Laboratory investigation of bitumen based on round robin DSC and AFM tests

Abstract

In the past years a wide discussion has been held among asphalt researchers regarding the existence and interpretation of observed microstructures on bitumen surfaces. To investigate this, the RILEM technical committee on nano bituminous materials 231-NBM has conducted a round robin study combining differential scanning calorimetry (DSC) and Atomic Force Microscopy (AFM). From this, methods for performing DSC and AFM tests on bitumen samples and determination of the influence of wax on the observed phases, taking into account thermal history, sample preparation and annealing procedure, are presented and critically discussed. DSC is used to measure various properties and phenomena that indicate physical changes such as glass transition temperature (T g) and phase transition such as melting and crystallization. In the case of existence of wax, either natural or synthetic, it can further indicate the melting point of wax, that could be used to determine wax content. The results from seven laboratories show

The bitumen microstructure: a fluorescent approach

“…If the similar size of the structures is taken into account, the fluorescent centers can reasonably be assumed to form the so called ''peri-phase'' often shown by AFM imaging [36,51,53] to surround the ''bee-like'' catana phase. As there is a sharp phasecontrast between the three phases, the name microcapsule is probably more correct then micelle due to the size of the structures (IUPAC definitions).…”

“…Small angle X-ray scattering (SAXS) and small angle neutron scattering (SANS) experiments have proven beyond doubt that ordered structures in bitumen exist [12,13,44,48,59]. Atomic force microscopy (AFM) and scanning electron microscopy (SEM) have revealed a morphology of characteristic and reproducible appearance, which is often described as ''bee-like'' structures of 1-5 lm [8,15,27,28,30,35,36,38,51,53,60,61]. Confocal laser scanning microscopy (CLSM) has uncovered the existence of fluorescent centers in bitumen of 1-10 lm size, indicating high concentrations of fluorescent species in definite volume elements evenly dispersed through the material [5,33].…”

“…This argumentation is based on several studies, which prove a strong correlation between wax/saturates content and the frequency of occurrence of structural features [27,33,51]. Key works in this area have been conducted by Redelius [46].…”

Impact of maltene and asphaltene fraction on mechanical behavior and microstructure of bitumen

“…The existence of ordered agglomerates has been proven by small angle X-ray scattering and small angle neutron scattering experiments [11][12][13] and the nature of asphaltene agglomeration is well established for different solvents, leading to problems and discussions regarding the size of the asphaltenes and their agglomerates [11,[14][15][16]. The existence of a bitumen microstructure and its visualization was performed by various techniques, ranging from confocal laser scanning microscopy (CLSM) and scanning electron microscopy (SEM) to atomic force microscopy (AFM) [17][18][19][20][21][22][23][24][25][26]. A detailed comparison of various imaging technique was performed by Bearsley et al [18].…”

“…This argumentation is based on several studies, proposing a strong correlation between wax/saturates content and the frequency of occurrence of structural features [5,22,27,28]. Additionally, mixed models have developed by combining both asphaltene precipitation and wax crystallization approaches [29].…”