Structural Assessment of a High Polymer-Modified Asphalt Concrete Mixture Using Full-Scale Pavement Testing
Jhony Habbouche (firstname.lastname@example.org), Virginia Transportation Research CouncilShow Abstract
Murugaiyah Piratheepan, University of Nevada, Reno
Elie Hajj, University of Nevada, Reno
Sailesh Bista, University of Nevada, Reno
Peter Sebaaly, University of Nevada, Reno
This paper presents the validation process for the structural layer coefficient ( a HP-AC ) determined mechanistically for high polymer (HP) asphalt concrete (AC) mixtures (i.e., 0.54) through full-scale laboratory testing of asphalt pavements prior to its full implementation. Two extensively instrumented experiments were conducted in the PaveBox at the University of Nevada, Reno. Experiment No. 1 evaluated a flexible pavement with a conventional polymer-modified asphalt (PMA) layer, and Experiment No. 2 evaluated a flexible pavement with a reduced-thickness HP AC layer. The two pavement structures had the same base and subgrade layer thicknesses and material properties. In general, the reduced thickness of the HP AC layer resulted in similar vertical surface deflections except under the center of the applied surface load (higher deflections); higher vertical stresses at the middle of the base layer; and similar vertical stresses at 6 inch (152 mm) and 24 inch (610 mm) below the subgrade surface. In addition, the mechanistic analysis using laboratory-developed performance models showed that the HP AC pavement will result in better fatigue and rutting performance in the AC layer; slightly higher rut depths in the unbound layers; and similar total rut depths. In general, the results and findings of this study supported the selection of a HP-AC equal to 0.54. A reduction in the recommended a HP-AC value might be warranted if the load-induced stresses in the unbound materials (in the base layer in particular) lead to excessive permanent deformations that exceed the rut depth limits.
Evaluation of the Effect of Aircraft Tire Inflation Pressure on Thin Asphalt Pavements
W. Jeremy Robinson (Jeremy.Robinson@usace.army.mil), U.S. Army Corps of Engineers (USACE)Show Abstract
Sixteen non-standard asphalt pavement test items were subjected to accelerated traffic testing to determine if reductions in aircraft tire inflation pressure had a meaningful effect on pavement performance. Materials evaluated included a strong and weak base course (limestone and gravel), three asphalt thicknesses (2.5 cm, 3.8 cm, and 6.3 cm), and two aircraft types (C-130 and C-17). Each single-wheel aircraft tire was operated at two tire inflation pressures, i.e., normal operating pressure and approximately 20% below normal, while maintaining total wheel load. Rutting behavior and surface cracking were the primary measured distress mechanisms and were used to evaluate pavement performance. It was found that reducing tire inflation pressure on the weak base course materials had little effect on rutting performance, suggesting that total load rather than tire pressure dominated performance. Conversely, tire pressure reductions on strong base course materials provided an improvement in rutting performance ranging from 15% to 73%. Improvement in surface cracking was observed in some cases with a reduction in tire inflation pressure; however, a meaningful amount of surface cracking was not observed in most test items until near or after 25.4 mm of rutting. Thus, it can be concluded that the primary mode of failure was pavement rutting rather than extensive fatigue cracking. Overall, it was found that a reduction in tire pressure on competent aggregate base improved pavement performance, which could permit for increased aircraft operations on thin flexible airfield pavements.
Laboratory and Full Scale Pavement Evaluation of Cracking Potential of Mixtures containing RAP
Fabricio Leiva-Villacorta, National Center for Asphalt Technology (NCAT)Show Abstract
Gregory Sholar, Florida Department of Transportation
The objective of this experiment was to evaluate cracking potential of asphalt mixtures containing RAP in the laboratory and in the field. A secondary objective of this work was to characterize the mixtures’ properties in the laboratory to determine which cracking tests might most successfully predict cracking resistance in the field. To complete this research, four mixtures were placed in 100-foot test strips at the NCAT Test Track in the 2015 test cycle. The mixtures varied in terms of binder type (PG grades: 64-28 and 76-22) and recycled material content (20, 25 and 30% RAP). The mixtures were evaluated for cracking potential using five different tests: Illinois flexibility index test (I-FIT), Energy Ratio from Florida, Cantabro test, Overlay test (OT) – NCAT modified version and dynamic modulus test. Laboratory results did not completely exhibit expected trends in terms of cracking potential. However, all test results were able to identify the worst performer in the lab and in the field. After 17 million ESALs, there is significant cracking in all sections (from 6% to 19% per lane). All sections followed the expected cracking trend except for the section with the highest RAP content. At 15 million ESALs, Energy Ratio and Cantabro test results have shown good correlations with field cracking performance with R2 values over 0.65.
