Thermooxidative properties of bituminous binders in relation to their inner chemical compatibility determined by single point precipitation titration

摘要

Some bituminous binders currently available on the Central European market contain a certain ratio of visbreaking residues, obtained during non-catalytic thermal cracking of atmospheric or vacuum crude oil residues. This paper deals with a potential presence of visbreaking residues in commercially available paving grade bitumens, and their impact on the thermooxidative properties of the bitumen. The presence of visbreaking residues can be possibly indicated by the compromised chemical compatibility of the bituminous binder that can be determined by Heithaus titration. However, Heithaus titration is a relatively complicated process. It is therefore sufficient to use a simplified alternative in practice - single-point precipitation titration using isooctane. All of the tested bitumens were submitted to the accelerated ageing procedure. The changes in parameters caused by the ageing process were determined by means of a dynamic shear rheometer and bending beam rheometer. The obtained data were subsequently compared with the results from laboratory prepared binders, which contained a known portion of visbreaking residues. The content of visbreaking residues in these binders ranged from 0% to 40%. The results showed that the presence of visbreaking residues has a negative impact on the properties of paving bitumens, especially with respect to their thermooxidative ageing. Particularly, the modified method of accelerated ageing RTFOT with an extended exposition time can differentiate between the individual binders very well, and is able to correlate their properties to the content of visbreaking residues. As the content of these residues increases, the extent of change increases proportionally for the analysed parameters describing the properties of the binders in middle and elevated service temperatures. The results of the analysis suggest that the disrupted chemical compatibility proved by single-point precipitation titration using isooctane may indicate a thermooxidatively unstable bitumen, and that this fact might be related to a higher content of visbreaking residues.