Determining re-refined engine oil bottom content in asphalt binders using a handheld X-ray fluorescence instrument

Re-refined engine oil bottoms (REOB) are major modifiers used to produce softer binders from stiffer binders. Studies have revealed that pavements constructed with REOB-modified binders experience premature cracking and ravelling problems much sooner than usual. Therefore, some state agencies in the US have enacted regulatory measures on the use of REOB-modified binders in their contracts. To implement these measures, there is a need of a well-verified, cost friendly test method that can accurately estimate REOB contents in binders used in these contracts on site. This paper presents a simple method that fulfils this objective. The method involves the measurement of element concentrations in an unknown sample using a portable X-ray fluorescence (XRF) instrument, the identification of the most likely sources of this sample using normalised sulphur-versus-vanadium concentration plot, and the estimation of REOB content in the sample using the calibration curves of zinc, calcium and molybdenum elements. Researchers developed and verified this method using 384 calibration and 24 verification samples. Test results show the proposed method can quantify REOB content in binders with reasonable accuracy. Test results also show that this portable XRF-based REOB estimation method is as effective as a previous benchtop instrument-based REOB estimation method.