Middle-Up Cracking Potential in Flexible Pavements with Stabilized Foundations
Mostafa Nakhaei, Auburn UniversityShow Abstract
David Timm, Auburn University
This investigation presents a new perspective on the structural behavior of stabilized foundation pavements through full-scale testing and simulation where the historical premise of bottom-up fatigue cracking has been challenged. Two full-scale pavement sections were constructed at the National Center for Asphalt Technology (NCAT) Test Track in 2018. One section featured a stabilized foundation under the asphalt layers while the other was a thick-lift asphalt section on conventional base and subgrade materials. Both sections were embedded with pavement response instrumentation and their behavior was observed over time under accelerated truck trafficking. In addition, computational simulations were executed to explain the observed behavior. The strain measurement at the bottom of AC for the thick-lift section showed a familiar trend in which the tensile strain at the bottom of AC increased exponentially with temperature. In contrast, the strain at the bottom of AC in the stabilized foundation pavement was predominantly in compression at elevated temperatures. Further analysis revealed that compressive strain at the bottom of AC increased exponentially with temperature similar to conventional flexible pavements but with a reversed sign. The results were confirmed by falling weight deflectometer (FWD) testing that was conducted directly above the embedded pavement sensors. Computational simulations confirmed the behavior and suggested that the maximum tensile strain could occur at shallower depths, possibly mid-depth of the AC, in stabilized foundation pavements. This indicates stabilized foundation pavements could be prone to middle-up cracking and subsequent precautions should be taken to avoid middle-up fatigue cracking.
Development of an Artificial Neural Network (ANN)-Based Procedure for the Verification of Traffic Speed Deflectometer Measurements
Hossam Abohamer, Louisiana State UniversityShow Abstract
Mostafa Elseifi (email@example.com), Louisiana State University
Zia Zihan, Iowa State University
Zhong Wu, Louisiana Department of Transportation and Development
Nathan Kebede, ARRB
Zhongjie Zhang, Louisiana Department of Transportation and Development
Since the 1980s, the Falling Weight Deflectometer (FWD) has been the primary deflection-measuring device in the United States to evaluate the structural conditions of in-service pavements. However, the stop and go nature of the FWD limits its application at the network-level. In the early 2000s, the Traffic Speed Deflectometer (TSD) was introduced as an alternate deflection-measuring device for network-level applications. TSD collects deflection measurements while traveling at traffic speed, which provides improved spatial coverage and no traffic disturbance. The verification of TSD measurements and its accuracy in measuring the structural capacity of in-service pavements are of great interest as many agencies move towards widespread implementation. This study aims at developing a reliable and straightforward procedure for the verification of TSD measurements using limited FWD-measured deflection measurements. The verification procedure employs a trained Artificial Neural Network (ANN) model to shift TSD deflections to their corresponding FWD deflections. The ANN model was trained and verified based on FWD and TSD measurements from two deflection-testing programs. The developed model accurately predicted FWD measurements with a coefficient of determination (R2) of 0.994. The suitability of the proposed verification procedure was evaluated using statistical and engineering-based measures and showed acceptable accuracy. Results also validated that the proposed method could be used to verify TSD measurements before its use for conducting deflection measurements at the network level.
