Airfield Pavement Design Research Articles

Cold Recycling Technology for Airfield Pavement Rehabilitation Practices

Cold recycling technology has recently achieved significant success in highway maintenance and construction applications. In this study, the potential of incorporating emulsion-based cold recycled layers into airfield pavement design is explored. The permanent deformation resistance of cold recycled (CR) mixtures was characterized under various stress states and loading conditions to provide a realistic representation of the loads induced by aircraft tires on typical airfield pavement structures. Finite element modeling simulations of several airfield structures incorporating a CR layer were leveraged to derive the triaxial stress states induced by the moving load of various aircraft tires on the CR layer. A mix design was developed using a common approach. The simulated stress states were then projected and applied to the developed mix design in triaxial compression repeated load permanent deformation experiments. The influence of time and temperature dependence of the material on permanent deformation was also studied. The experiment highlighted the sensitivity of the mixture to tire pressure, surface layer thickness, vehicle speed, and temperature. The results indicate that the selection of cold recycling applications for airfield pavement should account for the unique site-specific conditions and the structural composition of the pavement where the CR layer will be incorporated. The evident viscoplastic characteristics in CR mixtures in the triaxial repeated load experiments highlighted the importance of considering them in the structural design of the CR layer.

Airfield pavement resiliency assessment against extreme dynamic events by explicit axisymmetric finite element models

Infrastructure resiliency has become an essential element in ensuring community recovery after unexpected events. In airfield pavement, resilience can be achieved through an improved design approach by understanding the fundamental elements of damage mitigation and thus allowing rapid recovery. The objective of this study was to numerically evaluate easy-to-implement alternatives for mitigating damage in rigid airfield layered pavement systems when subjected to dynamic events such as blasts or high-velocity impacts. This was accomplished by developing an efficient axisymmetric explicit finite element model, which served as an analytical tool for the study. The model was developed in LS-DYNA and the methodology consisted of a comprehensive parametric analysis. The results showed that the concrete pavement layer parameters—mass density and compressive strength—have the most significant effect on the damage to the pavement when subjected to extreme dynamic events. The material parameters for the pavement layers were optimized to minimize the damage, caused by dynamic loads, achieving more than 70% damage mitigation. Furthermore, adding a granular base layer to the rigid airfield pavement design reduces the concrete pavement layer damage by almost 40%. An asphalt concrete overlay reduces the concrete pavement layer damage by about 55%. Moreover, adding an asphalt concrete overlay to the optimized rigid airfield pavement design reduces the damage by 10%. In contrast, adding a granular base layer to the optimized rigid airfield pavement design is ineffective.

Preliminary evaluation of the ACR-PCR system for reporting the bearing capacity of flexible airfield pavements

Assessing and reporting the bearing capacity of airfield pavements have always been significant tasks in airport engineering, since they support the decision making procedure, which is a core element of Airport Pavement Management Systems (APMS). The official reporting system utilized worldwide during the last four decades is the Aircraft Classification Number – Pavement Classification Number (ACN-PCN) system. However, recently an updated system has been introduced, aiming to overcome the defects of the ACN-PCN system that have been observed during its implementation. This system, referred as the Aircraft Classification Rating – Pavement Classification Rating (ACR-PCR), aims to incorporate the latest advances in airfield pavement design and evaluation and is expected to be fully applicable about 2024. Since this is a transfer period, the current investigation aims to identify any critical aspects arising from the application of the updated system, based on recent Federal Aviation Administration (FAA) airfield pavement evaluation techniques. On this basis, the transferability between the two system is examined, providing useful commentary and remarks for airport authorities, who would like to implement the ACR-PCR method to its full extent. The analysis shows that the transferability between the two systems seems not to be feasible and the implementation of the updated ACR-PCR may present several issues, such as the modification of the existing reported bearing capacity.

