Matching Items (220)
Description
Alkali-activated aluminosilicates, commonly known as "geopolymers", are being increasingly studied as a potential replacement for Portland cement. These binders use an alkaline activator, typically alkali silicates, alkali hydroxides or a combination of both along with a silica-and-alumina rich material, such as fly ash or slag, to form a final product with properties comparable to or better than those of ordinary Portland cement. The kinetics of alkali activation is highly dependent on the chemical composition of the binder material and the activator concentration. The influence of binder composition (slag, fly ash or both), different levels of alkalinity, expressed using the ratios of Na2O-to-binders (n) and activator SiO2-to-Na2O ratios (Ms), on the early age behavior in sodium silicate solution (waterglass) activated fly ash-slag blended systems is discussed in this thesis. Optimal binder composition and the n values are selected based on the setting times. Higher activator alkalinity (n value) is required when the amount of slag in the fly ash-slag blended mixtures is reduced. Isothermal calorimetry is performed to evaluate the early age hydration process and to understand the reaction kinetics of the alkali activated systems. The differences in the calorimetric signatures between waterglass activated slag and fly ash-slag blends facilitate an understanding of the impact of the binder composition on the reaction rates. Kinetic modeling is used to quantify the differences in reaction kinetics using the Exponential as well as the Knudsen method. The influence of temperature on the reaction kinetics of activated slag and fly ash-slag blends based on the hydration parameters are discussed. Very high compressive strengths can be obtained both at early ages as well as later ages (more than 70 MPa) with waterglass activated slag mortars. Compressive strength decreases with the increase in the fly ash content. A qualitative evidence of leaching is presented through the electrical conductivity changes in the saturating solution. The impact of leaching and the strength loss is found to be generally higher for the mixtures made using a higher activator Ms and a higher n value. Attenuated Total Reflectance-Fourier Transform Infrared Spectroscopy (ATR-FTIR) is used to obtain information about the reaction products.
ContributorsChithiraputhiran, Sundara Raman (Author) / Neithalath, Narayanan (Thesis advisor) / Rajan, Subramaniyam D (Committee member) / Mobasher, Barzin (Committee member) / Arizona State University (Publisher)
Created2012
Description
This study is about Thai English (ThaiE), a variety of World Englishes that is presently spoken in Thailand, as the result of the spread of English and the recent Thai government policies towards English communication in Thailand. In the study, I examined the linguistic data of spoken ThaiE, collected from multiple sources both in the U.S.A. and Thailand. The study made use of a qualitative approach in examining the data, which were from (i) English interviews and questionnaires with 12 highly educated Thai speakers of English during my fieldwork in the Southwestern U.S.A., Central Thailand, and Northeastern Thailand, (ii) English speech samples from the media in Thailand, i.e. television programs, a news report, and a talk radio program, and (iii) the research articles on English used by Thai speakers of English. This study describes the typology of ThaiE in terms of its morpho-syntax, phonology, and sociolinguistics, with the main focus being placed on the structural characteristics of ThaiE. Based on the data, the results show that some of the ThaiE features are similar to the World Englishes features, but some are unique to ThaiE. Therefore, I argue that ThaiE is structurally considered a new variety of World Englishes at the present time. The findings also showed an interesting result, regarding the notion of ThaiE by the fieldwork interview participants. The majority of these participants (n=6) denied the existence of ThaiE, while the minority of the participants (n=5) believed ThaiE existed, and one participant was reluctant to give the answer. The study suggested that the participants' academic backgrounds, the unfamiliar notion of ThaiE, and the level of the participants' social interaction with everyday persons may have influenced their answers to the main research question.
