Study on unified strength approach of asphalt mixture under different stress conditions

•The impact of loading rate on the strength was evaluated.•The impact of different loading mode on the strength was evaluated.•A simplified unified strength model was established. The material strength, as a critical input parameter for asphalt mixture design, has a significant impact on the asphalt road durability and service life, however, the material strength conducted under different stress modes varied a lot, which can cause the problem of inappropriate strength selection in the design stage. This research conducted a comprehensive evaluation to obtain a unified asphalt mixture strength model for various stress modes. In this research, four test modes of uniaxial compression tests, four-point bending tests, indirect tensile tests, and direct tensile tests at various loading rates were performed for the SBS (Styrene-Butadiene-Styrene) modified AC-13 asphalt mixture, the impact of asphalt mixture strength with different loading rate was achieved under various stress conditions, and the link between strength–strain rate and strength ratio–loading rate ratio was found and the asphalt mixture's unified strength master curve model was constructed. The results found that the loading rate has a significant influence on asphalt strength when it increased from 0.02 MPa/s to 220 MPa/s, and asphalt strength increased by 3.29 to 6.53 times for different test modes, and the strength increased in a power function with the increase of loading rate under different stress modes. The result also found that and compressive strength reached up to 12 times of indirect tensile strength, while the increasing rate of strength decreased as the loading rate climbed. This research also established the power function of σ/σ0 = 0.994 (v/v0)0.1173 between the strength ratio and loading rate ratio, which provided an effective model to calculate the asphalt mixture strength under different stress conditions.