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The impact resonance (IR) test is a nondestructive test method that is used to characterize the linear viscoelastic behavior of asphalt concrete. This method is preferred over other methods because the setup of the IR test is simpler, more efficient, and less expensive than standard axial compression dynamic modulus (|E*|) tests. Researchers originally developed the IR test method for cylindrical specimens of asphalt mixtures and concluded that this method can serve as an alternative to |E*| tests. However, the geometry (100 mm in diameter by 150 mm in height) of the cylindrical specimens used in these tests prohibits the use of IR tests for field cores. Therefore, researchers began to consider thin disk-shaped specimens for IR testing because thinner geometry of such specimens better represents slices of field cores. In this study, a test procedure was developed to evaluate the use of thin disk-shaped specimens for IR tests in order to determine the |E*| values of asphalt mixtures. The IR test protocol was optimized using 2 IR test methods (referred to as Case 1 and Case 2 in this work) under various test conditions to ensure the highest possible quality of the data. Optimal test methods were proposed based on the repeatability and variability of the resonant frequency and phase angle data and the ability of the different test conditions to provide data that best match the |E*| values obtained from standard axial compression |E*| tests. The results demonstrate that the |E*| values of thin disk-shaped specimens determined from the optimized IR tests are similar to the |E*| values of long cylindrical specimens determined from conventional |E*| AASHTO T 342-11 tests and IR tests.
Characterization of asphalt concrete is of paramount importance for the sound structural design and analysis of flexible pavements. Of equal importance is the availability of test methods that can provide an accurate and reliable measure of the required engineering properties of the material. For routine applications in material characterization, selected test methods should be reliable, simple, quick, repeatable, and cost eective. The use of nondestructive test (NDT) methods has proven to provide such characterization capabilities. Among those methods, the impact resonance (IR) test is a vibration based NDT method, and has been increasingly used for asphalt concrete evaluation and characterization in the past two decades. The majority of studies regarding the IR test in asphalt concrete applications have been focused on comparison of the IR test moduli with the moduli obtained from conventional asphalt concrete dynamic modulus tests and the predictive equations. In this dissertation, the IR test was utilized to characterize the properties of asphalt concrete mixtures and recycled asphalt pavement (RAP) binder through mixture testing at a range of temperatures. To this eect, several independent studies were conducted.The second order equation of motion assumption in rheological modeling of the IR test response was evaluated for asphalt concrete testing. A set of asphalt concrete specimens was tested with the IR test, and the obtained signals at a range of temperatures were evaluated by means of the Hankel matrix method. The results showed that the assumption is violated for asphalt concrete testing, especially at high temperatures, mainly due to the presence of noise in the obtained response. However, the Hankel method was employed to filter out the noise. It was seen that the assumption could be employed for asphalt concrete at a range of temperatures including high temperatures, provided that the filtering is performed on the obtained signal. The results also showed that the employed filtering procedure produced improvements for the IR test material dependent responses, resonant frequency and especially damping ratio calculations.The IR test results are influenced by specimen size and testing configurations. A study was conducted to investigate the influence of aspect ratio (length/diameter) of laboratory specimens on the frequency response of asphalt concrete when tested with the IR. The IR test, performed in a longitudinal mode, demonstrated that the test is repeatable and reproducible. The test results indicated that the frequency response increased as the aspect ratio increased approximately up to 0.7, and then it decreased with a nonlinear trend as the aspect ratio increased beyond 0.7, indicating that the tendency of the frequency response reached a plateau as the aspect ratio increased. It was inferred from the test results that there was a threshold aspect ratio at which the fundamental longitudinal frequency mode was not the dominant frequency mode. Velocity calculations from measured resonant frequencies indicated that the true material properties for the longitudinal mode could be attained at an aspect ratio of as low as 1.In another study, the sensitivity of the resonant frequency response of the IR testing of asphalt concrete to asphalt concrete mixture parameters was investigated. The IR tests were performed on disk-shaped asphalt concrete specimens at the transverse (flexural) mode of vibration at a temperature range of approximately -10 to 50oC. Test results revealed that the relationship between the resonant frequency and temperature was described by a polynomial fit, and it was shown through statistical analysis that the slopes of the fit were significantly aected by mixture parameters such as air void content and binder content. Also, the statistical formulation (predictive model) between the resonant frequency and the asphalt concrete mixture parameters were established for a given aggregate gradation of nominal maximum size and an aggregate specific gravity. The prediction accuracy of the model was evaluated by independent data sets, and the test results indicated that the maximum error between the measured and predicted resonant frequencies was not more than 9 percent.In an eort to characterize the properties of recycled asphalt pavement (RAP) binder with the IR test through asphalt concrete mixture testing, two approaches were utilized. An approach is proposed for determination of binder properties through the IR testing of mixtures with RAP and binders with known engineering properties. The IR tests were performed in the longitudinal mode at a range of temperatures between 3 and 35oC. Also, RAP binder and virgin binders were tested using dynamic shear rheometer (DSR) at the same temperature range as the IR testing. It was seen that the IR test ranked the expected trend of binder stiness with respect to the resonant frequency of mixtures. The results indicate the potential of the proposed concept and feasibility of the approach in determining binder properties, including properties of the RAP binder. A practical method is proposed for determination of binder properties based on mixture testing.In the second approach, the IR test potential to characterize the low-temperature properties of an RAP binder that incorporated a rejuvenating agent was investigated. This approach included testing of mixes with virgin binders and pure RAP mixes treated with a rejuvenating agent at dierent levels using the IR, as well as testing of blends of recovered RAP binder, rejuvenator, and virgin binder using bending beam rheometer (BBR). The results showed that the IR test can properly rank the expected stiness of binders through mixture testing. The results also indicated high linear correlations between mixture properties obtained from the IR test (modulus and phase angle) and binder properties obtained from the BBR test (stiness and m-value, a relaxation index). The results clearly demonstrate the potential of IR to be used for grading and optimization for the asphalt binder of RAP and rejuvenator content in lieu of the binder recovery method.
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.
TRB’s National Cooperative Highway Research Program (NCHRP) Report 702: Precision of the Dynamic Modulus and Flow Number Tests Conducted with the Asphalt Mixture Performance Tester describes the development of precision statements for the dynamic modulus and flow number tests conducted with the Asphalt Mixture Performance Tester.
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.
The modulus is one of the primary asphalt mixture properties used for the mechanistic performance prediction of asphalt pavements. Dynamic modulus testing is a common method of measuring mixture modulus as a function of loading frequencies and temperatures. This paper presented the results of a ruggedness study of dynamic modulus testing in indirect tension mode to evaluate the factors that were most likely to affect the final results. Specimen thickness, air void content, gauge length, test temperature, and horizontal strain level, which are the critical factors that affect the dynamic modulus of asphalt concrete, were selected for the ruggedness analysis. Two different asphalt mixtures with the participation of two laboratories were used in the study. Based on the selected values for the different variables, air void content was found to be the significant factor that affected dynamic modulus testing and dynamic modulus values. The other factors did not appear to have a major impact on the test results; however, reasonable tolerances were obtained for the other parameters investigated in this paper.
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.