AFD80, sponsor of the session, is concerned with the structural modeling and evaluation of pavement sections, including the strength and deformation characteristics of the layers. This poster session addresses the wide range of topics covered by the committee, including transient and permanent deformation, fatigue, and fracture as well as load- and environmentally induced changes in layer characteristics and both destructive and nondestructive test methods for structural assessment purposes.
Effects of Rayleigh Damping Parameters on the Subgrade's Apparent Nonlinearity
Gabriel Bazi, Lebanese American UniversityShow Abstract
Per Ullidtz, Per Ullidtz ApS
Peter Sebaaly, University of Nevada, Reno
Jeffrey Gagnon, Federal Aviation Administration
The effect of the subgrade’s apparent non-linearity captured during Falling Weight Deflectometer (FWD) testing has been a major challenge for pavement engineers in trying to backcalculate reliable layer moduli. The current state of the practice backcalculation software account for the subgrade’s apparent non-linearity by using a non-linear subgrade model or introducing an artificial rigid layer at a certain depth to obtain more realistic moduli. While these models tend to provide relatively acceptable results for typical pavements in many cases, they appear to be ineffective in backcalculating reliable moduli for rigid or thick and stiff flexible pavement structures. Dynamic models, which provide a more realistic approximation, tend to focus on the viscoelastic behavior of the asphalt concrete layer and the non-linear behavior of the unbound layers. This paper focuses on identifying the shortcomings of the current models and developing a simple and robust model that approximates the overall behavior of the entire pavement structure. A two-dimensional (2D) axisymmetric finite element (FE) model was developed addressing the limitations of the existing models, and properly incorporating the subgrade’s damping behavior. The model was used for the backcalculation of layer moduli for flexible and rigid pavement structures built over the same subgrade at the Federal Aviation Administration (FAA) National Airport Pavement Test Facility (NAPTF). The backcalculation with the new model produced reasonable layer moduli that are consistent with the type of material in each layer, and more importantly, it produced layer moduli that are almost equal for the same subgrade under the different pavement structures and types.
Structural Number Prediction for Flexible Pavements Based on Falling Weight Deflectometer Data
Ragaa Abd El-HakimShow Abstract
Sherif El-Badawy, Mansoura University
Hafez Afify, Tanta University, Tanta, Egypt
Hossam Abd El-Raof, Tanta University, Tanta, Egypt
Evaluation of the pavement structural capacity is a primary concern to pavement management engineers and decision makers. It plays a key role in Pavement Management Information Systems (PMIS) in order to produce reliable and effective maintenance decisions. Structural Number (SN) is a numerical value used as an indicator of pavement strength and structural capacity. This paper reviews the most recognized models; namely COST, Schnoor et al., Rohde, and Kim et al. models to predict the Structural Number (SN). These models predict SN based mainly on the Falling Weight Deflectometer (FWD) data. One major issue with these models, is that they disregarded the effect of temperature on the backcaluclated modulus of the Asphalt concrete (AC) layer and hence the predicted SN values. The accuracy of the investigated SN prediction models after applying temperature correction to the AC layer modulus (EAC) and the FWD peak deflection (Do) to a reference temperature of 21 oC was examined. For this purpose, FWD data and backcalculated moduli of pavement layers were retrospectively collected from the Long Term Pavement Performance (LTPP) database. Fourteen pavement test sections covering the different climatic regions in the USA with 461 FWD test points were used to evaluate and improve the accuracy of these models as compared to the AASHTO 1993 approach. The most prominent models were calibrated and/or simplified. The proposed calibrated /simplified models produced more accurate and lower biased SN predictions as compared to the original literature models.
