Browsing by Subject "Aggregates"
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Item A new mineralogical approach to predict coefficient of thermal expansion of aggregate and concrete(Texas A&M University, 2005-02-17) Neekhra, SiddharthA new mineralogical approach is introduced to predict aggregate and concrete coefficient of thermal expansion (CoTE). Basically, a modeling approach is suggested based on the assumption that the CoTE of aggregate and concrete can be predicted from the CoTE of their constituent components. Volume percentage, CoTE and elastic modulus of each constituent mineral phase are considered as input for the aggregate CoTE model, whereas the same properties for coarse aggregate and mortar are considered for the concrete CoTE model. Methods have been formulated to calculate the mineral volume percentage from bulk chemical analysis for different type of rocks commonly used as aggregates in Texas. The dilatometer testing method has been established to measure the CoTE of aggregate, pure minerals, and concrete. Calculated aggregate CoTE, based on the determined CoTE of pure minerals and their respective calculated volume percentages, shows a good resemblance with the measured aggregate CoTE by dilatometer. Similarly, predicted concrete CoTE, based on the calculated CoTE of aggregate and mortar and their respective volume percentages compares well with the measured concrete CoTE by dilatometer. Such a favorable comparison between predicted and measured CoTE provided a basis to establish the composite model to predict aggregate and concrete CoTE. Composite modeling will be useful to serve as a check of aggregate source variability in terms of quality control measures and improved design and quality control measures of concrete.Item Analysis of aggregate imaging system (AIMS) measurements and their relationship to asphalt pavement skid resistance(2009-05-15) Luce, Anthony DavidThis thesis consists of two parts. The first part includes analyses of the correlation between the results of two Aggregate Imaging System (AIMS) units. These analyses have led to refinements of the AIMS analysis methods of angularity and texture, which resulted in reduced variability in the results and better correlation between the two AIMS units. The refined analysis methods were used to establish a database of the shape characteristics of about 100 aggregate samples from the state of Texas and to propose a new method for the classification of aggregates based on their shape characteristics. This new method of classification is for use in the Texas Department of Transportation (TxDOT) wet weather accident reduction program (WWARP). The use of AIMS texture index and variability in texture within an aggregate source is proposed instead of the British Polish Value (BPV) for classifying aggregates used in pavement surfaces. The second part of the thesis investigates the relationship between shape characteristics and asphalt pavement skid resistance. Many states have implemented wet weather accident reduction programs aimed at maintaining acceptable levels of pavement skid resistance. Proper aggregate selection before construction aids in maintaining acceptable levels of skid resistance throughout the life of the pavement. Several predictive models of pavement skid resistance have been developed over the years. Some of these models account for the influence of aggregate characteristics on pavement skid resistance, primarily through incorporating the results of the BPV test in the model. However, the BPV test is known to have high variability and dependence on experimental factors that are not related to the actual aggregate resistance to polishing. AIMS offers a method to measure aggregate shape characteristics directly in a relatively short period of time. The new method for relating aggregate shape characteristics to pavement skid resistance was verified by relating skid resistance measurements from field test sections to measured aggregate properties from the laboratory. This methodology is expected to be the basis for further study to form a more comprehensive and verified model for the prediction of pavement skid resistance that incorporates measured aggregate properties from the AIMS system.Item Dynamics of Soil Aggregation, Organic Carbon Pools, and Greenhouse Gases in Integrated Crop-Livestock Agroecosystems in the Texas High Plains(2012-08) Fultz, Lisa; Moore-Kucera, Jennifer; Cox, Robert D.; Maas, Stephan J.; Schwilk, Dylan W.; Zobeck, Ted M.In the Texas High Plains (THP), marked by limited water availability and low soil fertility, management (i.e. tillage, irrigation, crop selection) has great potential to impact soil quality factors, in particular soil organic matter (SOM) and carbon (SOC), and in turn the global C cycle. Soil organic C in whole soil and physically isolated pools can be indicative of a soil’s potential for C sequestration and changes due to management. Measurement of greenhouse gas (GHG) fluxes (CO2 and N2O), can provide insight into soil microbial activity, and allow for tracing losses of SOC. Further analysis of C functional groups using mid-infrared (MidIR) Fourier Transform spectroscopy, a recently (~20 years) developed method, can allow for classification of the C within aggregate fractions. Combination of these methods can provide a detailed outlook of the C interactions and response to management practices in semi-arid systems. The purpose of this research was to thoroughly examine the impacts of alternative agroecosystems on SOC as it relates to aggregation and contributions to GHG concentrations. Conventional