Study on the Rheological Properties of Formic Acid Lignin Modified Asphalt

Lignin is a major waste product of biofuel and paper industries that can be used as a modifier to improve the relevant properties of asphalt. To investigate the effect of lignin and formic acid lignin wood incorporations into asphalt and the effect on asphalt binder that was unaged and aged for 85 min, 5 h, and 10 h, a series of tests were conducted, including high- and low-temperature rheological tests by a dynamic shear rheometer (DSR), followed by Fourier transform infrared spectroscopy (FTIR) tests, and finally by gel permeation chromatography (GPC). The test results show that the additions of lignin and formic acid lignin could improve the high-temperature performance and fatigue capacity of asphalt. In addition, at the glass-transition temperature, it was observed that the additions of lignin and formic acid lignin into asphalt can effectively improve cracking at low temperatures; however, the quantity of lignin and formic acid lignin should be controlled. Fourier transform infrared spectroscopy tests showed that the purity of lignin treated with formic acid decreased, and degradation and formylation of the same formic acid-treated lignin occurred, indicating that the lignin underwent chemical changes following acid treatment. The analysis of the results by gel permeation chromatography (GPC) showed that, with aging, the average molecular weight (Mw) of lignin-modified asphalt decreased. The reason was that lignin and formic acid lignin were cracked during aging, which reduced their molecular weights.