In-Situ Measurements of Variations of RAP Contents in Hot Mix Asphalt by a Handheld FT-IR Spectrometer

Abstract

Excessive use of reclaimed asphalt pavement (RAP) in hot mix asphalt (HMA) has a detrimental consequence on the performance of asphalt pavement. Continuous quality control is crucial during the production phase, but it remains challenging to do so. Handheld Fourier Transformed Infrared Spectrometer (FT-IRS) has an advantage over other test methods with respect to mobility and faster processing time which makes it a potential candidate for being a quality control tool. In this study, RAP mix from ten selected projects were investigated during the production phase using a handheld FT-IRS to determine the RAP content in the fresh mix. Carbonyl index of unaged binder (varies from 0.0166 to 0.0283) and RAP binder (varies from 0.0577 to 0.0924) were measured before the mixing began. Assuming a linear increase in carbonyl index with addition of RAP, the amount of added RAP in the mix was determined. Attenuated total reflectance (ATR) FT-IR spectrum was collected utilizing a small amount of binder which can be extracted in the field in 15 min by the quick extraction method developed in this study. At least five samples from each mix were collected at different intervals to investigate the amount of RAP in the mix. Plant samples showed the variation in RAP content within ±5% range which can be attributed to either inadequate blending or addition of variable amount of RAP. This study with ten field projects indicates that handheld FT-IRS has the potential to be used as an effective quality control tool.