Abstract:As a natural modifier of asphalt, rock asphalt has been widely used to improve its thermal stability and aging resistance. However, the thermal cracking resistance of asphalt modified by rock asphalt is unsatisfactory. In order to improve the thermal cracking resistance in low temperature, two kinds of modifiers-styrene-butadiene rubber (SBR) and nano-CaCO 3 -were selected as the compound modifiers, and then implemented to improve the low-temperature performance of the binder. Then, compound asphalt modified by Buton rock asphalt (BRA) was chosen as the study subject. The thermal stability and aging resistance of asphalt modified by BRA, compound-modified asphalt by BRA/SBR, and compound-modified asphalt by BRA and nano-CaCO 3 were determined to identify whether the compound modifiers in the asphalt would have a negative effect on the thermal stability and aging resistance of the asphalt. The dynamic shear rheometer (DSR) test was employed to evaluate the thermal stability. The thin film oven test (TFOT) and pressure aging vessel (PAV) were adopted to determine the aging resistance. The viscoelastic characteristics of asphalt with and without modifiers were revealed to evaluate the low-temperature crack resistance of asphalt modified by compound modifiers. The bending beam rheometer (BBR) creep test was conducted in three test temperatures in order to determine the creep stiffness modulus of the BRA compound-modified asphalt. The viscoelastic model considering the damage caused by loading was established; then, the creep compliance and parameters of the viscoelastic damage model were implemented to evaluate the low-temperature performance of the compound-modified asphalt. The results show that the compound modifiers have little negative effects on the thermal stability and aging resistance of asphalt. The thermal crack resistance of the compound-modified asphalt by BRA/SBR was the best, followed by the compound-modified asphalt by BRA and nano-CaCO 3 within the three materials. The accuracy of forecasting the characteristics of compound-modified asphalt was improved by using the viscoelastic model and considering the damage effect.

In order to reveal the difference and correlation of tensile modulus, compressive modulus, and flexural modulus, the four-point bending fatigue test is used on two kinds of asphalt mixtures—rock asphalt modified asphalt mixture and styrene butadiene styrene block copolymer modified asphalt mixture, were conducted using closed-loop test system. The fatigue damage variable was defined by the modulus attenuation based on the theory of damage mechanics, and the modulus attenuation equation was deduced. Under the same conditions, the initial value and the critical value of the tensile modulus were less than those of the compressive modulus, but the critical damage value and the attenuation slope of the tensile modulus were larger than those of the compressive modulus. The attenuation models of the tensile and compressive modulus of the asphalt mixture during the bending fatigue test were established. Based on the fatigue test results, a new concept of design and analysis was developed, in which the corresponding modulus and its evolution law is chosen according to its actual stress state at each point of asphalt pavement. The results indicate that under the bending fatigue stress state, there exists great differences between the attenuation law of the modulus of tension and compression for asphalt mixture and that the attenuation rate of tensile modulus is greater than that of compressive. Therefore, the tensile zone results in greater damage; the pavement structure of the tensile zone is damaged, which should be given more attention.

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The objective of this research was to improve the scientificity of the design method of the cold patching asphalt mixture (CPAM). Firstly, the curing temperature for CPAM was optimized. In addition, based on the traditional Marshall mix design method, the volume parameters of CPAM were converted, and the low-temperature workability index was added. This is the modified Marshall mix design method to determine the optimal asphalt aggregate ratio of CPAM. Then, the initial strength, forming strength, storage stability, water stability, and high-temperature stability of CPAM were tested. The properties of CPAM designed by using the modified Marshall mix design method were compared with those of CPAM designed by using the traditional Marshall mix design method and the empirical formula method. The test results show that the optimal asphalt aggregate ratio of CPAM is 5.38%. The recommended oven curing temperature for the CPAM specimen is 90 • C. The initial strength and forming strength of CPAM meet the requirements, and the forming strength can reach about twice the initial strength. The stability of CPAM increases with an increase in storage time. High-temperature performance is good. These properties of CPAM designed by using the modified Marshall mix design method were all superior to those of the CPAM designed by using the traditional Marshall mix design method and the empirical formula method, and the water stability is similar to that of the CPAM designed by the traditional Marshall mix design method. The CPAM designed by using the modified Marshall mix design method shows better road performance, which shows that the modified procedure in this study is feasible and can be recommended as the mix design method for CPAM.