Correlation of extensional bitumen properties with 4-point bending beam asphalt mixture fatigue life

Abstract

In South Africa, over the last two decades, there has been a need to improve on the ductility specification test and to better simulate ageing of the asphalt bitumen in the laboratory for the control of fatigue cracking distress. Focusing on the former, various extensional tests have been recommended to replace the ductility test. Initially, this brought the Force-Ductility (FD) test to South Africa followed by a wave of surrogate Dynamic Shear Rheometer (DSR) protocols. More recently, the Double-Edge-Notched Tension (DENT) test has been introduced. This paper aims to compare these extensional tests and their surrogates with Four-Point Bending Beam (4-PBB) asphalt mixture fatigue results of various bitumen, using similar mix designs in terms of binder content, voids, gradation and aggregate types. The DENT test provides a measure of strain tolerance in the ductile state under severe constraint, expressed as the approximate Critical Crack Tip Opening Displacement (CTOD). The CTOD property was identified to be the most accurate in relation to asphalt mixture fatigue life. This paper discusses the significance of CTOD as an improved parameter for predicting fatigue life in South African asphalt mixtures.