The Adhesion and Moisture Damage Resistance between Castor Oil-Based Bio-Asphalt and Aggregates under the Action of Thermal-Oxidative Aging

Abstract

This study aims to investigate the adhesion properties and moisture damage resistance between castor oil-based bio-asphalt (COBA) and aggregates under the action of thermal oxidation. Different dosages of castor oil-based bio-oil (5%, 10%, and 15%) were used to prepare the COBA by mixing it with petroleum asphalt. The short-term and long-term aging of COBA were simulated by the rolling thin-film oven test (RTFOT) over 85 min and 385 min, respectively. The boiling method, photoelectric colorimetry, contact angle test, and contact angle moisture susceptibility test (CAMSI) were used to evaluate the adhesion and exfoliation of the COBA–aggregates before and after thermal oxygen aging. Then, the aging degree of COBA was quantitatively evaluated by Fourier transform infrared (FTIR), and the correlation between aging condition and COBA–aggregates adhesion was analyzed. The results showed that the cohesion in COBA increased by 23.1% on average due to the addition of bio-oil. And the adhesion between COBA and aggregates increased by 5% due to the acidic compounds formed in the process of interaction with silicates on the surface of the aggregates. After short-term thermal oxidation, the adhesion between COBA and its aggregates was further improved as the polar components in the asphalt binder increased when the bio-oil dosage was less than 10%. However, with the continuous increase in the bio-oil amount and thermal oxidation degree, the adhesion decreased by 12.6% when compared to the virgin status; in addition, the adhesion grade decreased. Also, a low dosage of bio-oil was found to also improve COBA’s resistance to moisture damage, and helped to reduce moisture sensitivity during the interaction with asphalt binder. However, the acidic compounds that were generated by the reaction with hydrolyzed aggregates in the presence of asphalt binder reduced the adhesion between COBA and the aggregates. Finally, FTIR revealed a good correlation between IC=O and adhesion between COBA and the aggregates.