A mechanistic perspective for airfield pavements evaluation focusing on the asphalt layers’ behaviour

ABSTRACT The preservation of structurally sound airfield pavements is critical for the capacity of the air transportation network. As a standard practice, the design and evaluation of flexible airfield pavements are mainly based on the Multi-Layered Elastic Theory (MLET) in accordance with the Federal Aviation Administration (FAA) principles. However, Asphalt Concrete (AC) materials perform as temperature- and loading rate-dependent materials because of the viscous nature of asphalt binders. This in conjunction with the real moving loading conditions imply that the pavement analysis and evaluation outcome might be significantly different from what is assessed according to MLET. The research is concentrated on adopting a mechanistic framework for the assessment of airfield pavements considering both assumptions for AC material characterisation (i.e. elastic and viscoelastic). AC viscoelasticity is accounted as per the MEPDG suggestion for in-service pavements and an energy-based damage evaluation is performed based on the FAA recommendations. A thorough field experiment along an airfield runway pavement, including sample coring and non-destructive data, is organised to meet the research aim. Results demonstrate an applicable approach that seems to be conservative when AC is considered as a viscoelastic material. This is expected to profoundly affect the decision-making when managing airfield pavement infrastructure.

Implications of incorporating geosynthetics in airfield pavements

A majority of literature indicates that geosynthetic inclusion in flexible pavement bases, subjected to highway loading, improves performance by reducing rutting or vertical pressure on weak subgrade layers. Instances where geosynthetics were less successful in highway pavements included strong subgrade soils and/or thick pavement layers. Thus, understanding the improvement that can be expected from geosynthetic inclusion in airfield pavements, that are often more substantial than highway pavements, requires an evaluation of existing airfield pavement assets and design methodology. To achieve this objective, a number of tasks were performed: (1) review of in-service pavement thickness and subgrade strength to quantify military airfield pavement characteristics, (2) review of current Department of Defense (DOD) design methodologies to determine if geosynthetic inclusion can be adequately characterized in existing design procedures for new airfields, (3) evaluation to determine if (and in what conditions) an expected performance improvement is financially viable, and (4) implementation in military airfields in manners other than new construction. Results indicated that airfield pavements were generally thicker and stronger than highway pavements, and that in-service airfield pavements exceeded the pavement characteristics where geosynthetics have been identified to provide a meaningful performance improvement. A review of the existing DOD design methodology indicated that any improvement from geosynthetic inclusion in thicker pavements was hidden within the variability of the data used to formulate the existing design methodology. An initial cost evaluation suggested that design life extension (if any) could be the preferred means of quantifying geosynthetic improvement and that the reduction in aggregate thickness attributed to geosynthetic inclusion did not seem to provide an initial cost savings for military airfields. Geosynthetic inclusion in airfield damage repair or as a crack mitigation technique may be more beneficial than aggregate base reinforcement in new construction.

Fuzzy Knowledge Based System for Suitability of Soils in Airfield Applications

Proper design of roads and airfield pavements requires an in-depth soil properties evaluation to determine suitability of soil. Soft computing is used to model soil classification system's dynamic behaviour and its properties. Soft computing is based on methods of machine learning, fuzzy logic and artificial neural networks, expert systems, genetic algorithms. Fuzzy system is a strong method for mimicking human thought and solves question of confusion. This paper proposes a new decision-making approach for soil suitability in airfield applications without a need to perform any manual works like use of tables or chart. A fuzzy knowledge - based approach is built to rate soil suitability in qualitative terms for airfield application. The proposed model describes a new technique by defining fuzzy descriptors using triangular functions considering the index properties of soils as input parameters and fuzzy rules are generated using fuzzy operators to classify soil and rate its suitability for airfield applications. The data obtained from the results of the laboratory test are validated with the results of the fuzzy knowledge-based system indicating the applicability of the Fuzzy model created. The approach developed in this work is more skilled to other prevailing optimization models. Due to its system’s flexibility, it can be suitably customized and applied to laboratory test data available, thus delivering a wide range for any geotechnical engineer. Doi: 10.28991/cej-2021-03091643 Full Text: PDF

