Mechanistic-Empirical Pavement Design Guide Software Research Articles

An Appraisal of Mechanistic-Empirical Models (MEMs) in Pavement Deterioration

An Appraisal of Mechanistic-Empirical Models (MEMs) in Pavement Deterioration

Life cycle assessment of lightweight cellular concrete subbase pavements in Canada

ABSTRACT The use of Lightweight Cellular Concrete (LCC) as a subbase alternative to typical flexible pavement subbase material in cold regions is gaining attention. Since a setback of using LCC is its high cement content, which is a significant source of carbon dioxide (CO2) emissions, it becomes imperative to consider this aspect when proposing LCC for pavement applications. This study evaluated the environmental impact of three densities (400, 475, and 600 kg/m³) of LCC produced with two methods (wet and dry mix) and compared to two types of unbound granular material (granular A and B) as flexible pavement subbase. The pavement performance was predicted using MEPDG and WESLEA software and compared with measured field responses as a basis for maintenance strategy. The Life Cycle Assessment (LCA) results showed that lower-density LCC pavements decreased environmental costs by reducing total life CO2 emissions by up to 16% and reducing environmental impact for Carbon monoxide, Sulphur dioxide, Nitrogen oxide, Particulate Matter (PM)2.5, PM10 and total PM compared to granular A and B pavements. As LCC density increased, more emissions occurred, showing the importance of density to emissions output. This research demonstrates the potential benefits of using LCC as an alternative subbase pavement material.

Application of Mechanistic Empirical Pavement Design Guide Software in Saudi Arabia

The present study explores the structural pavement design techniques related to pavement distresses in terms of pavement rutting, cracking and International Roughness Index (IRI) based on the materials properties, roadbed characteristics, climate and traffic loads for highway network of Saudi Arabia (KSA). The study was focused on selected site conditions at four regions in KSA: Central (Riyadh); Eastern (Al-Ahsa); Western (Jeddah) and Northern (Arar). Mechanistic-Empirical Pavement Design Guide (MEPDG) software was used to calibrate and predict pavement design life according to the mentioned distresses for different regions in the KSA. This is the first time where the exact weather stations were selected to run analysis on the software determining realistic pavement distresses. In the study, the pavement structure design is different for low traffic (700 AADTT) and high traffic (2000, 6000, and 10,000 AADTT). The tests were run on the MEPDG software to analyze the distresses predicted by the software for an interval of 5, 10, 15, and 20 years. The results predicted by the software show that the preliminary example design satisfies all the target distresses for the mentioned design life, even for 20 years. The study provides a base pavement design for pavement designers that can be modified as per project requirements using the specific data for traffic, material properties, thickness, and distress limit to achieve target design life.

The effect of axle load spectra from AASHTO method on flexible pavement performance

Currently, methods used for pavement design are empirical and based on experiments conducted in the 1960s. Due to the number of variables that can influence an empirical analysis, the National Cooperative Highway Research Program (NCHRP) proposed a mechanistic-empirical method. Based on this method, the MEPDG (Mechanistic-Empirical Pavement Design Guide) software was developed and later, its improved version, the AASHTO Ware Pavement ME Design. In both software versions, default values were developed from traffic data of the United States. However, characteristics of the Brazilian traffic are different from characteristics in the United States. Therefore, this study aimed to verify the effect on national pavement performance due to the use of the default axle load spectra that are available on both software versions. Thus, computer simulations were performed using Brazilian axle load spectra, based on data collected at the Imigrantes Highway in Sao Paulo, and using the default load spectra of the software. The results show that the Brazilian axle load spectra studied damages more the national pavement than the default spectra of the software. Therefore, it is not recommended the use of default spectra for designing Brazilian highways similar to the one studied, because this would lead to under-designed structures.