A Proposed Road Track Pavement Testing (RTPT) Facility for the Dry-Freeze Region: A Benefit-Cost Analysis with Deterministic Life Cycle Approach
Benjamin Fosu-Saah, University of WyomingShow Abstract
Marwan Hafez, University of Wyoming
Khaled Ksaibati (firstname.lastname@example.org), University of Wyoming
The Wyoming Department of Transportation, in collaboration with the University of Wyoming, are conducting a feasibility study to evaluate the effectiveness of constructing a new road track pavement testing (RTPT) facility for the dry-freeze climatic region in Wyoming. The objective of this paper is to provide a comprehensive framework to determine the benefit-cost ratio (B/C) for RTPT facilities using a deterministic life cycle approach. The Benefit Cost Analysis (BCA) was applied with the economic evaluation of the states in the dry-freeze zone as a case study to address funding, increase accountability, and encourage partnership. The RTPT program is expected to improve pavement performance and economy through a better understanding of pavement behavior in the region. Direct benefits are expected to be in forms of improved pavement materials, performance, cost-effective designs, and efficient maintenance techniques. A 10-year analysis period was used for the life cycle analysis. The estimated overall B/C of the RTPT facility is found to be 9.0. However, there is an opportunity to increase the benefit-cost impact through funding support from FHWA and pavement industry. Therefore, a sensitivity analysis was undertaken to minimize the uncertainty in funding availability and assess the consequences of different funding scenarios. Promising results were found for the overall B/C to be ranged from 9.4 to 10.7. Such high values reflect a healthy return on investment in the feasibility stage. Cooperative sponsorships from federal government, industry, and dry-freeze states are encouraged to promote the cost-effectiveness of the proposed RTPT facility.
Effect of the Tandem-Axle Configuration on Flexible-Pavement Responses and Strain Recovery
Aravind Ramakrishnan (email@example.com), University of Illinois, Urbana-ChampaignShow Abstract
Imad Al-Qadi, University of Illinois, Urbana-Champaign
To understand the effect of loading configuration on asphalt concrete (AC) behavior, actual tandem loading and flexible-pavement characteristics were modelled using a finite-element model. The influence of a 4.5-ft spaced tandem axle on flexible pavement responses and strain recovery was qualitatively assessed. The effect of a tandem axle is highly pronounced for vertical strain on the subgrade, followed by that on the granular base and then transverse strain at bottom of the AC. Such responses could be approximately 1.5 times that of the single axle. Maximum transverse strain value increased as the speed decreased. However, when strain recovery is considered, transverse strain for higher speeds could be critical. Stress-pulse analysis suggested that a tandem axle could be simulated accurately in laboratory tests. Although stress-pulse magnitude and shape (when no overlap) are known to be independent of speed, loading-pulse duration can be calculated to identify the rest period. Similarly, domain analysis suggested that damage potential was affected by temperature and speed, which should be considered in platoon designs.
Instrumentation and Evaluation of Dynamic Load Responses of U.S. 23 Perpetual Pavement Experimental Roads
Junqing Zhu (firstname.lastname@example.org), Southeast UniversityShow Abstract
Shad Sargand, Ohio University
Issam Khoury, Ohio University
Derar Tarawneh, Ohio University
Tao Ma, Southeast University
Perpetual pavement experimental roads of varying asphalt concrete thicknesses (28 cm, 33 cm & 38 cm) were constructed and instrumented on U.S. Route 23 in Delaware County, Ohio. Controlled vehicle Load testings were performed to obtain dynamic load responses under vehicular load and to evaluate influence of vehicle speed, tire pressure and axle configuration. CVL tests were conducted in November 2012 and July 2013 to evaluate temperature effects on pavement responses. A linear elastic finite element model program was used to obtain layered elastic solutions of load resposnes to validate measured results. The elastic-viecoelastic correspondence principle was used to account for effect of dynamic loading. It was found that the calculated results were in good aggrement with the measure values, with the computed strains generally slightly smaller than the measured values. 33 cm section with stabilized subgrade performed the best with lowest strain responses. Strain responses tend to decrease as truck speed increases while tire pressure have minimal effect on strain resposnes. Tandem axle truck produced strains lower than single axle truck even though total weight was heavier. As temperature increases, the strain resposnes increase. Transverse strain tends to increase as lateral wheel offset increases.
