GC-MS identification of biomarkers in road asphalts and in their parent crude oils. Relationships between crude oil maturity and asphalt reactivity towards weathering

Asphalt cements (vacuum residues of petroleum) used as binders for road construction can undergo weathering phenomena or natural oxidation to various degrees depending on their chemical structures and on their origin. The first aim of this study was to determine the characteristics of the source rocks generating the parent crude oils. The second aim was to correlate the chemical structures of recovered asphalt cements to the genesis data of their parent crude oils in order to predict their sensitivity towards weathering. Towards these ends, saturated fractions of sixteen asphalt cements and their parent crude oils have been analysed by GC-MS (SIR). Many linear, branched and naphthenic compounds from the saturated hydrocarbon fraction have been identified. Hopanes (m/z = 191), norhopanes (m/z = 177, 163) and steranes (m/z = 217 and 218) have been selected to characterize original and weathered asphalts as well as their parent crude oils. Using geochemical indices (Ts/Ts + Tm, %C29 steranes, etc.), aliphatic structures of the asphalts and corresponding crude oils could be differentiated through principal component analysis (PCA). The selected variables involve geochemical indices and asphalt rheological characteristics. Results are in good agreement with the classification obtained from FTIR indices (linear alkanes, branched aliphatics, aliphatics versus aromatic structures, etc.). Moreover, good correlations in geochemical indices have been found between asphalts and their parent crude oils. Finally, it was also possible to predict some rheological properties (e.g., stiffness at low temperature) using a multilinear regression which involves geochemical indices of parent crude oils before any physical transformation (distillation, etc.) and FTIR indices of corresponding asphalt cements.