Browsing by Subject "Civil Engineering"
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Item Active membranes for containing and treating environmental contamination.(2009-12) Surdo, Erin MehleisMany hydrophobic compounds can diffuse through the hydrophobic high-density polyethylene (HDPE) geomembranes used to contain contaminated material in waste disposal and environmental engineering applications. Scavenger materials layered with or added to HDPE can intercept diffusing molecules via transformation or sorption, slowing the perceived rate of diffusion across the barrier. Diffusion of a variety of chlorinated organic contaminants across HDPE, HDPE sandwich membranes, and HDPE/poly(vinyl alcohol) (PVA) composites containing zero-valent iron and powdered activated carbon (PAC) was measured. Reaction of carbon tetrachloride with zero-valent iron and sorption of trichloroethylene to PAC in sandwich membranes were fast, effectively delaying breakthrough until scavenger activity was exhausted. The diffusion of 1,2,4-trichlorobenzene and 2,3',4',5-tetrachlorobiphenyl was measured for HDPE, PAC-containing HDPE, and an HDPE/PVA composite using PAC as a scavenger in the PVA layer. Because diffusion of these bulky aromatic compounds was slow, sorption rates within the HDPE matrix were limited by diffusion from the bulk membrane to the PAC particle surface. The reduced sorption rate allowed some contaminant molecules to leak across the barriers, but the PAC captured enough to substantially slow the overall contaminant flux. In both studies, scavengers were more effective (more of the scavenger was available for reaction or sorption) when placed in a hydrophilic matrix layered with the HDPE. Because PAC successfully intercepted such of variety of contaminants in our initial studies, factors controlling the sorption rate in active membranes were further explored via comparison of PAC- and single-walled carbon nanotube (SWCNT)-containing PVA films. This study highlights the role of macropore/micropore diffusion on the kinetics of uptake by membrane-bound sorbent particles. While SWCNTs exhibit similar sorption capacities as PAC in aqueous solution, access of 1,2,4-trichlorobenzene to the sorption sites on the SWCNTs was severely limited in the PVA matrix. This work provides experimental evidence for improved containment and a theoretical framework useful for the design of prototype and field-scale active membrane barriers. These findings also identify some limitations associated with the membrane encapsulation of scavenger materials and highlight the need for additional laboratory studies.Item An Analytical and Experimental Study of Reinforced Concrete Columns(1922-06) Staehle, Gilbert CobbItem Biodegradation of haloacetic acids in biofilters and water distribution systems: microbiology and modeling.(2011-07) Grigorescu, Alina SabinaThere is concern over the potential deleterious health effects of haloacetic acids (HAAs) in drinking water and their removal is of great interest for water utilities. The overall goal of this research was to obtain more detailed information about the diversity of HAA-degrading bacteria and their corresponding dehalogenase (deh) genes in drinking water systems and other environments. This research further aimed to model the biodegradation of HAAs in drinking water systems, thus demonstrating that biodegradation could be exploited as a means to effectively remove HAAs during water treatment. A direct plating technique was used to isolate HAA degraders from different environments (river water, tap water and agricultural soil). The obtained isolates included several species that were not isolated in previous studies: Mycobacterium sp., Streptomyces sp., Stenotrophomonas sp. and Pantoea sp. Furthermore, a deh gene was detected for the first time in a Gram positive bacterium. This gene had 89.4% nucleotide sequence similarity with the dehII sequence from an α-Proteobacterium, suggesting that lateral gene transfer of deh genes across unrelated bacterial species occurred. A culture-independent technique, the terminal restriction fragment length polymorphism (tRFLP) of two classes of deh genes (dehI and dehII), was then used to fingerprint the HAA degraders in drinking water systems. The tRFLP profiles of both deh genes showed similar patterns for all analyzed drinking water samples (from Minneapolis, MN; St. Paul, MN and Bucharest, Romania) and for one biologically-active granular activated carbon filter (Hershey, PA). The tRFLP profiles of dehI genes from the drinking water samples matched the pattern from Afipia spp. that were previously isolated from drinking water. The tRFLP profiles of dehII genes did not match any previously characterized dehII genes. Finally, a biodegradation kinetic model was developed to predict the fate of HAAs in biologically-active filters and water distribution systems. The model calculations indicated that biodegradation is likely to lead to significant HAA removals in biologically-active filters but not in most distribution systems. A sensitivity analysis showed that while the controlling parameter was the HAA-degrader biomass Bucharest, Romania) and for one biologically-active granular activated carbon filter (Hershey, PA). The tRFLP profiles of dehI genes from the drinking water samples matched the pattern from Afipia spp. that were previously isolated from drinking water. The tRFLP profiles of dehII genes did not match any previously characterized dehII genes. Finally, a biodegradation kinetic model was developed to predict the fate of HAAs in biologically-active filters and water distribution systems. The model calculations indicated that biodegradation is likely to lead to significant HAA removals in biologically-active filters but not in most distribution systems. A sensitivity analysis showed that while the controlling parameter was the HAA-degrader biomass physical parameters, such as water flow velocity and pipe length, also had an influence on the HAA removal.Item Bubble barrier technologies for common carp.