Browsing by Subject "Concrete"
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Item Advancements in concrete material sustainability : supplementary cementitious material development and pollutant interaction(2013-05) Taylor Lange, Sarah Clare; Juenger, Maria C. G.; Siegel, Jeffrey A.Calcined clay and fly ash supplementary cementitious materials (SCMs) used in cement based materials were examined for their chemical and mechanical performance, as well as their pollutant interaction. This dissertation addresses three primary research questions, namely: (i) can zincite additions facilitate the use of calcined clay as SCMs by compensating for reductions in early-age mechanical performance or by compensating for their reduced pozzolanic reactivity, (ii) can cement renders, containing metakaolin calcined clays, be engineered for passive carbon dioxide and ozone removal, and (iii) how do the specific activity and emanation fractions of concrete constituents, including fly ash and metakaolin, as well as assembled concretes impact concrete radon emanation and indoor radon concentrations? The first question relates directly to the development of new, sustainable material options, which can replace a portion of cement in a concrete mixture. Results from the experiments with zincite showed that the treatment method removed the dilution effect that occurs when using less reactive materials to substitute a portion of portland cement, but did not considerably influence mechanical properties. Therefore, zincite additions are not a good means of enhancing the utilization of non-kaolinite clays in concrete. As an integrated system, the latter two questions of this dissertation investigate the interaction between airborne pollutants and the cement based materials containing SCMs. The use of SCMs in render and concrete systems resulted in different pollutant uptake and exhalation behavior, relative to non-SCM control systems. For pollutant uptake, render systems containing metakaolin increased the carbon dioxide ingress while decreasing the ozone uptake. For radon exhalation rates, modeling results demonstrated that concretes without fly ash have a higher probability of containing less total radium and lower radon exhalation rates, when compared to samples with fly ash, assuming an emanation fraction of 5%, as suggested in the literature. Experimental results demonstrated that metakaolin, fly ash and control concretes had emanation fractions of 7%, 9% and 13%, respectively, confirming that (i) an assumed fraction of 5% would underpredict indoor radon concentrations and potential health consequences, and (ii) SCMs can reduce the total concrete emanation fraction. This dissertation demonstrates how the use of sustainable material selections, such as calcined clays and fly ashes, not only influences the microstructure and mechanical performance of the cement based materials, but also alters the interaction of the material with its surrounding environment.Item Aggregates in self-consolidating concrete(2007) Koehler, Eric Patrick; Fowler, David W.Self-consolidating concrete (SCC) is an advanced type of concrete that can flow under its own mass without vibration, pass through intricate geometrical configurations, and resist segregation. SCC constituent materials and mixture proportions must be properly selected to achieve these flow properties. The effects of any changes in materials or mixture proportions on hardened concrete performance must be considered in evaluating SCC. A research project was conducted to investigate the role of aggregates in SCC. The objectives of this research were to evaluate the effects of aggregate characteristics and mixture proportions on the workability and hardened properties of SCC, to identify favorable aggregate characteristics for SCC, and to develop guidelines for proportioning SCC with any set of aggregates. The research indicated that although SCC can be proportioned with a wide range of aggregates, the selection of favorable aggregates can significantly enhance the economy and performance of SCC. The effects of aggregate grading; maximum size; shape, angularity, and texture; apparent clay content; and packing density were evaluated. The main effect of aggregates larger than approximately 75 [mu]m was found to be on the minimum required paste volume for achieving SCC workability. It was found that dust-of fracture microfines, defined as mineral material finer than approximately 75 [mu]m produced during the crushing of aggregates, could be an economical choice to comprise part of the paste volume. Based on the results of this research, a mixture proportioning procedure for SCC was developed. The procedure is based on a consistent, rheology-based framework and was designed and written to be accessible and comprehensible for routine use. In the procedure, SCC is represented as a suspension of aggregates in paste. Aggregates are selected on the basis of grading, maximum size, and shape and angularity. The paste volume is set based on the aggregate characteristics in order to achieve workability requirements. The paste composition is established