AASHTOWare Pavement Mechanistic-Empirical Design Research Articles

Concrete Pavement Design Analysis Using AASHTOWare Pavement Mechanistic-Empirical Design Software

Local calibration of pavement performance models embedded in the AASHTOWare Pavement Mechanistic-Empirical Design (PMED) software may be needed to implement this design methodology. A recent survey showed that, despite local calibration, several state highway agencies in the U.S. are using the American Association of State Highway Transportation Officials (AASHTO) Guide for Design of Pavement Structures (1993 version) and the PMED software for comparative design of jointed plain concrete pavement (JPCP). This paper describes the recalibration process of the JPCP distress models in the PMED software and comparative designs obtained by the PMED software and 1993 AASHTO design guide. The results show that the calibration/recalibration process depends on the availability of measured performance data. Not all global coefficients must be changed in the calibration/recalibration process. The 1993 AASHTO design guide yielded higher JPCP slab thickness for projects with high truck traffic than the PMED software when no friction is assumed between the slab and a cementitious base. An assumption of full friction will have a discernible effect on the slab thickness obtained from PMED.

Effect of the Field-Stress State on the Subgrade Resilient Modulus for Pavement Rutting and IRI

The new Mechanistic-Empirical Pavement Design Guide (MEPDG) uses the subgrade resilient modulus (MR) as the key input parameter to represent the subgrade soil behavior for pavement design. The resilient modulus increases with an increase in confining pressure, whereas, for an increase in deviatoric stress, it increases for granular soils and decreases for fine-grained soils. The value of MR is highly stress dependent, with the stress state (i.e., bulk stress) a function of the position of the materials in the pavement structure and applied traffic loading. Applying excessive vertical stress at the top of the subgrade without knowing the appropriate stress state can result in permanent deformation. In situ stress must be calculated so the correct resilient modulus can be determined. To facilitate the implementation of MEPDG, this study develops a methodology to select the appropriate subgrade resilient modulus for predicting rutting and IRI. A comprehensive research methodology was undertaken to study the effect of in situ or undisturbed subgrade MR on pavement performance using the MEPDG. Results show that MR obtained from in situ stress is approximately 1.4 times higher than the MR estimate from NCHRP-285. Thus, the in situ stress significantly affects the calculation of subgrade MR and, subsequently, the use of MR in the predicted rutting, with IRI using the AASHTOWare pavement mechanistic-empirical design. Results also show that the pavement sections were classified as in “Good” and “Fair” conditions for rutting and IRI, respectively, considering in situ MR.

Recycled polyethylene (RPE) modified asphalt mixtures: Performance predictions using pavement Mechanistic-Empirical design and evaluation of return on investment

The objectives of this study were to evaluate the impact of using recycled polyethylene (RPE) on the predicted rutting and bottom-up fatigue cracking of RPE modified asphalt pavement sections and on the return on investment (ROI). The AASHTOWare Pavement Mechanistic-Empirical Design (PMED) was used to predict rutting and bottom-up fatigue cracking. Life-cycle cost analyses using FHWA RealCost were used to analyze the return on investment (ROI). Three Superpave 12.5-mm mixtures were evaluated: one control and two RPE modified mixtures designed using wet and dry processes. To increase the prediction accuracies, local laboratory-derived calibration coefficients were used in AASHTOWare PMED based on the repeated load permanent deformation test (RLPDT) and flexural bending beam fatigue tests. Using time versus asphalt concrete rutting and bottom-up fatigue cracking charts, the service life for initial construction and subsequent future pavement rehabilitation/preservation activities were determined for each pavement section. The ROI was then evaluated using a 30-year analysis period. The most cost-effective pavement over the 30-year analysis period was provided by the pavement section produced using the dry process followed by the wet process while the least cost-effective pavement was the control pavement section. Hence, the study presented in this paper beneficially contributed to the current state-of-the-practice by presenting how recycled plastics impact predicted rutting and bottom-up fatigue cracking performances and the return on investment (ROI) when using both wet and dry mixing processes.