(2011-03) Zielinski, Daniel PatrickGreat ecological benefit will be gained if effective barriers can be constructed to control the movement of invasive common carp. Carp feeding habits lead to an over-enrichment of nutrients in lakes that dramatically reduces water quality and ecosystem health. Bajer et al. [2010] demonstrated that in Minnesota lakes, juvenile carp are recruited from nursery lakes to larger water bodies through small connecting channels. Reducing juvenile carp recruitment through the use of a barrier at the entrances to the interconnecting channels could prove useful in an integrated carp management plan for the entire watershed. Current barrier technologies are not well suited for these sites due to the shallow water and rapidly changing water level. This research focuses on the use of bubble curtain barriers, which has been relatively ignored in previous barrier studies, as a barrier technology that shows promise for this application. Bubble curtains generate distinct acoustic and hydrodynamic fields, and through proper manipulation could be used to deter juvenile carp migration. The initial stage of the barrier design was to quantify and measure the physical fields generated by a bubble curtain. An understanding of the physical fields helps to design full barrier systems by exploiting certain features of the bubble curtains. Experimental data revealed that a coarse-bubble curtain created a weaker flow field, but a stronger acoustic field than a fine-bubble diffuser. The subsequent stage of research included barrier tests with live carp using a PIT tag tracking system, which allowed quantification of carp passage over a barrier sans video recording. Three incrementally stronger bubble barriers were designed. A single diffuser design exhibited a mildly retarding effect of carp passage time (passages were delayed 10-15 sec) but not on the actual number passage attempts. Two separate multi-diffuser barriers (varying in configuration and air-supply) exhibited approximately a 75% decrease in carp passages, in upstream and downstream directions. The reduction of passes for each barrier was calculated by taking the ratio of the number of passages during a barrier-on trial to the number of passages during a control (barrier-off) trial. Carp mobility remained constant between tests, indicating that the two larger barriers did not limit total carp activity, but limited carp passage over the barrier. This research represents the first stage of characterization of bubble curtain features with respect to carp sensory systems and rigorous testing of bubble barriers under controlled laboratory settings. The experimental results suggest that bubble barriers create a flexible barrier that appears to deter juvenile carp movement in shallow channels, and may prove to be an effective tool in an integrated carp management plan.Item Comparative evaluation of asphalt concrete performance tests.(2012-07) Koktan, Philip DaleThe Minnesota Department of Transportation, similar to most state agencies, relies on volumetrics for their asphalt mix designs. Although volumetric specifications are necessary for a quality asphalt concrete mix, little or no effort is placed on performance-based specifications. These specifications utilize mechanical tests to predict in-service performance of a mix. Research efforts are needed to explore the current availability of performance tests, their suitability, and their usage by state agencies. This thesis focuses on collecting information on both currently practiced and state of the art performance tests, and their suitability for performance prediction in cold-climate regions. Desirable criteria were developed to analytically discover the most promising test(s) currently available for cracking prediction. A comprehensive literature review found an exhaustive amount of tests available, with varying levels of effectiveness. Although no test is perfect, there are tests that have promise. Through comparative evaluation, the Disk-Shaped Compact Tension Test, Semi-Circular Bend Test, and Indirect Tensile Test were found to be the most viable tests available. Other tests researched showed promise on some criteria, but were not well-rounded enough to be considered viable.Item Comparison of thermal stress calculated from asphalt binder mixture creep compliance data(2010-08) Moon, Ki HoonLow temperature cracking represents a significant problem in asphalt pavements built in Northern US and Canada. As temperature decreases rapidly, thermal stresses develop in the restrained surface layer and, when the temperature reaches a critical temperature, cracking occurs. In this thesis, statical analyses were used to compare thermal stresses that develop in an idealized asphalt pavement layer calculated from experimental data obtained with three different test methods: 1) Asphalt mixture creep test using Bending Beam Rheometer (BBR) 2) Asphalt mixture testing using Indirect Tensile Test (IDT) 3) Asphalt binder creep test using BBR and an empirical Pavement Constant Thermal stresses calculated using mixture BBR and mixture IDT data were reasonably identical. Thermal stresses calculated using binder BBR data and an empirical Pavement Constant were significantly different than the other calculated thermal stresses. The effect of physical hardening on thermal stress evaluation was investigated for a limited number of