to achieve workability and hardened property requirements.Item Analysis and response mechanisms of blast-loaded reinforced concrete columns(2009-05) Williams, George Daniel; Williamson, Eric B., 1968-; Williamson, Eric B., 1968-Terrorism has been an international threat to high occupancy civilian structures, government buildings, and military installations for many years. Statistical data from past terrorist attacks show that transportation infrastructure has been widely targeted, and a bombing of an ordinary highway bridge is a realistic scenario. Recent threats to bridges in the U.S. confirm this concern and have caught the attention of the bridge engineering community. Given that many ordinary highway bridges in the United States support critical emergency evacuation routes, military transportation plans, and vital economic corridors, the loss of a key bridge could result in severe national security, economic, and socioeconomic consequences. Therefore, in this research, a simplified procedure is developed to predict blast loads on bridge columns, and an understanding of the mechanisms that cause damage and ultimately failure of blast-loaded reinforced concrete bridge columns is advanced. To that end, computational fluid dynamics models are constructed and validated using experimental data. These numerical models are used to characterize the structural loads experienced by square and circular bridge columns subjected to blast loads, which is followed by the formulation of a simplified load prediction procedure. Additionally, nonlinear, three-dimensional, dynamic finite element models of blast-loaded reinforced concrete bridge columns are developed and validated using qualitative and quantitative data from recent experimental tests. The results of these analyses illustrate the fact that circular columns cannot be assumed to experience less base shear demand than a square column simply because they experience less net resultant impulse. Furthermore, the column response models developed in this research are used to identify and explain the mechanisms that lead to the spalling of side cover concrete off blast-loaded reinforced concrete members observed in recent experimental tests. Therefore, the results of this research advance the understanding of the structural loads on and the resulting response of reinforced concrete bridge columns subjected to blast loads, and as such these contributions to the structural engineering community enhance the security of the U.S. transportation infrastructure.Item Assessment of long-term corrosion resistance of recently developed post-tensioning components(2012-08) Moyer, Kevin Lee; Breen, J. E. (John Edward), 1932-; Wood, Sharon L.; Wheat, Harovel G.The forensic analysis of fourteen post-tensioned beam specimens after six years of aggressive exposure testing is the focus of this thesis. Funding for this research came from TxDOT and FHWA. Current post-tensioning materials and construction practices have been deemed inadequate due to fairly recent corrosion failures. Recently developed post-tensioning components and systems were assessed to determine their suitability to prevent durability concerns that had been found in older structures. Testing was conducted on the following variables: Strand Type, Duct Type, Duct Coupler Type, Anchorage Type, Electrically Isolated Tendons. Non-destructive and destructive testing methods were used to study the specimens and were evaluated on their effectiveness in predicting corrosion. Service life analysis was done on a structure using the strands and ducts study in the project. Galvanized duct showed substantial pitting and area loss. The majority of the plastic ducts had no observed damage. However, tendon grout chloride concentrations in most cases were extremely elevated with both galvanized and plastic ducts. This indicated that moisture had entered the duct, through either the couplers and/or grout vents. Except for strands from one specimen, the strands had minor corrosion with occasional mild pitting. The exception had heavy mild pitting confined to a small portion of the strand due to a hole in the duct. Backfill quality was good but it did not bond well with the base concrete. Therefore, moisture and chlorides entered the anchorage region. The electrically isolated tendon did not perform as well as expected. The grout chloride concentrations and level of corrosion damage were comparable to the concentrations and corrosion damage from the more conventionally protected specimens.Item Behavior of the shear studs in composite beams at elevated temperatures(2015-12) Dara, Sepehr; Engelhardt, Michael D.; Helwig, Todd A; Williamson, Eric B; Ghannoum, Wassim M; Ezekoye, Ofodike AIn order to improve the fire safety and at the same time to provide more economical design of composite floors in fire, it is important to understand the behavior of these systems under fire exposure. An important step needed to reach this goal is to better understand the behavior of shear studs in composite beams at elevated temperatures, which was the focus of this research study. Typically, corrugated metal