Airfield and Highway Pavements 2017: Airfield Pavement Technology and Safety

Prescriptive or recipe-based specification of asphalt surface mixture design, production and construction is normal within the airport industry. However, reports of distress in generally compliant airport asphalt has eroded confidence in this traditional approach. As a result, there is increased interest in performance-based airport asphalt specification. This aims to allow innovation for risk reduction and to make asphalt producers more contractually responsible for the performance of their airport asphalt surfaces. Where performance-indicative test methods are available for the evaluation of airport asphalt performance requirements, performance-based testing is appropriate. However, where no such performance test exists, the traditional prescriptive requirements must be retained. A combination of prescriptive and performance-based specification requirements is appropriate. Future work is expected to focus on developing additional performance-indicative test methods where they do not currently exist.

Currently, several variations of F/HWD equipment exist on the market. The FAA National Airport Pavement Test Facility (NAPTF) Round-Up project provided an opportunity to examine different market available F/HWD equipment. This paper presents a case study of how the uncertainty of backcalculated in-situ moduli can be assessed and incorporated in the FAARFIELD design procedure to determine appropriate pavement thicknesses. The mean values and standard deviations of backcalculated layer moduli were computed and then input into FAARFIELD using Rosenblueth’s procedure to predict the reliability of a 20-year pavement design performance. The research shows that the proposed procedure can be used as an alternative decision-making tool for airport engineers to more realistically predict pavement life using F/HWD data.

Kansas City International Airport (MCI) airfield pavements were constructed during the 1990’s through the early 2000’s and consist primarily of portland cement concrete (PCC). The existing PCC pavements were originally constructed using locally available aggregate materials. Freeze-thaw durability distresses (D-cracking) forming within the surface of the existing PCC pavements have required repair and rehabilitation to prevent continuous generation of foreign object debris (FOD) on a daily basis. Stop-gap maintenance projects from 2008 to 2011 were not enough to extend the functional life of the pavements. In 2011, Runway 1L-19R was milled and overlaid using hot mix asphalt prior to meeting its 20 year design life and in 2012 Taxiway A was identified for the same rehabilitation requirement and completed in 2014. In 2014, the airport identified another major rehabilitation for Runway 1R-19L. A petrographic study to determine the underlying cause(s) of the deterioration in the PCC surface identified material related issues that would need to be addressed within the concrete pavement specification to alleviate the problem. During 2014 timeframe, the Federal Aviation Administration (FAA) released Advisory Circular (AC) 150/5370-10G (Draft) “Standards for Specifying Construction of Airports” with changes contained in the “P-501 Portland Cement Concrete Pavement” specification. Through coordination with the FAA, Kansas City Aviation Department (KCAD), Kansas City Metro Materials Board (KCMMB) and the American Concrete Pavement Association (ACPA), proposed updates and additions to the draft P-501 specification were vetted and accepted for use. This paper will discuss the various changes that were to establish a viable modified airfield PCC specification to produce a durable long lasting concrete mixture and how those changes were determined.

In 2015, 1,507 runway incursions capable of inducing collisions occurred at airports in the United States, so it is obviously very important to identify significant factors underlying such incursions, to predict potential runway incursion occurrences, and to prepare systematic programs for reducing the number of incursions and prevent runway collisions. Presence of a large volume of data, multiple variables, and complex interactions among them pose a significant challenge to resolving this problem. To tackle this challenge, we developed a data-driven prediction model using a component of advanced statistical theory, i.e., a generalized additive model (GAM). GAM can account for flexible modeling of multiple variables over a broad range of modeling distributions. We obtained, parsed, and transformed various predictor variables from many heterogeneous databases to create interpretable datasets for statistical modeling. We demonstrated promising performance of GAM while making systematic investigations into prediction accuracy of runway incursion at United States airports (including all types of commercial, military, and other general data). Results show that GAM can identify critical factors (airport complexity, number of operations, and visibility) in predicting a number of the runway incursions. Performance comparison of two popular GAM smoothers (i.e., cubic regression splines and thin plate regression splines) has demonstrated promising accuracy of both methods. These results imply that statistical predictions developed using GAM will help in better prediction of runway incursion when more data become available in the future.

