Investigation on fatigue characteristics of polyphosphoric acid modified high dosage bio-asphalt mixture under three-dimensional stress state

Abstract

Polyphosphoric acid modified high dosage bio-asphalt (PMBA) could provide a new direction for saving asphalt resources. The fatigue performance of asphalt mixture is one of the critical factors that should pay more attention in achieving a life cycle cost-effective. This study aims to investigate the strength and fatigue performances of the PMBA mixture. The stress states of mixture tests include indirect tension, direct tension, and unconfined compressive, respectively. The S-N fatigue equations, Desai yield surface, and normalized fatigue equation were determined. At the same loading rate, the strength values of indirect tension and direct tension are close, while the strength of unconfined compressive is much larger than theirs. The S-N fatigue equations parameter obtained based on stress levels vary significantly under different stress states, with unconfined compressive being much more significant than indirect tension and direct tension. The Desai strength yield surface gradually expands outward with the increase of loading velocities. The diffusion rate decreases as the loading velocities increase. According to the Desai yield surface, the new fatigue stress path and stress ratio were defined. The normalized fatigue equation for PMBA mixture under various stress states is Nf=Δ-4.58R2=0.99. The normalized n value of PMBA asphalt mixtures is 4.58, 2.7% lower than that of SBS modified asphalt mixtures. This study is meaningful for applying high dosage bio-asphalt. The application of PMBA also provides new ideas for low carbon and environmental protection in road engineering.