Search for a Laboratory Test to Evaluate Crack Resistance of Hot-Mix Asphalt
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Fatigue cracking is one of the predominant distresses that occur in hot-mix asphalt (HMA) pavements and often costs highway agencies millions of dollars in road maintenance and rehabilitation activities. Ways to minimize this distress include material screening and selecting appropriate mix designs that produce crack-resistant HMA mixes. However, no standardized laboratory tests for fatigue cracking have been universally adopted for routine mix design or screening purposes in the evaluation of HMA crack resistance. Four cracking test methodsoverlay tester (OT), direct tension (DT), indirect tension (IDT), and semicircular bending (SCB)were compared for their potential application as simple tests for the routine crack evaluation and screening of HMA mixes in the laboratory. The evaluation criteria, based on commonly used Texas mixes, included (a) rationality of the test concept and tie to field performance, (b) repeatability and variability, (c) simplicity and practicality, (d) specimen fabrication process, and (e) simplicity of data analysis. Compared with the repeated-loading OT test, preliminary findings indicated that although the monotonically increasing loading DT, IDT, and SCB tests were more repeatable, those tests could not adequately discriminate crack resistance among the mixes evaluated on the basis of the tensile strength and strain parameters. Thus none of these monotonic tests would be recommended as a simple fatigue cracking test. Additional development of the test protocols is strongly recommended, including exploration of the repeated-loading IDT and SCB tests, use of strainfracture energy concepts, establishment of pass-or-fail criteria for screening mixes, and validation with field performance data.
