Development of Domain Analysis to Predict Multi-Axial Flexible Airfield Pavement Responses Due to Gear and Environmental Loadings

Flexible pavement design procedures use maximum mechanistic strains to predict service life via empirical transfer functions. The conventional method of using predefined point locations for potential damage may not accurately represent realistic pavement scenarios. For instance, flexible airfield pavement analysis mainly considers the critical strain at the bottom of the asphalt concrete (AC), which may not characterize near-surface cracking potential. In lieu of point strains, domain analysis, a new method, accounts for the multi-axial behavior of pavements, as inherently excited by three-dimensional (3-D) and nonuniform aircraft tire–pavement contact stresses. Initially applied on highway pavements considering truck tire loading, this approach is an initial breakthrough for implementing domain analysis on flexible airfield pavements; in this study, A-380 and F-16 landing gear tire loads were considered. As anticipated, speed and temperature had significant influence on cumulative domain stress and strain ratios. The decrease in speed and increase in temperature not only increased the cumulative ratios up to 1.81, but nonlinearity of the problem became more prevalent at worst loading conditions (8 kph and 45°C). Minimal difference in ratios for F-16 cases suggests that the National Airport Pavement Test Facility pavement structure became less sensitive to conditions under low loads. Point response analysis revealed that critical strains were not significantly influenced by the tire-inflation pressure, for example, tensile strain at the bottom of the AC only increased up to 13.6% (considering 8 kph speed), whereas domain analysis quantified the increase with respect to 3-D stress or strain states

Development of Domain Analysis for Determining Potential Pavement Damage

A new approach for quantifying flexible pavement damage potential is proposed. The new method, domain analysis, utilizes multiaxial results from advanced finite element models to calculate the response of flexible pavements to tire loading. The output is a single scalar value, which is unique to a given pavement structure and loading configuration. The ability of the domain analysis to quantify bulk damage potential and overcome flaws of conventional approaches based on point responses is demonstrated by testing three case studies: (1) comparison of typical loading conditions of dual-tire assembly (DTA), new-generation wide-base tire (NG-WBT), and steer tire; (2) effect of tire-inflation pressures; and (3) influence of differential tire-inflation pressure for DTA. The proposed method provides a direct link between three-dimensional contact stresses at the tire-pavement interface and three-dimensional responses of a loaded pavement structure. Also, the applicability of the domain analysis method could easily extend to other pavement structures, tire types and configurations, and loading conditions, along with considering other failure criteria. Jaime Hernandez was affiliated with University of Illinois at Urbana–Champaign at the time of publication

Development of Adjustment Factors for MEPDG Pavement Responses Utilizing Finite-Element Analysis

The Mechanistic-empirical pavement design guide (MEPDG) provides theoretically superior methodology, as compared with its predecessor, for the design and analysis of pavement structures. The mechanistic part refers to simulating pavement–tire interaction to calculate critical responses within pavement. The empirical part means prediction of pavement distress propagation over time using transfer functions that link a critical pavement response to a particular pavement distress. The mechanistic part of MEPDG simulates tire–pavement interaction in three steps: subdivision of pavement layers; complex modulus calculation at the middepth of each sublayer, considering velocity and temperature; and running the multilayered elastic theory (MLET) software, JULEA. Although MEDPG has a grounded methodology for pavement analysis, it has a number of limitations and unrealistic simplifications that result in inaccurate response predictions. These limitations are primarily related to the pavement analysis approach used in the MEPDG framework, MLET. By contrast, finite-element (FE) analysis has proven to be a promising numerical approach for overcoming these limitations and simulating pavement more accurately and realistically. Although comparison of MLET with FE analysis has been studied, the difference between FE and MEPDG simulations has not been quantified. This study fills that gap by developing linear equations that connect pavement responses produced by these two approaches to pavement analysis. The equations are developed for ten different pavement responses, using a total of 336 cases simulated using FE and MEPDG analyses. The cases modeled in simulations were selected to capture extreme conditions, i.e., thick and thin pavement structures with strong and weak material properties. The equations developed can help pavement researchers understand quantitatively the effect of MEPDG limitations. In addition, the equations may be used as adjustment factors for MEPDG to compute pavement responses more realistically without using computationally expensive approaches, such as FE analysis

