Date of this Version
Report # MPM-10
This research targeted two primary purposes: to estimate current aggregate angularity test methods and to evaluate current aggregate angularity requirements in the Nebraska asphalt mixture/pavement specification. To meet the first research objective, various aggregate angularity tests were estimated with the same sets of aggregates and were compared by investigating their characteristics on testing repeatability, cost, testing time, workability, and sensitivity of test results. For the second objective, the effect of aggregate angularity on mixture performance was investigated by conducting laboratory performance tests (the uniaxial static creep test and the indirect tensile fracture energy test) of five mixes designed with different combinations of coarse and fine aggregate angularity, and statistical analyses of five-year asphalt pavement analyzer test results of field mixtures. Results from the indirect tensile fracture energy test were then incorporated with finite element simulations of virtual specimens, which attempted to explore the detailed mechanisms of cracking related to the aggregate angularity. Results from the estimation of various angularity test methods implied that for the coarse aggregate angularity measurement, the AASHTO T326 method was an improvement over the current Superpave method, ASTM D5821, in that it was more objective and was very simple to perform with much less testing time. For the fine aggregate angularity measurement, the current Superpave testing method, AASHTO T304, was considered reasonable in a practical sense. Rutting performance test results indicated that higher angularity in the mixture improved rut resistance due to better aggregate interlocking. The overall effect of angularity on the mixtures’ resistance to fatigue damage was positive because aggregate blends with higher angularity require more binder to meet mix design criteria, which mitigates cracking due to increased viscoelastic energy dissipation from the binder, while angular particles produce a higher stress concentration that results in potential cracks. Finite element simulations of virtual specimens supported findings from experimental tests. Outcomes from this research are expected to potentially improve current Nebraska asphalt specifications, particularly for aggregate angularity requirements and test methods to characterize local aggregate angularity.