Waste materials and by-products as mineral fillers in asphalt mixtures

Mineral filler has a significant effect on the asphalt mixtures performance. This paper presents the use of waste materials (marble and granite) and by-product material (steel slag) as alternative to the mineral conventional filler. A control mix with the limestone filler was designed by Marshall method then, a replacement of limestone filler by the waste and by-products materials was done. Two types of mastic asphalt samples were prepared (virgin and aged by the rolling thin-film oven) with the ratio of 1:1 (mineral filler/asphalt). The samples were tested in penetration, softening point and Brookfield rotational viscosity. Furthermore, the transition electron microscope for fillers and scanning electron microscopy for mastics tests were performed. Both virgin and RTFO granite mastics improved the penetration value; however, the marble mastics showed the highest softening point temperature and RV viscosity. Marshall results showed that mixtures containing waste marble yielded the highest stability. Moreover, results showed the ability of marble to improve the moisture damage resistance in terms of tensile strength ratio and loss of stability. Finally, the field performance was predicted using Quality-Related Specifications Software which is a simplification of the Mechanistic-Empirical Pavement Design Guide software. It was found that all materials enhanced rutting resistance compared to the traditional limestone filler.

Effect of local calibration of dynamic modulus and creep compliance models on predicted performance of asphalt mixes containing RAP

MEPDG software can predict long term performance of the asphalt mixes based on asphalt input data. When laboratory measured data of an asphalt mix are not available, this software uses the predictive models to estimate the mix properties. AASHTO recommended calibrating these input models based on local materials and mixes. Previous studies showed that local calibration of dynamic modulus (E∗) and creep compliance predictive model improved the reliability of the predictions. The purpose of this paper is to evaluate the impact of local calibration of E∗ and creep compliance models on long term performance of mixes containing reclaimed asphalt pavement (RAP), and to assess the sensitivity of the predicted distresses to RAP content. Three Levels of asphalt input data were considered; Level 1, calibrated Level 3, and Level 3. For calibrated Level 3, the predicted E∗ and creep compliance obtained from calibrated models were used as input data. The results showed that the Level 3 input data tend to overpredict the distress predictions of the asphalt mix compared to calibrated Level 3 or Level 1 asphalt input data. It was found that the calibrated Level 3 asphalt input data can be used for the design and analysis of mixes with comparable accuracy of Level 1 input. As conducting laboratory tests for individual mixes is expensive and time consuming, utilizing reliable calibrated models to predict E∗ and creep compliance can substantially reduce operating and testing expenses. Also, it was found that the predicted distresses are not sensitive to the RAP content.

A MECHANISTIC-EMPIRICAL IMPACT ANALYSIS OF DIFFERENT TRUCK CONFIGURATIONS ON A JOINTED PLAIN CONCRETE PAVEMENT (JPCP)

Until the last decade, the 1993 American Association of State Highway and Transportation Officials (AASHTO) design guide has been traditionally used for the design of flexible and rigid pavements in the USA and some parts of the world. However, because of its inability to meet the new traffic and material challenges, a Mechanistic Empirical Pavement Design Guide (MEPDG) was introduced based on an NCHRP 1-37 A study conducted in 2004. This study used the MEPDG software and associated models to determine, through comparative truck damage analysis, the effects of nine different truck configurations on a 12 inch-jointed plain concrete pavement (JPCP). The study recorded truck damages at the end of each analysis period (40 years) and comparatively analyzed the relative pavement damage in terms of fatigue cracking, faulting, and surface roughness. The results indicated that the most critical damage to the concrete pavement was caused by truck cases with high and uneven load distribution and relatively smaller size axles group (e.g. tandem). Other key findings included the following; (1) increase in damage when the truckloads were shifted between the same size axles, (2) decrease in truck damage when the truckloads were shifted from tandem axle to quad axles, and (3) no change in truck damage when the axle spacing was increased between wheels of a quad axle.

