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• The crumb rubber modifier dry process was modified and named the complex process. • Mechanical characteristics of asphalt mixtures significantly enhanced by utilising CRM complex method. • In a complex process, bitumen and aggregates were mixed, then the CRM was added. • CRM complex process provides the homogeneous mixtures and better results. • A complex method has a function of improving asphalt mixtures better than dry and wet methods. Mechanical characteristics of the asphalt binders and mixtures were enhanced by utilising modifiers. The crumb rubber modifier has been introduced to the asphalt modification as an environmentally friendly procedure of scrap tires, to improve the mechanical characteristics of the asphalt. This study aims to modify the dry method for mixing crumb rubber modifier with asphalt and aggregate based on the binder mix design. To achieve this goal crumb rubber modified asphalt mixtures were prepared and tested by applying various tests such as Marshall Stability test, indirect tensile strength test, and wheel tracking test. Three mixing methods of CRM were studied regarding evaluating the stability, rutting, and moisture susceptibility. The crumb rubber modifier dry mixing method was modified and named the complex process. Better results were achieved for enhancing mechanical properties. [ABSTRACT FROM AUTHOR]

A theoretical model was introduced for designing the rubberized asphalt mixtures and validated by mixture tests in this paper. This model is comprised of three parts: fine aggregate gradation design, coarse aggregate gradation design and mixture volumetric design. The rubberized asphalt mixture with a nominal maximum aggregate size of 13 mm (AR-13) was designed with this model. The orthogonal experimental design method was then employed to study the effect of design parameters (air voids (VV), voids in mineral aggregate (VMA) and Fuller-curve's exponent n) on the rutting performance of the mixture. The orthogonal experimental results indicate that the VV and VMA are the two key parameters which affect the rutting performance of the rubberized asphalt mixtures. The design parameter optimal combination and performance requirements of AR-13 were finally recommended based on the experimental results and previous experiences in China and America. [ABSTRACT FROM AUTHOR]

This study focused on the effects of different parameters related to air voids on the creep behavior of asphalt mixture based on micromechanical modeling and virtual test through three-dimensional discrete element method (DEM). By using DEM software named as Particle Flow Code in three dimensions (PFC3D), user-defined micromechanical modeling was conducted for asphalt mixture. And virtual uniaxial static creep test of asphalt mixture was conducted by PFC3D and verified by laboratory creep test. The effects of air void content, microstructure parameters including size, elongated index and orientation of air voids, and air void distribution on the creep behavior of asphalt mixture were investigated based on virtual creep test. It is proved that bigger content, size and elongated index of air voids lead to greater creep strain of asphalt mixture. Compared to vertical orientation, horizontal orientation of air voids is more harmful to the creep behavior of asphalt mixture. Nonuniform distribution of air voids within asphalt mixture also has negative effects on the creep deformation of asphalt mixture, especially for vertical nonuniform distribution of air voids. Therefore, guaranteeing and improving the content, distribution and microstructure of air voids within asphalt mixture are important to keep the high-temperature stability of asphalt mixture. [ABSTRACT FROM AUTHOR]