Impact of Pavement Layer Properties on the Structural Performance of Inundated Flexible Pavements
Mohamed Elshaer, University of New HampshireShow Abstract
Jo Daniel, University of New Hampshire
The assessment of the structural performance of flooded pavements remains complicated due to the lack of structural data in the aftermath of flooding and the fact that information about the pavement structure and materials is not always readily available. The objective of this study is to acquire a better understanding of the structural response of pavements that have been inundated and the foreseen changes in capacity using two approaches: a mechanistic approach using layer elastic analysis and the AASHTO empirical approach to determine the structural number. The relative impact of parameters such as unbound material type, layer thickness, traffic loads, and interlayer bond conditions on the reduction in expected strain values at critical locations were evaluated. The results show increases of 15 to 80% in vertical strains at the top of subgrade layer for low volume and interstate sections and 6 to 15% increase in horizontal strain at the bottom of asphalt layer for low volume sections and 3 to 8% for interstate sections. Accurate information on the layer thicknesses, traffic type, and interlayer bond condition were found to be most important for the evaluation of the change in expected horizontal strain. The type of base and subgrade materials are the most important factors for evaluating the change in expected vertical strain. The results of this study provide guidance on the type of information that is most important to collect for the assessment of the structural capacity of a pavement following inundation.
Development of Domain Analysis to Predict Multiaxial Airfield Pavement Responses Due to Gear and Environmental Loadings
Angeli Gamez, University of Illinois, Urbana ChampaignShow Abstract
Jaime Hernandez, University of Illinois, Urbana Champaign
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 necessarily be accurately representative of realistic pavement scenarios. For instance, airfield flexible pavement analysis solely considers 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 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 airfield flexible 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 the worst loading conditions (8 kph and 45°C). The minimal difference in ratios for F-16 cases suggests that the National Airport Pavement Test Facility pavement structure became less sensitive to condition under low loads. In cases that the influence of tire-inflation pressure was minimal with respect to the point response analysis, e.g., tensile strain at the bottom of the AC only increased up to 13.6%; considering 8 kph speed, the domain analysis determined the increase in 3-D stress/strain states.
Asphalt Pavement Analysis with 3-D FEM Model Using Actual Tire Pavement Contact Stresses Measured with Pressure Mapping System Device
Ali Bawono, tum create limitedShow Abstract
Bernhard Lechner, Technische Universität, München
Alhaz Ichwanul Fiddin, Technische Universität, München
The load of the vehicle is transferred to the pavement through tires. Conventionally, the contact pressures are assumed to be uniformly distributed over a circular contact area. This assumption might lead to early deterioration as the stresses that are applied to the pavement are underestimated.
This research aims to develop a method to analyze the actual tire-pavement contact stresses on asphalt pavement behavior in 3D FEM by using pressure mapping system device, Tekscan I-Scan. It allows indicating the precise position as well as the magnitude of the stresses applied to the pavement. The contact stresses data were processed with the help of a numerical computing tool, MATLAB. The processed data were then analyzed using 3D FEM software, ANSYS, in order to study the pavement responses. As a result, the method is successfully provided a better understanding of the effect of actual tire-pavement contact stresses on asphalt pavement responses.
Numerical Analysis of Permanent Deformation Increment in Flexible Pavement Based on Tire–Pavement Contact
Tianhao Yan, Southeast UniversityShow Abstract
Xiaoming Huang, Southeast University
Mihai Marasteanu, University of Minnesota, Twin Cities
Meng Zhang, Southeast University
Tire-pavement contact stress varies with tire loading conditions and tire rolling conditions, but how the change of tire-pavement contact stress affects the permanent deformation is seldom studied. In this study, the effect of tire-pavement contact stress on permanent deformation increment in flexible pavement is investigated by finite element (FE) method. To compute the permanent deformation increment, the tire-pavement interaction is decoupled into two steps. In the first step, a hyperelastic tire model for heavy truck dual-tire assembly is developed, and the tire-pavement contact stress is obtained by Arbitrary Lagrangian Eulerian (ALE) method. The flexible pavement is simplified as a rigid body in this step. In the second step, a viscoelastic flexible pavement model is developed. A strategy is proposed to apply the tire-pavement contact stress, calculated in the first step, to the flexible pavement model as a moving surface traction. The permanent deformation increment is obtained after the tire-pavement stress moves through the flexible pavement model. Finally, the effect of tire load, inflation pressure, torque and the slip angle on permanent deformation increment is studied. The results indicate that, vertical permanent deformation increment is mainly affected by tire load. The other factors (inflation pressure, torque and slip angle) mainly affect the horizontal (longitudinal and transverse) permanent deformation increment. At accelerating, braking and cornering conditions, the horizontal permanent deformation increment is at the same level with vertical permanent deformation increment, so the horizontal permanent deformation increment is also noteworthy in pavement engineering.
