in good agreement with the measured axial strain values, except for the very low shear strength material CL-1Csp.

Cognitive radio technology allows the unlicensed users to utilize spectrum by sensing it reliably. The main obstacles in this sensing are fading and shadowing effects which are overcome using cooperative strategies as: amplify-and-relay (AR) and detect-and-relay (DR). In these strategies, noise received at relay is also amplified and relayed along with the signal, which limits their detection performance at the detector or the end user. In this paper, wavelet denoising (WD) is used to denoise the received signal before energy detection as well as before relaying the signal, and therefore, improving the detection performance. A Chi-square approximation using the cumulants is used to compute the probabilities, and an inverse mapping pseudo-code is utilized to calculate the threshold values at a given false alarm rate. The agreement of analytical and simulation results show that AR and DR (with WD) strategies perform better than plain AR and DR (without WD) in terms of detection probability.

The Federal Aviation Administration initiated a runway instrumentation project in 1992 by installing 460 static and dynamic sensors in sixteen slabs in the take-off area of Runway 34R-16L at Denver International Airport. Static sensors such as embedded temperature and moisture gauges and dynamic sensors such as H-bar strain gauges, LVDTs, and position strain gauges were installed. The investigation was focused on measuring pavement response to aircraft loading and environmental conditions. Currently, the data collection system is severely damaged due to water infiltration and is not operational. Data was collected from 1995 through 1999 which included real-time pavement strains and deflections resulting from aircraft traffic. The slab strain and vertical deflection data was analyzed and compared to three-dimensional finite element model predictions. Overall, good agreement between measured and predicted strains and vertical deflections was observed. This information was used for, among other things, validating and calibrating the structural model in FAARFIELD. An important parameter missing in FAARFIELD is the effect of curling on pavement thickness design. Severe curling can cause premature cracking and incur high maintenance costs. The primary objective of this project is to restore the data collection system to at least measure slab deflections and strains. The future emphasis will be on characterizing slab curling under varying environmental conditions and incorporating it into FAARFIELD. Efforts are underway to restore the data collection system. The entire project is expected to be completed by September 2010. Once resurrected, the instrumentation project will provide valuable slab curling data for updating structural models in FAARFIELD. This paper describes in detail the restoration of the Denver International Airport instrumentation project and the ways in which the FAA plans to make use of the collected data.

The Federal Aviation Administration (FAA) National Airport Pavement Test Facility (NAPTF) is located at the William J. Hughes Technical Center, Atlantic City International Airport, New Jersey. The primary objective of the tests performed at the NAPTF is to generate full-scale pavement performance and response data for development and verification of airport pavement design criteria. Four construction cycles (CC1, CC2-OL, CC3, CC5-TS) for testing flexible pavements under heavy aircraft loading have been completed and the fifth one is under way. In both CC1 and CC3, deformation of the aggregate base and aggregate subbase due to densification was noted and contributed to the rutting of the asphalt pavement test sections. This paper will discuss if the Total Void (TV) calculation based upon historic data of CC1 and CC3 can be used to predict the total deformation of the aggregate base and subbase layers in flexible pavements, as well as, to investigate whether the FAA gradation specifications for subbase and base courses are susceptible to deformation based upon the total void calculation.

The National Airport Pavement Test Facility (NAPTF) is a fully enclosed instrumented test track 274.3 m (900 ft) long by 18.3 m (60 ft) wide. In construction cycle three (CC3), four new flexible pavement test items (LFC1 through LFC4) were constructed. The pavement structures were of conventional construction with 127-mm (5-in) asphalt surface, 203-mm (8-in) crushed stone base, varying subbase thickness, and a silty clay subgrade of 3 to 4 CBR. The test items were named LFC1 (thinnest subbase) through LFC4 (thickest subbase). Traffic tests were performed with 6-wheel loading in one wheel track and 4-wheel loading in the other wheel track. Rut depth and profile measurements were made on the asphalt surface during traffic testing. A fixed wander pattern was applied to the traffic during the tests. The wander pattern consisted of 66 repetitions, 33 traveling east and 33 traveling west. Sensors were embedded into the pavement layers to measure the pavement response to applied loads and included asphalt strain gages (ASG), multiple depth deflectometers (MDD), and soil pressure cells (PC). Subgrade pressure cells (2 inches, Kulite) were placed only in test item LFC4 and were placed 10 cm (4 inches) and 43 cm (17 inches) below the subgrade surface. This paper summarizes the subgrade vertical stress measurements under 6-wheel and 4-wheel landing gears at 245 kN (55,000 lb) and 289 kN (65,000 lb) wheel loads at different wander positions. There was no evidence of structural failure in LFC4 at the end of traffic testing.

