Browsing by Subject "Graphite"

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    Geology and Mineralization of a Cyclic Layered Series, Water Hen Intrusion, St. Louis County, Minnesota
    (University of Minnesota Duluth, 1990-03) Strommer, James; Morton, Penelope; Hauck, Steven A; Barnes, Randal J
    The Water Hen intrusion is an oxide-bearing (ilmenite + magnetite) ultramafic intrusion (OUI) that is emplaced along a pre-basement fault into the troctolitic series rocks of the Duluth Complex. The intrusion consists of medium-grained dunite and peridotite and local pegmatitic pyroxenite approximately 1,600 ft. x 500 ft. x 700 ft. in size. Oxide (>90% ilmenite) composes from 5-50% of the various lithologies. Sulfides are minor, about 2-5%, and are predominantly pyrrhotite with minor cubanite, chalcopyrite and pentlandite. Concentrations of 5-80% graphite also occur within the intrusion. Surrounding the Water Hen intrusion is a zone of mixed lithologies (Mixed Zone) consisting of the host rock troctolites, apophyses of OUI and local inclusions of footwall rocks. The Mixed Zone (M) is dominated by >60% troctolitic rocks with OUI composing the remainder. The OUI apophyses vary from 1-50 ft. thick and have sharp contacts with the country rock. The troctolitic host rocks for the Water Hen intrusion consist of medium- to coarsegrained troctolite to anorthositic troctolite (TA unit) and a troctolitic cyclically layered series (TL unit). The cyclically layered series is similar to troctolitic layered rocks at Bardon Peak. The individual cyclic layers are 6 in. to 10 ft. in thickness and the entire unit is over 300 ft. thick. The An content decreases from An80 at the bottom of the unit to An60 near the top of the unit. The individual cyclic layers are composed of ilmenite-dunite at the base and grade upward to anorthositic troctolite. The bottom contacts are sharp and each successive layer within the individual unit is identified by the occurrence of biotite or clinopyroxene. In the bottom olivine-rich layer, the oxides (<5%) are ilmenite >> magnetite. The sulfides in this same layer (3-5%) are coarse-grained with cubanite > chalcopyrite > pentlandite >> pyrrhotite. In the more feldspathic layers, the sulfides (1-3%) are fine-grained with chalcopyrite >> pentlandite = cubanite + pyrrhotite. The oxides (1- 5%) are also fine-grained with ilmenite >> magnetite. The footwall rocks in the Water Hen area consist of very fine-grained metamorphosed Virginia Formation and fine-grained hornfelsed basalt and/or troctolite. There are >100 ft. of basalt or chilled margin rocks within the footwall. This mafic hornfels commonly occurs between the Virginia Formation and the TA unit. Orthopyroxenite dikes and dikelets also occur in the mafic hornfels. These dikes contain anomalous PGEs and secondary sulfide mineralization. The copper-nickel sulfides are primary igneous sulfides associated with the troctolitic rocks. Violarite, pyrite and secondary magnetite in cross-cutting veinlets and other secondary sulfides indicate that the primary sulfides were altered and remobilized by a later event. Cu:Ni ratios have a bimodal distribution that is not followed by the PGEs. However, Cu, Ni, Ag, Au, Pt, Pd are all highly correlated with each other. This high interelement correlation suggests that the late-stage (secondary) remobilization locally redistributed and reconcentrated these elements.
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    Innovative Materials and Advanced Technologies for a Sustainable Pavement Infrastructure
    (Minnesota Department of Transportation, 2021-06) Le, Jia-Liang; Marasteanu, Mihai; Zanko, Lawrence M.; Matias de Oliveira, Jhenyffer; Calhoon, Thomas; Turos, Mugurel; Stricherz, Tyler; Hopstock, David M.; Hegg, Vern
    It is widely acknowledged that early detection of material damage and timely rehabilitation can lead to a significant reduction in the life-cycle cost of asphalt pavements. This research investigates the capabilities of damage detection and healing of graphite nanoplatelet (GNP)-taconite modified asphalt materials. The first part of the research is concerned with the application of GNP-taconite modified asphalt materials for damage detection using electrical conductivity. It is shown that, as compared to conventional asphalt materials, the GNP-taconite modified asphalt materials exhibit an improved electrical conductivity due to the electron hopping mechanism. Based on the mathematical analogy between the elastostatic field and the electrostatic field, a theoretical model is derived to relate the change of electrical conductivity to the damage extent of the material. Although, in principle, the material damage can be accessed using the electrical conductivity, the practical application of this method is complicated by the fact that the conductivity is influenced by the moisture content. The second part of the research investigates the damage healing capability of GNP-taconite modified asphalt materials heated by microwave. GNP-taconite modified asphalt materials can effectively absorb the heat generated by the microwave, and the rising temperature can effectively heal the microcracks in the binder. This damage-healing mechanism is verified by a set of semi-circular beam tests. Finally, microwave heating technology is applied to the tack coat system. It is shown that, with microwave heating, the GNP-taconite modified asphalt material can effectively improve the bond strength of the interface of the tack coat system.
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    Investigation of Asphalt Mixtures Compaction Using a Novel Approach Based on Tribology
    (Center for Transportation Studies, University of Minnesota, 2020-12) Yan, Tianhao; Turos, Mugurel; Kumar, Ravi; Marasteanu, Mihai
    Compaction is one of the most important factors that affects the durability of asphalt pavements. Many studies have been focused on developing methods to improve compaction. Previously, the authors found that the addition of small percentages of Graphite Nanoplatelets (GNPs) significantly increase the compactability of asphalt mixture. Traditional viscosity test results show that the increase in compactability is not a result of viscosity reduction, which implies that other mechanisms are responsible for the increase in compactability of GNP modified mixtures. This study investigates the lubricating behavior of the binder. A new test method, referred to as a tribological test, is conducted to evaluate the lubricating behavior of binders modified with different percentages of GNP (0%, 3%, and 6%). To better simulate the roughness of the aggregate surface, the tribological fixture is modified using textured contact surfaces instead of smooth ones. The results of rough surface tribological tests show that the addition of GNPs increases the lubrication behavior of the thin film binder between rough surfaces. It is hypothesized that the increase in compactability can be attributed to the increase in the lubricating behavior of the binder due to the addition of GNP.