In most countries, bitumens are graded according to traditional tests. In 1997, the USA introduced a different binder grading, based on fundamental, rheological measurements (SHRP). Rather than a binder being classified as 35 or 70 pen or Class 50 or 320, it is a "64-28" or a "58-22". The numbers relate to high and low temperature performance respectively. This paper investigates SHRP grades for unmodified bitumens (and relating the two systems) and speciality bitumens. Key results are: (1) For unmodified, conventional bitumens, there appears to be a linear relationship between high and low temperature grades and between high temperature grade and softening point; this suggests SHRP grades can be predicted from softening point for unmodified binders; (2) Speciality binders are displaced from this line; the degree of displacement indicates the performance benefit provided by the speciality product. (A)
Samenvatting