Development of a DSR-Based Ductility Test for Asphalt Binder

Abstract: The ductility of an asphalt binder is an important property that influences the performance of asphalt pavement, particularly contributing to its resistance against cracking. Currently, ductility of an asphalt binder is being evaluated using a ductilometer-based ductility test following AASHTO T51. However, this ductility test is a time and material consuming process. It is subject to reproducibility difficulties and can exhibit significant variability at low to intermediate temperatures (4º-25ºC). The objective of this study is to develop a dynamic shear rheometer (DSR)-based ductility test for asphalt binders using a Sentmanat Extensional Rheometer (SER) inside the DSR. Two unmodified and two modified binders, namely PG58-28, PG67-22, PG70-22, and PG76-22 binders were studied to investigate the ductility at two different temperatures (9°C and 15°C) for three different sample geometries (width X thickness: 1mm × 0.72mm, 2mm × 0.72mm, and 3mm × 0.72mm). A total of 120 samples (4 binders X 2 temperatures X 3 geometries X 5 replicates) were tested. Final strain at breakpoint or failure was calculated for each case. Results were analyzed to select test temperature and sample width based on two criteria: repeatability using standard deviation and sensitivity using percent reduction in strain. It was concluded that sample geometry of 3mm × 0.72mm at 9°C test temperature is the ideal combination for measuring the DSR-based ductility test for any binder. It is recommended that current ductility test by AASHTO T51 can be replaced by the proposed DSR-based ductility test.
Keywords: Asphalt Binder, strain, Sentmanat Extensional Rheometer, dynamic shear rheometer, ductility.