Sensibilidade de métodos empírico mecanísticos para análise de pavimentos flexíveis

The mechanistic-empirical method (E-M) of design the initial structure adopted for the pavement should be checked for performance criteria and changed if they are not met. In this context, the sensitivity analysis may help to understand that changes can be made. Thus, this study aims to compare the sensitivity of E-M AASHTO, applying the Mechanistic Empirical Pavement Design Guide (MEPDG) software, and the software ELSYM5 for variation in thickness and resilient modulus of flexible pavement layers. Therefore, simulations were performed on software to estimate the pavement performance. The results were adjusted by regression models and regression coefficients were used to determine the significant parameters in predicting performance and to compare applied methods as sensitivity. Distress estimated by the MEPDG software were sensitive to at least one of the parameters under consideration, while the performance predicted by the computer program ELSYM5 was sensitive to variations in the thickness of the asphalt layer and the sub-base and the subgrade resilient modulus. It was concluded that there are differences in sensitivity observed in both softwares, however, the ELSYM5 is a viable alternative to the use as an E-M method of design. Keywords: Sensitivity analysis, Mechanistic-empiral method, MEPDG software, Software ELSYM5.

Maneuvering MEPDG Input Variables to Improve Level-3 and Level-2 Mastercurve Predictions to the Accuracy of Level-1 Input Hierarchy

Abstract In this study, mix and binder input variables were optimized to investigate the problems related to the accuracy of mastercurves developed using Mechanistic Empirical Pavement Design Guide (MEPDG). Dynamic modulus testing over a wide temperature and frequency range was performed on Superpave mixes typically used for structural and surface coarse pavement construction by New Mexico Department of Transportation (NMDOT). Dynamic modulus mastercurves were produced using the MEPDG software and using Microsoft Excel for the actual test data. Mastercurves developed using actual test results were compared with mastercurves produced using MEPDG software at level-1, level-2, and level-3 input hierarchies. Finally, mix and binder input variables were optimized to determine appropriate shift factors to improve accuracy of mastercurves developed at level-2 and level-3 input hierarchies. The results show that mastercurves developed using level-1 input hierarchy accurately represent the test results. However, all predicted mastercurves at level-2 and level-3 input hierarchies underpredict actual test results and level-3 prediction results showed better accuracy than level-2 outputs for all mixes in this study. The MEPDG software was also re-run to predict mix mastercurves using optimized (shifted) input values and the resulting mastercurves from level-3 and level-2 MEPDG input hierarchies were found to overlap with mastercurves produced using level-1 MEPDG input hierarchy. Optimized mix input values suggest that aggregate variables can be eliminated from the E* model.

Optimizing Stability and Stiffness Through Aggregate Base Gradation

Pavement base layer quality is vital for long-term performance. Low stiffness and shear strength can result in a loss of support and increased tensile stresses under loads. To maintain uniform support under concrete pavements and ensure satisfactory performance, a stable, nonerodible, drainable base layer is necessary. The primary objective of this paper is to present the analysis and evaluations conducted as part of the associated research and to recommend improvements to base layer aggregate gradations for the Class 5 and permeable aggregate base specifications used by the Minnesota Department of Transportation. Improved aggregate classes are presented, considering gradation and aggregate shape properties. An analytical gradation analysis was introduced to establish an effective level of gravel-to-sand ratio of 1.4. Other analyses presented in this paper include the use of a revised resilient modulus model that was used in a Monte Carlo simulation to develop probabilities for resilient modulus values depending on gradation and season in Minnesota and the use of the Mechanistic–Empirical Pavement Design Guide for comparing gradation and gravel-to-sand ratio with expected pavement performance. The gravel-to-sand ratio of 1.4 was identified with the following analysis methods: a coordination number and packing analysis, a discrete element model for load-carrying capacity, and a pavement performance analysis using the Mechanistic–Empirical Pavement Design Guide software.

