Characterization of recovery properties of asphalt mixtures
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Recovery of a material refers to a process that the deformed material reduces its stored energy and restores its deformation after the load is removed. Characterization of recovery plays a significant role in damage measurement and prediction of asphalt pavements. However, major attention has been paid to the loading phase of a material, while much less attention is paid to the unloading phase, or the recovery phase. Even though there is some literature addressing this issue, the testing and analysis methods are empirical or phenomenological which emphasize correlation and not causation. To fill these research gaps, this paper presents a new test and analysis method to obtain the true mechanical properties in the recovery phase and characterize recovery based on its causal relationship. The internal stress is the key to derive the true mechanical properties in the recovery phase because it is the driving force for the recovery. A creep and step-loading recovery (CSR) test is innovated to measure the internal stress at different points during the recovery of an asphalt mixture specimen. Since such a test method is novel for asphalt materials, its validity and accuracy are examined by comparing the measured value to the theoretical value. The results show that the CSR test is valid and accurate to measure the internal stress for asphalt mixtures. The internal stress measured by the CSR test is used to define a new type of material property: the recovery modulus, which is an indicator of the material's capability to recover. The characteristics of the recovery modulus is studied at three different nondestructive loading levels and one destructive loading level. It is found that the recovery modulus of the undamaged asphalt mixtures does not change with the change of the loading level. However, the recovery modulus of the damaged asphalt mixtures is different from that of the undamaged asphalt mixtures. This difference is due to the loss by the damaged material of part of its capability to recover. The CSR test and internal stress model innovated in this paper can be applied to any viscoelastic materials to determine their recovery properties. Because the CSR test has been validated in this study, the entire test procedure can be shortened to two steps including a nondestructive and a destructive CSR tests. Based on the results of the two CSR tests, the internal stress can be simulated using the exponential model developed in this paper, and the recovery modulus is then determined during the recovery phase of the material. 2013 Elsevier Ltd. All rights reserved.
Construction and Building Materials
author list (cited authors)
Luo, X., Luo, R., & Lytton, R. L.
complete list of authors
Luo, Xue||Luo, Rong||Lytton, Robert L