Performance Evaluation and Prediction of Preservation Asphalt Overlay in Louisiana

The Louisiana Department of Transportation and Development (LaDOTD) has been using thin asphalt overlay (2 in.) as a preservation technique for asphalt-surface pavements. Although LaDOTD has specified the triggers for its application, it was not always applied on the recommended timing. It is unclear how the application timing affects the overlay performance. Additionally, no studies have been conducted to determine optimal application timing for the overlay and predict its performance using the available tools such as AASHTOWare Pavement Mechanistic-empirical design (Pavement ME) software. The objectives of the study are (1) to evaluate field performance of the preservation asphalt overlay and develop performance prediction models, (2) to determine optimal application timing for the overlay, and (3) to investigate if Pavement ME models are able to predict performance of the overlay by modifying model coefficients. To achieve the objectives, 33 preservation asphalt overlay projects were selected, and their performance was evaluated and predicted, then the optimal application timing was investigated based on the benefit and cost analysis. The results indicate that 58% of the preservation asphalt overlays had 10–20 years’ service life, and 42% had 7–10 years’ service life in relation to Pavement Condition Index threshold of 70. Additionally, good precondition or flexible base (asphalt concrete or unbounded base) can result in a longer service life in the overlay. It is also found that an average value of optimal timing of the next overlay application is the 9th year after construction. Finally, the rehabilitation models of asphalt overlay in Pavement ME software could be used for preservation asphalt overlay by modifying model coefficients.

Assessment of satellite-based MERRA climate data in AASHTOWare pavement mechanistic-empirical design

The pavement performance system depends on various factors including traffic loading, climate conditions, and material properties. Variations in ambient temperatures and moistures can change material properties and consequently affect the overall pavement performance. Collecting climate data has been a significant challenge. This study compares the pavement performance predictions of Iowa composite pavement systems in AASHTOWare Pavement ME Design (PMED) software using four climate data sources: (1) ground-based weather station, (2) North American Regional Reanalysis and (3) the Modern-Era Retrospective Analysis for Research and Applications (MERRA) version 1 and (4) MERRA version 2. The findings showed disagreement among climate data sources for some of the distresses due to the significant differences in percent sunshine hourly measurements. Database for ‘synthetic’ percent sunshine is developed using surface shortwave radiation (SSR) estimates directly provided by MERRA to improve pavement performance predictions. This study recommends the use of SSR as an input in PMED.

Pavement Fatigue Damage Simulations Using Second-Generation Mechanistic-Empirical Approaches

This article aims to demonstrate the advanced features of two second-generation mechanistic-empirical (ME) pavement analysis engines by focusing on their ability to conduct fatigue performance analysis. First, a comprehensive review is presented of both mechanistic and empirical damage models, underlining the additional features of CalME and FlexPAVE™ over AASHTOWare Pavement ME Design. Then, the capabilities of these methodologies are demonstrated by simulating the fatigue damage performance of an example study section. For these simulations the mechanical properties of four asphalt concrete mixtures, assembled in the laboratory with similar mix design attributes but diverse fatigue characteristics, were utilized. The empirical transfer functions were initially calibrated against field cracking for the unmodified mixture cracking predictions. After that, fatigue damage simulations for the other three mixtures were performed. The results showed a similar ranking in fatigue cracking performance for both software simulations. Polymer-modified mixtures exhibited higher fatigue cracking resistance, whereas the unmodified mixture showed the worst cracking resistance. However, significant differences in cracking initiation and progression rates were observed for all mixture simulations before and after calibration. This discrepancy was related to the different approaches to considering traffic loads in each software system, single axle in FlexPAVE™ and axle spectrum in CalME. Finally, current, and future enhancements for both analysis engines are briefly discussed.

Effect of climate on asphalt pavement performance using two mechanistic-empirical methods

ABSTRACT The objective of this study is to assess the impact of climate on the performance of bituminous pavements with two different methods, and then to examine their impact on actual design scenarios. Three climate cases were selected for the comparisons involving the effect of temperature: one in France (Bordeaux) and two in the United States (Seattle and Phoenix). The case of an experimental site in Québec was also used for comparisons concerning consideration for seasonal variations in ground bearing capacity. The analyses were based on French (Alizé-LCPC) and US (AASHTOWare Pavement ME Design) mechanistic-empirical pavement design approaches. Interesting features of the two design methods are outlined and their fatigue cracking models are linked together. The results of the study highlight the importance, for design purposes, of the empirical fatigue equations as a function of temperature. For the site studied in France, the design results in terms of AC base layer thicknesses indicate that both methods show a similar trend with an increase in temperature. For the site in Québec, which is submitted to severe freeze/thaw cycles, the results show that taking temperature and moisture into account for unbound materials leads to a prediction of more severe permanent deformation. Highlights Presentation of two mechanistic-empirical (ME) methods for pavement design Description of the fatigue equations governing asphalt mixes for design purposes Identification of the parameters used in the design of pavement structures Study of the influence of the climate in France and Québec on pavement performance Comparison of the French and US methods for pavement design and correspondence between them

