Overlay Tester: A Simple and Rapid Test for HMA Fracture Property

It is well known that fatigue cracking generally is a process of crack initiation and crack propagation. However, the crack propagation, in most cases, has not been fully considered in pavement analysis and design. One of the reasons is lack of a simple and rapid test for determining fracture properties of hot-mix asphalt (HMA) mixes. In this paper, an Overlay Tester-based test procedure was developed to determine fracture properties (A and n) of HMA mixes. The three main features of this Overlay Tester-based procedure are 1) its simplicity: neither a hole in the center nor a notch at the bottom of the specimen is required, since a crack is always automatically initiated in the first cycle. Also, no LVDT (Linear Variable Differential Transformer) is required to mount on the specimen; 2) its rapidity (short testing time): in contrast to other fracture types of tests (i.e. indirect tension or repeated direct tension test) which generally take long testing time, the proposed procedure only take about 20 minutes; and 3) its specific specimen size (150 mm long by 75 mm wide by 38 mm high): this size of specimen can be easily cut from samples compacted by the Superpave gyratory compactor or from field cores.