Study On The Relationship Between Asphalt Chemical Structure And The Macroscopic Properties

Asphalt is a kind of mixture composed by numerous complex compounds,whose modification,recycling,and development of alternative products greatly depend on the chemical composition and structure.At present,the quality characterization of asphalt is usually descripted by penetration,softening point,viscosity,etc.In order to provide theoretical and technical supports for materials selection and process optimazation,it is necessary to study the fine characterization of chemical composition and structure of asphalts and their fractions,then to explore the structure-activity relationship on the overall level.In this paper,we selected six kinds of asphalts originated from the same oil source and ten kinds of asphalts originated from different oil sources,and the chemical structure characteristics and macroscopic properties of asphalts were analyzed.Futhermore,the influences of chemical compositions and structures and interaction of asphaltenes and resins on the macroscopic properties were investigated.The results show that:The asphalts were divided into saturates,aromatics,resins and asphaltenes(SARA).The macroscopic properties of asphalts were measured respectively,such as softening point,penetration,viscosity,density and the rutting factor.Smaller differences in either asphalt macroscopic properties or fraction chemical structure characteristics between the asphalts from the same oil source were detected than those from the different oil sources.The penetration of six kinds of asphalts from the same oil source presented a good regularity with other properties.Linear correlation analysis and gray correlation analysis were used to study the influence of SARA contents on asphalt macroscopic properties.It is found that density presents a strong positive correlation with contents of asphaltenes and asphatenes plus resins.The content of asphaltenes plus resins is the main influencing factor of penetration,viscosity,density,colloid index,the high temperature stability and the temperature sensitivity.Element analysis,quantitative ~1H-NMR and quantitative IR were employed to explore the chemical structure of asphalt.The H/C and heteroatom contents are significantly different for different asphalts.Multiple linear regression model results in high fit degree with an adjusted R2 of 0.947 between asphalt density and the contents of HA,H?,H?,H?.Principal Component Analysis(PCA)was used to deal with the quantitative IR spectra of asphalts,resulting in a relatively good clustering for asphalts originated from the same oil source in the scatterd diagram while a bad clustering for those from different oil sources.The main factor of PCA revealed the moleculars containing polar functional groups and aromatic rings contributes great to the clustering of asphalt.Element analysis and quantitative ~1H-NMR were furthermore employed to explore the chemical structures of SARA.The H/C decreases in the order of saturates,aromatics,resins,asphaltenes.The heteroatom contents are bigger in the resins and asphaltenes than in the saturates and aromatics.The asphalt density presents a good linear correlation with the contents of HA,H?,H?,and H? of SARA respectively,which implies the molecular structures of SARA,especially resins and asphaltenes,may strongly influence the density.The ~1H-NMR Diffusion Ordered Spectroscopy(DOSY)was used to investigate the aggregation behavior of asphaltenes and the interaction between asphaltenes and resins in the deuterated toluene solutions by measuring the relative diffusivity of solutes.The results show that the relative diffusivity of solute may increase with the increasing of the asphaltene concentration in deuterated toluene until up to a stable value which varies with asphaltenes,implying asphaltene moleculars may aggregate to form a relative stable bigger supermoleculars(asphaltene aggregates).The resins significently interact with asphaltenes,possibly in different ways: resin moleculars may be attached to asphaltene aggregates to form resin-attached asphaltene-aggregates whose sizes are bigger than asphaltene aggregates,or resin moleculars may competitively aggregate with asphaltene moleculars to form asphaltene-resin aggregates whose sizes are smaller than asphaltene aggregates.The macroscopic properties of asphalts such as softening point,density,viscosity and rutting factor vary somehow in line with the sizes of the asphaltene aggregates as well as the interactions with resins.