The National Airport Pavement Test Facility (NAPTF) is located at the FAA William J. Hughes Technical Center, Atlantic City International Airport, New Jersey. It is used to generate full-scale pavement response and performance data for development and verification of airport pavement design criteria. During the Construction Cycle 5 — Test Strip, four flexible pavement test items were subjected to accelerated traffic tests using representative aircraft landing gear configurations. Pavements were constructed over two subgrades with similar california bearing ratio (CBR) (approximately 3) but different soil types (silty clay and clay). Two test items (LFC1-N and LFC1-S) were designed to fail in approximately 100 passes (4-wheel gear and 55,000 lbs wheel load) and the pavement structure consisted of 2.5-inch P401 HMA surface, 8-inch P209 crushed stone base, and 16-inch P154 subbase. The other two test items (LFC2-N and LFC2-S) were designed to fail in approximately 2000 passes and the pavement structure consisted of 2.5-inch P401 HMA surface, 8-inch P209 crushed stone base, and 24-inch P154 subbase. The test items exhibited permanent deformations at the surface (evidenced by rut depths) of over 4 inches and upheaval at the sides of the ruts in excess of 1 inch. This paper presents the results from Heavy Weight Deflectometer (HWD) tests, trafficking tests (rut depth measurements) and posttraffic tests (trenching study). The trenching involved removal of the P-401 AC layer, the P-209 base, and the P-154 subbase layer to reveal the subgrade interface and subsequent subgrade layers below. Tests conducted on the pavement component layers included CBRs, in situ densities and moisture contents. Layer interface profile measurements from trench walls clearly show shear flow in the subgrade, with vertical movement of the subgrade material in the upheaval areas. This information will be used for developing thickness design procedures and load evaluation of airport pavements.

Three rigid airport pavement test items (MRC, MRG, AND MRS) at the Federal Aviation Administration’s (FAA) National Airport Pavement test Facility (NAPTF) with 12-inch thick concrete slabs on different support systems (slab on crushed stone base, slab on grade, and slab on stabilized base) were rubblized with a resonant pavement breaker. All three test items were constructed on CBR 7 clay subgrade. After rubblization, the rubblized concrete was rolled and paved with a 5-inch thick P-401 (hot mix asphalt) overlay. Heavy-weight deflectometer (HWD) tests were performed using the FAA’s HWD equipment on a 10-foot (3.05 m) grid to study the uniformity of the pavement structures. The results showed that the pavement structure within a test item (for all rubblized test items) was fairly uniform. After the completion of uniformity tests, the overlaid pavements were subjected to full-scale accelerated traffic tests under the 4-wheel landing gear configuration (with wander) and 55,000-lbs (25-tonnes) wheel load. Straightedge rut depth measurements and transverse profile measurements were made at regular intervals during the traffic tests. No significant distresses were observed for 5000 passes after which the wheel load was increased to 65,000-lbs (29.5-tonnes) and 6-wheel landing gear was used for testing. The paper summarizes the results from pavement layer characterization tests, pavement structure uniformity from HWD tests and pavement performance during the traffic tests.

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 were measured at various depths in each of the 9 pavement test items at the National Airport Pavement Test Facility (NAPTF) for different combinations of wheel and truck configurations, and load levels. 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 analyses.