Fatigue Residual Strength and Damage Evolution Model of SMA-13 Asphalt Mixtures under Different Temperatures and Stress Levels

To reveal the strength degradation law of stone mastic asphalt with 13.2 mm nominal maximum aggregate size (SMA-13) asphalt mixtures under repeated load, direct tensile, compressive, and indirect tensile dynamic load strength tests were carried out under different temperatures (5°C, 15°C, and 25°C) and loading rates (5, 7.5, and 10 MPa/s). Based on this, the mechanical characteristics and applicability of various three-dimensional strength models were compared and analyzed. Subsequently, fatigue tests were conducted at different temperatures, stress levels, and stress states. Direct tensile, compressive, and indirect tensile specimens with different loading cycles (20%, 50%, 65%, and 80% fatigue life) were selected for residual strength testing. Finally, a fatigue damage evolution model considering the effects of temperature and load was established by defining parameters including residual three-dimensional strength ratio, life ratio, and damage sensitivity. The results show that compared with other strength models, the three-dimensional strength characteristics of asphalt mixtures can be better characterized by simplified Desai (S-D) and engineering strength (E-S) models. The three-stage decay law, including linear slow growth in the early stage of damage, power exponential rapid growth in the middle stage, and rapid growth in the late stage, during the fatigue process of asphalt mixture can be objectively reflected by the shrinkage of the S-D strength envelope and E-M envelope under different loading cycles. The E-S damage model, with its high accuracy, was selected to reflect the three-stage fatigue process of the asphalt mixture, achieving the unity of three-dimensional strength failure and fatigue failure. The results provide an important theoretical and experimental basis for estimating the residual strength of asphalt mixture layers with different service lives and for designing the fatigue resistance of asphalt layers. This is a proof-of-concept type of study and further investigation is needed to validate the findings.