Influencing factors and mechanism analysis for evaluation of fatigue characteristics of emulsified asphalt residues

The stress-strain response characteristics, fatigue damage characteristics, and fatigue life prediction of emulsified asphalt residues were investigated based on the simplified viscoelastic continuum damage (S-VECD) theory. Microscopic approaches such as Fourier transform infrared spectrometer (FTIR), scanning electron microscope (SEM), and atomic force microscope (AFM) were adopted to study the influence mechanisms of morphology structure, blending modification, and fatigue damage of emulsified asphalt residues. Research results show that the damage curves of common emulsified asphalt residues are staggered. The addition of modifiers makes the damage curves no longer staggered, and the fatigue performance of emulsified asphalt residues is improved. Furthermore, the improvement effect of the SBR modifier is more obvious. The damage curves of modified emulsified asphalt residues prepared by the EN and ASTM evaporation methods are smoother than those prepared by the DHM evaporation method, which indicates that the residues obtained by the EN and ASTM evaporation methods have stronger resistance to damage. From the perspective of the fatigue life improvement, the maximum fatigue life of common emulsified asphalt residues prepared by different evaporation methods is 56.9% higher than the minimum fatigue life, and the SBS and SBR modified emulsified asphalt residues increase by 179.1% and 67.8%, respectively. This means that the modified emulsified asphalt residues are highly affected by the evaporation methods, and the fatigue life of modified emulsified asphalt residues is the smallest under the DHM evaporation method. Functional group contents, colloid structures, and microscopic roughness will be changed by adding modifiers and adjusting evaporation methods. The DHM evaporation method is more likely to cause oxidation of modified emulsified asphalt residues and promote the production of more asphaltenes. It decreases the solubility of micelles and enhances the gelation. As a result, the fatigue performance of emulsified asphalt residues reduces, and the evaluation result of fatigue performance is affected. AFM test results suggest that the exchange condensation reaction between O^2- and H⁺ occurs in the molecular structure of modified emulsified asphalt residues prepared by the DHM evaporation method. In addition, chemical cementation structures may appear, and thus the accurate characterization and evaluation of fatigue performance of emulsified asphalt residues are affected.