ContributorsRogers, Uthairat (Author) / Gelderen, Elly van (Thesis advisor) / Mailhammer, Robert (Committee member) / Adams, Karen (Committee member) / Arizona State University (Publisher)
Created2013
Description
Properties of random porous material such as pervious concrete are strongly dependant on its pore structure features. This research deals with the development of an understanding of the relationship between the material structure and the mechanical and functional properties of pervious concretes. The fracture response of pervious concrete specimens proportioned for different porosities, as a function of the pore structure features and fiber volume fraction, is studied. Stereological and morphological methods are used to extract the relevant pore structure features of pervious concretes from planar images. A two-parameter fracture model is used to obtain the fracture toughness (KIC) and critical crack tip opening displacement (CTODc) from load-crack mouth opening displacement (CMOD) data of notched beams under three-point bending. The experimental results show that KIC is primarily dependent on the porosity of pervious concretes. For a similar porosity, an increase in pore size results in a reduction in KIC. At similar pore sizes, the effect of fibers on the post-peak response is more prominent in mixtures with a higher porosity, as shown by the residual load capacity, stress-crack extension relationships, and GR curves. These effects are explained using the mean free spacing of pores and pore-to-pore tortuosity in these systems. A sensitivity analysis is employed to quantify the influence of material design parameters on KIC. This research has also focused on studying the relationship between permeability and tortuosity as it pertains to porosity and pore size of pervious concretes. Various ideal geometric shapes were also constructed that had varying pore sizes and porosities. The pervious concretes also had differing pore sizes and porosities. The permeabilities were determined using three different methods; Stokes solver, Lattice Boltzmann method and the Katz-Thompson equation. These values were then compared to the tortuosity values determined using a Matlab code that uses a pore connectivity algorithm. The tortuosity was also determined from the inverse of the conductivity determined from a numerical analysis that was necessary for using the Katz-Thompson equation. These tortuosity values were then compared to the permeabilities. The pervious concretes and ideal geometric shapes showed consistent similarities betbetween their tortuosities and permeabilities.
ContributorsRehder, Benjamin (Author) / Neithalath, Narayanana (Thesis advisor) / Mobasher, Barzin (Committee member) / Rajan, Subramaniam D. (Committee member) / Arizona State University (Publisher)
Created2013
Description
Despite the vast research on language carried out by the generative linguistics of Noam Chomsky and his followers since the 1950s, for theoretical reasons (mainly their attention to the mental abstraction of language structure rather than language as a performed product), historical linguistics from the start lay outside their research interest. This study is an attempt to bridge the gap between the formalism and theoretical constructs introduced by generative grammar, whose ultimate goal is to provide not only a description but also an explanation to linguistic phenomena, and historical linguistics, which studies the evolution of language over time. This main objective is met by providing a formal account of the changes hwæðer undergoes throughout the Old English (OE) period. This seemingly inconspicuous word presents itself as a case of particular investigative interest in that it reflects the different stages proclaimed by the theoretical assumptions implemented in the study, namely the economy principles responsible for what has become known as the CP cycle: the Head Preference Principle and the Late Merge Principle, whereby pronominal hwæðer would raise to the specifier position for topicalization purposes, then after frequent use in that position, it would be base-generated there under Late Merge, until later reanalysis as the head of the Complementizer Phrase (CP) under Head Preference. Thus, I set out to classify the diverse functions of OE hwæðer by identifying and analyzing all instances as recorded in the diachronic part of the Helsinki Corpus. Both quantitative and qualitative analyses of the data have rendered the following results: 1) a fully satisfactory functional and chronological classification has been obtained by analyzing the data under investigation following a formal theoretical approach; and 2) a step-by-step historical analysis proves to be indispensable for understanding how language works at the abstract level from a historical point of view. This project is part of a growing body of research on language change which attempts to describe and explain the evolution of certain words as these change in form and function.
ContributorsParra-Guinaldo, Víctor (Author) / Gelderen, Elly van (Thesis advisor) / Bjork, Robert (Committee member) / Nilsen, Don L. F. (Committee member) / Arizona State University (Publisher)
Created2013
Description
Buildings consume a large portion of the world's energy, but with the integration of phase change materials (PCMs) in building elements this energy cost can be greatly reduced. The addition of PCMs into building elements, however, becomes a challenge to model and analyze how the material actually affects the energy flow and temperatures in the system. This research work presents a comprehensive computer program used to model and analyze PCM embedded wall systems. The use of the finite element method (FEM) provides the tool to analyze the energy flow of these systems. Finite element analysis (FEA) can model the transient analysis of a typical climate cycle along with nonlinear problems, which the addition of PCM causes. The use of phase change materials is also a costly material expense. The initial expense of using PCMs can be compensated by the reduction in energy costs it can provide. Optimization is the tool used to determine the optimal point between adding PCM into a wall and the amount of energy savings that layer will provide. The integration of these two tools into a computer program allows for models to be efficiently created, analyzed and optimized. The program was then used to understand the benefits between two different wall models, a wall with a single layer of PCM or a wall with two different PCM layers. The effect of the PCMs on the inside wall temperature along with the energy flow across the wall are computed. The numerical results show that a multi-layer PCM wall was more energy efficient and cost effective than the single PCM layer wall. A structural analysis was then performed on the optimized designs using ABAQUS v. 6.10 to ensure the structural integrity of the wall was not affected by adding PCM layer(s).
