X-ray fluorescence detection of waste engine oil residue in asphalt and its effect on cracking in service

Abstract

This paper documents the discovery of waste engine oil residues in pavements across Ontario, Canada. We have found that recovered asphalts from a large majority of poorly performing contracts test positive for zinc through X-ray fluorescence (XRF) analysis. In contrast, neither the aggregates nor any of the well-performing asphalts showed any signs of the metal. Since zinc dialkyldithiophosphates are universal additives in engine oils, we inferred that the use of waste oil residues in asphalt must be widespread. Further analysis of 2008 quality assurance samples taken for the Ontario Ministry of Transportation substantiated this, with most samples testing positive for zinc. XRF analysis of straight waste oil residues suggests that typical modification levels are in the 5–20% range. The damaging effect of this additive through increased physical and chemical hardening is briefly discussed with reference to previous studies on unexplained, premature and excessive thermal cracking.

Keywords:

• asphalt cement
• thermal cracking
• fatigue cracking
• waste engine oil residue
• physical hardening
• chemical ageing

Acknowledgements

The authors wish to thank Imperial Oil of Canada, EI du Pont Canada, the Ontario Ministry of Transportation, and the Natural Sciences and Engineering Research Council of Canada for their continuing financial support. Undergraduate students Eric Moult and Irsan Kodrat are thanked for the collection of samples and experimental data, and Ryan Marchildon is thanked for checking the proof. The Art Conservation program at Queen's University is thanked for allowing us to use their XRF analyser for this study. Appreciation is expressed to Maureen Garvie for the proofreading of the manuscript and to staff of the Ontario Ministry of Transportation for their assistance with the collection of contract information and experimental data. None of the sponsoring agencies necessarily concur with, endorse or agree to adopt the findings, conclusions or recommendations either inferred or expressly stated in subject data developed in this study.