One 1986 and three 1991 180/200 penetration grade Safaniya bitumens (from Saudi Arabia) produced by the Marsden Point Refinery were analysed by a range of procedures to detect any significant differences in chemical composition. Changes in chemical composition may have helped explain the unusually high incidence of chipseal stripping failures that occurred over the 1990/91 sealing period.
Elemental analysis, asphaltene content, differential scanning calorimetry, infrared spectroscopy and proton nuclear magnetic resonance spectroscopy all failed to detect the presence of significant differences between the 1986 and 1991 bitumens. Using these techniques did, however, allow easy differentiation between the Safaniya bitumens and other (used as controls), produced either by butane precipitation (at Marsden Point) or from a Venezuelan crude.
Thermogravimetric (TG) analysis in air did detect differences between the 1986 and 1991 Safaniya samples and, as a consequence, the study was expanded to analyse eight Safaniya 180/200 penetration bitumens produced between 1984 to 1992. Differences were also detected between these extra materials, but no trend or pattern relative to the date of production was observed.
The conclusion is that the differences revealed by the thermogravimetric analysis are simply batch to batch variation and analogous to the expected batch to batch variation in physical properties.
A simple laboratory adhesion test was also used to compare the relative adhesion of 1986 and 1991 bitumen productions. No significant differences in adhesion were observed.
Keywords: Adhesion, bitumen, chemical composition, Safaniya, roads