ContributorsStockwell, Amie (Author) / Rajan, Subramaniam D. (Thesis advisor) / Neithalath, Narayanan (Thesis advisor) / Mobasher, Barzin (Committee member) / Arizona State University (Publisher)
Created2013
Description
The alkali activation of aluminosilicate materials as binder systems derived from industrial byproducts have been extensively studied due to the advantages they offer in terms enhanced material properties, while increasing sustainability by the reuse of industrial waste and byproducts and reducing the adverse impacts of OPC production. Fly ash and ground granulated blast furnace slag are commonly used for their content of soluble silica and aluminate species that can undergo dissolution, polymerization with the alkali, condensation on particle surfaces and solidification. The following topics are the focus of this thesis: (i) the use of microwave assisted thermal processing, in addition to heat-curing as a means of alkali activation and (ii) the relative effects of alkali cations (K or Na) in the activator (powder activators) on the mechanical properties and chemical structure of these systems. Unsuitable curing conditions instigate carbonation, which in turn lowers the pH of the system causing significant reductions in the rate of fly ash activation and mechanical strength development. This study explores the effects of sealing the samples during the curing process, which effectively traps the free water in the system, and allows for increased aluminosilicate activation. The use of microwave-curing in lieu of thermal-curing is also studied in order to reduce energy consumption and for its ability to provide fast volumetric heating. Potassium-based powder activators dry blended into the slag binder system is shown to be effective in obtaining very high compressive strengths under moist curing conditions (greater than 70 MPa), whereas sodium-based powder activation is much weaker (around 25 MPa). Compressive strength decreases when fly ash is introduced into the system. Isothermal calorimetry is used to evaluate the early hydration process, and to understand the reaction kinetics of the alkali powder activated systems. A qualitative evidence of the alkali-hydroxide concentration of the paste pore solution through the use of electrical conductivity measurements is also presented, with the results indicating the ion concentration of alkali is more prevalent in the pore solution of potassium-based systems. The use of advanced spectroscopic and thermal analysis techniques to distinguish the influence of studied parameters is also discussed.
ContributorsChowdhury, Ussala (Author) / Neithalath, Narayanan (Thesis advisor) / Rajan, Subramanium D. (Committee member) / Mobasher, Barzin (Committee member) / Arizona State University (Publisher)
Created2013
Description
This study focuses on implementing probabilistic nature of material properties (Kevlar® 49) to the existing deterministic finite element analysis (FEA) of fabric based engine containment system through Monte Carlo simulations (MCS) and implementation of probabilistic analysis in engineering designs through Reliability Based Design Optimization (RBDO). First, the emphasis is on experimental data analysis focusing on probabilistic distribution models which characterize the randomness associated with the experimental data. The material properties of Kevlar® 49 are modeled using experimental data analysis and implemented along with an existing spiral modeling scheme (SMS) and user defined constitutive model (UMAT) for fabric based engine containment simulations in LS-DYNA. MCS of the model are performed to observe the failure pattern and exit velocities of the models. Then the solutions are compared with NASA experimental tests and deterministic results. MCS with probabilistic material data give a good prospective on results rather than a single deterministic simulation results. The next part of research is to implement the probabilistic material properties in engineering designs. The main aim of structural design is to obtain optimal solutions. In any case, in a deterministic optimization problem even though the structures are cost effective, it becomes highly unreliable if the uncertainty that may be associated with the system (material properties, loading etc.) is not represented or considered in the solution process. Reliable and optimal solution can be obtained by performing reliability optimization along with the deterministic optimization, which is RBDO. In RBDO problem formulation, in addition to structural performance constraints, reliability constraints are also considered. This part of research starts with introduction to reliability analysis such as first order reliability analysis, second order reliability analysis followed by simulation technique that are performed to obtain probability of failure and reliability of structures. Next, decoupled RBDO procedure is proposed with a new reliability analysis formulation with sensitivity analysis, which is performed to remove the highly reliable constraints in the RBDO, thereby reducing the computational time and function evaluations. Followed by implementation of the reliability analysis concepts and RBDO in finite element 2D truss problems and a planar beam problem are presented and discussed.
