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This project evaluated the procedures proposed by the Mechanistic-Empirical Pavement Design Guide (MEPDG) to characterize existing hot-mix asphalt (HMA) layers for rehabilitation purposes. Thirty-three cores were extracted from nine sites in Virginia to measure their dynamic moduli in the lab. Falling-weight deflectometer (FWD) testing was performed at the sites because the backcalculated moduli are needed for the Level 1 procedure. The resilient modulus was also measured in the lab because it is needed for the Level 2 procedure. A visual pavement rating was performed based on pavement condition because it is needed for the Level 3 procedure. The selected cores were tested for their bulk densities (Gmb) using the AASHTO T166 procedure and then for their dynamic modulus in accordance with the AASHTO TP62-03 standard test method. Then the cores were broken down and tested for their maximum theoretical specific gravity (Gmm) using the AASHTO T-209 procedure. Finally an ignition test was performed to find the percentage of binder and to reclaim the aggregate for gradation analysis. Volumetric properties were then calculated and used as input for the Witczak dynamic modulus prediction equations to find what the MEPDG calls the undamaged master curve of the HMA layer. The FWD data, resilient modulus data, and pavement rating were used to find the damaged master curve of the HMA layer as suggested for input Levels 1, 2, and 3, respectively. It was found that the resilient modulus data needed for a Level 2 type of analysis do not represent the entire HMA layer thickness, and therefore it was recommended that this analysis should not be performed by VDOT when implementing the design guide. The use of Level 1 data is recommended because FWD testing appears to be the only procedure investigated that can measure the overall condition of the entire HMA layer.
An accurate measurement or estimation of dynamic modulus (|E*|) of a hot mix asphalt (HMA) mix is important to understand stress-strain behavior of flexible pavements under loading and unloading conditions. The Mechanistic Empirical Pavement Design Guide (MEPDG) (Transportation Research Board, Washington, D.C., 2004) recommends that |E*| be used in all three levels of design (i.e., Level 1, Level 2, and Level 3). For Level 1, |E*| is measured in the laboratory, while it is estimated using the Witczak models for Level 2 and Level 3 designs. The measurement of |E*| in the laboratory is not always feasible because it requires costly equipment and skilled personnel. Consequently, use of empirical models seems to be a reasonable approach to estimate |E*|. Several researchers have reported that the accuracy of the Witczak models varies with local materials and volumetric properties. The present study was undertaken to compare the measured and the estimated |E*| for some commonly used mixes in Oklahoma. Specifically, |E*| of five different HMA mixes, comprised of aggregates from several sources and sizes, binder grades, and air voids, were measured in the laboratory. The Witczak 1999 model (Andrei , 1999) was used to estimate |E*| for each of these mixes. A comparison was made between the measured and the estimated |E*| at four different levels of air voids, namely, 6%, 8%, 10%, and 12%. It was observed that the Witczak 1999 model overestimates |E*| at all four levels of air voids. To address these overestimates, the Witczak 1999 model was calibrated. The calibrated model was similar in form to the Witczak 1999 model but having different numerical coefficients. Verification of this model was done using a mix that was not used in the calibration process. Furthermore, two full depth field cores were obtained to further verify the accuracy of the calibrated model. Three different criteria, namely, goodness-of-fit statistics, matching the measured and the estimated |E*|, and average relative error (%), revealed that the calibrated model exhibits much better performance compared to the Witczak 1999 model. It is expected that the calibrated model would be useful in estimating |E*| for the Level 2 and Level 3 designs for the implementation of the MEPDG in Oklahoma.