decks are used in construction of composite beams. These decks act as formwork and provide reinforcement for the concrete. For this study, however, the corrugated deck was not included. Rather, this study focused on cases where there is a solid concrete slab over the steel beam. The purpose of this limitation was to first gain a thorough understanding of shear stud behavior under fire exposure for this simpler configuration. This study on shear stud behavior at elevated temperature in solid slabs included both experiments and numerical simulations. The objective of the experimental test was to develop additional data on the load-slip behavior of shear studs in solid concrete slabs at elevated temperatures, and to compare the measured shear stud strength values with the limited test data and code provisions available in the literature. Two different specimen heating scenarios were introduced. One was meant to result in a temperature gradient in the specimen to simulate a fire condition. The other scenario was meant to result in a uniform temperature throughout the specimen for comparison purposes with the other scenario. One of the conclusions was that the shear stud strength and initial stiffness in the shear stud load-slip behavior have strong correlations with bottom of stud temperature, regardless of the heating scenario. Therefore, choosing the bottom of stud temperature as a reference temperature in predicting the shear stud ultimate strength and initial stiffness is reasonable. The objective of the numerical simulations was to develop a finite element (FE) model which can predict the thermal and mechanical behavior of shear studs in solid concrete slabs at elevated temperatures, and to validate the model against the experimental data. Different aspects of modeling the specimen using the general purpose finite element software, Abaqus, were discussed. Results of the analyses were compared with the experimental results of this study. Temperatures resulting from the heat-transfer analysis were found to be in a good agreement with experimental results at some locations in the specimen. However, at some other locations the difference between the experimental and FE results were more than 100 ºC. The existing level of uncertainty in the input data highly contributes to the errors in the temperature results, and emphasizes the difficulty that exists in heat transfer modeling. The load-slip curves found from FE analysis were presented for all the tests. The ultimate strength and the initial stiffness of the specimens were predicted well by the FE analyses. However, the slip capacity did not match between the experiments and FE analyses. Several parametric studies using the finite element model were conducted to investigate the sensitivity of the analysis results to various model parameters, both for heat transfer analysis and structural response analysis. The studied parameters included thermal conductivity of concrete, convective heat transfer coefficient, resultant emissivity, thermal joint conductance coefficient, Concrete Damaged Plasticity model parameters, steel stress-strain curves recommended by two different code provisions, and concrete tensile strength. The current gaps in our knowledge about these parameters were discussed.Item BIM-based construction waste estimation algorithms for institutional projects(2018-09-11) Guerra, Beatriz Chinelato; Leite, Fernanda L.; Faust, Kasey M.Crucial part of the estimation of construction waste (CW) is a reliable quantification of the amounts of materials needed for building construction. In this research the use of Building Information Modeling (BIM) is proposed as a solution for retrieving project data effectively for CW estimation purposes. Two algorithms that were developed to quantify concrete and drywall waste are presented to demonstrate a proposed CW estimation methodology. The main idea of this methodology is that the portion of materials purchased that are not needed to be incorporated into the actual structure are considered waste. The amounts of materials purchased are available on general contractors purchasing records and amounts of materials needed for construction are retrieved from BIM models. This research uses the BIM model of a recently completed institutional building as a testbed to perform the waste estimation. The validation of the proposed algorithms is performed by comparing the estimated waste to actual waste data from the project. Furthermore, numbers found on the literature are used to validate these estimations. This study is part of a larger ongoing project that seeks to develop algorithms for the estimation of the major CW streams and implement them to enable a fully automated estimationItem Characterization of fly ash for evaluating the alkali-silica reaction resistance of concrete(2012-12) Jasso, Andres Jose; Folliard, Kevin J.; Ferron, RaissaFly ash has been used extensively to control deleterious alkali-silica reaction in concrete. The majority of fly ashes can be used to control ASR induced expansion. Fly ashes with high CaO contents are less effective at reducing expansion and