ABSTRACT
Asphalt is subjected to aging, leading to physical and chemical modifications reducing its performance. Recently, the Western Research Institute developed the SAR-AD method that allowed the separation of asphalt into eight fractions (saturates, aromatics 1, aromatics 2, aromatics 3, resins, asphaltenes 1, asphaltene 2, and asphaltenes 3). In this work, this analytical method was used to study asphalt aging processes in greater detail. Several asphalts of different origins and reconstituted blends were studied. These products were aged during several durations using a PAV (pressure aging vessel) between 0 and 48 h to collect information on the evolution of each SAR-AD fraction. Different evolutions were observed according to the initial asphalt composition and SAR-AD fraction studied. The saturated subfamily seemed to be slightly impacted by aging. The amount of three aromatic subfamilies decreased with a larger decrease of aromatics 3 than aromatics 2, itself larger than aromatics 1. The content of the resin subfamily increased after 48 h of PAV aging. The asphaltene 1 and asphaltene 2 subfamilies exhibited an increasing trend. Moreover, the quantity of asphaltenes 2 created seemed to correlate to the initial asphaltene content. The evolutions of the asphaltene 3 subfamily were not significant. However, a specific behavior was highlighted for the most asphaltenic sample. For this specific sample, the increase of resin content was weaker, the mass of asphaltenes 1 decreased, and the amount of asphaltenes 3 increased during aging. Given the large amount of data generated, an original approach was developed to statistically identify the most affected SAR-AD subfamily and determine correlations among them. Two PCAs (Principal Component Analysis) were conducted on asphalt SAR-AD data. This statistical analysis indicated two generic asphalt aging pathways. The first aging pathway could be the conversion of aromatics 2 into resins, with no evidence that resins could contribute to asphaltene creation. The second aging pathway showed the conversion of aromatics 3 directly into asphaltenes 2. These two aging pathways highlighted that the conversion of molecules in more polar ones during aging could skip SAR-AD subfamilies, meaning that asphaltenes could be created without involving resins.
ABSTRACT
For decades, it has been known that the creation of oxygenated functional groups, especially carbonyl and sulfoxide, is among the main causes of chemical aging and degradation of asphalt. However, is the oxidation of a bitumen homogeneous? The focus of this paper was to follow the oxidation phenomena through an asphalt puck during a pressure aging vessel (PAV) test. According to the literature, the asphalt oxidation process that leads to the creation of oxygenated functions can be divided into the following successive main steps: the absorption of oxygen in asphalt at the air/asphalt interface, diffusion into the matrix, and reaction with asphalt molecules. To study the PAV oxidation process, the creation of carbonyl and sulfoxide functional groups in three asphalts were investigated after various aging protocols by Fourier transform infrared spectroscopy (FTIR). From these experiments performed on different layers of asphalt puck, it was observed that PAV aging resulted in a nonhomogeneous oxidation level inside the entire matrix. Compared to the upper surface, the lower section exhibited carbonyl and sulfoxide indices 70% and 33% lower, respectively. Moreover, the difference in the oxidation level between the top and bottom surfaces increased when the thickness and viscosity of the asphalt sample increased.
