Influence Of Particle Shape On HMA’s Performance: DEM Results

HMA (Hot Mixture of Asphalt) is a kind of composite with asphalt binder, aggregates particles and air voids. Coarse and fine aggregates occupy about 90% of HMA by both weight and volume. So the performance of HMA is influenced by the properties of coarse aggregate to a great extent. Among all the influence factors, aggregate shape characteristics are thought to be the second most important set of parameters of all, only after gradation. Recent years, most researches in aggregate shape are done by indoor experiments and he results varies a lot and cannot be reproduced precisely, which maybe a waste of both human and time. Nowadays, discrete element method has been proved to be a reasonable and efficient method in HMA research. The results of these existing studies indicate that using non-spherical DEM model not only improves the simulations of granular particles, but also enables researchers to study the effect of particle shape on the engineering properties of asphalt mix systematically.As the angularity of particles have important effects on the mechanical properties of mixtures. To simulate these effects, the glue-sphere method was used to create an arbitrary polyhedron particle firstly. Unlike past studies, this paper aims to fill a polyhedron with the fewest spheres through constrained nonlinear optimization technology in order to reduce computational cost. Three main content areas are discussed:how to create a non-sphere aggregate particle and control the particle sieve size using a particle minimal bounding box; the algorithm for filling a polyhedron through an optimization method; the computing method for particle shape parameters. The algorithms for this study are programmed by numerical computation software. The computing results proved the effectiveness of the proposed method.Moreover, to study the effects of aggregate shape on the strength of mixtures, the glue-sphere ellipsoid particles are used to create cylinder samples, and triaxial tests are simulated with DEM. Here, we discuss how to simulate the triaxial performance of HMA skeleton and how to choose coarse aggregates for HMA according to shape factors. By computation, a nephogram about triaxial strength varying with Flatness and Elongation was finally given, and the cubical and part of rod aggregate show much better in strength than others. Then a new index for blade particles:Q, is raised for grading control. The results are proved to be consistent with the result of indoor tests.