Comparison of mixed mode I/III fracture toughness data obtained from the ENDB specimens manufactured by gyratory cylinders with two diameters of 100 and 150 mm

Abstract

Different specimens have been developed to characterise the fracture parameters. Recently, a disc shape specimen entitled 'edge notched disc bend' (ENDB) sample was introduced; it is used for conducting pure mode I, III, and related fracture mode mixities. In this paper, to extend the application of ENDB specimen, a large number of mode I, III, and I/III fracture toughness experiments were conducted on HMA at three different low-temperatures (-5, -15, and -25 degrees C) and by applying two rates of loading (1 and 5 mm/min). The effect of ENDB radius (i.e. 50 and 75 mm) for a constant thickness of 30 mm was investigated experimentally. Based on the data, both ENDB diameters result in nearly the same mixed I/III fracture toughness values,. The difference between the fracture toughness of both ENDB sizes was less than 8%. Hence smaller size of ENDB sample with a diameter of 100 mm can be employed successfully instead of 150 mm (that is commonly used in many asphalt fracture toughness studies). The results also indicated that the fracture toughness values in the full ranges of mode I/III case increase as the test temperature decreases (about -7% and -15% by increase from -25 to -15 degrees C and -5 degrees C).