Monitoring Oxidation of Asphalt Pavements with a Portable Infrared Spectrometer

There is an increasing tendency to use higher percentage of reclaimed asphalt pavement (RAP) by transportation agencies, which calls to improving quality control of production and placement of RAP-containing mixes. A pilot study described in this paper has been conducted by the Idaho Transportation Department in order to explore the feasibility of using portable infrared spectrometers (PIRS) to monitor in-situ RAP content in mixes at production plants and on paving sites. The paving projects included in the pilot were located in southern and northern Idaho and utilized 17 to 54 percent RAP. For each project, first a calibration curve was developed based on an oxidation parameter derived from the absorbance spectra of the mix samples prepared in the laboratory in accordance with the job mix formulas. Next, the oxidation measurements were taken on the paving day on plant samples and for the corresponding paved surface.The observed differences between plant, in-place, and laboratory mixes in oxidation index as measured by PIRS were analyzed. This study demonstrated high repeatability and acceptable reproducibility of the proposed method with standard deviation within 10 percent of the mean. Also, a good agreement of plant, in-place, and laboratory measurements for a given RAP content was reported. The results of this trial study suggest optimism about incorporating portable infrared technique as a supplemental quality control method for monitoring oxidation and cracking susceptibility of pavements built with RAP.