Abstract
Eight asphalt samples with grades ranging from AC10 to AC30 from four different sources were examined using NMR, FTIR, and differential scanning calorimetry. The crystallization process of asphalt is very time dependent. Slow heating or annealing before analysis to experimentally realize a near-equilibrium state is necessary to study the system with more thermodynamic rigor. Indeed, the annealing method developed in this work resolves a number of low-temperature transitions characteristic of a given crude and/or refinery source; thus, comparison of thermograms from an unknown source with reference thermograms from documented sources allows one to identify the unknown source. The crystallization process of a selected AC-20 asphalt, ACB, was systematically studied by doping with the following pure crystalline hydrocarbons: octadecene-1, eicosane, and octacosane. The impact of doping on the crystalline fractions in asphalt varies from asphalt to asphalt. The crystalline components in asphalt exhibit distinct endothermic patterns that depend on their chemical structure, the interactions with the amorphous phase, and among themselves. The most significant endothermic effect is produced by cocrystallization of components with similar crystalline chain lengths. For example, the crystalline components of asphalt ACB do not interact with octadecene-1, but do cocrystallize with eicosane and octacosane.
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