Average molecular structure models of unaged asphalt binder fractions

Asphalt binder is a complex compound comprising a diverse and intricate range of hydrocarbons which makes it difficult to accurately ascertain its chemical structure. This study aimed to analyze the chemical composition of asphalt binder and establish an accurate molecular structure model of unaged asphalt binder fractions. An unaged asphalt binder was separated into four fractions based on their polarities, referred to as saturates, aromatics, resins and asphaltenes (SARA fractionation). A combination of results from analytical techniques including Fourier transform infrared spectrometer, 1H-Nuclear magnetic resonance, Gel permeation chromatography and Elemental analysis was used to analyze the chemical composition of the different fractions of asphalt binder. The parameters relating to the average molecular structure were calculated to construct an average molecular structure using an improved Brown-Ladner method. The results show that the improved Brown-Ladner method can be used to obtain the effective average molecular structure of the SARA fractions. This study also provides, perhaps for the first time, model molecular structures for each polar fraction using real asphalt binder samples that can be used in future studies on molecular modeling and simulation. The average molecular structure of saturates was seen to be relatively simple. However, there were many unsaturated aromatic compounds and polar functional groups in resins and asphaltenes. The presence of carbonyl groups in resins indicated that it could be more easily aged than other fractions. The average molecular weight increased from several hundred to nearly two thousand with an increase in polarity of the fraction (saturates, aromatics, resins, and asphaltenes). Similarly, the aromatic carbon ratio increased from 0.28 to 0.52, and the cycloalkane carbon decreased from 0.29 to 0.08 with an increase in polarity.