Evaluating mode I fracture resistance in asphalt mixtures using edge notched disc bend ENDB specimen with different geometrical and environmental conditions

Abstract

Till now, several test specimens have been used for obtaining the value of fracture toughness (KIc) in asphalt concretes. The majority of proposed test configurations in this regard are in the shape of cylindrical, disc or semi-disc specimens. However, despite many engineering materials like metals, polymers, ceramics and rocks, there is no popular test procedure and test specimen for determining a valid and representative KIc value for the asphalt concretes. Recently, a new disc shape specimen, called “edge notched disc bend – ENDB” specimen has been suggested by the authors and coworkers that can be successfully used for conducting pure mode I fracture toughness experiments in hot mix asphalt mixtures. The practical ability of this specimen has already been demonstrated experimentally via conducting very limited fracture toughness tests on a typical HMA mixture. In this paper, to extend the application of ENDB specimen for wider geometries and environmental conditions, a large number of mode I fracture toughness tests are conducted on HMA mixtures containing different air void percentages and at three low temperature test conditions (0, −12 and −24 °C). Furthermore, the effect of ENDB size (i.e. the thickness of disc) is investigated experimentally on the fracture load and fracture toughness values. Based on these new and comprehensive test results, it was concluded that the mode I fracture toughness of HMA mixtures becomes more by decreasing the air void content and test temperature or increasing the size of ENDB specimen. Meanwhile, the scatter of results was studied thorough a regression analysis and a linear regression model was extracted for predicting the KIc value in terms of void content, ENDB size and temperature. Based on this model, the size of specimen had the highest effect on the value of fracture toughness. Consequently, due to some primary advantages, the ENDB specimen can be used as a suitable candidate specimen for measuring the fracture toughness in asphalt mixtures.