Study On Chemical Structure Characteirstic Of Asphalt Using Molecular Simulation

The asphalt binders were generally graded based on its physical characters. Buttests found that the performance on pavement frequently were various for initially samegrading asphalts, because the chemical structure usually was different for them. There isa need to understanding the relationship between chemical composition of asphalt andits properties. The component of asphalt was so complex that it was difficult to study itusing the test means, so molecular method was used to analyze the characteristic of itschemical structure.Based on solubility parameters, asphalt was classified into asphaltene, resin, andmaltene. Using one compound to represent each part, two model asphalt systems werebuilt for molecular simulations. The accuracy of model was tested from aspects ofmolecular degree of order, viscosity, and other physical performance index.Temperature-dependent effects of physical characters of model was analysed, and theglass transition temperature was obtained from it.The agglomeration variable pattern of asphalt molecules was studied using theradial distance function which computed the spatial structure. The results showed thatasphaltenes formed layer accumulation structure because of π-π aromatic stackinginteractions, but the alkane chain on asphaltenes would enlarge torsion angle betweenaromatic rings and weaken this effect. With the increased of temperature, torsion anglebetween aromatic rings increased, so layer accumulation structure between asphaltenemolecule were destroyed, and the interpenetrating or vertical structures were formed.The resins and maltenes would increase the distance between asphaltenes, but made itslayer accumulation structure more stable. Asphaltenes and resins aggregated togetherand floated in maltenes, and the stability of aggregated structure was influenced byasphaltene molecular structure.Styrene-butadiene-styrene (SBS) modified asphalt has been used in many roadprojects. One type of ordinary SBS model and two types of maleic anhydride modifiedSBS models (MAH-g-SBS1, MAH-g-SBS2) were added into two asphalt models,respectively, then six kinds of modified asphalt models were built. The physicalcharacters of the model were computed, and the results showed that after adding theSBS modifier, the density of systems increased, and the glass transition temperature hadalready exceeded the simulative temperature zone, The diffusion rates of all componentsdecreased after the adding of modifier, and their variations decreased with the increased of the molecular weight, but the temperature-dependent law of them did not change.The viscosity of model SBS modified asphalts was higher than model based asphalts,and the viscosity difference of three kinds of SBS modified asphalts was little.The impact of SBS on molecular aggregation behavior of asphalt binders wasstudied by means of radial distance function. Results of calculation showed that threetypes of SBS had impact on the molecular aggregation behavior of asphalt binders. Theimpact content of modifiers was largely dependent on the molecular structure ofasphaltene, and the colloidal structure of asphalt binders was more susceptible to SBSwhen the asphaltene alkane side branches were shorter. The difference of influence onasphalt binders among three types of SBS was little. The affection pattern of SBSmodifier on agglomeration variable pattern of asphalt molecules was analysed, and theaffection pattern had volume effect, space block effect and attract effect.