A research version of the FAA Rigid and Flexible Iterative Elastic Layer Design (FAARFIELD) Program (version 2.0) was developed; it includes top-down cracking along with bottom-up cracking as failure modes to support calculation of more reasonable pavement thicknesses than previous versions. The software employs three-dimensional finite element (3D-FE) response models that take a significant amount of analysis time for computing critical pavement responses. This paper proposes two different approaches for implementing an artificial neural networks (ANN) based prediction model for more efficiently computing critical rigid pavement responses for a given aircraft type: (1) ANN models trained several times for each case with determination of a final ANN model based on the maximum correlation coefficient (R²), and (2) an approach using the average of network outputs after several training activities. A total of 1,000 cases, 500 for mechanical loading and 500 for simultaneous mechanical and thermal loading, were simulated in batch mode by varying different input parameters under a Boeing B767-300ER airplane loading. It was found out that the final ANN models produced similarly accurate critical pavement responses for both approaches so that one approach could not be considered superior to the other. However, the study highlights the importance of training the ANN models several times using a random initialization of weights before arriving at the best-performance model.

Federal Aviation Administration (FAA) built the National Airport Pavement Test Facility (NAPTF) to investigate airfield pavement responses due to complex gear loadings of new generation aircraft (NGA). One of the latest series of full-scale flexible pavement tests conducted with available field data is referred to as the Construction Cycle 5 (CC5) test, part of which is the subject of the analyses presented in this paper. The NAPTF CC5 test database includes individual pavement responses collected using installed sensors, such as multi-depth deflectometer (MDDs) due to the proximity applications of six-wheel dual-tridem gear. Pavement test sections in CC5 built with a dense graded aggregate (DGA) layer met New Jersey highway specifications, over a low strength subgrade that was selected for the analyses. The unbound aggregate base/subbase MDD data have been analyzed to investigate the layer deformation trends of pavement sections. It was seen that initially shakedown was occurring in the P209 base layers while at the same time the DGA subbase layer was deteriorating. Also, the pavement section did not show an apparent increase in residual deformations due to increased traffic. Upholding an FAA priority for research and development in the area of improved methods for airport pavement damage analyses, this paper focuses on investigating the deterioration behavior of granular layers under heavy aircraft loading.

Understanding and avoiding debonding failures is extremely important as the only repair is removal and replacement, which is very costly and time consuming. However, mechanical modeling of interface layer slippage is complex, requiring advance modeling techniques, commonly resulting in the assumption of full bonding in modeling pavement response to loading. A case study is presented analyzing a debonding failure at one of the nation’s busiest international airports. For this high risk situation the newly developed 3D-FAST (3-dimensional Fourier analysis of pavement structures under transient loading) software was used. It was selected because it is capable of analyzing pavement under dynamic loading with visco-elastic material characterization. 3D-FAST is also capable of analyzing pavement responses under fully bonded and partially bonded conditions at layer interfaces. Furthermore, it has been verified using rheological models, as well as has been validated using several case studies. Heavy aircraft dynamic loads under take-off, taxi and landing conditions were simulated and analyzed using 3D-FAST. In the analyses, layers were considered fully bonded, however, as shear stress exceeded the critical value a slippage factor was used to address interface shear transfer characteristics. The results of this case example illustrate the contribution of debonding to airfield pavement service life. It also illustrates the use of a powerful analytical model for estimating airfield and highway pavement responses under dynamic loading available in the public domain.

The safe operation of aircrafts is thought to be the primary goal that has to be achieved by the airport authorities. In order to achieve this goal, particular attention should be paid to one of the most important airport facilities, which are airfield pavements. The major objective of these pavements is to provide adequate load-carrying capacity and good ride quality. For this reason a proper pavement design is essential. The present research study deals with the verification of a runway’s flexible pavement design, using the analytical method of the Federal Aviation Administration (FAA). This approach is considered to be of particular interest for airport authorities internationally, who, at the time being, often face the challenge of combining previously adopted empirical design methods with advanced analytical tools as well. During the verification procedure several critical aspects were raised and detailed analysis concerning the principles of the analytical FAA design procedure was performed.