materials and it was found that this effect significantly affect thermal stress magnitude.Item Computational analysis of rigid pavement profiles(2012-06) Franta, Daniel PaulThe analysis of concrete pavement profiles has been an important part of pavement management for years. “Built-in” curling is a key input parameter for the Mechanistic-Empirical Pavement Design Guide (MEPDG). Built-in curling pertains to permanent curvatures found in concrete slabs due to early age properties. Currently, no comprehensive procedure exists to model or estimate the long-term, effective built-in curling. Curling refers to the way a concrete slab changes curvature due to an internal temperature gradient. Concrete surface profiles possess and show curl within slabs. However, due to the magnitudes of deflection from temperature gradients, extracting these temperature induced curl profiles can be difficult. For example, for a 12’x15’, 10” thick, single concrete slab containing a 15°F temperature gradient, computational models predict a maximum deflection of approximately 0.0174 inches, transversely from the middle of a slab to the edge. This small magnitude of deflection, coupled with the error involved in recording road profile data out in the field, makes it difficult to find consistencies in data that is not generated artificially. A Hilbert-Huang Transform (HHT) based algorithm was developed to analyze both field road profile data and artificially generated slab profile data in the hope that smoothed, consistent profiles could be extracted from noise-filled data sets using empirical mode decomposition (EMD). The application of this algorithm to concrete surface profiles resulted in the successful separation of the intrinsic mode functions contained within the data. The separation revealed intrinsic mode functions correlating to “noise”, “curl" and “base trend” data. ISLAB2005 artificial slab profiles, containing randomly induced error, were clearly identified. Trends in ALPS2, Minnesota IRI, Wisconsin LTPP, Georgia LTPP, Utah LTPP, and Arizona LTPP sections were also found. Arizona LTPP slab profiles were shown to contain consistent “curl” deflections for the same slab over a 20 month time-span and during both winter and early fall seasons. The consistent slab shape is likely due to early age built-in curl. Some of the profiles analyzed appeared to be dominated by noise. Artificial pavement profiles, corresponding to wide ranges of temperature gradients (-30°F to +30°F or ≈ -34.4°C to -1.1°C), were generated using the finite element program ISLAB2005. Cubic splines were applied through FORTRAN software to build a computationally efficient slab surface model, capable of back-calculating temperature gradients through artificially generated slab profiles. Optimization packages in DAKOTA used this FORTRAN model to back-calculate temperature gradients for ISLAB2005 slab profiles with known thicknesses, lengths and surface profiles. ISLAB2005 slab profiles containing induced random error were successfully smoothed by applying the developed Hilbert-Huang based profile analysis algorithm, and their corresponding temperature gradients were accurately back-calculated. Real road slab profiles were also smoothed using the Hilbert-Huang based algorithm, but the magnitudes of their deflections correlated to extreme temperature gradients in ISLAB2005. The large deflections are likely due to built-in curl, and the correlating extreme temperature gradient from ISLAB2005 is due to the model not taking into account early age built-in curl during temperature deflection estimations.Item Cracking of the PCC layer in composite pavement.(2011-12) Saxena, PriyamAn asphalt concrete (AC) overlay of a jointed plain concrete pavement (JPCP) is intended to extend the service life of the existing pavement structure. Also known as composite pavements, such pavements exhibit features of both rigid and flexible pavements. While behavior of rigid pavements is mainly elastic, behavior of asphalt layer is load-duration dependent. At the same time, temperature curling causes non-linear interaction with the foundation. The available models of composite pavement ignore the behavior of the load duration dependent asphalt layer when the composite pavement is subjected to a combination of temperature curling and traffic loads. This research concentrates on the improvement of structural modeling of composite pavements subjected to slow developing temperature curling and instantaneous traffic loads. A finite element (FE)-based model accounting for the viscoelastic behavior of the asphalt layer in composite pavements is developed and verified using comparisons with semi-analytical solutions obtained in this study. In order to maintain compatibility with the Mechanistic-Empirical Pavement Design Guide (MEPDG) framework, a simplified procedure is developed. The procedure uses a different asphalt modulus for curling than for axle loading and determines the total stresses in the pavement as a combination of the stresses from solutions of three elastic boundary value problems. The simplified procedure is compared with the existing MEPDG model for fatigue cracking in AC overlaid JPCP. A framework for the implementation of the proposed model into the MEPDG is also developed.Item Cracking performance of asphalt mixtures containing taconite tailings using traditional and multiple freeze-thaw moisture conditioning methods.