Investigation of Modified Asphalt Binders through Fourier Transformation Infrared Spectroscopic Analysis

Abstract

Modification of asphalt binders causes changes in asphalt chemistry that can impact performance. The main goal of this study was to look for any appreciable alterations in asphalt chemistry brought on by aging and modification. The secondary objective was to explore any indication of changes in mechanical properties from spectroscopic analysis. For this study, two neat performance-grade (PG) binders (PG 64-22) from two different sources were modified with different combinations of three types of commonly practiced modifiers: polyphosphoric acid, styrene-butadiene-styrene, and Cloisite 11B nanoclay. Many researchers consider nanoclay as a potential alternative to conventional modifiers. Thus, Cloisite 11B nanoclay has also been considered in this study. To this end, Fourier transform infrared (FTIR) spectroscopic analysis was employed on these sample binders, followed by further chemical analysis, including pH measurements and saturate, aromatic, resin, and asphaltene (SARA) analysis. Furthermore, mechanical test results were compared to find any possible indications of changes in the rheological properties from spectroscopic analysis. It was observed that modification caused significant variations in asphalt chemistry. The sulfoxide index (S═O) was found to be related to the pH values, particularly for the polymer-modified binder samples. Moreover, the carbonyl index (C═O) increased significantly with aging, which was eventually found to be an identification parameter for aging. In addition, changes in aromatic and aliphatic indices were able to explain the variations observed in chemical fractions in different aging conditions after modification. Finally, this study was able to find some trends between rheological properties and changes in the ratio of bonding. This study investigates modified asphalt binders from a chemistry perspective and establishes relationships between chemical and rheological properties. The rheological and chemical tests were performed on the asphalt binder samples under different aging conditions. Both chemical and rheological test results and analyses suggest that the chemical components and their bonds of aged binders were significantly different from their unaged counterparts. Also, the chemical test results were found to be related to the specimens’ viscoelastic properties. The findings of this study are expected to be helpful for asphalt binder manufacturers to gain a better understanding of the functional performance of their products.