Alkali-silica reaction (ASR) is a common deterioration mechanism responsible for numerous concrete durability issues. Since ASR was first discovered in the 1940's, a significant number of investigations have been carried out in order to understand its mechanisms. However, due to the complexity of the reaction and to the numerous factors that affect its development, many aspects still remain unexplained. The research described in this document was funded by the Texas Department of Transportation (TxDOT), and it focused on a specific type of reactive aggregates, known as 'pessimum'; they present an unexpected behavior with respect to the relation between the amount of material present in the mixture and the extent of ASR related damage. The main objective of this investigation was to determine a method for identifying aggregates that exhibit the 'pessimum' behavior by means of a short-term testing regime. Modified versions of the Accelerated Mortar Bar Test (AMBT) and the Concrete Microbar Test (CMBT) were considered for this purpose. In addition, the behavior of a selected group of 'pessimum' aggregates in the Concrete Prism Test (CPT) and the Chemical Method was evaluated. The petrographic characteristics for a reduced number of the aggregates studied were linked to their performance in the ASR tests. The results obtained from the experimental program conducted were combined with results from previous investigations performed at UT Austin to draw conclusions about the overall behavior of ‘pessimum’ aggregates. ‘Pessimum’ aggregates were successfully identified with a modification proposed to the AMBT. As for their behavior, it was found that depending on the amount of reactive constituents present in each test, these aggregates are classified as reactive (for low chert contents) or as non-reactive (for chert contents above the 'pessimum' proportion). Whether these aggregates will generate durability problems depends on the amount of reactive silica in the concrete mixture. / text

Concrete bridges in Texas have developed large cracks in bent caps and pretensioned trapezoidal bridge girders. The bridges show premature concrete deterioration due to alkali-silica reaction (ASR) and delayed ettringite formation (DEF). There is concern that deterioration due to ASR/DEF may lead to a loss of structural capacity. However, there are no quantitative guidelines to relate the level of concrete deterioration due to ASR/DEF to structural performance. Using such guidelines, the need for rehabilitation of beams with ASR/DEF cracking can be assessed. The goal of this research was to determine the shear capacity of pretensioned trapezoidal box girder specimens exhibiting varying degrees of ASR and/or DEF cracking and to use the shear testing results to evaluate the severity of the problem that may exist in Texas bridge structures. To achieve this goal, beams that were severely deteriorated due to ASR/DEF over a period of more than ten years were transported to the University of Texas for testing to failure. Both severely deteriorated and uncracked beams were tested in shear. The test results were used to evaluate the shear performance of trapezoidal box beams affected by ASR/DEF. In addition, three different types of forensic analyses were conducted on the beams to understand the nature of the ASR/DEF cracks and severity of the deterioration. After testing, it is found that the shear capacity of the test specimens was not significantly reduced even with heavy ASR/DEF cracking. Assessment using current US design provisions for bridges or buildings (ACI 318-08 and AASHTO LRFD 2008) and the proposed provision from an earlier project (TxDOT Project 5253) yielded conservative estimates of strength. Results from forensic analyses provided a qualitative indication of ASR/DEF damage but did not correlate with the observed levels of ASR/DEF deterioration. / text

Across the State of Texas and many other areas of the world, relatively young concrete structures have developed signs of premature concrete deterioration. Large cracks form on the surface of the concrete due to expansive forces from alkali-silica reaction (ASR) and delayed-ettringite formation (DEF). The goal of this project is to assess the effect of ASR/DEF on the trapezoidal box beam bridges in the US 59 corridor and Katy Central Business District (CBD) HOV lanes in Houston, TX. Five dapped-end beams were rejected during the casting process and have been in storage at a local precast yard for nearly fifteen years. These beams have been subject to accelerated deterioration and represent the potential severity of the ongoing ASR/DEF distress within the dapped end regions of the in-service trapezoidal box beams. The results from five load tests, corresponding strut-and-tie models, and forensic investigation are used to provide insights into the relationship between the severity of the deterioration and the capacity margin. / text

