Aging behaviour and mechanical characterisation of maltenes and asphaltenes

Abstract

The analysis of bitumen is challenging due to its complex and ever-changing chemical composition. Fractionation techniques based on solubility and polarity properties facilitate the examination process, shedding more light on composition, structure and aging behaviour. However, these separation experiments are often performed post-aging, making it difficult to understand the behaviour and mechanical properties of individual subfractions. Hence, the focus of this study was to separate maltenes and asphaltenes in large quantities and age them at various temperatures (80, 130 and 180°C), followed by analysis with chemical and mechanical methods. Results showed that both maltenes and asphaltenes display viscoelastic properties: maltenes are more viscous, while asphaltenes are more elastic compared to the base binder. Maltenes aged at 180°C became extremely stiff with a nearly temperature-independent phase angle, while asphaltenes aged at 130°C exhibited the stiffest and most elastic behaviour. Decomposition of sulfoxides at high temperatures was observed for both fractions, while additional decarboxylation occurred in the asphaltenes. During the aging of the maltenes, a significant amount of asphaltenes were formed, which most likely originated from both the aromatics and resins fraction. Furthermore, no major discrepancies between oxidation products in bitumen and in the maltenes were detected, indicating that asphaltenes might not crucially influence the qualitative aging process. This study demonstrated a possible approach for obtaining bituminous subfractions in large quantities, allowing for a detailed analysis of their mechanical and aging properties.