Investigation on the Mechanical Properties and Structural Behaviour of Novel Pervious Interlocking Paver Block
ARJUN SIVA RATHAN R.T (email@example.com), National Institute of Technology, TiruchirappalliShow Abstract
ARA V, National Institute of Technology, Tiruchirappalli
SUNITHA V, National Institute of Technology, Tiruchirappalli
The present research work aims to develop a novel Pervious Interlocking Paver Block (PIPB). The primary aim of developing a PIPB is to mitigate the problems faced by the conventional pervious concrete such as the reduction in strength and difficulty in compaction. The above disadvantages can be overcome by the hydraulic press compaction process of the precast PIPB. The objective of the present study is to evaluate the mechanical properties of PIPB and structural behaviour of the PIPB pavement section. In the current explorative research work, the influence of aggregate gradation, and the percentage of fines on these parameters is evaluated. The mechanical properties such as compressive strength, split tensile strength, flexural strength, and skid resistance are assessed. The structural behaviour of the PIPB pavement section is found using plate load test and large-scale direct shear test. FEM based software, PLAXIS, is used to validate the test results. Infiltration test is conducted on the plate load test section to understand the infiltration rate. Finally, 2D image processing is performed using MATLAB to validate the test results. The test results proved that the grade III mix possesses desirable mechanical properties, lower deflection, higher shear strength, and required permeability. The present study affirms that the IPPB can be an effective pavement material for the low volume roads, urban heat island and pavements with drainage problems.
Utilization of Cold Central Plant Recycled Asphalt in Long-Life Flexible Pavements
David Timm, Auburn UniversityShow Abstract
Brian Diefenderfer, Virginia Transportation Research Council
Benjamin Bowers, Auburn University
Gerardo Flintsch, Virginia Polytechnic Institute and State University (Virginia Tech)
Long-life flexible pavements are well-documented and used widely across the U.S. Found in every climate zone and traffic classification, long-life pavements do not experience deep structural distresses such as bottom-up fatigue cracking or substructure rutting. Full-scale test sections, built in 2003 at the National Center for Asphalt Technology (NCAT) Test Track, provided the basis for an optimized design approach that utilizes strain distributions for long-life thickness design. These sections, containing only virgin materials, were subjected to 30 million standard axle loadings with excellent performance in terms of rutting, cracking, and roughness. In 2012, three new sections were built at the Test Track using cold central plant recycled asphalt materials as the base layer. These layers, made from nearly 100% reclaimed asphalt pavement (RAP), supported hot mix asphalt layers that also included RAP with one section featuring in-place stabilization of the existing aggregate base. This paper provides a direct comparison between the sets of sections to compare and contrast their performance histories, structural characterization, and consider their economic and environmental impacts. None of the recycled sections are exhibiting any surface deterioration despite heavy trafficking, and the section with a stabilized base is exhibiting lower strains than established long-life pavement thresholds. The economic analysis suggested that the recycled sections can deliver similar performance at a lower average structure normalized section cost than the non-recycled sections. Furthermore, the section with the stabilized base and 76% recycled material is likely a long-life pavement and potentially outperform the sections with no recycled content.
