Storage Stability and Compatibility in Foamed Warm-Mix Asphalt Containing Recycled Asphalt Pavement Binder

Applying foamed warm-mix asphalt (FWA) containing recycled asphalt pavement (RAP) binder in pavement construction technology is an energy-saving and resource-recycling approach. However, the effectiveness of blended binders in improving road performance depends on the storage stability and compatibility in the binder's composition to be effective and durable. To address the compatibility and storage stability issues of the foamed warm reclaimed asphalt (FWRA) in the actual practice, 15 FWRA samples were designed considering varying RAP binder contents and storage conditions. The conventional binder index properties, rheological property, storage stability, and compatible performances were fully characterized. Fourier transform infrared spectroscopy (FTIR) analysis was conducted to understand the internal chemical reactions and corresponding mechanisms, and bivariate correlation analysis was employed to evaluate the relationship between independent variables. The testing results showed that the proposed testing configurations were validated to simulate the storage condition in the actual practice. Increased RAP binder content can worsen the compatibility of unstored FWRA, but relatively satisfactory compatibility can be obtained when the RAP binder content is relatively low. Regardless of the content of RAP binder, the blended FWRA binder is less compatible after the final storage stability test, and thus appropriate modification methods should be proposed to improve the compatibility after storage in the future. FTIR results showed the macromolecular asphaltenes of RAP binder migrate downward during the storage stability test, leading to poor compatibility of FWRA. The B of FTIR is suggested as the microscopic evaluation index, and G*/sin delta difference (35 degrees C) is suggested as the macroscopic performance verification index of storage stability for FWRA.