Influence of castor oil-based bio-oil on the properties and microstructure of asphalt binder

Abstract

This study intends to investigate the influence of castor oil-based bio-oil on the properties and microstructure of asphalt binder. Castor oil-based bio-asphalt (COBA) were prepared by mixing 0%, 5%, 10%, and 15% bio-oil with petroleum asphalt. Their conventional performance was evaluated based on three indexes, including penetration, ductility and softening point. The high- and low-temperature properties of COBA were obtained by dynamic shear rheometer (DSR) and bending beam rheometer (BBR), and the thermostability was analyzed by thermogravimetry (TG). Meanwhile, the moisture-induced shear-thinning index (MISTI) was tested to evaluate the resistance to moisture damage of COBA. Furthermore, the change of microstructure of asphalt modified by bio-oil was revealed by fourier transform infrared reflection (FTIR). The results showed that castor oil-based bio-oil could soften asphalt and reduce its consistency. As the bio-oil was added, the high-temperature performance of COBA was weakened to some extent by decreasing of complex modulus (G*) and rutting factor (G*/sinδ). The thermostability of COBA was slightly higher than that of matrix asphalt, but it would decrease with the addition of bio-oil. Under the same temperature, the ductibility and m value of bio-asphalt increased with added bio-oil, which change trend was opposite for S value and k value. It indicated that the bio-oil increased the low-temperature flexibility and ductibility of petroleum asphalt. MISTI showed that COBA had better resistance to moisture damage than matrix asphalt. FTIR identified castor oil-based bio-oil as a compound mainly composed of light components, and it is mainly physically blended with petroleum asphalt. Also, the amount of acidic compounds in COBA increased with the increase of bio-oil content. Under the impact of the amide groups in bio-oil, the π-π interaction between the asphaltene stacks of COBA changes, resulting in the change of asphaltene clusters. As a result, the bio-oil enhances the liquidity and improves the low-temperature performance. In terms of high-, low-temperature performance and moisture susceptibility, the COBA containing 5% bio-oil was recommended for the construction of traffic infrastructures.