ContributorsDeivanayagam, Arumugam (Author) / Rajan, Subramaniam D. (Thesis advisor) / Mobasher, Barzin (Committee member) / Neithalath, Narayanan (Committee member) / Arizona State University (Publisher)
Created2012
Description
The primary topic of this dissertation is the grammaticalization of negation in three Sinitic language varieties: Hakka, Mandarin, and Southern Min. I discuss negative morphemes that are used under different modality or aspect contexts, including ability, volition, necessity, and perfectivity. Not only does this study examine Southern Min affirmative and negative pairs, but it also highlights the grammaticalization of negation and parametric differences in negation among the languages under investigation. This dissertation also covers the reanalysis of negatives into interrogatives. I approach the investigation of Southern Min negation from both synchronic and diachronic perspectives. I analyze corpus data in addition to data collected from fieldwork for the contemporary linguistic data. For my diachronic research of Chinese negation, I use historical texts and etymological dictionaries. Diachronically, many of the negative morphemes originate from full-fledged verbs and undergo an analogous grammaticalization process that consists of multiple stages of reanalysis from V to T (aspect; modality), and then T to C (interrogative; discourse). I explain this reanalysis, which involves head-to-head movement, using generative frameworks that combine a modified cartographic approach and the Minimalist Economy Principles. Synchronic data show that Southern Min affirmative modals are characterized by a certain morphological doubling. These doublings consist of two near synonyms used in sequence, resulting from the loss of features in a verb and a second verb added as a renewal. In the negation paradigm, some negatives project a negative phrase, while the others serve a dual function, occupying a modal/aspect head as well as a negative head. The latter system is gradually shifting to the former. This study uncovers evidence to counter the long-established paradigm, where negation is tied to its independent modality (abilitive, volitional and necessitive) or aspect (perfective and perfect). I observe a mismatch between the use of interrogatives and their modality/aspect and attribute this phenomenon to feature loss during their reanalysis from negatives to interrogatives. Results however show that consistency occurs in the grammaticalization of negation within Southern Min and intra-linguistically among the three Sinitic languages, and that parametric differences are found at the morphological level.
ContributorsYang, Huiling (Author) / Gelderen, Elly van (Thesis advisor) / Adams, Karen (Committee member) / Gillon, Carrie (Committee member) / Sun, Chaofen (Committee member) / Arizona State University (Publisher)
Created2012
Description
Spanish-speaking (SS) dual language learners (DLLs) have shown differential developmental profiles of the native language (L1). The current study examined whether or not the Spanish acquisition profile, specifically accusative clitics, in predominantly SS, Latino children continues to develop in an English-language contact situation. This study examined (1) accuracy rates of clitic production, total substitutions, and total omissions across 5-, 6-, and 7-year-olds; (2) accuracy rates of clitic production, total substitutions, and total omissions across low and high English proficiency groups; and (3) whether or not there was a trend to use the default clitic lo in inappropriate contexts. Seventy-four SS children aged 5;1 to 7;11 participated in a clitic elicitation task. Results indicated non-significant effects of age and proficiency level on the accuracy of clitic production. These results suggest dual language learners are in an environment that does not foster the maintenance of the L1, at least in the accuracy of accusative clitic pronouns.
ContributorsFigueroa, Megan Danielle (Author) / Restrepo, María A (Thesis advisor) / Gelderen, Elly van (Committee member) / Ingram, David (Committee member) / Arizona State University (Publisher)
Created2012
Description
The beginning of college is a period in which increased alcohol use often coincides with greater involvement in romantic relationships. Existing literature yields inconsistent findings regarding the influence of different relationship statuses on drinking behavior, perhaps because these studies have not accounted for recent changes in the way college students engage in dating/sexual relationships. In the current college environment, many students who define themselves as non-daters are nonetheless sexually active, a phenomenon referred to as the 'hook up' culture. The present study sought to address this issue by examining the effects of both relationship status and sexual activity on heavy episodic drinking (HED) among 1,467 college students over the course of their first three semesters. Results indicated that the effects of relationship status depended on whether or not an individual was sexually active. Non-dating but sexually active students reported rates of heavy drinking comparable to students who defined themselves as casual daters, but non-dating students who were not sexually active reported drinking behavior similar to those involved in committed relationships. Further, transitions between low and high risk relationship/sexual activity statuses were associated with corresponding changes in HED. Transitioning into a high risk status was associated with greater levels of heavy episodic drinking, whereas transitioning into a low risk status was associated with decreases in this behavior. Together, results indicate that engaging in nonexclusive dating or sexual relationships may play an important role in the development of problematic patterns of alcohol use during the early college years. These findings have potentially important implications both for future research and for prevention and intervention efforts targeting high risk college drinkers.
ContributorsZalewski, Suzanne (Author) / Corbin, Willaim (Thesis advisor) / Doane, Leah (Committee member) / Chassin, Laurie (Committee member) / Arizona State University (Publisher)
Created2012