Field Test Method to Determine Presence and Quantity of Modifiers in Liquid Asphalt.

摘要

Asphalt modified with styrene butadiene styrene (SBS) polymer and/or ground tire rubber (GTR) is widely used in the U.S. to enhance its performance. However, there are very few field tests developed to verify the content of modifier(s) in asphalt during construction. In this study, a comprehensive literature review and a nationwide questionnaire survey were first conducted on available tests/tools and current agency practices for modifier detection and quantification in asphalt binders. Based on the findings from the review and survey, the Fourier transform infrared spectroscopy (FTIR) test by portable devices was chosen for further evaluation. A laboratory experiment was designed and conducted for this purpose, which included measurements with two portable and one desktop FTIR devices on two sets of SBS binders and two sets of GTR binders prepared in the laboratory and several binder samples from field paving projects. It was found that the portable FTIR devices can give measurements very similar to those from a desktop FTIR spectrometer. For SBS-modified binders, the SBS content may be calculated from the peak height at 966 cm-1 of a sample’s absorbance spectrum, based on a standard curve calibrated for each type of asphalt. Estimation error, however, increases significantly for binder samples with more than 5 percent SBS. For GTR-modified binders, no firm conclusion can be made regarding the effectiveness of the FTIR test to quantify GTR content, although it seems promising that the baseline slope of a sample’s absorbance spectrum may be used as a predictor for GTR content. The library search function of the TruDefender FTX FTIR analyzer has a potential to quickly identify a binder sample (and therefore its polymer content) in the field, provided a suitable material library is used. Recommendations on preliminary implementation of portable FTIR devices and future study and evaluation are provided in the report.