A Notched Disk Crack Propagation Test for Asphalt Concrete

Cracking is a major distress in asphalt pavement which can lead to premature pavement failures and can cost agencies millions of dollars in maintenance and rehabilitation costs. Even with modern advances in pavement engineering, attempts to quantify and model cracking in asphalt pavements have proved extremely challenging; this is due to the visco-elastic behavior of asphalt concrete and the complex stress states that exist in pavement layers due to loading or thermally induces stresses. Since its introduction to asphalt concrete by Majidzadeh [1] fracture mechanics has been used to characterize cracking in flexible pavement design and laboratory evaluation of crack resistance of asphalt concrete. Several tests have either been developed or adopted from other fields to evaluate asphalt concrete fracture in the laboratory. The more common laboratory fracture tests include the indirect tension test (IDT) [2], semi-circular bend test (SCB) [3], direct compact tension test (DCT) [4], Fénix test [5], single edge notched beam (SEB) [6,7], and the Texas Overlay Tester (OT) as shown in Figure 1. Linear elastic fracture mechanics (LEFM) parameters that can be calculated from data obtained from these tests include: stress intensity factor (K) and fracture energy (G), which require the assumption of linear elastic material behavior [8]. The J parameter can also be obtained from certain tests and assumes elastic-plastic behavior. Although the aforementioned tests deserve great merit and consideration, a standard test or a single parameter has not been fully developed that can provide reliable fracture properties of asphalt concrete [4]. More recently Walubita et al. [9] conducted a study to compare four cracking test methods in order to investigate methods to screen and select crack resistant HMA mixes which can potentially mitigate fatigue cracking. The four laboratory tests included the overlay tester (OT), direct tension (DT), indirect tension (IDT), and semicircular bending (SCB). Authors used an evaluation criteria based on: test rationality, comparison to field performance; repeatability, variability and practicality, ease of specimen fabrication, and effort required for data analysis. Authors determined that the DT, IDT and SCB tests produced more repeatable results, however; they could not properly distinguish crack resistance based on tensile strength and strain parameters. The OT test produced less repeatable results than the other tests included in the study. Authors concluded that none of the tests considered would be recommended as a simple laboratory test to assess fatigue. The study recommended further evaluation of the IDT and SCB tests using repeated loading and comparison to field performance. Of the two, the IDT was recommended as the primary choice for further analysis. The C* Line Integral has been used to a limited extent in asphalt concrete cracking evaluation and was identified as a promising test method [10]. The test provides a fracture mechanics parameter (C*) and also the crack growth Volume 3 Issue 5 2017