Fatigue performance assessment of recycled tire rubber modified asphalt mixtures using viscoelastic continuum damage analysis and AASHTOWare pavement ME design

Improving fatigue cracking resistance of asphalt mixtures is an important issue that concerns roadway agencies, public and industry. There are various, well-established methods for improving the material characteristics, such as polymer modification methods. Recycling/reusing scrap tire rubber in asphalt pavements has also been an interest of engineers. As such, many different methods of scrap tire rubber (herein called crumb rubber) modification alternatives are being developed. This study focused on a comparative evaluation of the fatigue cracking resistance of various base and recycled tire rubber modified asphalt mixtures, including the relatively new and innovative devulcanized rubber (DVR), crumb rubber terminally blend (CRTB), crumb rubber wet process (CRWET), original/base PG58-28 and softer PG58-34 binders, by using Push-Pull Viscoelastic Continuum Damage (PP-VECD) analysis and AASHTOWare Pavement Mechanistic Empirical Design (Pavement ME) software. The results of the study revealed that rubberized asphalt mixtures provided better fatigue lives than the base and softer binders did. Especially, DVR mixtures outperformed at high strain levels, implying they can be used for heavy traffic roads to enhance the fatigue life of asphalt pavements. Both PP-VECD and Pavement ME produced results that showed similar trends.

Moisture effects on moduli of pavement bases

ABSTRACT Mechanistic-Empirical (ME) pavement design approaches consider seasonal moisture variations in the subgrade and unbound aggregates base (UAB) layers as an important design parameter. Understanding such moisture variation is essential for modelling the pavement section and predicting its performance. The Enhanced Integrated Climate Models (EICM) are often used to predict the moisture contents in the UAB and subgrade layers for different seasons so that the resilient moduli of the layers can be adjusted. This paper provides an in-depth analysis of the moisture effects on the moduli of a UAB material with four different gradations. Commonly used laboratory and field-testing methods were conducted to measure the moduli of the specimens prepared at different moisture contents and fine contents from the same UAB source. The UAB moduli decreased with the increase in the moisture content. However, the patterns in the reduction in modulus depended on the laboratory or field test method used. Although the EICM module of the AASHTOWare Pavement ME Design software can predict the laboratory resilient moduli at moisture contents greater than the optimum moisture content, it was not possible to measure the moduli at those elevated moisture contents for the selected UAB.

Effects of Mix Factors on the Mechanistic-Empirical Flexible Pavement Design

This study investigates the sensitivity of the mechanistic-empirical flexible pavement design performance parameters such as cracking, rutting, and smoothness to mix factors for 11 categories of hot-mix asphalt (HMA) mixtures. For each category of HMA mixture, the variations in the pavement performances for different effective binder content (Vbe), air void (Va), voids-in-mineral aggregates (VMA), voids-filled-with asphalt (VFA), and asphalt content (AC) are examined by the AASHTOWare Pavement Mechanistic-Empirical Design, simply the AASHTOWare software analysis. Five types of distresses: international roughness index (IRI), total rutting, rutting in the HMA layer, bottom-up fatigue cracking, and top-down longitudinal fatigue cracking are considered in the analysis. Results show that the prediction of distresses values after 20-year of service life using the AASHTOWare software may differ by up to 170% for different specimens of a certain mix design. All distresses, except rutting, increase in Va, VMA, and VFA. Rutting in HMA increases with an increase in VMA and VFA, and is insensitive to Vbe, Va, and AC in the study range of these parameters.

Comparative Analysis between Modern-Era Retrospective Analysis for Research and Applications and Updated Mechanistic-Empirical Pavement Design Guide Climate Database in the State of Tennessee

The Mechanistic-Empirical Pavement Design Guide addresses climate effects on pavement design in a comprehensive way, which allows for investigating the effect of climate on pavement performance. However, it requires detailed climate inputs, which might not be readily available for most of the state departments of transportation. The AASHTOWare Pavement Mechanistic-Empirical Design (PMED) version 2.3 (v2.3) climate database encompasses 12 weather stations in the state of Tennessee, which does not satisfactorily represent all climatic regions in the state. The terrain in Tennessee varies from flat in the west to mountainous in the east. To evaluate the effectiveness of the updated AASHTOWare PMED v2.3 climate data input, this study analyses the performance of selected pavements in the state of Tennessee using the Modern-Era Retrospective Analysis for Research and Applications (MERRA) and the AASHTOWare PMED v2.3 databases as sources of PMED climate data inputs. A comparative analysis of the two climate data sources is conducted using eight long-term pavement performance (LTPP) sites in the state of Tennessee. The study revealed that MERRA as a climate data source for the state of Tennessee offers better geographic coverage, and therefore provides more precise distress predictions than the AASHTOWare PMED v2.3 climate database.