Decision Support in Selecting Airfield Pavement Design Alternatives Using Life Cycle Assessment: Case Study of Nashville Airport

The Federal Aviation Administration (FAA) has taken measures to improve safety, reduce costs, increase resilience, and improve the sustainability of the United States (U.S.) airfield infrastructure by using a life-cycle cost analysis methodology to increase the efficient use of economic resources needed for expanding and preserving the airfield system. However, a life-cycle assessment (LCA) approach for evaluating the environmental impacts of decisions regarding airfield infrastructure has yet to be fully developed and applied. The objective of this study is to demonstrate the use of the airfield LCA framework that was developed for the FAA and can be used by U.S. airports. The comparison of alternative pavement designs at Nashville International Airport (BNA) is presented. The scope of the study was from cradle to laid; materials, materials transportation, and construction stages of the pavement life cycle are considered, and the maintenance, use and end of life stages are not considered. Primary data were acquired from BNA and secondary data were used in situations of unavailability of primary data. The case study showed that performing LCA provides opportunities for airports to consider energy use and environment-related impacts in the decision-making process.

Havaalanı Kaplamalarını Asfalt ve Beton ile Yeniden Kaplamanın Karşılaştırmalı Dizayn ve Ekonomik Analizi

Overlays for airfield pavements are one of the cost effective and efficient pavement rehabilitation options. In this study, the Federal Aviation Administration’s state-of-the-art mechanistic-empirical overlay design methodology (FAARFIELD) was explained, design examples using FAARFIELD version 1.42. for both concrete and asphalt overlays were presented, and the results of these examples were compared. For the overlay design scenarios on existing asphalt surface layers, it was found that, overlay thickness decreases, as existing asphalt surface layer thickness increases, and calculated concrete overlay thicknesses were higher than calculated asphalt overlay thicknesses for the same existing asphalt surface layer thicknesses. On the other hand, for the overlay design scenarios on existing concrete surface layers, both asphalt and concrete overlay thicknesses were found to be very similar to each other. Based on FAARFIELD-calculated overlay thicknesses, an economic analysis was carried out to find out the most economic overlay design options for a variety of design scenarios. Although for some overlay cases concrete overlay design thicknesses were found to be higher than asphalt overlay design thickness, cost of concrete overlays was found to be less than that of asphalt overlays. This is because unit cost for concrete materials is less than that for asphalt materials. Incorporating a state-of-the-art mechanistic-empirical overlay design for airfield overlay pavements as well as considering local cost in the economic analysis to determine which type of overlay would be a more suitable option for a variety of pavement design cases would be very beneficial to Turkish airfield pavement design practices.

Refined assessment of strength of concrete pavement probabilistic method

The object of research is the method of calculating the strength of cement concrete airfield pavement. According to the current regulatory documents, the calculation of the strength of the coating is carried out according to the first limit state, taking into account the internal forces arising in the slab from the impact of the wheel load and temperature. The repeated impact of loads from the wheels of the main supports of various types of air is replaced by the influence of the main support of the heaviest aircraft, causing the greatest bending moment in the design section of the plate. However, the calculations do not take into account the stochastic nature of such factors as the take-off weight of aircraft, the plate thickness, the bed ratio of the elastic foundation, the probability of the combined effect of operating loads from the main bearing wheels and temperature in the calculated section of the plate, as well as the probability distribution of loads from the aircraft spectrum across the width of the airfield elements. The article proposes a method for taking into account the probabilistic-statistical variability of operating loads, physical and mechanical properties of materials and the geometric characteristics of the plate, recommended when developing a new regulatory framework for the design of rigid airfield pavements. The method of statistical linearization of random functions of several random arguments was chosen as the research method. Using the mathematical apparatus of the theory of random functions, the statistical coefficient of the working conditions of the plate is analytically determined, and a numerical analysis of the obtained analytical solution is carried out. It has been established that with the same unfavorable combination of variability of basic arguments, the calculated absolute value of the statistical coefficient of the working conditions of the slab is more influenced by the coefficient of variation of the slab thickness than the coefficient of variation of the strength of cement concrete in bending. The condition for calculating the required thickness of the hard airfield slab of monolithic cement concrete is determined.

