Investigating properties and intermolecular interactions of sludge bio-oil modified asphalt

Abstract

Bio-asphalt is a binder composed of bio-oil and petroleum asphalt under certain conditions. In this study, sludge bio-oil (wt 10%) was added into matrix asphalt to prepare sludge bio-asphalt for the first time. The effects of sludge bio-oil on asphalt performance and the essence of interaction between components were investigated using performance test, molecular dynamics (MD) simulation, and density functional theory (DFT). Chemical analysis showed that the ester compound containing ester functional group (COOH) was the main component of sludge bio-oil. Physical and rheological tests were performed to examine whether the properties of sludge bio-asphalt could be improved. The results found that sludge bio-oil can be used to soften the hard asphalt. Furthermore, the existence of bio-oil reduced complex modulus G* of master curves and stiffness, also increased Jnr and m-value, which means that sludge bio-oil had a positive effect on the low-temperature thermal cracking resistance performance while sacrificing the high-temperature rutting resistance performance to some extent. Fourier infrared spectroscopy (FTIR) and fluorescence spectrum (FM) analysis indicated that sludge bio-oil evenly dispersed in the asphalt, and the bio-asphalt structure resembled that of the conventional binder. The results of MD simulation further showed that O atom of COOH and H atom in the asphalt molecules formed hydrogen bond (OH⋯O, OH⋯C) interaction. This changed originally existed conformational packing of agglomeration and further prevented the agglomeration of component molecules. In addition, the analysis of cohesive energy density (CED) and solubility parameters (SP) revealed that sludge bio-oil significantly influenced the compatibility of asphaltene-asphaltene, resin-resin, and asphaltene-resin components. These, in turn, may explain some of the observed improvements in rheological properties.