Surfactants both change the wettability and lower the interfacial tension by various degrees depending on the type of surfactant and how it interacts with the specific oil. Ultra low IFT means almost zero capillary pressure, which in turn indicates little oil should be produced from capillary imbibition when the surfactant reduces the IFT in naturally fractured oil reservoirs that are mixed-wet or oil-wet. What is the transport mechanism for the surfactant to get far into the matrix and how does it scale? Molecular diffusion and capillary pressure are much too slow to explain the experimental data. Recent dynamic laboratory data suggest that the process is faster when a pressure gradient is applied compared to static tests. A mechanistic chemical compositional simulator was used to study the effect of pressure gradient on chemical oil recovery from naturally fractured oil reservoirs for several different chemical processes (polymer, surfactant, surfactant-polymer, alkali-surfactant-polymer flooding). The fractures were simulated explicitly by using small gridblocks with fracture properties. Both homogeneous and heterogeneous matrix blocks were simulated. Microemulsion phase behavior and related chemistry and physics were modeled in a manner similar to single porosity reservoirs. The simulations indicate that even very small pressure gradients (transverse to the flow in the fractures) are highly significant in terms of the chemical transport into the matrix and that increasing the injected fluid viscosity greatly improves the oil recovery. Field scale simulations show that the transverse pressure gradients promote transport of the surfactant into the matrix at a feasible rate even when there is a high contrast between the permeability of the fractures and the matrix. These simulations indicate that injecting a chemical solution that is viscous (because of polymer or foam or microemulsion) and lowers the IFT as well as alters the wettability from mixed-wet to water-wet, produces more oil and produces it faster than static chemical processes. These findings have significant implications for enhanced oil recovery from naturally fractured oil reservoirs and how these processes should be optimized and scaled up from the laboratory to the field. / text

The overall objective of this research was to gain an insight into the challenges encountered during chemical flooding under high hardness conditions. Different aspects of this problem were studied using a combination of laboratory experiments and simulation studies. Chemical Flooding is an important Enhanced Oil Recovery process. One of the major components of the operational expenses of any chemical flooding project, especially Alkali Surfactant Polymer (ASP) flooding is the cost of softening the injection brine to prevent the precipitation of the carbonates of the calcium and magnesium ions which are invariably present in the formation brine. Novel hardness tolerant alkalis like sodium metaborate have been shown to perform well with brines of high salinity and hardness, thereby eliminating the need to soften the injection brine. The first part of this research was aimed at designing an optimal chemical flooding formulation for a reservoir having hard formation brine. Sodium metaborate was used as the alkali in the formulation with the hard brine. Under the experimental conditions, sodium metaborate was found to be inadequate in preventing precipitation in the ASP slug. Factors affecting the ability of sodium metaborate to sequester divalent ions, including its potential limitations under the experimental conditions were studied. The second part of this research studied the factors affecting the ability of novel alkali and chelating agents like sodium metaborate and tetrasodium EDTA to sequester divalent ions. Recent studies have shown that both these chemicals showed good performance in sequestering divalent ions under high hardness conditions. A study of the geochemical species in solution under different conditions was done using the computer program PHREEQC. Sensitivity studies about the effect of the presence of different solution species on the performance of these alkalis were done. The third part of this research focused on field scale mechanistic simulation studies of geochemical scaling during ASP flooding. This is one of the major challenges faced by the oil and gas industry and has been found to occur when sodium carbonate is used as the alkali and the formation brine present in situ has a sufficiently high hardness content. The multicomponent and multiphase compositional chemical flooding simulator, UTCHEM was used to determine the quantity and composition of the scales formed in the reservoir as well as the injection and production wells. Reactions occurring between the injected fluids, in situ fluids and the reservoir rocks were taken into consideration for this study. Sensitivity studies of the effect of key reservoir and process parameters like the physical dispersion and the alkali concentration on the extent of scaling were also done as a part of this study. / text

A new design AMTEC converter model was developed, and its effectiveness as a design tool was evaluated. To develop the model, requirements of the model were defined, several new design models were successively developed, and finally an optimal new design model was developed. The model was created within Sinda/Fluint, with its graphical interface, Thermal Desktop, a software package that can be used to conduct complex thermal and fluid analyses. Performance predictions were then correlated and compared with actual performance data from the Road Runner II AMTEC converter. Predicted performance results were within 10% of actual performance data for all operating conditions analyzed. This accuracy tended to increase within operating ranges that would be more likely encountered in AMTEC applications. Performance predictions and parametric design studies were then performed on a proposed new design converter model with a variety of annular condenser heights and with potassium as a working fluid to evaluate the effects of various design modifications. Results clearly indicated the effects of the converter design modifications on the converter's power and efficiency, thus simplifying the design optimization process. With the close correlation to actual data and the design information obtained from parametric studies, it was determined that the model could serve as an effective tool for the design of AMTEC converters.