Life Cycle Assessment of Aggregate Quarry By-Product Applications in Pavements
Issam Qamhia, University of Illinois, Urbana-ChampaignShow Abstract
Erol Tutumluer (firstname.lastname@example.org), University of Illinois, Urbana-Champaign
Hasan Ozer, Arizona State University
Heather Shoup, Illinois Department of Transportation
Andrew Stolba, Illinois Department of Transportation
Quarry byproducts (QB) pose a major environmental challenge for quarries as they accumulate in large quantities and their beneficial uses are continually sought out. More than 175 million metric tons of QB are generated in over 3,000 quarries in United States each year. Recent research at the Illinois Center for Transportation introduced seven applications to utilize QB in chemically stabilized base/subbase pavement layers. These applications were evaluated for field performance through accelerated pavement testing. The QB layers were stabilized with cement or Class C fly ash. This paper presents results for the environmental benefits and trade-offs of including QB or blends of QB with recycled materials in pavements using a life-cycle approach. The seven QB applications and a conventional (control) section with a granular base material were evaluated in terms of environmental impacts using life-cycle assessment (LCA). The LCA was conducted in accordance to International Standard Organization ISO 14044:2006 guidelines. The life cycle impacts of using the proposed QB applications were calculated in terms of energy consumption and global warming potential. Three scenarios for as-constructed and as-designed pavement thicknesses and thinner pavement sections for local roads were considered. Results from LCA analyses showed that when the normalized impacts and the response benefits based on Falling Weight Deflectometer resilient deflections in the three scenarios are considered, cement-stabilized QB pavement layers, particularly those having QB blended with other recycled pavement materials, can have relatively lower initial environmental impacts from materials and construction stages when normalized over pavement life and anticipated traffic.
Moving Wheel vs. Impact Deflections and Their Use in Pavement Evaluation
Douglas Steele, Applied Research Associates, Inc. (ARA)Show Abstract
Hyung Suk Lee, Applied Research Associates, Inc. (ARA)
Curt Beckemeyer, Applied Research Associates Inc
Thomas Van, Federal Highway Administration (FHWA)
Nondestructive deflection testing has played an important role in pavement evaluation, design, and management for several decades. During this period, the tool of choice for structural evaluation has been the falling weight deflectometer (FWD), due to its ability to measure the pavement’s structural response from an impact load delivered to the pavement surface. Over the last two decades, various moving wheel deflectometers have been developed to collect deflection data from instrumented truck-trailer combinations traveling at normal highway speeds. Manufacturers have used various techniques to measure the surface deflections produced by the trailer’s loaded axle with sufficient accuracy for network-level evaluation. One version of this is the Rolling Wheel Deflectometer (RWD) developed by the Federal Highway Administration (FHWA). One barrier to RWD data implementation has been its inherent differences with FWD data, which constitutes the current standard for pavement structural evaluation. This study compares the unique loading characteristics of each device and their effect on resulting deflections using both theoretical and field data, and provides RWD-based strain correlations for network-level evaluation. The field study included side-by-side FWD and RWD testing on 23 test sites in Mississippi.
High-Fidelity Model Development for Pavement Repair Performance
Aaron Pullen, Applied Research Associates IncShow Abstract
Robert Bocchieri, Applied Research Associates Inc
Alexander Zeigle, Applied Research Associates Inc
Jim Hall, J H Consulting
Jeff Fisher, Applied Research Associates Inc
Alessandra Bianchini, Consultant
The Air Force Civil Engineer Center (AFCEC) is conducting research to develop pavement repair capabilities that minimize disruptions to military airfield operations. This work includes the investigation of hot-mix asphalt and rapid-setting flowable fill repair technologies. Pavement repairs pose unique challenges in terms of equipment availability, operational limitations, time available for construction, geometric boundaries and constructability. Initial traffic loadings may be applied within two hours of the repair completion. Consequently, materials degrade quickly, restricting their operational life. High-fidelity modeling and simulation can provide a mechanistic understanding of failure modes and causes of material degradation during aircraft wheel loading. Validated models can provide a tool for predicting the response of a wide variety of repair configurations as well as material and design concepts. Optimized repair designs will save costs and improve performance during operations. A phased research project is underway to systematically perform the testing and validation needed for model development. Models include nonlinear finite element analysis (FEA) and transient heat transfer analysis. Phase 1 has been completed and covers the first generation of a FEA model for a full-scale pavement repair. Experiments supporting this effort include nonlinear materials characterization testing as well as two full-scale experiments to validate the models. The first was a well-instrumented thermal test that measured through-thickness temperatures at various locations, and the second measured stress and strain levels during F-15E load cart traffic. This paper provides an outline for the modeling project and a detailed overview of the two full-scale validation tests performed.
