Browsing by Subject "Surface Energy"
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Item Adhesion and the Surface Energy Components of Natural Minerals and Aggregates(2011-10-21) Miller, Clint MatthewA range of geochemical reactions are controlled by the interfacial characteristics of rocks and minerals. Many engineered and natural systems are affected by geochemical reactions that occur at interfaces. Asphalt-aggregate adhesion in road construction is influenced by the interfacial characteristics of the aggregate. Likewise, the remediation of nonaqueous-phase liquid contaminants, such as trichloroethylene or methyl tert-butyl ether, is controlled by the interactions between mineral surfaces and the organic liquid. Many natural systems are also influenced by reactions at interfaces. The migration of petroleum in sedimentary basins is influenced by the wettability of the surfaces of the basin pore space. Adhesion of organisms, such as bacteria or lichens, to rock surfaces is controlled by the interactions of proteins and mineral surfaces. Rock and mineral surfaces are described by surface energy. Surface energy is a thermodynamic construct defined as the amount of work required to form more of a surface. Surface energy can be divided into van der Waals, Lewis acid, and Lewis base components. The ability to predict the magnitude of surface energy components is valuable in understanding species behavior. Surface energy is controlled by three master variables: surface chemistry, surface morphology, and surface coatings. While the surface energy of a number of minerals and aggregates has been characterized, there has not yet been a comprehensive study of the surface energies of a variety of the most common minerals and aggregates using consistent methodology. In addition there has not yet been a study of the effect of these three master variables on surface energies of natural minerals and rocks. This study measured the surface energy of 22 common minerals and 7 aggregates. The samples? bulk and surface chemistries were characterized with wavelength and energy dispersive spectra analyses on an electron microprobe and x-ray photoelectron spectroscopy. The XPS was also used to quantify the organic and inorganic coatings on the surfaces. Results showed that van der Waals surface energy is typically between 40 and 60 ergs/cm2. Polar surface energy varies by 1 to 3 orders of magnitude, and thus is likely the most important component in accounting for changes between natural minerals.Item Application of surface energy measurements to evaluate moisture susceptibility of asphalt and aggregates(Texas A&M University, 2005-08-29) Zollinger, Corey JamesMoisture damage in asphalt mixes can be defined as loss of strength and durability due to the presence of moisture at the binder-aggregate interface (adhesive failure) or within the binder (cohesive failure). This research focuses on the evaluation of the susceptibility of aggregates and asphalts to moisture damage through understanding the micro-mechanisms that influence the adhesive bond between aggregates and asphalt and the cohesive strength and durability of the binder. Moisture damage susceptibility is assessed using surface energy measurements and dynamic mechanical analysis (DMA). Surface energy is defined as the energy needed to create a new unit surface area of material in vacuum condition. Surface energy measurements are used to compute the adhesive bond strength between the aggregates and asphalt and cohesive bond strength in the binder. DMA testing is used to evaluate the rate of damage accumulation in asphalt binders and mastics. The DMA applies a cyclic, torsional strain controlled loading to cylindrical asphalt mastics until failure. The DMA results are analyzed using continuum damage mechanics that focuses on separating the energy expended in damaging the material from that associated with viscoelastic deformation. A new approach is developed to analyze the DMA results and calculate the rate of damage. The developed approach is used to evaluate six asphalt mixtures which have performed either well or poorly in the field. The resistance of the field mixes to moisture damage is shown to be related to the calculations of bind energies and the accumulated damage in the DMA.