A functional nanometer-scale hybrid coating layer with multi-walled carbon nanotubes (MWCNTs) and/or nanoclays, as mechanical enhancement to ‘heal’ surface microcracks and environmental barrier layer is applied to alkaliresistant glass (ARG) fibres. The nanostructured and functionalised traditional glass fibres show both significantly improved mechanical properties and environmental corrosion resistance. Early warning material damage can be achieved by carbon nanotubes concentrated interphases in the composites. / Eine funktionale nanometerskalige Hybridbeschichtung mit multi-walled carbon nanotubes (MWCNTs) und/oder Nanoclay wurde als mechanische Verbesserung des „Ausheilens“ von Oberflächen-Mikrorissen und Barriereschicht gegenüber Umwelteinflüssen auf alkaliresistente Glasfasern (ARG) appliziert. Die nanostrukturierten und funktionalisierten traditionellen Glasfasern zeigen signifikant verbesserte mechanische Eigenschaften und Korrosionsbeständigkeit. Die Frühwarnung des Materialversagens kann durch Carbon Nanotubes, konzentriert in der Grenzschicht der Composites, erreicht werden.

Die Arbeit befasst sich mit der thermodynamischen Modellierung des British Gas-Lurgi-Vergasungsprozesses (BGL). Es werden auftretende Schwachstellen des Prozesses analysiert und auf das Verhalten der Mineralstoffkomponenten zurückgeführt. Auf Grundlage einer Stoffbilanz sowie zahlreicher Prozessdaten (BGL-Vergaser der SVZ Schwarze Pumpe GmbH) wurde das in SimuSage erstellte Stufenmodell an Nichtgleichgewichtszustände und Transportvorgänge angepasst. Das Modell erlaubt die qualitative und quantitative Beschreibung eines Alkalikreislaufes, welcher durch KCl geprägt ist. Mit dem Modell werden wirksame Maßnahmen abgebildet, um die Anreicherung von KCl und die damit verbundenen technischen Störungen zu vermeiden.

