Comparative evaluation of an experimental binder in hot-mix asphalt: correlating the predicted performance of the binder with asphalt testing

Abstract

The binder is an important constituent of an asphalt mix and it affects the overall performance of the mix, especially with regards to permanent deformation and fatigue cracking. The stiffest binder available from the Chevron refinery in the Western Cape is a 70/100 penetration grade bitumen. This has resulted in numerous role players in the industry developing experimental binders (closer in stiffness to a 50/70 penetration grade binder) to provide an improved performance with regards to asphalt applications. This paper presents the evaluation of an experimental binder in terms of comparisons with 50/70 penetration grade bitumen of known good performance. Comparative testing was done using the current South African bitumen specification as well as performance grade properties with reference to AASHTO MP19 / M320 and the complex shear moduli. Furthermore, the comparative performance of the binders in identical asphalt mixes containing the same aggregate, grading and binder content were evaluated. The asphalt performance-related tests conducted on the mixes included repeated axial load permanent deformation (rutting indicator), beam fatigue (cracking indicator), dynamic modulus (stiffness indicator) and modified Lottman (durability indicator). The test results were evaluated comparatively to establish whether the performance of the asphalt mixes differed. The close correlations between some binder tests and the asphalt tests in predicting performance were found to be of interest.