(2012-09) Baker, Justin JoelCrushed aggregate resources for use in infrastructural applications are depleting and use of alternative resources is necessary to meet the demand. With annual consumption of approximately 1.2 billion tons of aggregates in the United States, significant environmental impact is caused. Annually, more than 125 million tons of fine grained crushed siliceous material is generated through iron ore mining in Northern Minnesota. This material is typically referred to as “taconite tailings” and usually ends up as landfills near mining operations. Research is being conducted on the potential usage of taconite tailings in asphalt mixtures to improve sustainability of highways. This study is focused on the key pavement failure mechanism of moisture damage, typically evident in the form of pot-holes during winter and spring seasons. The mechanical performance of asphalt concrete rapidly deteriorates in presence of moisture and is significantly accelerated through incur of freeze-thaw cycles. Currently there are no standardized tests which condition asphalt mixtures through multiple freeze-thaw cycling. Therefore, this study explored a method for subjecting specimens to multiple freeze-thaw cycles using temperatures which better represent actual climatic conditions. A field conditioning method was also employed by placing samples outside over a period of winter and spring months. These proposed conditioning methods were compared with a conventional conditioning process used for AASHTO T-283 procedure. The evaluation of moisture damage in asphalt mixtures containing taconite tailings was conducted using the conventional AASHTO T-283 test procedure and a fracture energy based approach. Testing results indicate that mix containing taconite tailings has acceptable moisture damage resistance after multiple freeze-thaw and field conditioning, which more accurately represents typical climatic conditions. The mechanical behavior of field and multiple freeze-thaw conditioned samples was quite different as compared to those conditioned in lab using the traditional AASHTO procedure.Item Determining the flexural strength of asphalt mixtures using the Bending Beam Rheometer.(2010-12) Turos, Mugurel IoanAsphalt mixture creep stiffness and strength are needed in the AASHTO Mechanistic Empirical Pavement Design Guide low temperature algorithm to predict low temperature performance. A procedure for obtaining creep stiffness by testing thin mixture beams using a Bending Beam Rheometer was previously developed at University of Minnesota. The possibility of performing strength tests on thin mixtures beams using a slightly modified Bending Beam Rheometer is investigated in this thesis. First, standardized strength tests, such as Indiredt Tension Test, Thermal Stress Restrained Specimen Test, and Direct Tension Test are performed on a group of eleven mixtures. Then, on the same eleven mixtures, three sets of tests are performed using the proposed method called Bending Beam Strength (BBS). The first set of tests is performed to investigate the reliability and reproducibility of BBS testing method, and the validity of the measuring concept. Weibull modulus is calculated as part of the analysis. The second set of tests is used to investigate the joint effect of temperature, conditioning time and loading rate, on the measured strength of three different mixtures, by using a 23 factorial design The third set consists in tests performed on a second group of eight mixtures tested at three temperatures. The different test results are then compared. Initially the measured values were put side by side. Promising results were obtained but the values were statistically different. The measured values are transformed taking into account the size of the samples and the testing method difference. The statistical analysis performed on the corrected values show that the BBS strength values are similar to the values obtained with other test methods.Item Development Of A Comprehensive Backcalculation Procedure For Rigid Pavement Design Parameters Using Slab-Edge Deflection Basins(2016-06) Paitich, SamuelBackcalculation of structural parameters for rigid pavements is commonly conducted with falling weight deflectometer (FWD) deflection basins measured at the center of slabs. Although a number of established techniques exist to backcalculate pavement parameters for the slab-center location, a reliable technique to backcalculate such parameters at the neighboring slab-edge location does not exist. The slab-edge location is critical to the design and management of rigid, concrete pavements because high stress levels and early signs of degradation originate at the slab edge. An edge backcalculation procedure accounting for the load transfer efficiency (LTE) of inter-slab joints is developed in this study. The proposed procedure is based on finite element modeling and dimensional analysis. Testing and validation of the edge backcalculation procedure is performed using FWD basins measured at the slab-edge location of in-situ pavements, along with measured LTEs, via the Long Term Pavement Performance (LTPP) program. Some prospective applications of the new procedure, in conjunction with the LTPP database, are presented. It is shown that the new edge backcalculation procedure is robust and satisfactory, particularly for pavements in good structural condition.Item Development of next generation ramp metering algorithm based on freeway density.