Evaluation of Asphalt Aging Using Multivariate Analysis Applied to Saturates, Aromatics, Resins, and Asphaltene Determinator Data

Asphalt is subjectedto aging, leading to physical and chemicalmodifications reducing its performance. Recently, the Western ResearchInstitute developed the SAR-AD method that allowed the separationof asphalt into eight fractions (saturates, aromatics 1, aromatics2, aromatics 3, resins, asphaltenes 1, asphaltene 2, and asphaltenes3). In this work, this analytical method was used to study asphaltaging processes in greater detail. Several asphalts of different originsand reconstituted blends were studied. These products were aged duringseveral durations using a PAV (pressure aging vessel) between 0 and48 h to collect information on the evolution of each SAR-AD fraction.Different evolutions were observed according to the initial asphaltcomposition and SAR-AD fraction studied. The saturated subfamily seemedto be slightly impacted by aging. The amount of three aromatic subfamiliesdecreased with a larger decrease of aromatics 3 than aromatics 2,itself larger than aromatics 1. The content of the resin subfamilyincreased after 48 h of PAV aging. The asphaltene 1 and asphaltene2 subfamilies exhibited an increasing trend. Moreover, the quantityof asphaltenes 2 created seemed to correlate to the initial asphaltenecontent. The evolutions of the asphaltene 3 subfamily were not significant.However, a specific behavior was highlighted for the most asphaltenicsample. For this specific sample, the increase of resin content wasweaker, the mass of asphaltenes 1 decreased, and the amount of asphaltenes3 increased during aging. Given the large amount of data generated,an original approach was developed to statistically identify the mostaffected SAR-AD subfamily and determine correlations among them. TwoPCAs (Principal Component Analysis) were conducted on asphalt SAR-ADdata. This statistical analysis indicated two generic asphalt agingpathways. The first aging pathway could be the conversion of aromatics2 into resins, with no evidence that resins could contribute to asphaltenecreation. The second aging pathway showed the conversion of aromatics3 directly into asphaltenes 2. These two aging pathways highlightedthat the conversion of molecules in more polar ones during aging couldskip SAR-AD subfamilies, meaning that asphaltenes could be createdwithout involving resins.