The aims of this thesis were to: 1) develop a new method for the determination of interstitial pH at rest and during exercise in vivo, 2) systematically explore the effects of different ingestion regimes of 300 mg.kg-1 sodium citrate on blood and urine pH at rest, and 3) to combine the new interstitial pH technique with the findings of the second investigation in an attempt to provide a greater understanding of H+ movement between the extracellular compartments. The purpose of the first study was to develop a method for the continuous measurement of interstitial pH in vastus lateralis was successfully developed using microdialysis and 2,7-bis-(2-carboxyethyl)-5-(and-6)-carboxyfluorescein (BCECF). To avoid the presence of an artificial alkalosis during exercise, it was necessary to add 25 mM HCO3- to the perfusate. The outlet of the probe was cut less than 10 mm from the skin and connected to a stainless steel tube completing the circuit to a microflow-through cuvette (8 fÝl) within a fluorescence spectrophotometer. This prevented the loss of carbon dioxide from the dialysate and any subsequent pH artefact. Interstitial pH was collected from six subjects before, during and after five minutes of knee-extensor exercise at three intensities 30, 50, and 70 W. Mean,,bSEM interstitial pH at rest was 7.38,,b0.02. Exercise reduced interstitial pH in an almost linear fashion. The nadir value for interstitial pH at 30, 50 and 70 W exercise was 7.27, 7.16 and 7.04, respectively. The lowest pH was obtained 1 min after exercise, irrespective of workload, after which the interstitial pH recovered in a nearly exponential manner. The mean half time of interstitial recovery was 5.2 min. The changes in interstitial pH exceeded the changes in venous blood pH. This study demonstrated that interstitial pH can be measured using microdialysis and that it is continuously decreased during muscle activity. The purpose of the second study was to establish an optimal ingestion regime for the ingestion of 300 mg.kg-1 of sodium citrate and maximise the alkalotic effect while minimising any side effects. Increasing the effectiveness of alkali ingestion may lead to further increases in muscle performance. Ingesting 300 mg.kg-1 sodium citrate at a rate of 300 mg.min-1 was identified as the optimal ingestion regime to maximise alkalosis at rest, which occurred 3.5 h post-ingestion. This was determined by monitoring eight human subjects ingesting 300 mg.kg-1 sodium citrate at five different rates, control (no ingestant), bolus, 300, 600 and 900 mg.kg.min-1 on five days separated by at least 48 hours. Sodium citrate was ingested in capsule form with water ad libitum, with the exception of bolus, which was combined with 400 ml less than 25 percent orange juice and consumed in less than 1 min. Arterialised blood (mean 71.3,,b3.5 mmHg) acid-base and electrolyte status was assessed via the withdrawal of ~5 ml of blood every 30 min across an eight hour duration, placed on ice and analysed within five minutes. No alkalotic difference was found between ingestion rates (mean 7.445,,b0.004, 7.438,,b0.004 and 7.442,,b0.004 for 300, 600 and 900 mg.min-1, respectively). All experimental ingestion regimes were associated with elevations in [HCO3-] (29.6, 29.7, 29.8, 29.9 and 26.3 mmol.l-1 for bolus, 300, 600, 900 and control, respectively). The 300 ingestion regime had the greatest impact on [H+], a 0.66 meq.l-1,,e10-8 change. Bolus ingestion (3.93,,b0.08 mmol.l-1) of sodium citrate had no effect on control (4.06,,b0.08 mmol.l-1) blood [K+], however, 300 mg.min-1 decreased blood [K+] (p less than 0.05). There was no effect of sodium citrate on blood [Cl-], but after 2.5 h blood [Cl-] was lower than pre-ingestion values (p less than0.05). All ingestion rates of sodium citrate increased (p less than 0.05) urine pH above control. This is the first study to investigate the effect of varying ingestion rates on acid-base status at rest in humans. The results suggest that ingesting sodium citrate in small doses in quick succession induce a greater blood alkalosis than the commonly practised bolus protocol. Using the interstitial pH technique described above and the optimal ingestion regime (300 mg.min-1) identified above, the final experiment was designed to assess the influence of sodium citrate ingestion on interstitial pH at both rest and during exercise. Five subjects ingested 300 mg.kg-1 sodium citrate at 300 mg.min-1 again in capsule form with water ad libitum. Prior to ingestion, each subject had a cannula placed into their cephalic vein and one microdialysis probe (CMA-60) inserted into their left thigh, orientated along the fibres of vastus lateralus. This probe was used for the measurement of pH as described above. At the end of this period, an exercise protocol required five subjects to perform light exercise (10 W) for 10 min, before starting an intense exercise period (~90-95% leg VO2peak) to exhaustion followed by a 15 min recovery period. Dialysate and blood samples were collected across all periods. Mean,,bSEM interstitial pH for placebo and alkalosis were 7.38,,b0.12 and 7.24,,b0.16, respectively. Sodium citrate ingestion was not associated with an interstitial alkalosis. An exercise induced acidosis was observed in the interstitium during placebo but not during alkalosis (p less than 0.05). Mean,,bSEM venous pH were 7.362,,b0.003 and 7.398,,b0.003 for placebo and alkalosis, respectively. Sodium citrate ingestion was not associated with a venous alkalosis. Sodium citrate ingestion was associated with an increase in mean,,bSEM venous [HCO3-] (placebo 25.5,,b0.2, alkalosis 28.1,,b0.2). This increase in the blood bicarbonate buffer system was not associated with an increase in time to exhaustion (placebo 352,,b71, alkalosis 415,,b171). This was the first study to investigate the effects of sodium citrate ingestion on interstitial pH. The results of this study demonstrated that an interstitial alkalosis does not ensue after alkali ingestion, however, it was associated with the lack of an exercise induced acidosis suggesting an improved pH regulation during exercise.

Copies of author's previously published articles inserted. / Bibliography: leaves 195-230. / xx, 320 leaves : ill. (some col.) ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / In this study the soil aqueous phase chemistry of Zn and Cu in alkaline sodic soils are investigated. The chemistry of trace metal ions at indigenous concentrations in alkaline sodic soils are reported. Metal ions at low concentrations are measured by the graphite furnace atomic absorption spectrometry (GFAAS) technique. / Thesis (Ph.D.)--University of Adelaide, Dept. of Soil Science, 1998