Systematic Method for Quantifying Re-Refined Engine Oil Bottom Content in Binders: Using X-Ray Fluorescence Spectroscopy

Abstract

Re-refined engine oil bottom (REOB) has been used to modify asphalt binders for a long time. Recent studies revealed that pavements constructed with REOB-modified binders cracked much faster than those constructed with binders containing no REOB. Therefore, some state transportation agencies enforced a complete ban while others set an upper limit for its use. It is imperative to quantify REOB content in binders. This paper presents a systematic method to address this need. Researchers prepared 414 asphalt binder–REOB blends using 16 base binders and six REOBs at five dosages, and measured intensities of 11 key elements using wavelength dispersive X-ray fluorescence (XRF) spectroscopy. XRF tests showed that element intensities depended directly on (a) binder source, (b) binder performance grade, (c) REOB source, and (d) REOB content. This method has three major steps. In the first step, potential sources and performance-grade levels of binders that were used to prepare an unknown sample on the basis of its closeness to calibration standards in an intensity plot of sulfur versus vanadium were identified. In the second step, potential sources of REOBs were determined on the basis of calibration curves of the ratio of calcium and potassium intensities. In the final step, the REOB content in an unknown sample was estimated by using the calibration curve of the zinc intensity of the selected binder source, binder performance grade, and REOB source. The reasonableness of this method was verified by preparing and testing some additional blends. These tests showed that the new method can quantify REOB content in asphalt binders with reasonable accuracy.