The Federal Aviation Administration (FAA) has introduced the first major changes to its FAARFIELD standard pavement design software since the last version was released in 2010. These program upgrades accompanied a thorough revision of Advisory Circular (AC) 150/5320-6 covering airport pavement design and evaluation. The newly released program, designated FAARFIELD 1.4, includes significant modifications to both rigid pavement and flexible pavement design models, and adds new features to improve the user experience. This paper summarizes the principal technical changes to structural models, failure models and design logic that affect thickness design using FAARFIELD. It is shown by examples that designs performed using FAARFIELD 1.4 typically are less conservative than in the previous version (FAARFIELD 1.3); however, exceptions to this general statement may be found. This paper also includes discussion of programming changes implemented in the FAARFIELD overlay design procedures that improve both speed and accuracy.

Hartsfield-Jackson Atlanta International Airport (H-JAIA) is the world’s busiest airport, handling approximately 104 million passengers in 2016, serving 70 international and 150 domestic cities. A total of five (5) parallel runways provide landing and takeoff operations, measuring from 9,000 to 12,390 ft in length. One of the runways, 08L-26R, 9,000 feet long was constructed in 1984 and has been in service for 30 years, well beyond its design life. Due to pavement deterioration and other distresses, the City of Atlanta made the decision to reconstruct this runway. 110,000 square yards of concrete pavement was removed and replaced on a 29-day, fast-track schedule. Replaced section constituted of 16 in. of Portland Cement Concrete on 6 inches of cement treated base and 6 in. of soil cement. New section consists of 20 in. of Portland Cement Concrete on 2 in. of asphalt leveling base, after milling the existing 6-in. CTB. Overall scope of the project was to remove and replace the keel section leaving in place the outer slabs and following the existing joint layout. A project cost of $38 million was accomplished with a minimized schedule which in turn translates in to significant savings and reduced impact on aviation operations.

The FAA uses a heavy vehicle simulator-airfield (HVS-A) to conduct full scale performance testing on pavement surface layers at the National Airport Pavement and Materials Research Center at the William J. Hughes Technical Center. The HVS-A applies load to an instrumented test section approximately 36 ft in length. During trafficking pavement data including temperature, strain, pressure, and rut depth are collected. The data are then analyzed to characterize the pavement performance with respect to variables such as pavement temperature, tire pressure, and load. During analysis, rut depth is typically determined at a single location, but sensors are located along the test section. This implicitly assumes that pavement performance is uniform along the length of the test strip. Pavement cross sections collected at 4-in. intervals longitudinally throughout testing were compared to determine the longitudinal variation in rut depth and assess the sensitivity of rut depth to the choice of location at which rutting is determined.

As part of Construction Cycle 8 (CC8) at the National Airport Pavement Test Facility (NAPTF), the Federal Aviation Administration (FAA) is conducting full-scale tests on an unbonded concrete overlay test pavement. In preparation for receiving the Portland cement concrete (PCC) overlay, the relatively thin existing PCC surface layer was damaged by simulated heavy aircraft gear traffic applied by the NAPTF test vehicle. Data obtained from this initial trafficking phase will be used by the FAA to evaluate current ICAO standards for allowable aircraft overloads on rigid pavements. This paper discusses various aspects of the overload testing, including: pavement design, construction, and instrumentation, PCN evaluation, overload test procedures, and traffic test results. The difference in applied coverages to failure was used to evaluate the effect of the overload. In addition, the cause and failure mechanism of observed distresses were discussed. This overload test generated a unique full-scale test data set, which be used by the FAA to evaluate current ICAO standards for allowable aircraft overloads on rigid pavements.

The Federal Aviation Administration (FAA) uses a heavy vehicle simulator-airfield (HVS-A) to conduct full scale accelerated pavement tests (APT) on pavement surface layers at the National Airport Pavement and Materials Research Center (NAPMRC) located at the William J. Hughes Technical Center, Atlantic City, NJ. The objectives of Test Cycle 1 (TC1) included tire pressure effects on P401 hot mix asphalt (HMA) and warm mix asphalt (WMA), effect of binder grade on pavement performance, and comparison of P401 HMA and WMA performance under aircraft wheel loads, and high pavement temperatures. This paper presents the results of full scale APT test on P401 HMA with PG64-22 and PG76-22 under two different tire pressures (210 and 254 psi) at pavement temperature of 120°F measured two inches below HMA surface. A third test area in the same test lane was tested at design condition used in FAARFIELD (HMA modulus–200 ksi) and at 254 psi tire pressure. The Failure criterion was surface rut of one inch. Progression of rut depth and HMA strains are presented in this paper.