Forensic Investigation of HMA Test Sections for Laboratory and Field Comparisons
Thomas Thornton, Minnesota Department of TransportationShow Abstract
Jacob Calvert, Minnesota Department of Transportation
Michael Vrtis, Minnesota Department of Transportation
Proper forensic analysis must be conducted to assess the validity of field performance data before it can be used for future laboratory testing comparisons, model development, and design calibration. The objective of this paper was to conduct a forensic investigation explaining the field performance results and to assess the validity of the results for further laboratory to field performance comparisons. Deflection data from the Falling Weight Deflectometer (FWD), responses from embedded instrumentation within the pavement structure, visual distress surveys, rutting measurements, and roughness measurements from test cells at the MnROAD research facility were analyzed. Eight hot-mix asphalt test cells were constructed with varying low temperature cracking susceptibility. The sections were constructed on westbound interstate 94 and over 2.7 million equivalent single axle loads were applied during the study from November 2016 to June 2020. Significant cracking was observed in the sections however most of the cracking was not low temperature related. Despite the cracking, roughness remained fairly consistent throughout. Rutting performance were acceptable for all cells. FWD data indicated that the base and subgrade in the highly modified asphalt binder (HiMA) cell were not consistent with the other cells and therefore it is not recommended to utilize HiMA performance data further in laboratory to field comparisons. The best field performance was observed in Cell 20 which used a PG 52S – 34 binder with 30% RAP.
Analysis of Shear Stress and Rutting Performance of Semi-Rigid Base Asphalt Pavement on Long and Steep Longitudinal Slope
Ruikang Yang, Tongji UniversityShow Abstract
Huailei Cheng, Tongji University
Yi Li, Tongji University
Lijun SUN (email@example.com), Tongji University
Liping Liu, Tongji University
Rutting is the most common distress occurring on long and steep longitudinal slope of semi-rigid base asphalt pavement. Previous studies have shown that shear stress is the main cause of rutting. Therefore, the analysis of shear stress is important for evaluating rutting performance. Firstly, considering truck speed, temperature, horizontal force, non-uniform load, and interlayer bonding, the spatial distribution characteristic of shear stress was investigated and the calculation method suitable for rutting performance evaluation was put forward. Among them, truck speed can be affected by different gradients and slope lengths. The truck speed was measured and the relationship between truck speed and gradient, slope length was obtained. Finally, the rutting performance was evaluated based on the calculated shear stress, truck speed, and the existed rutting model. The analysis shows that along the depth direction, the maximum shear stress in the horizontal plane locates from the edge to the center of the load area. The horizontal force changes the position of maximum shear stress, but other factors aren’t. The profile at the load center is appropriate to represent the shear stress distribution of the whole asphalt layer. The shear stress calculated through the proposed method has corresponded with the rutting development process and the critical position of rutting. With the gradients and slope lengths increase, the rutting of the middle layer increases fast. As for the sections with horizontal force and poor interlayer bonding, the critical locations are in the upper layer and lower layer respectively.
Full-Scale Testing of Cold In-Place Recycling (CIR) Asphalt Mixtures Using Accelerated Truck and Aircraft Loading
Ahmed Saidi, Rowan UniversityShow Abstract
Ayman Ali (firstname.lastname@example.org), Rowan University
Yusuf Mehta, Rowan University
Mohamed Elshaer, U.S. Army Engineer Research and Development Center
The objective of this research was to evaluate the field performance of full-scale cold in-place recycling (CIR) sections using Accelerated Pavement Testing (APT). A balanced mix design approach was followed to optimize the binder contents of CIR mixtures, and these CIR mixtures were subsequently used to construct three full-scale sections (7.6 m by 3.7 m) at Rowan University’s Accelerated Pavement Testing Facility. Foamed asphalt was added in varied contents: 2%, 3%, and 4% by total mix weight. All CIR mixtures were prepared at a constant water content of 3%. Each full-scale section was instrumented with asphalt strain gauges, pressure cells, and thermocouples to evaluate the structural responses within each section. A Heavy Vehicle Simulator (HVS) was utilized to apply accelerated loading on each full-scale pavement section. A truck tire was utilized to apply a 40 kN load while an aircraft tire was utilized to apply a 100 kN load. As accelerated loading was applied, a number of field tests and visual inspections were performed to determine: (1) permanent deformation using a surface profiler (2) the structural integrity using a Heavy Weight Deflectometer before and after APT, and (3) cracking potential by assessing stress and strain responses. The results showed that the CIR section with 2% binder content presented the best rutting performance under truck loading and the highest rutting susceptibility under aircraft loading. On the other hand, the CIR section with 3% binder content presented the highest cracking resistance under both accelerated truck and aircraft loading.