Evaluation of Pavement Performance due to Overload Single-Trip Permit Truck Traffic in Wisconsin

This study investigated the impacts of overweight (OW) permit truck traffic on flexible pavement performance in Wisconsin using field investigation and analysis utilizing the AASHTOWare Pavement ME Design software. A database of overweight single-trip permit truck records was analysed to produce a network of Wisconsin corridors heavily travelled by OW trucks. Four Wisconsin highways were selected for investigation due to high levels of OW truck traffic. The research included field work (traffic counts and visual pavement surface distress surveys) and AASHTOWare Pavement ME Design. Comprehensive analyses were conducted to evaluate pavement performance due to normal traffic loads as well as normal traffic loads plus the OW truck traffic loads. The use of mechanistic-empirical (ME) pavement analyses provided a methodology for estimating the proportion of pavement deterioration attributable to OW truck traffic. OW axle load distributions were developed and integrated with baseline truck traffic levels to develop axle load spectra and other traffic input parameters for the ME pavement analysis. The predicted total pavement deterioration levels from the AASHTOWare Pavement ME Design software were generally consistent with the levels of deterioration observed. The proportion of pavement damage and deterioration attributable to OW truck traffic was predicted to constitute a relatively minor proportion of total deterioration, with most distress indices showing relative increases of approximately 0.5% to 4%, with a few outliers. However, due to the small proportion of OW vehicles relative to the overall traffic levels, the OW vehicles were generally predicted to cause up to ten times the per-truck damage as compared with a typical legal-weight truck, depending on the distress mode and the test site.

Dynamic modulus and phase angle models for New Mexico’s Superpave mixtures

This study modifies the viscosity (η)-based Witczak dynamic modulus (|E*|) predictive equation which is used in the recently developed AASHTOWare pavement Mechanistic-Empirical design software. A total of 21 Superpave asphalt concrete mixtures with different gradations and binder grades were tested for |E*| at different temperatures and frequencies of loading. Results show that the η-based Witczak model underestimates the |E*| for New Mexico’s Superpave mixes. Therefore, the revised model is developed using regression analysis. A phase angle (φ) predictive model is also developed using the φ-values obtained during the |E*| testing. It was found that the revised η-based Witczak model determines the |E*| more accurately compared to the original η-based Witczak model.

Determining temperature and time dependent Poisson’s ratio of asphalt concrete using indirect tension test

Poisson’s ratio (ν) of Asphalt Concrete (AC) is a fundamental input parameter to any numerical analysis based on elastic and viscoelastic constitutive properties. To this date, temperature- and time-dependent ν-value has been determined by either a static or a relaxation test at a single temperature in diametrical mode. This study, for the first time, performs relaxation tests at different temperatures in diametrical mode. In addition, cyclic load testing is conducted at different temperatures and loading frequencies to determine the temperature- and frequency-dependent ν-value of AC. Relaxation test results show that the ν-value of AC increases with testing time and temperature. Dynamic load test results show that ν-value of AC decreases with loading frequency; however, increases with temperature. To this end, measured ν-value of AC is compared with the ν-value predicted using model available in the new AASHTOWare Pavement Mechanistic-Empirical (ME) Design software. The measured ν-value matches with the predicted ν-value by the AASHTOWare Pavement ME Design software especially for AC that possesses high dynamic modulus.

Optimal pavement design and rehabilitation planning using a mechanistic-empirical approach

This paper presents the development of a pavement design and rehabilitation optimization decision-making framework based on Mechanistic-Empirical (ME) roughness transfer models. The AASHTOWare Pavement ME Design (the software of Pavement ME Design) is used to estimate pavement deterioration based on the combined effects of permanent deformation, fatigue, and thermal cracking. The optimization problem is first formulated into a mixed-integer nonlinear programming model to address the predominant trade-off between agency and user costs. To deal with the complexity associated with the pavement roughness transfer functions in the software and to use the roughness values as input to the optimization framework, a dynamic programming subroutine is developed for determining the optimal rehabilitation timing and asphalt concrete design thickness. An application of the proposed model is demonstrated in a case study. Managerial insights from a series of sensitivity analyses on different unit user cost values and model comparisons are presented.