Laboratory testing of road performance and mechanism study of SBR/APAO composite modified asphalt and its mixtures

Styrene butadiene rubber (SBR) modified asphalt, favored for its excellent low-temperature performance, is extensively applied in cold regions. However, SBR modified asphalt mixture is prone to typical distresses, such as rutting and shoving, at high temperatures. Therefore, amorphous poly-alpha-olefin (APAO) with outstanding high-temperature stability was used for the composite modification of SBR modified asphalt. Firstly, the optimum dosage of composite-modified asphalt was decided through conventional physical properties and rheological tests. Subsequently, fluorescence microscopy (FM) and Fourier transform infrared spectroscopy (FTIR) tests were performed to investigate the phase structure and modified mechanism of SBR/APAO composite modified asphalt, respectively. Finally, the mechanical performance and pavement properties of composite modified asphalt mixtures under complex stress conditions were studied through systematic experimental research. The results show that a composition of 3% SBR and 5% APAO significantly enhances high-temperature stability and fatigue resistance of the asphalt. the optimal mixing and compaction temperatures of the asphalt are 170~175°C and 159~164°C, respectively. A spatial network structure with SBR particles as nodes and APAO uniformly dispersed around them is formed; the modification mechanism involves both physical mixing and chemical reactions. The established three-dimensional failure envelope surface model and dynamic modulus master curve, as well as road performance test results show that compared with SBR modified asphalt, the strength and stiffness of the composite modified asphalt mixture were significantly enhanced, with thermal stability increasing by 173.6%. Additionally, both water stability and fatigue durability showed marked improvements. The comprehensive analysis results indicate that the addition of APAO and SBR for composite modification can improve the micro and rheological properties of SBR asphalt. • A spatial network structure with SBR as the nodes and APAO particles uniformly dispersed around them was formed in SBR/APAO composite modified asphalt. • A three-dimensional stress state failure criterion of composite modified asphalt mixture and a dynamic modulus master curve model considering the tensile-compressive difference were established. • The fatigue durability, thermal stability, and water stability of asphalt were improved after composite modification.