Comparison of Flexible Pavement Responses Computed from Dynamic and Backcalculated Moduli
Kenneth Tutu, Auburn UniversityShow Abstract
David Timm, Auburn University
Dynamic modulus (|E*|) testing is gaining popularity as an asphalt concrete (AC) characterization procedure for mechanistic-empirical design. In contrast, falling weight deflectometer (FWD) testing is used for field characterization of AC modulus. Considering the differences in the test procedures, attempts have been made to develop relationships between |E*| and FWD backcalculated AC modulus to allow comparison of AC behavior under laboratory and field conditions. The interconversion between field- and laboratory-measured AC modulus has focused on time-frequency relationships. This study investigated the relationship between mechanistic pavement responses computed from |E*| and backcalculated AC modulus to identify an |E*| loading frequency that produced a match between the two types of AC modulus. Data were obtained from seven test sections at the National Center for Asphalt Technology Test Track. The cross sections were modeled to conduct two sets of mechanistic analysis: one set used |E*| and the other backcalculated AC modulus. Graphical and statistical analyses of the pavement responses showed that |E*| measured at 10 Hz and 40oF correlated with backcalculated AC modulus at a similar temperature. Considering the FWD load pulse as a haversine function with an angular frequency of duration between 0.025 and 0.030s is supported by this study. It is recommended that |E*| testing at 10 Hz and 40oF be used to predict in-situ AC modulus. |E*| measured at 10 Hz and at temperatures exceeding 40oF were significantly different from the backcalculated AC modulus, and resulted in significant differences between their pavement responses and those determined from backcalculated AC modulus.
Field Testing and Modeling Analysis of Heavy Weight Deflectometer and Its Relationship to Moving Tire Loading on Airfield Pavement
Hao Wang, Rutgers, The State University of New JerseyShow Abstract
Maoyun Li, Rutgers, The State University of New Jersey
Richard Ji, Federal Aviation Administration
This study focused on evaluating airfield pavement responses under Heavy Weight Deflectometer (HWD) and moving aircraft loading using integration of field testing and modeling analysis. Finite element (FE) models were developed to predict pavement responses subject to stationary impact loading and rolling tire loading, respectively. HWD devices and the testing vehicle at the National Airport Pavement Test Facility (NAPTF) were used in the field testing to validate FE modeling results. The developed FE models show acceptable accuracy in terms of surface deflections under HWD loading and compressive stresses under both HWD and aircraft tire loading. The results indicate that good correlations were obtained between strain responses and deflection basin parameters, such as tensile strains and Area under Pavement Profile (AUPP) and shear strains and Surface Curvature Index (SCI). At the low taxiing speed, aircraft tire loading causes the greater compressive strains at shallow depth of asphalt layer and the longer pulse duration at the bottom of asphalt layer as compared to HWD loading. The correlations between strain responses under HWD loading and aircraft loading were found at the specific speed and wheel configuration. The study findings showed promising potential of using synthetic database to develop quantitative relationships between pavement responses under HWD and aircraft tire loading at specific conditions.
