Abstract
Cracking is one of the major deterioration mechanisms of asphalt pavements at low temperatures. Over the last decades, fracture mechanics has been used as a tool to investigate this phenomenon. For this purpose, two related measures namely, fracture toughness and to some extent, fracture energy are used to investigate the performance of asphalt mixtures at low ambient temperature conditions. Various types of laboratory specimens have been used in previous research studies to investigate the fracture toughness and fracture energy of Hot Mix Asphalt (HMA) mixtures. Recently, a new specimen called ENDB (Edge Notched Disk Bend) has been proposed by researchers which features additional advantages over the widely used Semi-Circular Bend (SCB) specimen. However, very little research has been conducted on the appropriate geometry of this specimen in fracture tests. This article presents the results of a study on the effect of ENDB specimen geometry on the fracture toughness and fracture energy of two widely used asphalt mixture types namely, HMA and Stone Mastic Asphalt (SMA) at low temperatures. For this purpose, a set of 54 ENDB specimens was produced in three thicknesses of 30, 50 and 70 mm, three crack depth ratios of 0.2, 0.4 and 0.6 for two types of HMA and SMA mixture types. The nominal maximum size of aggregates used in the experiments was 9.5 mm and the specimens were tested under mode I fracture toughness at −15 °C. The results of the fracture tests in these conditions indicated that the thickness of the specimens has a significant effect on the fracture toughness of both HMA and SMA mixtures. The results showed that under the studied conditions, it would be appropriate to use ENDB specimens with at least 50 mm and preferably 70 mm thickness. The results also indicated that a crack depth ratio of 0.4 would be appropriate for the HMA and SMA specimens. However, when a study is only concerned with the SMA mixture type and specimens with 70 mm thickness are used, a crack depth ratio of 0.2 would be more appropriate.
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