fly ashes with high alkali contents can be counter active. Class C fly ashes are less effective at reducing the pH of the pore solution because they are less pozzolanic. The pozzolanic reaction in Class F fly ashes enhances the ability for the hydration products to bind alkalis. This prevents the availability of these alkalis for ASR. This project aims to characterize fly ash in a way that best predicts how it will perform in concrete with an emphasis on ASR. Fly ashes with a variety of chemical compositions were evaluated using a range of analytical and characterization techniques. Research data from several universities were used to correlate their long term data with this project’s accelerated tests. This research aimed at evaluating the mineralogical, chemical, and physical characteristics that most affect the ability of a given fly ash to prevent ASR-induced expansion and cracking.Item Clustering of air voids around aggregates in air entrained concrete(2007-05) Naranjo, Andy, 1977-; Folliard, Kevin J.Recent research reports have suggested that one of the potential causes of low compressive strengths in air-entrained concrete is the clustering of air voids around the aggregates. The phenomenon of clustering of air voids has been associated with the use of non-vinsol resin air-entraining admixtures and retempering (i.e. the late addition of water). The clustering is thought to reduce the bond strength at the aggregate-paste interface resulting in substantial reduction of compressive strength. The purpose of this research was to try and reproduce the clustering of air voids around aggregates in the laboratory by retempering, determine the severity of the clustering, and to evaluate its effects on concrete strength properties. Review of low strength field cases was also performed to determine if any correlations exist. This research evaluated three different types of air-entraining admixtures (wood and gum rosin, vinsol resin, and a synthetic formulation) and two types of coarse aggregates (siliceous river gravel and crushed limestone). A total of 43 concrete mixtures were made in the laboratory. The mixing procedure focused on retempering the concrete with water followed by an agitation period, and was successful at producing clustering of air voids around the aggregates. However, compressive, splitting tensile, and flexural strengths all showed no signs of strength loss that could be attributed to clustering of the air voids. Review of available field data and petrographic reports found that the phenomenon of air void clustering has a good correlation with the use of non-vinsol resin air-entraining admixtures and retempering of field concrete.Item Defining structurally acceptable properties of high-strength steel bars through material testing(2015-09-15) Slavin, Chase Meany; Ghannoum, Wassim M.; Engelhardt, Michael D.Low-cycle fatigue tests were performed on reinforcing bars in order to assess the acceptability of newly developed high-strength reinforcing bars in seismic applications. The steels tested are classified as grade 60 A706, grade 80 A706, grade 80 A615, and grade 100. The high-strength reinforcing bars tested represent the two most common manufacturing processes used today: microalloying and quenching-and-tempering. The results of these tests are presented along with comparisons between the fatigue life of bars based on steel grade and other bar properties. A statistical analysis of the test results is presented in order to assess the impact of many parameters on the low-cycle fatigue performance of grade 60 A706 and higher-strength reinforcing bars.Item Designing for deck stress over precast panels in negative moment regions(2017-10-27) Munsterman, Keaton; Helwig, Todd Aaron, 1965-One of the leading causes of structural deficiencies in the United States Bridge Inventory is related to deterioration and durability problems with concrete bridge decks (NCHRP 2004). The primary issue with bridge decks is related to cracking of the concrete that provides a direct conduit for moisture and other corrosion agents to permeate and attack the reinforcing steel. Adequate reinforcing steel is needed in the deck to minimize crack widths and therefore limit corrosion of reinforcing steel. A particular case of interest occurs when the bridge deck is constructed using partial-depth precast concrete deck panels (PCP) with cast-in-place (CIP) concrete topping. When this type of deck construction is used over the negative moment region of continuous steel or concrete girders, the amount of reinforcing steel that should be placed within the CIP concrete topping to provide adequate crack control is not currently well understood. This thesis is part of a larger study being conducted for the Texas Department of Transportation that is examining this issue. In the study reported in this thesis, two newly constructed bridges were instrumented to monitor the behavior of the bridge deck. These bridges did not use continuous girders, but rather had simply supported prestressed concrete girders, with a bridge deck constructed using a “poor-boy” construction joint detail over