Mechanistic Analysis of Superheavy Loads on Flexible Pavement Structures
Yongsung Koh, Iowa State UniversityShow Abstract
Halil Ceylan, Iowa State University
Sunghwan Kim, Iowa State University
In Ho Cho, Iowa State University
Superheavy Load (SHL), a specially-manufactured vehicle for transporting superheavy cargo such as wind turbines, has weight, size, and loading configurations that differ from general truck traffic, e.g., the 13 vehicle classes defined by Federal Highway Administration (FHWA). To characterize non-generic configurations of SHLs, an innovative analysis method is needed to predict unexpected damages that can be occurred in flexible pavement subjected to SHL loading. In this paper, the superposition method and a nucleus segment approach are introduced to characterize the loading range and magnitude of each SHL. To identify potential damages by SHLs on flexible pavement, a set of experimental matrices considering pavement properties and loadings from the nucleus segment of each SHL is established. That is to say, a total of 3,456 cases of flexible pavement analysis, varying in thickness and modulus of elasticity of each layer, and in types of loading, are performed using a Layered Elastic Theory (LET)-based analysis program, MnLayer. As a result of the mechanistic investigation, critical pavement responses under SHLs and FHWA class 9 truck (reference vehicle) are determined. Furthermore, damage ratios using transfer functions available in Mechanistic-Empirical Pavement Design Guide (MEPDG): A Manual of Practice are calculated for each SHL compared to the reference vehicle, FHWA class 9 truck. Finally, multivariate analysis related to critical pavement responses and damage ratios are performed to determine trends depending on each variable. Keywords: Superheavy Load (SHL), Layered Elastic Theory (LET), Superposition Method, Nucleus Segment, Damage Ratio
Fatigue and Reflective Cracking Mechanisms: Modeling and Accelerated Pavement Testing Validation
Nirmal Dhakal, Louisiana State UniversityShow Abstract
Mostafa Elseifi (email@example.com), Louisiana State University
Imad Al-Qadi, University of Illinois, Urbana-Champaign
Tyson Rupnow, Louisiana Department of Transportation and Development
Mechanisms of flexible pavement fatigue cracking and reflective cracking, from a cement-treated base (CTB) layer, were investigated. Three-dimensional finite-element (FE) models were developed to simulate typical pavement structures for low-, medium-, and high-volume traffic. The FE models simulated a dual-tire assembly as well as surface vertical and tangential contact stresses. The FE model was validated using stress and strain measurements obtained from the Louisiana Accelerated Loading Facility. The shrinkage strain induced by a CTB layer was converted to displacement in the base layer and was used to simulate the tensile stresses caused by shrinkage cracking. The results showed that the initiation of surface fatigue cracking is due to vertical shear strain within the AC layer exacerbated by high tensile strain at the surface due to loading. Furthermore, the incorporation of transverse tangential stresses increased the surface tensile strains by more than 50% irrespective of the asphalt concrete (AC) layer thickness. Longitudinal tire contact stresses had minimum effect (less than 10%) on the surface and bottom AC tensile strains, however. Tensile stresses due to shrinkage strains in the CTB were observed to be higher than the tensile strength of the material after a few weeks of curing, suggesting the potential initiation of shrinkage cracks shortly after construction. The addition of fly ash to the CTB may significantly reduce reflective cracking potential after construction.
