Browsing by Subject "Discrete element method"

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    Quantifying Moisture Effects in DCP and LWD Tests Using Unsaturated Mechanics
    (Minnesota Department of Transportation Research Services & Library, 2014-02) Tan, Danielle; Hill, Kimberly; Khazanovich, Lev
    Minnesota counties and the Minnesota Department of Transportation (MnDOT) use the Dynamic Cone Penetrometer (DCP) and the Lightweight Deflectometer (LWD) for in situ evaluation of stiffness and strength of soil and aggregate bases. The in situ test of choice (DCP or LWD) varies somewhat by county and region, depending partly on the local soil conditions and partly on historical preferences. The LWD is considered a measure of modulus while the DCP is considered a measure of shear strength. Recent field and laboratory tests have provided calibration for these tests for several specific granular samples. However, the results are likely less reliable for a broader range of potential granular materials used for granular bases. The objective of this research is to build on a mechanistic model developed for dry aggregate bases under LRRB INV 850 to increase its applicability to more materials and tests used in Minnesota. There were three primary thrusts to these new additions: (1) A model for the LWD test has been added so that computational predictions for DCP tests could be compared with those from LWD tests; (2) Particle-scale models for moisture and fine particle content have been included for the user to input these among the other existing material input parameters, and (3) Analogous algorithms have been developed for the DCP and LWD tests to be used with PFC3D, a commercial code maintained by Itasca Consulting Group.
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    Rheology of Granular-Fluid Systems and Its Application in the Compaction of Asphalt Mixtures
    (2019-04) Man, Teng
    The United States has more than 2.7 million miles of paved roads, of which 94\% are surfaced with asphalt pavement. The resilience and durability of asphalt materials have important consequences for transportation safety. Previous research showed that the porosity, i.e. the fraction of air voids in an asphalt pavement, which is largely influenced by the compaction during the installation process, has a significant influence on the durability of installed asphalt pavements. Therefore, understanding the compaction process of asphalt mixtures has become an essential topic of research. However, the existing modeling approaches are mostly phenomenologically based. Very few studies have focused on developing a physics-based predictive model for the compaction of asphalt mixtures. The development of a physics-based computational model is complicated by the complexity and variability of the asphalt mixture. Asphalt mixtures consist of (1) aggregates (sand, pebbles, and rocks) up to 3\ cm in size, (2) fine aggregate mixtures or FAM consisting of the sand portion of the aggregates, asphalt binder, and other additives coats. During the compaction process, the FAM surrounds the coarser aggregates and ultimately as the mixture cools and solidifies, binds them like glue. The details of each component vary considerably across the country. Part of the difficulty in modeling the compaction of such a complex multiphase mixture is to developing reliable rheology for the constitutive behavior of the mixture. In this study, we developed a multi-scale discrete element method (DEM) model for compaction of asphalt mixtures. The model is anchored by the representation of the asphalt as a two-phase mixture: (1) liquid-like FAM and (2) individual gravel particles. On the macroscopic level, only coarse (large) aggregates are considered in the simulation as non-spherical particles. The interaction between these aggregates is mediated both by the coarse particle properties and the properties of the interstitial fluid-like slurry FAM. We derive the dependence of the FAM rheology to the fluid properties of the asphalt binder and the solid properties of the finer particles using discrete element model (DEM) simulations. We use larger scale DEM simulations with coarse aggregates and the modeled FAM to model the gyratory compaction process of hot mixed asphalt with different viscosity of asphalt binder and different aggregate size distributions. The results of the thesis are comprised of three primary components described in this thesis: (1) the small scale model of particles and fluid which provide more macroscale and particle scale information about slurry flow behavior; (2) the larger multi-scale model framework of the asphalt compaction process itself as a process. The results can provide a systematic method for improving the mix design of asphalt mixtures and the compaction procedures toward a more efficient compaction process.