interior bents. Each bridge utilized three different reinforcement layouts centered over an interior bent within the poor-boy joint detail. Strain gages in each portion provided constant readings to display the distribution of strain across the bridge deck. Each bridge was monitored over a period from when the deck was cast until when the bridge was opened to traffic. Live load tests were also conducted to provide data on strains induced by heavy trucks. Based on the field data, no clear correlation was found between the amount of steel added and the strain measured. However, based on the measured data combined with field observations of cracking, the current standard reinforcement appears to be adequate in controlling the crack widths for the poor-boy deck detail. While the poor-boy deck joint detail is different from deck details used over negative moment regions of continuous girders, this data provides useful insights in to bridge deck behavior that will help guide future phases of the larger study.Item Designing the Fin-de-Siecle(1990-04-04) Kostof, SpiroAudio files are EID restricted. Individuals without an EID should send an email request to apl-aaa@lib.utexas.edu.Item Determination of aggregate shape properties using X-ray tomographic methods and the effect of shape on concrete rheology(2005) Erdoğan, Sinan Turhan; Fowler, David W.; Garboczi, Edward J.The shape of aggregate particles can significantly influence certain properties of concrete, both in its fresh and hardened states. Therefore, there is a need to be able to completely characterize the shape of aggregate particles, in three-dimensions, in order to develop computational models which accurately predict properties. In the past, numerous methods have been suggested for this task; however these methods are often only applicable to two-dimensional images of particles, they output a single or a few values, and fail to characterize the true shape of the particle. X-ray tomographic techniques allow the capturing of the true shape of particles and have been applied to concrete aggregates. Computed tomography has been used to characterize coarse and fine aggregate particles, while X-ray microtomography has been used to characterize particles passing the 75µm sieve. Sample preparation methods and scanning parameters applicable to concrete aggregates have been developed. The spherical harmonic method was used to efficiently store shape information, and to calculate useful parameters for individual particles, such as volume and surface area. Comparisons of the results to properties determined using other techniques were made and it was determined that the results of indirect or two-dimensional shape and size characterization methods can be misleading. The shapes of aggregate particles particularly influence the rheological properties of concrete mixtures. However, it is not clear to what degree different-scale shape properties (the overall shape, angularity and texture) influence flow separately. Artificial aggregates were prepared in the laboratory and simplified test cases were chosen to independently investigate the effect of overall shape and surface texture on the yield stress and plastic viscosity of mixtures and to obtain a set of results which could be used to calibrate computational models. These tests revealed that the overall shape of coarse aggregate particles significantly influences the plastic viscosity of a mixture, but does not affect the yield stress visibly. Particle surface texture does not seem to noticeably influence either viscosity or yield stress, for the cases tested. The results were also used to verify the “Dissipative Particle Dynamics” model and showed good correlation with the predictions.Item Development and laboratory testing of Ultra High Performance Concrete(2016-12) Hernandez, Jason Allan Abedania; Folliard, Kevin J.Ultra-High Performance Concrete (UHPC) is an emerging material technology that exhibits a combination of high compressive strength, high tensile strength, high toughness and ductility, and improved durability when compared to normal concrete. These characteristics lead to applications in bridge structures across the various department of transportations in the country. The objective of this research was to characterize proprietary and non-proprietary UHPC mixtures in the laboratory, with the ultimate goal aimed at implementing UHPC in bridge applications in Texas, particularly for field-cast connections and closure pours.Item Development of rapid, cement-based repair materials for transportation structures(2013-05) Zuniga, Jose Ricardo; Folliard, Kevin J.The deterioration of today's infrastructure particularly roadways and bridge decks has continued to increase over the years due to the larger axle loads, higher traffic volumes of densely populated cities. These highly congested areas have required the need to repair and rehabilitate the affected pavements in a timely manner with minimal traffic interruptions. Different rapid hardening binders were tested in this project to evaluate and characterize their performance when subjected to concrete distresses