Research Implementation of AASHTOWare Pavement ME Design in Louisiana

Since the release of the first research version of Mechanistic–Empirical Pavement Design Guide software, the State of Louisiana has conducted a series of studies in preparation for adopting the new AASHTO design guide. The objective of this study was to develop an implementation guideline for the full implementation of the AASHTOWare Pavement ME Design program (Pavement ME) in Louisiana. For this purpose, a Louisiana default input strategy that reflected state and local conditions and practices was first developed. Design reliability and performance criteria were established on the basis of a consensus survey and pavement management system (PMS) distress triggers. A total of 162 projects were selected from the existing Louisiana highway network, including flexible pavements with five types of base, rigid pavements with three types of base, and rehabilitation with asphalt overlays. Performance data were retrieved from the PMS database and validated through additional field performance surveys. Through comparison of the performance predicted by the Pavement ME with the measured performance recorded in the PMS database, distress models were evaluated and calibrated according to local Louisiana conditions. Subsequently, a Louisiana Pavement ME Design Guideline that contains all necessary design input information and calibration coefficients was developed. Finally, the practical and economic benefits of the full implementation of the Pavement ME for Louisiana pavement design were demonstrated by a direct comparison with the current 1993 AASHTO design method through a group of thickness design examples and life-cycle cost analyses.

Sensitivity Analysis of Flexible Pavement Sections Using Mechanistic-Empirical Pavement Design Guide

In damage analysis of flexible pavement sections, the AASHTO 2002 design guide, also called as MEPDG (Mechanistic-Empirical Pavement Design Guide), adopted a mechanistic-empirical approach. In the MEPDG, the pavement performance is computed using different input parameters that characterize pavement materials, design features and condition. However, these input parameter values are expected to differ to varying degrees and, therefore, the predicted performance may also vary to some degree depending on the input parameter values. The current study evaluated the influence of four input parameters, namely, reliability level, climate, traffic characteristics and modulus values on the performance of selected pavement sections using MEPDG software. Knowledge gained from the sensitivity analysis of different pavement sections using MEPDG is expected to be useful to pavement designers and others using MEPDG for future pavement design. Specifically, this paper focuses on the sensitivity study of flexible pavement sections at four different locations namely, Chicago in Illinois, Grand Forks in North Dakota, Oklahoma City in Oklahoma, and Houston in Texas, for addressing sensitivity towards climatic conditions. For addressing effect of reliability and traffic three levels of reliability (80%, 90%, 95%) and traffic (low, medium, high) were used, respectively, for designing flexible pavement sections. Additionally, sensitivity towards modulus of subgrade soil was evaluated by designing pavement sections containing 6% lime, 15% class C fly ash (CFA), and 15% cement kiln dust (CKD). The performance of each pavement section was monitored for 240 months (20 years) using MEPDG software by generating plots for rutting, alligator cracking, and International Roughness Index (IRI). It was found that rut predicted by MEPDG is sensitive towards climate, modulus values of chemically stabilized layer and reliability level. IRI values showed sensitiveness toward only reliability and traffic level. Alligator cracking showed sensitiveness toward climate with unexpected trend, modulus of chemically stabilized layer, reliability and traffic level.

Effects of using screening materials in the graded aggregate base layer of flexible pavements

In this paper, the potential use of screening materials in Graded Aggregate Base (GAB) layer of pavements was investigated using aggregate sources in Georgia. Three content levels of screening materials in GAB, i.e. 0%, 25% and 50%, were studied. Morphological analysis of aggregates and Proctor test were conducted to reveal the characteristics of the modified GAB materials, followed by the California Bearing Ratio (CBR) test and Mechanistic-Empirical Pavement Design Guide software simulation to evaluate how the GAB strength and overall pavement performance change with varying amount of screening materials in the GAB layer. The results indicated that the effect of using screening materials in GAB varies and depends on the amount of screening materials used, which changes gradation, and the aggregate types and sources, which exhibit significantly different morphological properties.