Impact of Wide-Base Tires on Pavements: A National Study

This paper summarizes a multi-year effort comparing the new-generation wide-base tires (NG-WBT) and dual-tire assembly from a holistic point of view. The tires were compared considering not only pavement damage but also environmental impact. Numerical modeling, prediction methods, experimental measurements, and life-cycle assessment were combined to provide recommendations about the use of NG-WBT. A finite element (FE) approach considering variables that are usually omitted in the conventional analysis of flexible pavement was used for modeling pavement structures combining layer thickness, material properties, tire load, tire-inflation pressure, and pavement type (interstate and low volume). A prediction tool, ICT-Wide, was developed based on an artificial neural network to obtain critical pavement responses in cases excluded from the FE analysis matrix. Based on the bottom-up fatigue cracking, permanent deformation, and international roughness index, the life-cycle energy consumption, cost, and green-house gas emissions were estimated. To make this research useful for state departments of transportation and practitioners, a modification to AASHTOware is proposed to account for NG-WBT. The revision is based on two adjustment factors, one accounting for the discrepancy between the AASHTOware approach and the FE model of this study, and the other addressing the impact of NG-WBT. Although greater pavement damage may result from NG-WBT, for the analyzed cases, the extra pavement damage may be outweighed by the environmental benefits when NG-WBT market penetration is considered

Numerical prediction of three-dimensional tire-pavement contact stresses

The objective of this study is to develop a numerical modeling to simulate tires and investigate the effects of different tire and vehicle conditions on tire-pavement interactions. A three-dimensional (3-D) finite element (FE) representation of a dual-tire assembly is constructed to predict tire-pavement contact stress distributions. The tire is considered as a composite structure, including rubber and reinforcements. The tire material properties are calibrated based on the experimental measurement and data provided by tire manufacturer. The tire rolling process at different states is simulated using the arbitrary Lagrangian-Eulerian (ALE) formulation. Slide-velocity-dependent friction coefficient is used in the modeling. The constructed tire FE representation is calibrated and validated with experimental measurements of contact area, deflection, and maximum vertical contact stress. The developed FE tire-pavement interaction model is used to evaluate the contact area and mechanism of contact stress distributions at the tire-pavement interface under various tire and vehicle conditions.Taxas A&M UniversityOpe

Pavement Rehabilitation Strategy Course Development

Pavement rehabilitation and preservation treatments have become standard practice for state and local transportation agencies. The ultimate goals include maintaining a safe and reliable level of service for all users, maximizing pavement service life, and optimizing budget allocations for infrastructure construction projects. The essential key to meet these goals requires transportation agencies to identify the right treatment for the right pavement at the right time. Based on the manuals of Bureau of Design and Environment (BDE) within the Illinois Department of Transportation (IDOT), training course materials were developed in this project. The goals of the training course are to enhance the understanding of fundamental concepts of pavement rehabilitation and preservation strategies, establish consistent practices following the guidance manuals and minimize potential errors by selecting appropriate treatments. The training course is designed to be completed in one-and-a-half days, covering seven blocks: (1) Introduction, (2) Preservation and Rehabilitation Definitions, (3) Distresses, (4) Condition Rating Survey, (5) Testing, (6) Treatments, and (7) Selection Guidelines. The final completed deliverables of this project include PowerPoint slides for in-class instruction, a stand-alone online platform, and review and final examination questions for the initial three blocks.IDOT-R27-170Ope

Impact of curing time on warm mix asphalt short-term performance

The emerging use of warm mix asphalt (WMA) technology has led to economic and environmental benefits for transportation agencies and road users. Among these benefits is the reduced mixing and compaction temperatures of WMA. However, decreased temperatures may affect the resulting complex modulus to withstand traffic loads. A performance evaluation of WMA over various ‘curing’ periods would determine the evolution of the complex modulus over time. This allows to identify the optimum time for opening WMA paved surfaces to traffic. The effect of curing time on the short-term performance of the warm stone matrix asphalt (warm-SMA), produced with chemical WMA additives, is investigated. The curing periods include: three, six and 12 hours; one, three and seven days; and three, six and 12 weeks. The main objective of this study is to experimentally characterize the short-term performance of WMA produced with two types of chemical additives: EvothermTM 3G and Rediset® LQ-1106. The results were analyzed for statistical significance and the effect of warm-SMA on the life cycle cost analysis and life cycle assessment was evaluated. It was determined that the warm-SMA had comparable mechanical properties to the conventional SMA, while providing economic and environmental advantages

