Microscale Property Evaluation of the Interface between Cement Emulsified Asphalt and Aged Asphalt in Emulsified Asphalt Cold Recycled Mixture

To study the microscale properties of the interface between cement emulsified asphalt and aged asphalt in the emulsified asphalt cold recycled mixture, the PeakForce quantitative nano mechanics (PF-QNM) technology of atomic force microscope (AFM) and dynamic shear rheological (DSR) test were used. The results showed that at the microscale, the cement products were spot-like distribution in the surface morphology of the composite system consisting of cement emulsified asphalt and aged asphalt. The approximate interface area could be distinguished by the distribution of the cement products. The gradient of the microscale mechanical properties between cement emulsified asphalt and aged asphalt could quantify the interface thickness. When the penetration of aged asphalt was less than 20 (0.1 mm) and the cement content was 1.0%–2.0%, the mechanical properties of interface were relatively close, and the theory of black aggregate was basically applicable. At the macroscale, the rheological property of the composite system had a good correlation with the microscale modulus of the interface, and a quantitative model of the correlation was proposed. When the penetration of aged asphalt was less than 30 (0.1 mm), the fatigue property of the composite system was relatively close under the same cement content, and the fatigue resistance of the composite system could be improved to a large extent by decreasing the cement content appropriately. Finally, to obtain a more general conclusion, it is necessary to choose a variety of emulsified asphalt and carry out a comparative analysis of different emulsified asphalt content.