Mechanistic-Empirical Design Of New Research Articles

Investigation causes of pavement structure destruction using new AASHTO mechanistic-empirical procedures for improving roads function in different climatic condition of Iran

In recent years, procedure of AASHTO (American Association State Highway and Transportation Officials) Guide for Design of Pavement Structures distanced from first empirical procedure and advanced toward mechanistic-empirical procedures. “Guide for Mechanistic-Empirical Design of New and Rehabilitated Pavement Structures” in 2004 and its attached software M-EPDG is the result of this new procedure that AASHTO presented it through projects NCHRP 1-37 A and NCHRP 1-40 B with cooperation of NCHRP (National Cooperative Highway Research Program) and FHWA (Federal Highway Administration) institutions. In this paper, required data for software analyzing of three real pavement structures pieces collected from three different climatic areas and pavement structures modeled in software by entering data into software. Modeled sections by this software were analyzed destructions, and, regarding to obtained results, common designing pavement structures procedures compared with the new way of AASHTO, and efficiency rate of related software investigated in three different climatic areas of Iran. Toward this process, Save, Hamadan and Qazvin, Boin Zahra cities selected as a case study and then studied. Results of software analyzing showed that the designs of old AASHTO method in tempered climate of country met all criteria of designing but in both of cold and warm areas, some destructions at designed pavement structures via this method exceeded from allowed rate and according to presented destructions, will be excessed more in future. This destruction in case project of cold area was longitude crack and was furrowing of pavement structures bed in warm area. Then, probable causes of mentioned destructions studied in pavement structures projects and procedures designed for rehabilitating pavement structures for met all of the designated criteria. Also, in Iran some suggestions indicated about required conductions for application of new method of AASHTO.

Investigation causes of pavement structure failure using new AASHTO mechanistic-empirical procedures for optimization roads performance in different climatic condition of Iran

Abstract
 In recent years, procedure of AASHTO (American Association State Highway and Transportation Officials) Guide for Design of Pavement Structures distanced from first empirical procedure and advanced toward mechanistic-empirical procedures. “Guide for Mechanistic-Empirical Design of New and Rehabilitated Pavement Structures” in 2004 and its attached software M-EPDG is the result of this new procedure that AASHTO presented it through projects NCHRP 1-37 A and NCHRP 1-40 B with cooperation of NCHRP (National Cooperative Highway Research Program) and FHWA (Federal Highway Administration) institutions. In this paper, requireddata for software analyzing of three real pavement structures pieces collected from three different climatic areas and pavement structures modeled in software by entering data into software. Modeled sections by this software were analyzed failure, and, regarding to obtained results, common designing pavement structures procedures compared with the new way of AASHTO, and efficiency rate of related software investigated in two different climatic zone of Iran. Toward this process, Save- Hamadan and Qazvin- Boin Zahra cities selected as a case study and then studied. Results of software analyzing showed that the designs of old AASHTO method in tempered climate of country met all criteria of designing but in both of cold and warm areas, some failure at designed pavement structures via this method exceeded from allowed rate and according to presented failure, will be excessed more in future. This destruction in case project of cold area was longitude crack and was rutting of pavement structures subgrade in warm area. Then, probable causes of mentioned failures studied in pavement structures projects and procedures designed for rehabilitation pavement structures for met all of the designated criteria. Also, in Iran some suggestions indicated about required conductions for application of new method of AASHTO.

Volume-Change Behavior of a Compacted Low-Plasticity Clay From Double-Odometer Tests

Abstract The compressibility of compacted soils is not only a function of soil type and density but also stress state, which is influenced by the existing matric suction and can be described using the fundamentals of unsaturated soil mechanics. This paper presents data from double-odometer tests on low-plasticity clay that demonstrates the effects of dry density and water content on volume-change behavior. Using the data set developed, the drained constrained modulus is determined using the stress–strain relations obtained from conventional odometer tests on soaked specimens, as well as specimens at their molding moisture content. The change of modulus with respect to degree of saturation is discussed and placed in context with the model used in the Guide for Mechanistic-Empirical Design of New and Rehabilitated Pavement Structures [ARA, ERES Consultants Division, 2004, “Guide for Mechanistic-Empirical Design of New and Rehabilitated Pavement Structures,” Final Report NCHRP Project 1-37A, Transportation Research Board of the National Academies, Washington, D.C.]. A procedure for predicting the undrained modulus from the constitutive relation for drained loading and the predicted excess pore pressure caused by loading based on a modification of Hilf’s equation [Hilf, J. W., 1948, “Estimating Construction Pore Pressures in Rolled Earth Dams,” Proceedings of the 2nd International Conference on Soil Mechanics and Foundation Engineering, Vol. 3, International Society for Soil Mechanics and Foundation Engineering (ISSMGE), London, pp. 234–240] is also presented and discussed.