An experimental design-based evaluation of sensitivities of MEPDG prediction: investigating main and interaction effects

The mechanistic–empirical pavement design guide (MEPDG) uses mechanistic–empirical models by analysing the impacts of traffic, climate, materials and pavement structure to predict performances of pavement. The MEPDG software uses a three-level hierarchical input to predict performance in terms of terminal International Roughness Index, permanent deformation, total cracking (reflective and alligator), asphalt concrete (AC) thermal fracture, AC bottom-up fatigue cracking and AC top-down fatigue cracking. However, these inputs with different levels of accuracy may have significant impact on performance prediction. This study focuses on the sensitivity of the inputs of MEPDG distresses to identify the effect of the accuracy level of inputs based on experimental design. A local sensitivity analysis is carried out to identify the main effect of inputs considering them as independent variables. Interaction effects are also analysed based on random combination of the inputs. Sensitive input variables and their combinations are evaluated through a multiple regression analysis for respective distresses.

Sensitivity analysis of longitudinal cracking on asphalt pavement using MEPDG in permafrost region

Longitudinal cracking is one of the most important distresses of asphalt pavement in permafrost regions. The sensitivity analysis of design parameters for asphalt pavement can be used to study the influence of every parameter on longitudinal cracking, which can help optimizing the design of the pavement structure. In this study, 20 test sections of Qinghai–Tibet Highway were selected to conduct the sensitivity analysis of longitudinal cracking on material parameter based on Mechanistic-Empirical Pavement Design Guide (MEPDG) and single factorial sensitivity analysis method. Some computer aided engineering (CAE) simulation techniques, such as the Latin hypercube sampling (LHS) technique and the multiple regression analysis are used as auxiliary means. Finally, the sensitivity spectrum of material parameter on longitudinal cracking was established. The result shows the multiple regression analysis can be used to determine the remarkable influence factor more efficiently and to process the qualitative analysis when applying the MEPDG software in sensitivity analysis of longitudinal cracking in permafrost regions. The effect weights of the three parameters on longitudinal cracking in descending order are air void, effective binder content and PG grade. The influence of air void on top layer is bigger than that on middle layer and bottom layer. The influence of effective asphalt content on top layer is bigger than that on middle layer and bottom layer, and the influence of bottom layer is slightly bigger than middle layer. The accumulated value of longitudinal cracking on middle layer and bottom layer in the design life would begin to increase when the design temperature of PG grade increased.

Alternative Source of Climate Data for Mechanistic–Empirical Pavement Performance Prediction

The AASHTO Mechanistic–Empirical Pavement Design Guide (MEPDG) and accompanying Pavement ME Design software emphasize the influence of climate on pavement performance. Several hundred weather history files from ground-based operating weather stations (OWSs) are provided with the MEPDG software. An alternate climate data source, the Modern Era Retrospective–Analysis for Research and Application (MERRA) product from the National Aeronautics and Space Administration, is evaluated here. MERRA is a global climate reanalysis procedure that combines computed model fields with ocean-, airborne-, and satellite-based observations. MERRA has the advantage of uniform worldwide spatial coverage at an approximately 0.5° by 0.67° (latitude and longitude) horizontal resolution, continuous hourly time series from 1979 to the present, and a high level of data quality control. Comprehensive statistical comparisons between MERRA climate data and those from various conventional ground-based sources are presented. Comparisons of MEPDG performance predictions with MEPDG OWS and MERRA climate data for 20 locations distributed across the contiguous United States are also summarized. The statistical and performance prediction comparisons support the conclusion that MERRA is an acceptable and advantageous source for climate data that can be used in place of conventional ground-based OWSs.