Effect of Wide-Base Tires on Nationwide Flexible Pavement Systems: Numerical Modeling

The pavement responses obtained from the validated finite element modeling of new-generation wide-base tires (NG-WBTs) and a conventional dual-tire assembly (DTA) are presented. Features of the adopted finite element model, such as three-dimensional contact forces, dynamic analysis, and nonlinear anisotropic base materials, are not considered in the conventional analysis of flexible pavements. Furthermore, the input for the model was intended to simulate a large range of scenarios for the national pavement system. The NG-WBT showed consistently higher pavement responses than the DTA, and the difference decreased as pavement thickness increased. (Pavement thickness varied from 225 to 1,012.5 mm.) The average percentage difference of the longitudinal tensile strain at the bottom of the asphalt concrete layer was 14.7% and 23.2% for thick and thin pavements, respectively. In a few cases of vertical shear strain in the subgrade for thin pavement, the response was higher for the DTA than for the NG-WBT. For the same responses in thick pavement, the average percentage difference was 4.4%. If critical pavement strains are used as inputs into transfer functions, which estimate pavement life, results of this study could serve as indicators of increased potential damage when NG-WBTs are used. However, market penetration of the NG-WBT and its use within the truck axle configuration need to be taken into consideration. Additionally, environmental and economic benefits of using NG-WBTs may offset the potential increase in pavement costs

Quantitative Assessment of the Effect of Wide-Base Tires on Pavement Response by Finite Element Analysis

Various studies have shown that the new-generation wide-base tire (WBT) for trucks causes more damage to pavement than does the dual-tire assembly (DTA). However, there is no substantive approach that quantifies the difference in pavement responses produced by WBTs and the DTA. This study filled this gap by developing linear equations that connect pavement responses produced by these two tire types. Equations were developed for 10 different pavement responses through 480 finite element method simulations (240 for the DTA and 240 for WBTs) that were run in ABAQUS with the same material properties and pavement structures. The only difference was the contact stresses and contact areas that were measured under the same axle load for WBTs and the DTA. The cases modeled in simulations were selected to capture extreme conditions, that is, thick and thin pavement structures with strong and weak material properties. The equations will help pavement researchers to understand quantitatively the effect of WBTs on pavement responses as compared with the DTA. The low resultant prediction error, 10%, allows linear equations to be implemented through the application of adjustment factors on mechanistic pavement design guides such as the Mechanistic–Empirical Pavement Design Guide, which are unable to simulate WBT loading realistically. To predict pavement damage accurately, the pavement analysis should consider the WBT market penetration in the United States (approximately 10%) and the partial use of WBTs on truck axles. The impact of WBTs on pavement should be evaluated in the context of economic and environmental benefits

Analytical Approach for Predicting Three-Dimensional Tire–Pavement Contact Load

Three-dimensional tire–pavement contact loads of two truck tires–-a new-generation wide-base tire (WBT) and a dual tire assembly (DTA)–-were measured and analyzed. Extreme and typical values of tire inflation pressure (552, 690, 758, and 862 kPa) and tire loading (26, 35, 44, 62, and 79 kN) were considered in the experimental program. The measurements were performed with the stress-in-motion Mk IV system at the Council for Scientific and Industrial Research in South Africa. Peak values in three directions were compared, and the importance of tangential contact stresses was highlighted. In addition, characteristic variations of the measurements in the longitudinal, transverse, and vertical directions were identified. A function depending on two regression parameters, applied load, and distance along the contact length was proposed to represent the contact load in the vertical and transverse directions. An analysis was performed on the measurements to obtain the regression parameters, and a simplified procedure was proposed to determine tire–pavement contact loads. The contact area and contact length of the WBTs and the DTA were also compared