Effects of Aggregate Angularity on Mix Design Characteristics and Pavement Performance

2009PDFTech ReportMPM-10AggregatesAngularityAsphalt pavementsAsphalt mixturesPerformance testsBituminous mixturesPavement performanceMechanical testsUnited StatesNebraska Transportation CenterKim, Yong-RakSouza, Leonardo T.University of Nebraska--Lincoln. Dept. of Civil EngineeringNTL-HIGHWAY/ROAD TRANSPORTATION-Pavement Management and PerformanceNTL-HIGHWAY/ROAD TRANSPORTATION-MaterialsUS Transportation CollectionThis research targeted two primary purposes: to estimate current aggregate angularity test methods and to evaluate currentaggregate angularity requirements in the Nebraska asphalt mixture/pavement specification. To meet the first researchobjective, various aggregate angularity tests were estimated with the same sets of aggregates and were compared byinvestigating their characteristics on testing repeatability, cost, testing time, workability, and sensitivity of test results. Forthe second objective, the effect of aggregate angularity on mixture performance was investigated by conductinglaboratory performance tests (the uniaxial static creep test and the indirect tensile fracture energy test) of five mixesdesigned with different combinations of coarse and fine aggregate angularity, and statistical analyses of five-year asphaltpavement analyzer test results of field mixtures. Results from the indirect tensile fracture energy test were thenincorporated with finite element simulations of virtual specimens, which attempted to explore the detailed mechanisms ofcracking related to the aggregate angularity. Results from the estimation of various angularity test methods implied thatfor the coarse aggregate angularity measurement, the AASHTO T326 method was an improvement over the currentSuperpave method, ASTM D5821, in that it was more objective and was very simple to perform with much less testingtime. For the fine aggregate angularity measurement, the current Superpave testing method, AASHTO T304, wasconsidered reasonable in a practical sense. Rutting performance test results indicated that higher angularity in the mixtureimproved rut resistance due to better aggregate interlocking. The overall effect of angularity on the mixtures\u2019 resistance tofatigue damage was positive because aggregate blends with higher angularity require more binder to meet mix designcriteria, which mitigates cracking due to increased viscoelastic energy dissipation from the binder, while angular particlesproduce a higher stress concentration that results in potential cracks. Finite element simulations of virtual specimenssupported findings from experimental tests. Outcomes from this research are expected to potentially improve currentNebraska asphalt specifications, particularly for aggregate angularity requirements and test methods to characterize localaggregate angularity.92