Crystallinity of Bitumen via WAXD and DSC and Its Effect on the Surface Microstructure

Abstract

It is well documented that most bituminous binders contain crystallisable material. This crystallisable fraction, often referred to as paraffinic or natural wax, is associated with the bitumen’s origin and has an influence on its rheological performance. In the literature, Differential Scanning Calorimetry (DSC) is the primary technique used to determine the melting and crystallisation behaviour of this waxy fraction. However, in bitumen, thermal transitions in DSC are typically very broad and can be combined with recrystallisation effects upon reheating. This work explores the potential crystallisation and melting process of a waxy and a wax-free bitumen via three different approaches: DSC, Wide-Angle X-ray Diffraction (WAXD) and Confocal Laser Scanning Microscopy (CLSM). The findings reveal that the DSC transitions of the waxy bitumen are in good agreement with the corresponding occurrence of WAXD signals and to some extent with the formation and disappearance of the surface microstructures which were followed at two cooling and heating rates. WAXD results additionally demonstrate that the crystalline material in bitumen is organised in an orthorhombic unit cell, typical for straight chain aliphatic structures. On the other hand, DSC and WAXD support the lack of crystallinity for the wax-free bitumen which could explain its featureless CLSM surface. Overall, the originality of this work resides in the disclosure of connections between crystallographic properties, thermal transitions and the surface micromorphology of bitumen.

Variable-Temperature Raman Spectroscopy Study of the Phase Transition Mechanism in Asphalt Binders

“…The wax content in asphalt is positively correlated with the integral area of the ordered-to-disordered phase transition region. This order–disorder phase transition of asphalt can be discussed by previous studies on DSC . Saturated hydrocarbons form an aggregative solid structural crystalline phase in accordance with the laws of structural phase transitions and the nucleation mechanism of thermodynamic phase separation.…”

“…This order− disorder phase transition of asphalt can be discussed by previous studies on DSC. 52 Saturated hydrocarbons form an aggregative solid structural crystalline phase in accordance with the laws of structural phase transitions and the nucleation mechanism of thermodynamic phase separation. Asphaltenes create over a relatively long-time aggregative solid structurally amorphous (liquid) phase as a result of relaxation structural glass transition by a spinodal thermodynamic phase separation mechanism.…”

Study on the Wetting and Permeation Properties of Bio-Oil as Bitumen Rejuvenator

“…Bitumen is a complex organic mixture of hydrocarbons and nonhydrocarbons, with relatively large molecular weight. In order to study the chemical composition of bitumen, people have carried out a lot of research work, including nuclear magnetic resonance (NMR), small-angle neutron scattering (SANS) and small-angle X-ray scattering (SAXS) [ 52 ]. However, due to the complex chemical composition and diverse sources of bitumen, the specific molecular formula of bitumen is still uncertain and divergent [ 53 ].…”

Laboratory Study on Influence of Blending Conditions on Chemo-Thermal Characteristics of Lignin-Modified Bitumen

“…The results showed that washing processes changed the thermal characteristics of lignin samples [34]. Another important research area in the study of lignin-modified bitumen is the use of Differential Scanning Calorimetry (DSC) testing to evaluate its thermal properties, including the glass transition temperature (T g ) and degree of crystallinity [35,36]. The glass transition temperature (T g ) and degree of crystallinity are critical factors in assessing and determining the performance characteristics of bitumen [37].…”