State of the practice in pavement structural design/analysis codes relevant to airfield pavement design

An airfield pavement structure is designed to support aircraft live loads for a specified pavement design life. Computer codes are available to assist the engineer in designing an airfield pavement structure. Pavement structural design is generally a function of five criteria: the pavement structural configuration, materials, the applied loading, ambient conditions, and how pavement failure is defined. The two typical types of pavement structures, rigid and flexible, provide load support in fundamentally different ways and develop different stress distributions at the pavement – base interface.Airfield pavement structural design is unique due to the large concentrated dynamic loads that a pavement structure endures to support aircraft movements. Aircraft live loads that accompany aircraft movements are characterized in terms of the load magnitude, load area (tire-pavement contact surface), aircraft speed, movement frequency, landing gear configuration, and wheel coverage.The typical methods used for pavement structural design can be categorized into three approaches: empirical methods, analytical (closed-form) solutions, and numerical (finite element analysis) approaches. This article examines computational approaches used for airfield pavement structural design to summarize the state-of-the-practice and to identify opportunities for future advancements. United States and non-U.S. airfield pavement structural codes are reviewed in this article considering their computational methodology and intrinsic qualities.

Turning Maneuver Effect on Near-Surface Airfield Pavement Responses

Airport pavement structures experience heavy aircraft tire loading through a localized contact area. Distributed three-dimensionally and non-uniformly, tire-pavement contact stresses directly influence the near-surface behavior of flexible airfield pavements. The resulting high shear stress levels induced by aircraft tire loading may lead to instability through shoving or slippage cracking. As the tire turns during taxiing, the risk of near-surface damage is exacerbated. In this study, numerical modeling of an inverted pavement system and a conventional flexible pavement structure loaded with a single tire from the A-380 landing gear was developed. The analysis matrix included two tire-inflation pressures, two speeds, and rolling conditions that varied from free-rolling to two turning maneuvers. Two analysis approaches were performed: 1) use of traditional critical point strains, and 2) domain analysis, which characterizes bulk pavement behavior using multiaxial stresses and strains. The critical strains, which are used as inputs for airfield pavement design, changed negligibly under varying tire turning conditions despite the asymmetric contact stress distribution. On the other hand, domain analysis not only captured the asymmetric pavement behavior, but also identified that altering the tire movement from a free-rolling condition to turning could induce a significant increase in the potential damage.

Neural Network–Based Multiple-Slab Response Models for Top-Down Cracking Mode in Airfield Pavement Design

AbstractThe Federal Aviation Administration (FAA) has recognized for some time that its current rigid pavement design model, involving a single slab loaded at one edge by a single aircraft gear, is...

COMPUTER TECHNOLOGIES FOR CONCRETE AIRFIELD PAVEMENT DESIGN

The purpose of the research is to develop formulas, expressions and a computer program for concrete airfield pavement design under the impact of all Airbus 380 main landing gears taking into consideration the design factor of tensile stresses at the top and bottom of a concrete slab. The top-down cracking in concrete slabs has not been directly simulated in structural analysis models used for one- and two-layer concrete airfield pavement design by the Ukrainian Standard. Empirical formulas for the calculation of top tensile stress and the coverages to failure using the criterion of top tensile stress are obtained. Computer program “Aerodrom 380” has been developed for the design of concrete airfield pavement thickness. It provides the required thickness of a concrete slab needed to support an Airbus 380 over a particular subgrade and uses the bottom and top tensile stresses as design factors. “Aerodrom 380” contains a fatigue function for determining the number of coverages to failure permissible for a concrete slab before it has top-bottom and bottom-up cracks. The results obtained with this program are compared to other solutions using the Ukrainian Standard SNiP 2.05.08–85, “LIRA-SAPR”, software and the FAARFIELD computer program. The anticipated life of a concrete airfield pavement calculated using computer program “Aerodrom 380” is about 70% of the FAARFIELD pavement life.