Seasonal and Diurnal Variations of Backcalculated Layers Moduli in Flexible Pavements and FWD Testing Guidelines
Syed Haider, Michigan State UniversityShow Abstract
Hamad Muslim, Michigan State University
Karim Chatti, Michigan State University
The LTPP SMP data for flexible pavements were analyzed for various FWD deflection-based parameters (moduli of HMA, base, and subgrade) within each climatic region. The effects of seasonal and diurnal changes were quantified, and the ambient temperatures at the time of FWD measurements were related to formulating general guidelines for these measurements. The results show that seasonal and diurnal changes impact the backcalculated layer moduli for flexible pavements in a different way in all climatic regions. The HMA layer moduli showed minimal variation in the spring and fall seasons in every climatic region. Also, the HMA layer moduli were consistently higher, based on the deflections measured before noon. However, temperature correction, generally applied to HMA layer moduli, can eliminate the season, time, and temperature impacts of the FWD measurements. Since the base and subgrade layer moduli are backcalculated from the single measured deflection basins on the surface, temperatures, and moisture conditions at the time of measurements can affect those material properties. Any guidelines concerning FWD testing should, therefore, take into account this fact. The base and subgrade moduli showed minimal variation within the temperature ranges occurring in the spring and fall seasons. Also, the unbound layer showed no effect of time within a day, suggesting no limits for FWD measurements with regards to a better time for conducting these tests. Based on the results, the preferred temperature ranges for FWD measurements are 55 to 70 ᵒ F and 65 to 75 ᵒ F in freeze and non-freeze regions, respectively.
MULTISCALE MODELING OF ASPHALT CONCRETE AND VALIDATION THROUGH INSTRUMENTED PAVEMENT SECTION
Zafrul Khan (firstname.lastname@example.org), University of New MexicoShow Abstract
Rafiqul Tarefder, University of New Mexico
Hasan Faisal, Anton Paar GmbH
In this study, macroscale responses of asphalt concrete (AC) are predicted from the responses of its corresponding microscale representative volume element (RVE) within a finite element framework using quasi-static and dynamic analyses. Nanoindentation test was performed on the mastic and aggregate phase of an AC sample to determine the viscoelastic and elastic properties of RVE elements. Aggregate-mastic proportions in the RVE were obtained from the morphological image analysis. Macroscale model responses were compared with the AC pavement responses obtained from an instrumented pavement section subjected to Falling Weight Deflectometer (FWD) loading and a class 9 vehicle. Model responses are very close to the actual responses. The multiscale analyses show that tensile strain in microscale RVE is 5-10 times higher than that in a macroscale element. Furthermore, multiscale analyses also show that variations in the microscale RVE, such as the reduction in the aggregate-mastic ratio or increment in the voids, can increase the maximum tensile strain at the bottom of the AC in macroscale model by around 25%.
An Improved Model for Predicting Asphalt Concrete Master Curve using FWD Data
Gabriel Bazi (email@example.com), Federal Aviation Administration (FAA)Show Abstract
Matthew Brynick, Federal Aviation Administration (FAA)
Tatiana Bou Assi, Lebanese American University
Jeffrey Gagnon, Federal Aviation Administration (FAA)
The dynamic backcalculation of the asphalt concrete master curve using Falling Weight Deflectometer (FWD) data has been puzzling researchers for several years, and limited practical success has been reported. A dynamic backcalculation application was developed in 2019 that uses a finite element (FE) dynamic implicit analysis for the forward calculation of the pavement surface deflections and the Newton-Raphson’s method for iteratively improving the variables. The application was recently upgraded to improve the prediction of the master curve. The upgrade significantly improved the master curve prediction by 35% from 17 to 28 out of the 32 evaluated combinations, where the combinations consisted of three simulated flexible pavement structures and two asphalt concrete mixes at temperatures ranging from 30 to 100°F. The improvement can be attributed to the enhancements in the Jacobian matrix calculation and the additional FWD parameters that were used in the backcalculation process. The upgrade also reduced the error in the asphalt concrete moduli at the FWD’s most dominant frequency of 17 Hz and in the sublayers’ variables. Improvements to the model are still recommended before analyzing field measured FWD data or even using simulated FWD data with random and systematic errors.
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