such as alkali-silica reaction, delayed ettringite formation, corrosion, freezing and thawing, salt scaling, sulfate attack, material incompatibility and volume changes. Among the cements tested were calcium aluminate cement, calcium sulfoaluminate cement, accelerated portland cement, alkali-activated fly ash, and three other proprietary blends available to the public. This thesis will summarize the preliminary findings of a comprehensive laboratory study focusing on rapid repair materials -- the final results of this study will be included in future publication (theses and final project report).Item Durability testing of rapid, cement-based repair materials for transportation structures(2014-05) Garcia, Anthony Michael; Folliard, Kevin J.; Drimalas, Thanos, 1980-For repairing concrete transportation infrastructure, such as pavements and bridges, much importance is placed on early-age strength gain as this has a major impact on scheduling and opening to traffic. However, the long-term performance and durability of such repair materials are often not satisfactory, thus resulting in future repairs. This research project focuses on the evaluation of the durability of various rapid-setting cementitious materials. The binders studied in this project include calcium aluminate cement (CAC), calcium sulfoaluminate cement (CSA), Type III portland cement, alkali-activated fly ash (AAFA) , and various prepackaged concrete materials. In addition, selected CAC and CSA mixtures were further modified with the use of a styrene-butadiene latex. The durability aspects studied include freezing-and-thawing damage and the implications of air entrainment in these systems, alkali-silica reaction, sulfate attack, and permeability of the concrete matrix and potential corrosion.Item Effect of Portland cement concrete characteristics and constituents on thermal expansion(2014-08) Siddiqui, Md Sarwar; Fowler, David W.; Juenger, Maria W; Bhasin, Amit; Won, Moon; Wheat, Harovel GThe coefficient of thermal expansion (CTE) is one of the major factors responsible for distresses in concrete pavements and structures. Continuously reinforced concrete pavements (CRCPs) in particular are highly susceptible to distresses caused by high CTE in concrete. CRCP is a popular choice across the U.S. and around the world for its long service life and minimal maintenance requirements. CRCP has been built in more than 35 states in the U.S., including Texas. In order to prevent CRCP distresses, the Texas Department of Transportation (TxDOT) has limited the CTE of CRCP concrete to a maximum of 5.5 x10-6 strain/oF (9.9 x10-6 strain/oC). Coarse aggregate sources that produce concrete with CTE higher than the allowable limit are no longer accepted in the TxDOT CRCP projects. Moreover, CTE is an important input in the Mechanistic-Empirical Pavement Design Guide (MEPDG). Small deviations in input CTE can affect the pavement thickness significantly in MEPDG designs. Therefore, accurate determination of concrete CTE is important, as it allows for enhanced concrete structure and pavement design as well as accurate screening of CRCP coarse aggregates. Moreover, optimizing the CTE of concrete according to a structure’s needs can reduce that structure’s cracking potential. This will result in significant savings in repair and rehabilitation costs and will improve the durability and longevity of concrete structures. This study found that the CTEs determined from saturated concrete samples were affected by the internal water pressure. As a result, the TxDOT method yielded higher values than did the American Association of State Highway and Transportation Officials (AASHTO) method. To further investigate the effect of internal water pressure, an analytical model was developed based on the poroelastic phenomenon of concrete. According to the model, porosity, permeability, and the rate of temperature change are the major factors that influence the internal water pressure development. Increasing the permeability of concrete can reduce the internal water pressure development and can thus improve the consistency of measured CTE values. Preconditioning concrete samples by subjecting them to several heating and cooling cycles prior to CTE testing and reducing the rate of temperature change improved the consistency of the CTE test results. Concrete CTE can be reduced by blending low-CTE aggregates with high-CTE aggregates and reducing the cement paste volume. Based on these findings, a concrete CTE optimization technique was developed that provides guidelines for the selection of concrete constituents to achieve target concrete CTE. A concrete proportioning technique was also developed to meet the need for CTE optimization. This concrete proportioning technique can use aggregate from any sources, irrespective of gradation, shape, and texture. The proposed technique has the potential to reduce the cement requirement without sacrificing performance and provides guidelines for multiple coarse and fine aggregate blends.Item Effects of low-level silica fume replacement in ASTM C 1260 and ASTM C 227 mortar-bar testing(2004-12-18) Maas, Andrew