This paper presents a comparison study of the experimental results from the falling weight deflectometer (FWD) test and laboratory resilient modulus test on granular subgrade materials and its application in flexible pavement design. Field and laboratory testing programs were conducted to develop a practical methodology for estimating resilient modulus (Mr) values of subgrade soils for use in the design of pavement structures. Soil characterization database was established for lab testing. A multiple regression model can be used to predict Mr value using several factors including soil properties, soil type and state of stresses for three popular American Association of State Highway and Transportation Officials (AASHTO) soil types (A-4, A-6, and A-7-6) in Indiana, and these prediction models developed were verified compared with laboratory Mr tests with high R2 value. In situ Mr seasonal variation based on abundant FWD test data in five field testing sites spread in Indiana was conducted in order to find the correlation between resilient modulus, temperature, and precipitation for the period from 2006 to 2012. The proposed method can accurately predict subgrade Mr of lab testing. However results from lab testing are significantly lower than recommended range by mechanistic-empirical pavement design guide (MEPDG) and backcalculation one using an adjust factor of 3. The design examples showed that the seasonal variation of temperature and precipitation as well as traffic can affect the design thickness by as much as 15 to 20 % in general. The findings of this study are expected to be helpful in the implementation of the pavement design in Indiana and elsewhere.
Complex modulus is one of the key parameters in the Mechanistic-Empirical Pavement Design Guide (MEPDG). The purpose of this study is to implement an accurate and high-efficiency mechanical method to measure and calculate the complex modulus gradient of asphalt concrete cores in different field locations. Because field cores are different from the asphalt mixtures made and compacted in the lab, field cores should not be substituted by lab made lab compacted (LMLC) asphalt mixtures perfectly. For field cores complex modulus measuring methods, except some expensive pavement field testers, empirical and semiempirical models are widely used, but an accurate mechanical test method is more desired. In this research, Arizona, Yellowstone National Park and Texas field cores and three types of asphalt mixtures including hot mix asphalt (HMA), foaming warm mix asphalt (FWMA), and Evotherm warm mix asphalt (EWMA) were used. There were nearly forty field cores with different aging times from these three locations have been collected and tested using this new viscoelastic method. The complex modulus at a random depth and the depth of highly aged pavement can be calculated and estimated from these stiffness gradient figures. After analyzing the results, a strong correlation between test results and solar radiation and some other models have also been established which can be used for estimating the complex modulus of an in-service pavement. The electronic version of this dissertation is accessible from http://hdl.handle.net/1969.1/151814
This research study aimed to determine the dynamic modulus, bending stiffness and fatigue properties of four representative Superpave Hot Mix Asphalt (HMA) mixtures used in the construction of base layers of Kansas flexible pavements and to compare the measured values with those predicted by the National Cooperative Highway Research Program (NCHRP) Design Guide. To achieve these objectives, asphalt concrete beams were tested in third point-bending at constant strain, at four temperatures and four levels of strain. Dynamic resilient modulus tests were performed on asphalt cylindrical specimens at five temperatures and five loading frequencies. Multi-linear regression analysis was performed to develop a linear relationship between the bending stiffness and the fatigue life for the asphalt mixes tested.
Resilient modulus (Mr) of subgrade soil is a key input parameter in all three hierarchical levels of the new mechanistic-empirical pavement design guide (MEPDG). A successful implementation of the MEPDG requires a comprehensive evaluation of Mr database(s) for local subgrade soils and its assessment to determine desired input parameters. To this end, a database containing subgrade Mr values, index properties, standard Proctor, and unconfined compressive strengths for 712 soil samples from 39 different counties in Oklahoma was developed. A total of five stress-based regression models were evaluated using a statistical software package ("SPSS," Version 17), and material constants (k1, k2, and k3) for these soils, categorized in accordance with the American Association of State Highway and Transportation Officials Classification system, were determined. The goodness of fit and the significance of these models were ranked with respect to their R2 and F values, respectively; the MEPDG recommended octahedral model was found to outperform the others. Furthermore, reasonably good correlations of material constants with routine soil properties were established for Level 2 analysis and design. Typical Mr values of common Oklahoma soils for Level 3 analysis and design were also estimated. The findings of this study are expected to help the implementation of the MEPDG in Oklahoma.