Evaluation of Application of Thin HMA Overlay on the Existing Flexible Pavement for High-Traffic-Volume Rural Highways

Thin hot mix asphalt (HMA) overlay of flexible pavement is a conventional method for preventive maintenance of the existing flexible pavements especially in high-traffic-volume rural roads. In this research, MEPDG software is used to investigate the effects of thin HMA overlay on the pavement performance improvement by considering various scenarios for applying overlay layer under dierent climatic conditions. These scenarios consist of applying dense graded asphalt concrete (DGAC) and gap graded asphalt rubber concrete (GGARC) as thin overlay layer with and without thin milling the existing asphalt concrete layer. The analyses are made for the climatic conditions of three cities in Iran. According to the obtained results, the effect of mean annual air temperature on thin HMA overlay performance is more than rainfall. The results also indicate that the performance of GGARC in retention of fatigue cracking is better than DGAC. Furthermore, the results suggest that thin HMA overlay remarkably increases the service life of existing flexible pavement for heavy trac rural highways.

Development of regression equations for local calibration of rutting and IRI as predicted by the MEPDG models for flexible pavements using Ontario's long-term PMS data

Local calibration is an important step before a transportation agency adopts the American Association of State Highway and Transportation Officials' (AASHTO) mechanistic-empirical pavement design guide (MEPDG). This paper presents the challenges of and findings from the local calibration of flexible pavements in provincial highways under the jurisdiction of the Ministry of Transportation of Ontario (MTO). A calibration database was developed that involved a hierarchical framework of the input parameters required for AASHTOWare Pavement ME (the MEPDG software) and the historical field performance data based on the MTO's second-generation pavement management system. A regression analysis is carried out for preliminary calibration of rutting and international roughness index (IRI) models by comparing the predicted distress to observed distress. The analysis suggested that whereas the MEPDG provided fairly unbiased prediction of the IRI value, it often over-predicted the total rutting. Calibrated predicted IRI and rut depth are found for Ontario's local conditions from MEPDG distress prediction models. A further clustering analysis based on Functional Class and geographical zone for the rutting and IRI, respectively, improved the precision of the locally calibrated models.

Simple Design Procedure for New Flexible Pavement Structures Based on Mechanistic–Empirical Pavement Design Guide

This study developed a set of design tables to be used by the New York State Department of Transportation (DOT) to design new flexible pavement structures. To use the tables, the designer selects the design life of the pavement (10 or 15 years), the type of subgrade soil, and the average daily truck traffic volume in the design lane in the first year. The design tables were built for each of the 11 regions of the New York State DOT by assembling the design solutions obtained by running the Mechanistic–Empirical Pavement Design Guide software starting from typical design scenarios. The scenarios followed the design solutions given in the Comprehensive Pavement Design Manual (CPDM) currently used by the New York State DOT. The work included the analysis of New York State DOT traffic data, the compilation of a database of material characterization data for the pavement materials used in New York State, and the regional calibration of distress models used in the design guide for new flexible pavements. The comparison of the newly created design tables with those given in the CPDM shows that the new design solutions are more sensitive to traffic volume than are the design solutions provided in the CPDM. For low traffic volume–-annual average daily truck traffic (AADTT) < 500 vehicles per day–-the recommended total thickness for the hot-mix asphalt (HMA) layers is less in the new design table than in the CPDM, whereas for medium and high traffic volume (AADTT > 500), the recommended total thickness for the HMA layers is slightly higher in the new design tables than in the CPDM.

Structural contribution of open-graded friction course mixes in mechanistic–empirical pavement design

Open-graded friction course (OGFC) is often believed to have no contribution to the structural capacity of flexible pavement. In this study, five types of OGFC mixtures were prepared and tested for rutting potentials, and three of them were tested for dynamic moduli, which were further used to analyse pavement's response and performance based on the procedures in the mechanistic–empirical pavement design guide (MEPDG). It was found that the tensile strain at the bottom of asphalt concrete layers and the compressive strain at the top of sub-grade layer are sensitive to the availability of OGFC, regardless of mixture type. The fatigue and permanent deformation damages of a flexible pavement can be effectively reduced after adding the OGFC layer, due to the alteration of loading frequency, thermal gradient and modulus ratio. Trial designs using MEPDG software in two different climates verify the above observations.