(2011-02) Srivastava, AnupamFreeway ramp metering has been widely employed as an effective strategy to reduce congestion and increase the freeway operational efficiency for over two decades. Over the years, a number of isolated and coordinated metering strategies have been developed and deployed various parts of the world. Minnesota, first through the Zone metering algorithm, and later through its successor, the Stratified Zone Metering algorithm, has been among the states that extensively use freeway on-ramp metering. Based on MnDOT Regional Traffic Management Center (RTMC)’s recommendation, alternatives for developing the next generation strategy to address limitations and substantially enhance the performance of the currently deployed Stratified Ramp Metering strategy were explored. Following a different approach, the Next Generation strategy was developed by focusing on density rather than flow. This is because (as shown in earlier research) while values of occupancy near capacity are quite stable, bottleneck capacity has stochastic variations and a control strategy based on flow thresholds is likely to be inefficient. This variability in the capacity flow would mean that a control strategy based on flow thresholds would be likely to either under-load the freeway during the uncongested regime of traffic flow, or overload the system after the occurrence of the breakdown. While the former might lead to early onsets of congestion (congestion not being delayed as much as possible since the full capacity of the system is not utilized), the later might mean that the system is unable to recover from congestion efficiently (due to an over-load on the system). Critical occupancy however, and therefore density, iii is known to have stable behavior at capacity. This suggests that using a density based control approach can potentially enhance the overall performance of the system. During the first part of the study we developed a methodology to estimate densities with space and time based on data from loop detectors. The methodology is based on solving a flow conservation differential equation (using LWR theory) with intermediate (internal) freeway mainline boundaries, which is faster and more accurate than previous research using only external boundaries. Capacity drop phenomenon is inherently incorporated in the density estimation process, and the effect of the stochastic nature of capacity flow is minimized by identifying bottleneck threats and zones based on critical density values. Results compared with micro-simulation of a long freeway stretch show that this model produces reliable and accurate results. We further extended this density estimator using a two-value capacity (before and after the occurrence of a breakdown) and we integrated it in the LWR formulation. By carefully analyzing empirical data of active bottlenecks in the Twin Cities Metropolitan Area we noticed that (i) there are many cases where capacity is underutilized (4 min ramp delay constraint is misinterpreted by the algorithm) and (ii) the system once congested is unable to return to a state of flow near capacity for too long. One of the main reasons for the above inefficiencies is that capacity is considered constant during all times at all bottlenecks. This is concluded based on two empirical findings: (i) a significant capacity drop after the breakdown in many locations (varying iv 0-15%) and (ii) the total capacity of a bottleneck (sum of mainline + on ramp) is a function of the ratio of the two flows. More specifically, when ramp flows are higher the capacity is smaller (~5-10%). This happens very often in MN ramps because of the 4 minute constraint in ramp delays. Instead of a layer-based algorithm, we proceed with a dynamic zone-based algorithm. The whole freeway system is divided into zones, where the length of each zone is dynamic and is estimated in real-time. Within each zone the metering rates are chosen independently of conditions in other zones. The algorithm’s goal is to keep the car density levels at all ramps below the congestion thresholds and not to allow low speeds to occur in the mainline, by constraining the ramp delays. The ramp rates become stricter when mainline density is close to the congestion threshold, and the ramp rates increase when ramp waiting times are close to the ramp delay threshold. When it is not possible to keep both uncongested because of high on-ramp and mainline demands, the algorithm seeks to delay as long as possible the violation of both thresholds. The effectiveness of the new control strategies has been assessed by comparison with the current Stratified Zone Metering (SZM) version through microscopic simulation for the H-169 site. Under the new control strategy the total travel time on the mainline decreased by 1.5%, the ramp total travel time dropped by nearly 20%, the total system (freeway and ramp) travel time decreased by about 3% and total delays decreased by 8%. This finding suggests that in this case the new strategy is very effective since it reduces not only ramp delay, but also total system delay. The results clearly indicate that the new control strategy is very effective in keeping ramp wait times below the maximum allowed and in reducing ramp delay time. Another interesting observation made by analyzing the simulation results is that the new strategy substantially reduces ramp queues, while the overall ramp delay for the peak period was reduced by nearly 30%. The effectiveness of the newly developed control strategy is then assessed using the AIMSUN traffic micro-simulator against the currently deployed strategy. The new metering strategies is deployed on a simulated network and implemented using the AIMSUN API module. The strategy is compared against the current strategy using various measures of effectiveness and is found to succeed in delaying the onset of breakdown, accelerating system recovery after breakdown, and improving the overall freeway and ramp performances (through improved speeds and throughputs and reduced delays and stoppages). A proposal for field implementation of the new strategy and of comparison studies of performance based on ‘before’ and ‘after’ studies is suggested as a follow up for the study.Item The Disposal of Creamery Wastes(1922-06) del Plaine, Carlos WerterItem The effect of carbon inputs on microbial community structure and function: the role of fermentation processes in groundwater.