Permanent deformation or rutting is one of the failure mechanisms used for designing flexible airfield pavements. Current model used in the FAA design software relates pavement rutting life to vertical strain at the top of subgrade layer. This paper proposes a more fundamental model that can predict the accumulation of permanent deformation in each individual unbound layer. The process for calibrating the proposed model using the accelerated pavement testing data is reviewed in the paper. It was found that vertical strain at the top of unbound layer is a valid option for correlating with permanent deformation. It is believed that the process outlined in this paper can be used to further calibrate the model with extra data sets and eventually lead to a better rutting model for use in mechanistic-empirical airfield pavement designs.

Building upon a solid foundation is one of the longevity keys for airfield pavement performance. For new or replacement airfield pavement on subgrades with good foundational characteristics, the design process is straight forward as defined in FAA Advisory Circular (AC) 150/5320-6F, Airport Pavement Design and Evaluation. However, airfield pavements can be designed to perform on marginal foundations/subgrades. These marginal subgrades often present Engineers and Contractors with certain challenges, which may include the following: optimization the pavement section—design a cost-effective pavement section for the requisite or desired performance life; and constructability—a recognition that though the marginal subgrade may adequately support the pavement, marginal subgrades often need improvement for the interim support of construction equipment and to create a solid working platform. This paper will discuss the subgrade requirements contained in AC 150/5320-6F. The paper will also discuss various subgrade improvement methodologies use in airfield pavement design, including the following: shallow ground treatments for pavements in poor soil conditions, including: cement, lime and fly ash stabilization of subgrade soils; traditional undercut of unsuitable subgrade material; and use of geotextiles and other premanufactured products. Deep ground treatments for pavements in poor soils conditions, including: use of light weight aggregates or flowable fills; preloading/surcharge of subgrade soils to induce consolidation; and rigid inclusions (grout columns) with a load transfer blanket. Finally, the paper will discuss the construction of the aforementioned subgrade improvement methodologies by providing examples of their uses at various airports across the United States.

Cold-applied asphalt mixtures are often used for pavement repair, primarily because of the small quantities involved and/or the unavailability of hot-mixed asphalt. These cold-applied mixtures have poorer rutting resistance than hot-mixed asphalt, because additives, often solvent, are required to provide adequate workability for placement at ambient temperatures. This study evaluated the rutting performance of nine commercial cold-applied asphalt materials using laboratory wheel tracking data and field rutting measurements to determine their suitability for airfield pavements. Products included traditional cutback-cold mixtures as well as water-activated mixtures. Laboratory and field rutting measurements agreed and showed that water-activated materials outperformed cutback materials. No cutback products achieved the target threshold of less than 25 mm of rutting after 100 passes of simulated F-15E aircraft traffic at any cure time; water-activated products met the F-15E rutting criteria at longer cure times (24 to 72 h) but not at the 2-h expedient cure time.

Based upon the past performance of airfield portland cement concrete slabs, the FAA has provided guidance for runways slabs sizes. The guidance recommends for a runway of 150 ft wide, the standard size slabs should be 18.75 ft wide by 18.75 ft or 20 ft long. A test slab was placed and instrumented at double the standard size of 37.5 ft by 37.5 ft. Had the slab been constructed with normal portland cement concrete it would have surely tried to crack into quarters. The test slab was constructed rapidly using a calcium sulfoaluminate cement which has less than 1/3 the shrinkage of portland cement concrete and no cracking has been observed after 1 year. This paper discusses the construction and instrumentation of the test slab. The concrete portion of the test pavement was placed in 47 min using volumetric mixing trucks. The rapid setting properties of the belitic calcium sulfoaluminate (belitic CSA) cement was intentionally retarded to allow for achieving a 400-psi flexural strength in 4 h rather than 550 psi in 1 h if not retarded. Vibrating wire strain gauges were installed prior to placing the concrete layer. Survey markers were installed on the slab in nine locations and elevations were surveyed periodically for 1 year. This paper also discusses the advantages that would be achieved using this high strength, very low shrinkage, and high longevity cement with double the slab size. This belitic CSA concrete pavement would likely have a 75 year or more pavement life, with less joints, less distress due to load and non-load related deterioration, and low maintenance.

