In order to reveal the effects of aging on fatigue damage evolution pattern of asphalt mixture, and to reveal the fatigue damage patterns of asphalt pavement during its service life more accurately, the viscoelastic fatigue damage model for the aged asphalt mixtures was proposed based on the Burgers viscoelastic model. The dissipation energy was taken as the damage variable, and the direct tension fatigue tests for asphalt mixture in five different aging degrees were conducted. The viscoelastic parameters of the aged asphalt mixtures were obtained.The calculationmethod of the cumulative fatigue damage was proposed, which considers the aging effects. Moreover, the critical fatigue damage degree and fatigue life calculation equations were derived by employing the fatigue damage model, which were calculated and compared. The calculation errors range from 3% to 18%, which was within an acceptable error range of 30%. The research results show that the aging has a prominent impact on fatigue properties of asphalt mixtures, which could be illustrated by the change of the parameters of the viscoelastic fatigue damage model for the aged asphalt mixtures. The prediction precision of fatigue life is acceptable for using the proposed viscoelastic fatigue damage model.

In order to characterize the ability of tension and compression deformation of asphalt mixture more truly and to improve the test efficiency and scientificity of the tension and compression moduli, the synchronous test method based on the indirect tension test was proposed. The analytical algorithms of the tension and compression resilient moduli of the indirect tension test were derived by integrating the functions of the horizontal and vertical radial strain at the center of a specimen, which was based on Hooke’s law in the two-dimensional stress state and the principle of calculus. The direct tension, unconfined compression, and indirect tension moduli tests were conducted in both dynamic and static loading states, and the test results were compared in different loading states. The research results indicated that the synchronous testing method based on the indirect tension test is effective, and there is a significant difference between the tension and compression moduli of asphalt mixture, and the dynamic resilient modulus from the indirect tension test increases by a power function with the increase of loading frequencies.

In this paper, two types of Styrene-Butadiene-Rubber (SBR) were adopted to modify the Buton-rock asphalt (BRA) modified asphalt, aiming to select a binder with excellent comprehensive performances. Powder SBR and latex SBR (0%, 2%, 4%, 6%, and 8%), were mixed with the 15 w% BRA modified asphalt. The characterization of rheological properties included dynamic shear rheometer, rotational viscometer, and bending beam rheometer test. The short-term aging performance was characterized by the ratio of the complex shear modulus from the un-aged and rolling thin film oven (RTFOT) -aged asphalt. Besides, Fourier transform infrared spectroscopy and scanning electron microscopy were conducted to reveal the modification mechanism. It was observed that the two kinds of BRA-SBR modified asphalt had preferable anti-crack capacity at low temperatures than the BRA modified asphalt. Compared with latex SBR, the powder SBR significantly improved the high-temperature performance, and the anti-aging capacity was stable. However, some negative influence occurred by the addition of latex SBR on the anti-rutting and short-term aging property. According to the micro-mechanism analysis, adding powder SBR and latex SBR into BRA modified asphalt was a physical blending process, and they improved the dispersion state of BRA in asphalt. Based on the comprehensive performance, the recommended combination was BRA and powder SBR.

The objective of this article is to establish a fatigue equation based on the true stress ratio for cement-treated aggregate base materials. The true stress ratio herein means the ratio of the stress and the true strength of the cement-treated aggregate base materials related to loading rates and curing times. The unconfined compressive strength tests and compressive resilience modulus tests were carried out under various loading rates and curing times of 3, 7, 14, 28, 60, 90 days, respectively. According to the test results, the relationship between the unconfined compressive strength (a mix design parameter in China) and the compressive resilience modulus (a structural design parameter and the construction quality control parameter in China) of the cement-treated aggregate base material with different curing times was established. However, it was found that the strengths varied with the loading rates, which is not reflected in the existing fatigue equations. Therefore, it is questionable to obtain the stress ratio of fatigue tests with a fixed strength value obtained from the standard strength test where the loading rate is fixed (in China, the fixed loading rate is 1 mm/min for cement-treated aggregate base materials). Thus, in this paper, the four-point bending strength (i.e., flexural strength) test was carried out at different loading rates to resolve such deficiencies. Based on the strength test results at different loading rates, the true stress ratio of the fatigue test corresponding to the fatigue loading rate can be calculated. Then the four-point bending fatigue test was conducted to establish an improved fatigue equation characterized by the true stress ratio. The results show that the patterns of variation for unconfined compressive strength increasing with the curing time were similar to that of the compressive resilience modulus. The fatigue equation curve based on the true stress ratio can be extended to the strength failure point of (1, 1), where both the true stress ratio and the fatigue life value are one. The internal relationship between the strength failure and the fatigue failure was unified. This article provides a theoretical method and basis for unifying the mix design parameters and the construction quality control parameters.