Development of rapid three-dimensional finite-element based rigid airfield pavement foundation response and moduli prediction models

Abstract Designing pavement foundation for rigid airfield pavements and understanding the contribution of pavement foundation elements to overall pavement performance and pavement failure have been challenges for the rigid airfield pavement design community. While many models have been developed to best simulate pavement foundation behavior for rigid airfield pavements, many of them have focused only on the failure of Portland Cement Concrete (PCC) layer and did not sufficiently consider the contribution of pavement foundation to the failure. The Federal Aviation Administration’s (FAA’s) pavement design software, FAARFIELD, considers the maximum horizontal stress at the bottom edge of the concrete slab for bottom-up cracking failure of a PCC layer, but does not consider the critical responses for failure of subbase and subgrade layers in rigid pavement design. It is clear that incorporating critical pavement foundation responses into pavement design procedures is of great interest. The primary objective of this paper is to investigate the feasibility of developing rapid three-dimensional finite-element (3D-FE)-based pavement foundation response and moduli prediction models for design of both new and rehabilitated rigid airfield pavement structures. The three case studies investigated in the development of the models include: (1) rigid pavement foundation response prediction models for different wide body aircraft loading conditions, (2) rigid pavement foundation response prediction models for Heavy/Falling Weight Deflectometer (H/FWD) loading conditions, and (3) single rigid-pavement moduli prediction model. The development procedure and results based on rapid 3D-FE based prediction models are presented in this paper along with other significant findings and recommendations for employing the developed models in the structural design and evaluation of rigid airfield pavement systems. It was found that the developed models were able to successfully predict 3D-FE pavement solutions for all cases investigated in this study, could account for rigid pavement foundation related distresses, and could be potentially integrated into FAARFIELD as surrogate forward response prediction models in the future.

Analysis of stiffness and fatigue resistance of cold recycled asphalt mixtures manufactured with foamed bitumen for their application to airfield pavement design

Cold recycled bound materials (CRBMs) provide an economic and environmental advantage for pavements since they decrease energy and raw material consumption. However, design methods for airfield pavements do not include key CRBM properties. In this paper an empirical-mechanistic method is used to study airfield pavement design with CRBM in order to develop design guidance. The aim of the paper is to obtain the inputs related to material properties needed for use in this method. For this purpose, CRBM containing reclaimed asphalt, with fly ash, cement and foamed bitumen as stabilising agents, was characterised. The methodology included indirect tensile stiffness modulus (ITSM) and indirect tensile fatigue tests (ITFT) in strain control mode. The inputs needed for a pavement design analysis with CRBM were then obtained. The results showed the importance of further study on CRBM fatigue to understand the behaviour of these mixes under cyclic loading.

The Selected Problems of Multi-layer Pavements – Influence of Composite Impacts Vehicles and Climatic Factors on the Behavior of Roads Pavements

Multi-layer pavement models, which utilize solutions such as the one of Boussinesq, Burmister, Kogan, Odemark and others, contain many simplifications that have a significant influence on the estimated real value of stress, strain, deflection as well as on the coefficient of pavement layers interaction.In the article based on the experiments carried out, we want to present our own layered- pavement models and solutions to them, which can be used mainly in the diagnostics of bearing capacity. The estimation of bearing capacity is conducted on the basis of full time data obtained with the FWD device.In order to prove the climatic factors impact on the bearing capacity of the multilayer pavement structure a theoretical analyses of the joined dynamic and thermal impacts has been performed. Additionally qualitative and quantitative changes of road surface deflection in a thermo-viscoelastic model were presented. In the proposed model it was examined the impact of the relevant climatic factors, inter alia, such as: stream of solar radiation, humidity and wind speed on the surface pavement deflection bowl under load dynamic.Moreover, the conclusions implicated by the above mentioned analysis are of big importance in design and operation process of road and airfield pavements. They pertain not only to the influence of modulus and thickness of particular layers but also to the way of pavement layers interaction, Poisson's coefficient and others.

