Microstructural Evolution of Asphalt Binder under Combined Action of Moisture and Pressure

Moisture-induced damage in asphalt mixes can lead to various distresses in the pavement. The primary cause of such distresses is the loss in adhesion and cohesion properties of the asphalt mixes. One of the factors that lead to the loss of adhesion is the impact of moisture on the properties of asphalt binder. This study provides insight into the evolution of microstructures of asphalt binders before and after moisture conditioning. Moisture conditioning of virgin and antistripping agent or rejuvenator-modified binders was carried out using the Moisture-Induced Stress Tester (MiST), which simulates the conditions prevailing in the field. The surface morphology of the samples was investigated using atomic force microscopy (AFM) before and after moisture conditioning over a period of 1week. The greatest change was noted for the microstructure of the control binder. The binder with a specific rejuvenating agent had microstructures that were different from those of the other binders. All MiST-conditioned binders had rougher surfaces with less evidence of patterns compared with their corresponding unconditioned binders. Such understanding of microstructure will help in better material design and improved pavement performance.