Accurate estimation of the elastic modulus of pavement layers is essential when examining the condition and load bearing capacity of an airfield pavement. Pavement surface deflections obtained from heavy weight deflectometer (HWD) has been widely used as a non-destructive testing method to obtain the elastic modulus of the pavement layers. The method involves a backcalculation procedure. The accuracy of the backcalculated modulus depends upon the accuracy of the forward calculation method as well as the iteration technique. This paper presents findings from implementing a number of tools and methodologies developed for HWD test analysis using data from the National Airport Pavement Test Facility’s HWD Round-up study. Selected tools for backcalculation of the test data represent a variety of methodologies from the typical multilayer elastic theory to the method of equivalent thickness and the artificial neural network. The findings presented in this study formed the basis of the recommendation for improving and upgrading BAKFAA to be used more effectively as a comprehensive and state-of-the-practice airfield pavement backcalculation.

Four outdoor flexible pavement test lanes and two indoor test lanes were constructed at the Federal Aviation Administration’s (FAA) National Airport Pavement and Materials Research Center (NAPMRC) to study the effect of high tire pressure on the performance of hot mix asphalt (HMA) and warm mix asphalt (WMA) surface layer. The airport pavement test vehicle (heavy vehicle simulator—Mark VI Airport) was used to perform the full-scale tests. A series of heavy weight deflectometer (HWD) tests and portable seismic pavement analyzer (PSPA) tests were conducted to evaluate the uniformity of the pavement structure within each test lane before the full-scale tests. Deflection basin shape factors (AREA and AUPP) and impact stiffness modulus (ISM) were calculated from the HWD deflection measurement. The seismic moduli of surface layer were determined based on PSPA test results. Both HWD and PSPA test results show that the pavement structures within a test lane are fairly uniform. The PSPA test results indicate seismic modulus of P401 HMA is higher than WMA. The HWD results also show that HMA is stiffer than WMA.

The United States Air Force (USAF) uses PAVER, a computerized pavement management system (PMS), to aid in the planning and cost allocation of airfield pavement maintenance and rehabilitation activities. The ability to model and predict pavement condition accurately is critical to the success of PMS programs. Pavement deterioration prediction techniques are used by PAVER and other pavement management software programs to estimate pavement condition over time. Pavement management literature indicates that the deterioration trend is curvilinear and monotonically decreasing in nature. In practice, the deterioration curve is often assumed to be linear. This research used the consolidated USAF PAVER database to characterize the shape of the deterioration curve for United States Air Force airfield pavements as linear or non-linear. The database contains over 10,000 pavement condition index (PCI) inspections comprising more than 20 years of PCI data gathered on military airfields. Statistical analyses were performed to establish typical deterioration rates of like pavements in the database with similar ages at time of inspection. The results were compared to determine if deterioration rates varied with age, indicating a curvilinear relationship, or were constant with age, indicating a linear relationship.

Environmental considerations are an important aspect of sustainability. Life cycle assessment (LCA) is an approach that can identify and quantify the life cycle environmental impacts of a system such as airfield infrastructure. A literature review found few detailed airfield pavement LCA studies. A framework and guidelines have been developed for the FAA for the use of LCA to evaluate airfield airside features and land-side pavement to support decision-making to improve their environmental sustainability. The guidelines cover pavement, and other airside features, and provide recommendations for all stages of LCA, including goal and scope definition, life cycle inventory development, impact assessment, interpretation, critical review, and reporting. The guidelines follow existing standards, and are similar to those recently developed for highway pavements, but include aspects unique to airfields. It is expected that these guidelines will be updated as experience is gained from airfield LCA case studies.