A New French Rational Design Method for Airfield Pavements

The current design procedure for airfield pavements used in France has shown limitations in the past decades. This empirical-based approach does not consider correctly new material performances, temperature effects, or new complex landing gear configurations. For flexible pavements, on which this paper is focused, the empirical California Bearing Ratio (CBR) is used to characterize the bearing capacity of the pavement for the design. These limitations, among others, led the STAC to make new developments to overcome them. Hence the development of a new method inspired by the rational approach which has been used for roads and highways for more than 30 years. This method is based on the computation of resilient stresses and strains in the pavement structure using a multi-layer linear elastic model. The calculation of a damage parameter in the pavement is made for all the materials, considering fatigue of bound materials and permanent deformations of untreated materials and soils. The cumulative effect of the loadings applied by the various aircraft of the design traffic mix is taken into account as well as the effect of complex landing gears and wheels interaction. The design thickness of the pavement structure is then determined so as to reach failure at one of the critical level in the pavement after all the aircrafts of the design traffic mix have passed. This corresponds to a damage parameter equal to one. The development of a specific version of the French software dedicated to airfield pavement design is in progress. This paper describes the basis of both design methods for flexible pavements and then a comparison of the input parameters that are taken into account is presented.

Recommendations for the Minimum Thickness of Concrete Pavements Supporting F-15 and C-17 Aircrafts

AbstractThe procedure for the design of military rigid airfield pavements contained in the Unified Facilities Criteria 3-260-02 gives the minimum thickness of airfield concrete pavements as 152 mm (6 in.). The introduction of the C-17 aircraft and the requirement of dowel bars as a joint load transfer mechanism bring into question the validity of the 152-mm (6-in.) minimum thickness. With the objective of updating such minimum thickness criteria, a full-scale test section was constructed and trafficked with loads simulating F-15, B-52, and C-17 aircraft landing gear. Evaluation of the test section performance and analysis of the strain data supported a U.S. Army Engineer Research and Development Center team recommendations that the minimum pavement thickness be increased to 203 mm (8 in.) for any doweled airfield pavement and that the minimum thickness of 279 mm (11 in.) should be required for those pavements supporting C-17 aircraft.

UK airfield pavement design using French asphalts

The requirement to build durable, sustainable and low-maintenance airfield infrastructures has become more important in recent years due to the expected air traffic increase and its impact on the environment. The high customer expectation of infrastructure availability and minimum traffic delay during maintenance has also become significant. This paper introduces French asphalt mix design methods for use in airfield pavement construction as an alternative to conventional UK materials, to offer improved performance and better whole-life cost solution. A case study at Sumburgh Airport in the Shetland Islands, UK is presented.

Unsaturated Soil Modeling for Airfield Pavement Design

This study presents results of one of the first in situ assessment studies on the use of the Mechanistic-Empirical Pavement Design Guide (M-EPDG) methodology applied to the design of airfield pavements. The M-EPDG’s Enhanced Integrated Climatic Model (EICM) introduces unsaturated soil modeling techniques into the prediction of moisture changes in the unbound materials throughout the life of pavements for highway conditions. Field soil moisture content changes measured at several Air Force bases in the U.S. were collected from historic studies and compared to MEPDG predictions. Details and outcomes from this comparative study are presented herein. Despite significant differences in structural dimensions and geometric design, this study showed that the EICM promises to be a suitable predictive methodology to be adapted for airfield pavement conditions and has the potential to become a tool for the incorporation of unsaturated soil modeling for the design of airfield pavements, provided that several enhancements are made to the model applied to highway design. Also, a discussion on possible sources of uncertainty in the predictions of the MEPDG and a series of alternative revisions and enhancements required to incorporate the EICM with current airfield pavement design methodologies are presented.