production in this area typically consists of continuous cotton (CTN), although the implementation of alternative agroecosystem management practices such as integrated crop-livestock (ICL) systems is growing. Studied systems ranged from those established in 1997 to 2007 and represented various management practices. Specifically, seven systems were selected for monitoring of soil quality factors including mean weight diameter (MWD), aggregate proportions and SOC content, and total nitrogen (TN) content. Additionally, two systems were also utilized for monitoring of GHG fluxes. To examine these changes soil analysis was done at the whole soil level as well as within free aggregates (Elliott, 1986) and intra-aggregate (Six et al., 2000) fractions using physical dispersion. Stability of SOC was examined using the novel technique, MidIR spectroscopy, which can be used to identify C functional groups. Measurements of soil GHG fluxes, specifically CO2 and N2O, were done to aid in the estimation of the global warming potential in these semi-arid systems. Chapters 2 and 3 focus on the impacts of land management practices, including conventional and alternative agroecosystems, in seven systems located in the THP. Chapter 2 examines the changes over time as well as the differences between an ICL and conventional CTN system. Significant increases in SOC were measured within the ICL system, while no significant change was measured in the CTN. In general, MWD and SOC was greatest in systems which utilized alternative management practices (i.e. no-till, perennial vegetation, rotational cropping). Chapter 3 examined the impacts of multiple agroecosystems and associated vegetation components on SOC, aggregate stability, and nutrient content. The complexity of the systems made determination of distinctive impacts difficult. However, similar to the findings in Chapter 2, alternative management techniques resulted in increased SOC content and mean weight diameter. Chapter 4 focuses on fluxes of GHG from two of the systems identified in Chapter 3. This chapter compares fluxes of CO2 and N2O from five vegetation components managed as either irrigated or dryland systems. It was determined that perennial vegetation management resulted in significantly greater fluxes of CO2. In the case of N2O, fluxes were episodic and greatest in bermudagrass, following significant rainfall events but did not contribute significantly to global warming potential. Soil moisture, temperature, and SOC content were the major driving factors for GHG emissions. Chapter 5 examines the use of MidIR to characterize C functional groups from aggregates obtained in Chapter 2. Analysis indicates that SOC within intra-aggregate particulate organic matter was significantly different from all remaining fractions and that further separation based on C functional groups was possible in the intra-aggregate particulate organic matter and silt+clay fractions. The level of degradation associated with the intra-aggregate microaggregate fraction resulted in no significant difference in absorbance spectrum based on vegetation management. Chapter 6 compares the fractionation process when done on field-moist soils (for DNA extraction) and air-dried soils (for SOC analysis). Significant correlation was measured in fractions which produced significantly different results due to pre-fractionation conditions. This correlation may be improved by the inclusion of soil moisture at time of sampling and allow for the estimation of water stable aggregates using fractionation of field-moist soils.Item Investigating prokaryotic communities : group activities and physiological heterogeneity(2013-12) Wessel, Aimee Katherine; Whiteley, MarvinBacterial communities engage in social activities, exhibiting behaviors such as communicating with small signaling molecules (quorum sensing [QS]) and building antibiotic-resistant biofilms. The opportunistic human pathogen Pseudomonas aeruginosa produces both freely diffusible QS molecules, as well as a QS molecule that is packaged or transported across cell membranes via the production of outer membrane vesicles. Despite the ubiquity of vesicle production in bacteria, the mechanism of outer membrane vesicle production has not been fully elucidated. In addition, most of our understanding of QS and biofilm formation arises from in vitro studies of bacterial communities containing large numbers of cells, often with greater than 10⁸ bacteria. However, many bacterial communities are comprised of small, densely packed aggregates of cells (≤10⁵ bacteria), and it is unclear how group behaviors and chemical interactions take place in densely packed, small populations. This dissertation has two main goals: i) to provide insights into the mechanism of bacterial membrane vesicle production, and ii) to understand how population size and the spatial distribution of cells affect cell-cell interactions and the nutritional microenvironment within a small (≤10⁵ bacteria) prokaryotic community.Item Methods development and measurements for understanding morphological effects on electronic and optical properties in solution processable photovoltaic materials(2012-12) Ostrowski, David Paul; Vanden Bout, David A.; Rossky, Peter J; Holliday, Bradley J; Korgel, Brian A; Dodabalapur, Ananth JThe effects of morphology on electronic and optical properties in solution processable photovoltaic (PV) materials have been studied through two different approaches. One approach, scanning photocurrent (PC) and photoluminescence (PL) microscopy, involved mapping PC generation and PL in functional PV devices on