Development of a Test Method to Measure RAP Percentage in Asphalt Mixes in the Field Using a Handheld FT-IR Spectrometer

In this study, a handheld Fourier transform-infrared spectrometer (FT-IRS) is used as the primary equipment to determine the reclaimed asphalt pavement (RAP) content in a mix by quantifying the extent of aging of a fresh mix. Binders of different performance grades and sources were used for laboratory aging and were analyzed to comprehend and compare different aging processes in terms of a carbonyl index (ICO). The results show that the ICO of the RAP from 10 different sources varies from 0.0275 to 0.0607. Standard PAV aging produces ICO of only 0.0239, which indicates the significantly higher oxidation reaction in a service life than the laboratory aging. Attenuated total reflectance (ATR)-FTIRS data collection requires a small amount of the binder, which can be extracted in the field in 15 min by following the quick extraction method developed in this study. A spectral analysis of an unaged binder and RAP can predict the ICO in the fresh mix. The predicted and the measure ICO values were found to be in good agreement in two different plant mixes. So, the handheld FT-IRS has the potential to be used as a quality control tool in the field by precisely and quickly detecting the presence of aged RAP in the mix.