J.; Juenger, Maria C. G.Replacement of a percentage of cement by supplementary cementing materials (SCM) can control deleterious alkali-silica reaction. Silica fume, a commonly used SCM, and can be used to mitigate alkali-silica reaction (ASR). As-produced, silica fume is very small (0.1 μm) and requires densification for economical distribution. The densification, transportation and storage process may produce larger agglomerated silica fume (up to mm in size). Recently there have been some discrepancies in data reported in the literature as to the effect of these silica fume agglomerates on alkali-silica reaction in laboratory and field experiments. These results led to an investigation of the root causes of these differences. This thesis presents finding from an extensive investigation into the effects of silica fume replacement on alkali-silica reaction. Three different silica fumes (two densified and one undensified) were tested in various combinations with four different aggregates (two non-reactive, one reactive, and one highly-reactive). Results from ASTM C 1260 and preliminary results from ASTM C 227 mortar bar expansion tests are presented. Scanning electron microscopy was used to analyze epoxy-impregnated 28-day mortar samples from the ASTM C 1260 tests. It was observed that one type of silica fume agglomerates was alkali-silica reactive, while another neither increased nor decreased alkali-silica expansion. The undensified silica fume effectively controlled alkali-silica expansion with all aggregates except the highly-reactive aggregateItem Effects of photocatalysis on concrete surfaces(2012-05) Terpeluk, Alexandra Lee; Juenger, Maria C. G.; Fowler, David W.Highway air pollution is a significant environmental threat that has staggering implications for human health worldwide. Photocatalytic materials have the potential to reduce air pollution levels near major highways using ultraviolet radiation. This project, funded by the Texas Department of Transportation, evaluated photocatalytic efficiency and durability of several commercially-available photocatalytic coatings for use on concrete structures near highways. The research presented in this thesis involved obtaining concrete highway barriers and creating concrete slabs for outdoor testing and laboratory chamber testing. Three commercially-available coatings were applied to the specimens for testing: Keim Soldalit ME paint, TxActive Stucco Cement, and Pureti Clean. Field sites were set up near major highways in Houston and Austin, Texas. Durability and photocatalytic efficiency were regularly monitored at the field sites using ion chromatography and spectrophotometry. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were conducted on samples from each of the specimens taken before and after placement at the field sites in order to understand durability of the photocatalytic materials that were exposed outdoors. SEM results from this research project revealed that the photocatalytic material in the TxActive stucco and Keim paint remained in their original distribution after the exposure period, while the photocatalytic material in the Pureti Clean product appeared to decrease. XRD results remained fundamentally consistent for all coatings. Ion chromatography results showed that TxActive specimens had the highest surface levels of nitrates and nitrites between rainfall events, which indicates photocatalytic activity. Spectrophotometry results revealed a decrease in brightness for the Keim paint-coated specimens and no change or an increase in brightness for the TxActive stucco over time. The spectrophotometry results indicate how many surface contaminants are accumulating on the surface of a specimen, and thereby how efficiently sunlight is reaching the surface and activating the photocatalytic process. Results obtained from this research project may be influential in the selection of a means for reducing highway pollution in Texas.Item Effects of prestress on strains and deflections in pretensioned beams(2013-12) Koutrouvelis, Stergios; Tassoulas, John LambrosIn this research, nonlinear structural analysis along with finite element analysis were carried out for a pretensioned concrete beam at different levels of pretension in order to examine the effect of the change in the tendon force on the geometric stiffness of the beam. Several results were obtained for deflection, horizontal displacement and surface strains to investigate how they are affected by the level of pretension under the application of the same load in each case. These computations were compared with the tendon force to conclude whether they can be used to estimate the pretension level by means of simple measurements. The purpose was to develop a methodology for quantifying the prestress losses by taking advantage of the dependence of the prestressed concrete beam stiffness on the tendon force.Item Elizabeth Danze Habitat studio(1994) Danze, ElizabethAudio files are EID restricted. Individuals without an EID should send an email request to apl-aaa@lib.utexas.edu.
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