the length scale of around 250-500 nm. Additionally, local diode characteristics were studied from regions of interest in the PV through local voltage-dependent photocurrent (LVPC) measurements. In a PV made from a Copper Indium Gallium Selenide (CIGS) nanocrystal (NC) "ink", two morphological features were found to cause the spatial heterogeneity in PC generation. Cadmium Sulfide (CdS) aggregates lowered PC generation by blocking incident light to the photoactive layer, and cracks in the CIGS-NC film enhanced PC generation through improved charge carrier extraction. LVPC measurements showed all regions to have similar diode characteristics with the main difference being the PC generated at zero bias voltage. For another PV made from a donor/acceptor blend of poly(9,9-dioctylfluorene-co-bis-N,N-(4-butylphenyl)-bis-N,Nphenyl- 1,4-phenylenediamine (PFB) and poly(9,9-dioctylfluorene-co-benzothiadiazole)(F8BT), two incident laser wavelengths were used to selectively illuminate only one or both polymers. The results showed that when F8BT is illuminated, the PFB-rich regions produced the most PC and when both polymers are illuminated (but mostly PFB), the F8BT-rich regions produce the most PC; showing PC generation is more affective when less absorber material is present in the morphology. The other approach to study morphological effects on PV properties was to fabricate particles that mimicked morphological variations known to occur in solution-processable PVs. Through solution processing of an oligothiophene molecule, a range of weakly coupled H-aggregate particles were made. These particles, identifiable by shape, were shown to have a varying degree of energetic disorder (as gauged by the 0-0 vibronic band intensity in the emission spectrum), despite all particles showing a similarly high degree of molecular order from fluorescence dichroism (FD) measurements. A trend was observed correlating a decrease in energetic disorder with an increase in the local contact potential (LCP) difference as measured with Kelvin probe force microscopy (KPFM). The LCP difference was found to range by 70 mV between particles of moderate to low energetic disorder.Item Synthesis, stabilization, and controlled assembly of organic and inorganic nanoparticles for therapeutic and imaging applications(2009-12) Tam, Jasmine Man-Chi; Johnston, Keith P., 1955-Nanoparticles have garnered much attention in pharmaceutical and biomedical fields because their small size and high surface area facilitate drug absorption, improve access to cells and organs, and enhance optical imaging. However, delivery of nanoparticles to the body is not always feasible or effective. Here, nanoparticle assemblies (flocs or clusters) for pulmonary drug delivery and biomedical imaging in cells are shown to facilitate delivery, interactions with cells, and manipulation of optical properties of inorganic/organic nanocomposites. The formation of aggregates by physical techniques and their mechanisms are described in detail. For pulmonary delivery, particles with aerodynamic diameters between 1-5 [mu]m deposit efficiently in the deep lungs. However, crystalline, non-porous, poorly water soluble drugs of this size require long dissolution times, limiting absorption by the body. Therefore, drug dissolution must be “decoupled” from deposition to improve absorption. To address this challenge, drug nanoparticles were dispersed within 4-[mu]m water droplets when administered via nebulization or as micron-sized flocs using a pressurized metered dose inhaler (pMDI). Upon deposition in aqueous media, the aerosolized nanoparticle assemblies dissociated into constituent nanoparticles, raising the available surface area for dissolution and increasing dissolution rates, relative to solid particles. Poorly water soluble drug nanoparticles were prepared using a controlled precipitation (CP) or thin film freezing (TFF) process, in which stable nanoparticles (30-300 nm in diameter) with high potencies (>90 wt% drug) were produced by rapidly nucleating drug solutions in the presence of strongly adsorbing polymers or by freezing, respectively. Amorphous, nanoparticles prepared by CP produced stable aqueous dispersions with high fine particle fractions (FPF) of 77% and total emitted doses (TED) of 1.5 mg/min upon nebulization. CP and TFF also produced anisotropic particles (aspect ratios >5), which formed stable suspensions in a hydrofluoroalkane propellant. Inefficient packing of anisotropic particles formed loose, open flocs that stacked upon each other to prevent settling. Upon pMDI actuation, atomized propellant droplets shear apart and template portions of the floc to yield porous particles with high FPFs (49-64%) and TEDs (2.4 mg/actuation). The controlled assembly of gold nanoparticles into clusters is also of great interest for biomedical imaging and therapy because clusters exhibit improved near infrared absorbance (where blood and tissue are most transparent), relative to single spherical particles, and can biodegrade into clearable particles. Gold nanoparticles (5 nm) were assembled into clusters between 30 to 100 nm in diameter with high gold loadings, resulting in strong NIR absorbance. The assembly was kinetically controlled with weakly adsorbing polymers by manipulating electrostatic, van der Waals, steric, and depletion forces. Furthermore, clusters assembled with a biodegradable polymer deaggregated back into primary particles in physiological media and within cells. This kinetic assembly platform is applicable to a wide variety of fields that require high metal loadings and small particle sizes.