Incorporation of Subgrade Modulus Spatial Variability in Performance Prediction of Flexible Pavements

Recent efforts under the auspices of the National Cooperative Highway Research Program (NCHRP) have resulted in the development of a Guide for Mechanistic-Empirical Design of New and Rehabilitated Pavement Structures. The recently developed Mechanistic-Empirical Pavement Design Guide (MEPDG) employs an iterative procedure for accumulating damage over the entire design period. It follows by mechanistically computing the pavement response (i.e., stresses and strains) and empirically translating these responses into individual distresses and pavement roughness. In the current procedure, the subgrade is divided into several sublayers, and an average modulus is used to define the mechanical behavior of each sublayer, without any consideration of the spatial variability in the subgrade modulus. This paper aims to evaluate the effect of such variability on the overall performance of flexible pavements. To achieve this objective, actual field data were collected and analyzed to determine the frequency distribution of the subgrade modulus, which was incorporated in three-dimensional (3D) finite element models of typical flexible pavement structures. The response obtained from the 3D finite element analysis was used to predict the pavement performance using the MEPDG transfer functions. The results of this study showed that the higher the variability is in the subgrade resilient modulus, the higher the variability is in the pavement response. Furthermore, the effect of the spatial variability in subgrade modulus was more pronounced on the prediction of rutting than that of the fatigue cracking.

Comparison of Dynamic Moduli for Asphalt Mixtures Determined from Different Geometries and Compactions

Abstract The MEPDG (ARA, Inc., “NCHRP 1–37A Final Report: Guide for Mechanistic-Empirical Design of New and Rehabilitated Pavement Structures,” NCHRP Program 1–37A Project, National Research Council, Washington, D.C., 2004) introduces the dynamic modulus as the material property to characterize asphalt concrete. One of the challenges of acquiring the dynamic modulus from existing pavements is the standard dimensions of the test specimen. The specimen size specified in AASHTO TP62–07 (2007, “Standard Method of Test for Determining Dynamic Modulus of Hot-Mix Asphalt Concrete Mixtures,” AASHTO, Washington, D.C.) cannot be obtained from many pavement layers. This study evaluates two other geometries, indirect tension specimens and prismatic specimens, to determine whether the measured dynamic modulus is the same as the modulus obtained from TP62 protocol. This study provides a comparison of the effects of a non-uniform state of stress and anisotropy. These effects are isolated by comparing specimens prepared by Superpave gyratory compaction and vibratory steel-wheel compaction. The comparisons are verified using four 12.5-mm surface course mixtures with different aggregate shapes and binder types, and one 25.0-mm base mixture. The results show that the difference between the dynamic modulus values obtained from different geometries is statistically insignificant. The results provide justification for using alternative methods for acquiring the dynamic modulus experimentally—specifically, for previously constructed pavements.

Predicting the Resilient Modulus of Asphalt Concrete from the Dynamic Modulus

The NCHRP 1-37A Guide for Mechanistic-Empirical Design of New and Rehabilitated Design Structures introduces the dynamic modulus as the material property to characterize asphalt concrete. This is a significant change from the resilient modulus used in the previous AASHTO pavement design guide. This paper presents an analytical method of calculating the resilient modulus from the dynamic modulus. It involves the application of multiaxial linear viscoelastic theory to linear elastic solutions for the indirect tension test developed by Hondros. The prediction method is verified by using three 12.5-mm surface course mixtures with different aggregate shapes and binder types and one 25.0-mm base mixture. Results show that the predicted and measured resilient modulus values are in close agreement. The results provide a forward model for the potential back-calculation of the dynamic modulus from resilient modulus databases already available in highway agencies, such as the Long-Term Pavement Performance Materials Database.

Assessment of Distress in Conventional Hot-Mix Asphalt and Asphalt-Rubber Overlays on Portland Cement Concrete Pavements: Using the New Guide to Mechanistic-Empirical Design of Pavement Structures

The purpose of this study is to assess the way distresses are predicted by using the new Mechanistic-Empirical Design of New and Rehabilitated Pavement Structures (design guide), developed under NCHRP Project 1-37A. Two pavement sections were used: a conventional hot-mix asphalt reconstruction and an asphalt-rubber overlay on a portland cement concrete (PCC) pavement. The design guide does not include rehabilitation design for asphalt-rubber overlays. However, many large-scale asphalt-rubber overlays on interstate highways in Arizona have been built and monitored for performance, providing an opportunity to determine to what degree the design guide can predict their performance. The input data for both types of pavements were derived from two different projects on the same highway, Interstate 40. The actual data measurements that summarize the pavement performance were compared with calculated values obtained by using the design guide. Three pavement performance parameters were evaluated on the basis of t...

Evaluation of the Effect of Lime Modification on the Dynamic Modulus Stiffness of Hot-Mix Asphalt: Use with the New Mechanistic-Empirical Pavement Design Guide

Hydrated lime is often used as a mineral filler or antistripping additive in hot-mix asphalt (HMA). Many agencies across North America require the use of lime in all HMA mixtures being placed on high-volume roadways. Despite this wide use of lime, its effects on the HMA mixture dynamic modulus (E*) stiffness have rarely been evaluated. The new mechanistic-empirical (M-E) pavement design guide, Guide for Mechanistic-Empirical Design of New and Rehabilitated Pavement Structures, developed under NCHRP Project 1-37A uses E* as the primary material property of asphalt mixtures for the HMA characterization. A comprehensive study was completed at Arizona State University to assess the effect of lime addition on the E* stiffness of HMA mixtures. The study demonstrated that the standard test and design methodologies of the new M-E pavement design guide could be used effectively for lime-modified HMA mixes. With these methodologies, hydrated lime was found to increase the E* of HMA mixtures by 17% to 65% across the...