(2009-12) Nelson, Denice KarenCarbon inputs to groundwater aquifers include intentional applications, as in bioremediation practices, and unintentional spills. The addition of carbon to an aquifer environment promotes the growth of a diverse and complex microbial community capable of generating several fermentation products, including some regulated compounds and methane, an explosive gas. This dissertation focuses on the fermentative community that develops in response to carbon application in an aquifer environment. Research was conducted to specifically examine 1) how fermentation processes affect partitioning of trichloroethene (TCE), a common groundwater contaminant, 2) the extent that continuous or pulsed carbon inputs affect microbial community structure and function, and 3) how an ethanol-based fuel (E85) stimulates fermentation processes, including methane generation, and the effect of ethanol toxicity on plume longevity. Remediation of groundwater plume source areas is challenging because lingering contaminants are often present as non-aqueous phase liquid (NAPL) and sorbed mass, and therefore difficult to remove via biodegradation or other commonly used remedial methods. Experimental results indicated that enhanced dissolution of TCE NAPL was possible through the addition and/or subsequent fermentation of a dilute molasses solution. Two mechanisms were responsible for the enhanced dissolution of NAPL; the addition of fresh molasses increased TCE solubility (>200%), thereby increasing the concentration gradient and subsequent mass transfer of NAPL to the dissolved phase, and mixing NAPL with fermented molasses solution significantly increased the surface area of the NAPL through formation of an emulsion, thereby increasing the mass flux of NAPL to the dissolved phase. In addition, the fermented liquid may have also decreased the soil partitioning coefficient (Kd) of TCE, indicating that enhanced transfer of sorbed mass to the aqueous phase could also occur in the presence of fermented molasses. These results can be used to optimize remedial systems to increase NAPL and sorbed-mass dissolution and are therefore important, particularly when bioremediation is used to polish residual source zones. The addition of organic carbon to a groundwater aquifer for biostimulation purposes promotes the growth of a diverse fermentative community as well as organisms targeted for contaminant degradation. Engineered carbon application systems commonly include either a continuous low dose of carbon, or periodic high doses of carbon. Experimental results indicated that a monthly pulse of a high dose (10% by volume) of molasses generated several fermentation products at high levels following each application, while a continuous feed of low molasses solution (0.4%) reached steady-state in 130 days, after which no further detection of fermentation products occurred. Methane generation in both systems was similar, indicating that methane production was not affected by the carbon addition strategy. Significant shifts in both Eubacteria and Archaea community structures were observed after carbon introduction, with the greatest changes correlating to the higher concentrations of carbon provided by the pulsed system. The total quantity of bacteria and methanogens was higher along the pulsed-fed column compared to the continuously-fed system. The continuously-fed column exhibited greater biofouling behavior. Taken together, biofouling did not appear to be a result of biomass quantity, rather a function of community structure. In summary, the method of carbon introduction (pulsed high-dose versus continuous low-dose) can result in significantly different community structures, functions, and densities of indigenous organisms. These data suggest that systems can be engineered to control fermentation product generation and biofouling behavior by manipulating the style of carbon application. Methane, however, will need to be controlled in either system. A spill of ethanol-based fuel will not only contaminate an aquifer, but will also serve as a food source to stimulate fermentative organisms that can generate potentially regulated compounds and create an environment conducive for production of explosive methane gas. Experimental results indicated that a continuous supply of a dilute ethanol-based fuel (E85) resulted in a profound shift in the community structure of Eubacteria and Archaea accompanied by the production of volatile fatty acids and butanol, a compound with a groundwater regulatory standard in Minnesota. Data also indicated that dissolved methane was produced at concentrations that could accumulate to an explosive level (>2 mg/L) in headspace. Quantitative polymerase chain reaction (qPCR) data showed a statistically significant increase in methanogenic populations, when compared to a control column. These results strongly correlated to areas of the column containing acetate, a breakdown product of ethanol. Toxicity data indicated that microbial growth was completely inhibited at approximately 6% (vol/vol) ethanol. These results suggest that even though ethanol is readily degradable, the core of an E85 spill may serve as a long-term source of contamination, and subsequent methane production, as it cannot be degraded until significant dilution has occurred. The research presented in this dissertation shows that the addition and subsequent fermentation of molasses can enhance the mass transfer of TCE, and that the style of carbon application affects the microbial community