Development of TSD Structural Condition Thresholds Based on Pavement Management Condition Data
Shivesh Shrestha, Virginia Polytechnic Institute and State UniversityShow Abstract
Samer Katicha, Virginia Polytechnic Institute and State University
Gerardo Flintsch, Virginia Polytechnic Institute and State University
In this paper, thresholds to classify the pavement structural condition obtained from Traffic Speed Deflectometer (TSD) testing were developed for a small subset of the Pennsylvania secondary road network. The thresholds are based on the Overall Pavement Index (OPI), which combines all observed distresses into a single measure that ranges from 0 to 100. The pavement structural condition is characterized by the Deflection Slope Index (DSI) which is the difference between the measured deflection 100 mm from the applied wheel load and the measured deflection 300 mm from the applied wheel load. The approach used to develop the thresholds consisted of two steps. In the first step, a regression model that relates the OPI to the DSI and the pavement (surface) age was developed. In the second step, thresholds for the DSI were set so that the OPI predicted from the model for a 10-year-old pavement surface was equal to the OPI threshold value for Good/Fair and Fair/Poor that PennDOT uses. One advantage of the proposed approach is that it links the structural condition to the actual field-observed pavement surface condition and therefore should relatively easily integrate into the Pavement Management System (PMS).
Determination of Loading Frequency and Asphalt Concrete Modulus Through Instrumented Pavement Section
Zafrul Khan, University of New MexicoShow Abstract
Mesbah Ahmed, Colorado State University, Pueblo
Rafi Tarefder, University of New Mexico
This study demonstrates a methodology to determine loading frequencies in pavement layers and in-situ modulus of Asphalt Concrete (AC) through embedded sensors such as strain gauges and pressure cells. To facilitate, stress-strain data were collected from an instrumented pavement section on Interstate-40 (I-40) near Albuquerque, New Mexico. These data were collected from January 2015 through March 2017. Noise removal schemes such as Savitzky-Golay filter and detrending is applied to the stress-strain data to enhance the signal to noise ratio. Fast Fourier Transformation was applied to the enhanced signal data to obtain the frequency spectrum. Frequency spectrum under class 9 vehicle is used to determine the Dominant Frequency Content (DFC) in AC, base, subbase, and subgrade. Frequency spectrum under FWD 9-kip test load and Spectral Analysis of Surface Wave (SASW) are used to determine in-situ AC modulus. In a conventional SASW test, both source and receivers are placed on pavement surface. In the proposed SASW analysis, source is FWD 9-kip test load and receivers are asphalt strain gages installed at 11.1-inch below the pavement surface. From the results, it is observed that conventional Odemark’s based solution always under predicts DFC value for AC layer and overpredicts DFC value for unbound layers, which may lead to inaccurate flexible pavement design through Mechanistic-Empirical analysis of pavement. In addition, by using the SASW principle, AC modulus is successfully determined without any iterative process such as FWD backcalculation.
Identification of Potential Location and Extent of Localized Interface Debonding in the Wheelpath of Asphalt Pavements
David Hernando, University of FloridaShow Abstract
Jeremy Waisome, University of Florida
Jian Zou, University of Florida
Reynaldo Roque, University of Florida
Debonding between asphalt layers is usually modeled as a global or ‘smeared’ phenomenon that occurs across the entire lane. However, field evidence indicates that debonding may be limited to a portion of the interface. The objective of this study was to determine the potential location and extent of localized interface debonding in asphalt pavements so that more realistic interface conditions and pavement responses can be employed in future performance predictions. A parametric study was conducted to locate stress states potentially conducive to interface debonding. Factors considered included asphalt concrete (AC) layer thickness, AC-to-base stiffness ratio, interface compliance, tire size and traffic wander. The parametric study showed existence of a zone of high shear stress coupled with low confinement for a broad range of depths (1 to 3 in below the surface) and extending to 2 in from the tire edge. Given the drop in confinement immediately outside the tire edge and that shear stress magnitude in this zone was similar to shear strength values reported in the literature, it was concluded that the repetition of these critical stress state conditions can cause localized debonding of an interface located about 2 in below the pavement surface. Existence of a potential zone of localized interface debonding around the edge of a tire can promote a debonded strip below the wheelpath as truck traffic travels the highway, which is consistent with field observations. The width of the debonded strip can extent to 42 in in the case of new-generation wide-base tires and a traffic wander standard deviation of 10 in. Future research efforts should examine the stress redistribution associated with the presence of a debonded strip below the wheelpath.