Relationships between Simple Asphalt Mixture Cracking Tests Using Ndesign Specimens and Fatigue Cracking at FHWA’s Accelerated Loading Facility

Abstract

Current methods and criteria for asphalt mix design and quality assurance testing are unable to discern the true impact of recycled materials, such as reclaimed asphalt pavement, recycled shingles, ground tire rubber, re-refined engine oil bottoms, or products aimed at enhancing performance such as polymer modified binders, fibers, or even warm- mix asphalt technologies. There is an urgent need to implement reliable tests to assess the cracking resistance of asphalt mixtures. This study used test specimens compacted to Ndesign in four simple tests: the Cantabro test, a modified version of the Texas overlay test (OT), the semi-circular bend (SCB) test, and the indirect tensile (IDT) test from which IDT strength and two other index parameters were obtained. Relationships between results from these tests and the fatigue cracking of the FHWA’s Accelerated Loading Facility (ALF) test lanes were used to assess how well test methods could differentiate actual performance. The study also examined variability data for test results and how that impacted the utility of the tests to discern mixtures from one another. Results of this study indicate that the IDT Nflex factor and the Cantabro test provide the strongest relationship to fatigue cracking in the field and are able to detect differences among common mixture variables. Both tests are simple, quick, and have very low costs to implement.