structure, density of biomass, and subsequent production of fermentation processes. Similarly, an input of E85 will result in the generation of fermentation products, some of which are regulated, and produce methane at levels that can potentially accumulate to explosive levels. This research furthers our understanding of the importance of fermentation processes resulting from carbon inputs to a groundwater environment. These results can be used to optimize bioremediation systems that incorporate carbon addition in order to manage fermentation product formation and biofouling impacts, and to mitigate potential human health hazards stemming from ethanol-based fuel spills through more accurate fate and transport modeling efforts.Item Effects of Heavy Agricultural Vehicle Loading on Pavement Performance(2011-01) Lim, JasonAgricultural equipment manufacturers have been producing equipment with larger capacity to meet the demands of today’s agricultural industry. This rapid shift in equipment size has raised concerns within the pavement industry, as these heavy vehicles have potential to cause significant pavement damage. At present, all implements of husbandry are exempted from axle weight and gross vehicle weight restrictions in Minnesota. However, they must comply with the 500 lb per inch of tire width restriction which may lead to very large loads as long as the tires are sufficiently wide. A full scale accelerated pavement test was conducted at the MnROAD test facility. Both flexible and rigid pavements were tested in this study. This thesis presented analysis performed on the flexible pavement sections. The flexible pavement sections consisted of a “thin section” which represented a typical 7-ton road and a “thick section” which represented a 10-ton road. Both sections were instrumented with strain gages, earth pressure cells, and LVDTs to measure pavement responses generated by these heavy agricultural vehicles. These response measurements were compared to responses generated by a typical 5-axle semi truck. Additionally, tire contact area and contact stresses of these vehicles were measured. Through this research, it was determined that traffic wander, seasonal changes, time of testing, pavement structure, and gross vehicle weight have profound effects on pavement response measurements. The effect of vehicle speed and benefits of flotation tires over radial ply tires were not significant in this study. Additionally, all agricultural vehicles loaded above 80% of full capacity generated higher subgrade stresses compared to the 80-kip 5-axle semi truck. Layered elastic programs, BISAR and MnLayer were used in the modeling analysis. The contact areas of these vehicles were approximated through multi-circular area estimation. This detailed modeling of the contact area yielded a more realistic representation of the actual vehicle footprint. DAKOTA-MnLayer optimization framework was introduced to perform backcalculation analysis to determine Young’s moduli of the pavement layers. The backcalculated Young’s moduli resulted in a close match between predicted responses and field measurements.Item The effects of physical variables on zooplankton distributions in stratified lakes.(2007-10) Spitael, Maria SusanZooplankton play a vital role in lake ecosystems. They serve as an important food source for fish, as well as being major consumers of algae, which contributes to greater water clarity. To understand the dynamics in a lake, it is necessary to understand zooplankton and how they are affected by the physical environment around them. The purpose of this research was to address the question of how turbulence and temperature stratification affect zooplankton aggregations in lakes. Laboratory experiments were performed to quantify the effects of temperature and turbulence on zooplankton distributions in a stratified tank. These measurements were designed to measure zooplankton aggregations and to provide detailed information on the physical conditions causing them. Comprehensive field measurements were taken throughout one summer, covering five 24-hour periods, in order to investigate the effects of temperature and turbulence on zooplankton aggregations in the field. A high-frequency sonar measurement device was developed to take the measurements by modifying the output of a commercial fish-finder and calibrating it to match zooplankton net counts. Our results showed that zooplankton distributions are strongly affected by temperature and turbulence, and that these effects are species-specific, and are different between day and night.Item Efficient computational methods for uncertainty quantification of large systems.(2011-05) Gaurav, GauravThe quest to design environment-friendly and sustainable engineering systems has witnessed more and more fervent efforts in recent years. With the growth of affordable large-capacity computing resources, predictive, science-based computational models have become instrumental in this pursuit. The present work develops efficient computational methods for the uncertainty analysis of large dynamical and mechanical systems with local nonlinearities and uncertainties. Two approaches have been utilized: (i) reduction of the size of the system, and (ii) use of parallel computing resources. The first approach utilizes the response of a nominal system to efficiently compute the response of related systems; three types of analysis methods have been developed. The first method can be utilized for efficient modal analysis of undamped linear systems with local stiffness uncertainties. The second method can perform efficient frequency domain analysis of linear systems with local damping and stiffness uncertainties. The third method can