Molecular Agglomeration Index: Quantification of the Incidence of Asphaltene Molecular Agglomeration in Aged Asphalt Binders Through Rheological Measurements

Abstract

The phase angle (φ) has long been recognized as a powerful tool to detect variations in asphalt binders’ chemistry and microstructure. A recent study applied unsupervised multivariate approaches to uncover hidden pattern structures in data sets and settled the most relevant reduced frequency to investigate the evolution of the phase angle master curve with aging. Considering that study’s findings, this paper revisits the δ-method—that is, an approach that estimates the apparent molecular weight distribution (AMWD) of a given asphalt binder based on its rheology—and proposes a simple indicator that quantifies the incidence of asphaltene molecular agglomeration named Molecular Agglomeration Index (MAI). Laboratory- and field-aged binders were tested and a limiting value for MAI indicating an increased binder cracking susceptibility is established in agreement with other failure criteria found in the literature.