A Rapid In Situ Test Method for the Determination of Oxidative Field Aging Using a Handheld FTIR Spectrometer

In this study, a rapid (<45 min including analysis of results) and mildly invasive method was developed to extract a small amount of asphalt mixture (<20 gm) from an in-service road and perform the Fourier-transform infrared (FTIR) spectrometer analysis to determine its degree of oxidative aging. A handheld attenuated total reflectance (ATR) FTIR spectrometer was used as the primary equipment to investigate the carbonyl index (CI) values of six different roads in northern Louisiana. The CI value was calculated as the ratio of the peak height of the carbonyl functional group at 1,695 cm^–1 and the aliphatic functional group at 2,920 cm^–1. Three small half-inch diameter cores were made on each of the roads with a hand drill to collect the sample, while dichloromethane (DCM) was used as the quick extraction solvent. The result showed that the CI values changed from 4.79% to 10.95% for the six in-service roads, while the average CI of three different original binders from multiple sources was found to be 3.04%. It was found that the CI value of a road depends significantly on its service age, the intensity of sunlight during the daytime, and the annual average daily traffic (AADT) loading. The CI value was found higher for the roads having high service age, high AADT loading, and high ultraviolet (UV) radiation exposure. It was also found that the extracted asphalt binder on the no-loading area (which is just outside the white line) of a road encounters less aging compared to the main wheel pathway. The gradual increase in CI values with the increase in service age validates the efficacy of this method. The study will help to understand different influential factors for oxidative field aging as well as develop a rapid and reliable in situ method to investigate the aging of different service roads.