be utilized for efficient time domain analysis of systems with local nonlinearities and uncertainties. These methods provide gains in computational efficiency approaching three orders of magnitude for moderately-sized computational models compared to the corresponding conventional methods. The gains in computational efficiency are expected to be more pronounced as the dimensionality of the system is increased. The second approach to increase computational efficiency utilizes modern parallel computing devices, specifically, graphics processing units (GPUs) to perform uncertainty analysis of computational models. A variety of uncertainty quantification methods have been implemented on a GPU. The gains in computational efficiency compared to corresponding CPU-based implementations range from one to three orders of magnitude. These GPU implementations are expected to serve as initial bases for further developments in the use of GPUs in this field.Item Environmental analysis of using recycled asphalt shingles in pavement applications.(2011-02) Austin, JasmineRecycled asphalt shingles have been used in paving applications for more than two decades and have growing acceptance in the industry. The cost of asphalt binder has steadily increased, fueling pressure to find suitable recycled materials to supplement virgin materials. The Minnesota Department of Transportation has dedicated several studies for using asphalt shingle scrap in asphalt pavements. There are two types of shingles that can be used in pavement: manufacturer waste shingle scrap and tear off shingle scrap. As a result of the studies performed, the Minnesota Department of Transportation currently allows up to 5% of manufacturer waste shingle scrap in paving applications. Research on tear off shingle scrap is continuously developing, and a draft specification from the Minnesota Department of Transportation indicates that up to 5% can be used in asphalt pavement. In this thesis, both types of shingles were used in asphalt mixtures that were tested for performance to determine if the addition of shingles affects the physical properties. In addition, an environmental analysis was performed. The objective of this research was to determine if it physically makes sense to use shingles in pavement and to understand the environmental implications—which include reducing virgin materials which can yield energy savings. The analysis suggests up to 3% tear off shingle scrap in asphalt mixtures results in an effect on low temperature properties similar to the addition of up to 5% manufacturer waste shingle scrap, if combined with recycled asphalt pavement addition of more than 20%. The results of our research do support previous research efforts regarding the use of recycled asphalt shingles in pavement; however, based on these results, the Minnesota Department of Transportation draft specification for the use of tear off shingle scrap in asphalt pavement should state that up to 3%, not 5%, shingles can be used.Item Evaluation of local fields and effective behavior of viscoelastic heterogeneous materials(2010-07) Pyatigorets, Andrey V.The dissertation is concerned with the study of the mechanical time-dependent behavior of viscoelastic composite materials and structures. The analysis of such materials should not only take into account their complex structure, but also the time-varying properties of one or more constituents. The first part of the dissertation is concerned with the calculation of local time-varying fields in the viscoelastic fiber-reinforced composites and porous media. A two-dimensional model that represents a section perpendicular to the axes of the fibers is employed. The analysis adopts the correspondence principle based on the Laplace transform, and the problem is treated with the use of a direct boundary integral approach. The unknown boundary parameters are approximated by the truncated Fourier series. The procedures of the analytical (for the case of porous viscoelastic media) and numerical (for the case of fiber-reinforced composites) inversion of the Laplace transform are used to obtain time-varying fields anywhere in the matrix or inside the inclusions. The developed approach possesses several advantages in regard to computational efficiency and accuracy if compared with conventional methods based on the use of collocation and discretization techniques. The second part of the dissertation is concerned with the evaluation of the effective transverse properties of the viscoelastic fiber-reinforced composites. The developed approach relies on the knowledge of local stress fields and adopts the equivalent inhomogeneity technique modified for the case of viscoelastic composite's matrix. The solution is obtained in the Laplace domain, and the Laplace inversion is required to arrive at the time-varying effective properties. The developed approach directly takes into account the interactions between the inhomogeneities. The final part of the dissertation is dealing with the problem of thermal stress evolution in viscoelastic composite structures. These stresses are due to mismatch between the coefficients of thermal expansion of the composite's constituents. The proposed approach employs the Volterra correspondence principle and relies on the ability to obtain the analytical solution for the corresponding elastic problem. The approach adopts the discrete (matrix) representation of Volterra type operators. Particular attention is devoted to the analysis of thermal stress evolution in viscoelastic asphalt binders at low temperatures.Item An evaluation of methods for the design of R/C flexible twin-walled bridge piers.(2010-10) Scheevel, Christopher J.Abstract summary not available