ABSTRACT
Bitumen imparts most of its properties to the asphalt mixture. The chemical composition and molecular structure are the key factors affecting the ageing of bitumen. The objective of this study is to construct the average molecular structure of bitumen and study the effect of ageing on its micro characteristics. To achieve this goal, the chemical characteristics of bitumen was analyzed by Fourier Transform Infrared Spectroscopy (FTIR), Nuclear Magnetic Resonance (NMR), Gel Permeation Chromatography (GPC) and Elemental Analysis. Then the average molecular structure parameters were calculated by the improved B-L method. Results show that bitumen is a complex compound composed of aromatic rings, naphthenic and alkyl chains. After ageing, the molecular mass and polydispersity increased obviously. The oxygen reacted with bitumen to form polar functional groups. The aromatization and ring scission may occur during ageing. There were more aromatic rings, less naphthenic rings and the ring structure became more complicated.
