ASU Electronic Theses and Dissertations
This collection includes most of the ASU Theses and Dissertations from 2011 to present. ASU Theses and Dissertations are available in downloadable PDF format; however, a small percentage of items are under embargo. Information about the dissertations/theses includes degree information, committee members, an abstract, supporting data or media.
In addition to the electronic theses found in the ASU Digital Repository, ASU Theses and Dissertations can be found in the ASU Library Catalog.
Dissertations and Theses granted by Arizona State University are archived and made available through a joint effort of the ASU Graduate College and the ASU Libraries. For more information or questions about this collection contact or visit the Digital Repository ETD Library Guide or contact the ASU Graduate College at gradformat@asu.edu.
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- All Subjects: Alkali activated
- All Subjects: Creep
- Creators: Mobasher, Barzin
Description
The concept of Creep is a term used to define the tendency of stressed materials to develop an increasing strain through time under a sustained load, thus having an increase in deflection or having an elongation with time in relation to the short term strain. While the subject of compression creep of concrete is well developed, use of concrete under tension loads has been limited at best due to brittleness of concrete. However with the advent of using fiber reinforced concrete, more and more applications where concrete is expected to carry tensile loads due to incorporation of fibers is gaining popularity. While the creep behavior of concrete in tension is important, the main case of the study is what happened when the concrete that is cracked in service is subjected to sustained loads causing creep. The relationship of opening cracks under these conditions are of utmost importance especially when the serviceability criteria is addressed. Little work has been reported in literature on the long-term behavior of FRC under sustained flexural loadings. The main objective of this study is to investigate the Long Term Flexural Behavior of Pre-Cracked Fiber Reinforced Beams under Sustained Loads. The experimental reports document the effect of loading and temperature on the creep characteristics of concrete. A variety of study has been carried out for the different responses generated by the creep tests based on factors like effect of temperature and humidity, effect of fiber content, effect of fiber type, and effect of different loading levels.
The Creep Testing Experimental Methodology is divided into three main parts which includes: (1) The Pre-cracking Partial Fracture Test; (2) Creep Test; (3) Post Creep Full Fracture Test. The magnitude of load applied to a specific specimen during creep testing was based on the results of average residual strength (ARS) tests, determined using EN14651. Specimens of the synthetic FRC mixture were creep tested at loads nominally equivalent to 30% and 50% of the FR1 value. The creep tests are usually continued until a steady Time versus CMOD response was obtained for the specimen signifying its presence in the secondary stage of creep. The creep recovery response is generated after unloading the specimen from the creep set up and later a full fracture test is carried out to obtain the complete post creep response of the beam under flexure.
The behavior of the Creep Coefficient versus Time response has been studied using various existing models like the ACI 209-R 92 Model and the CEB-FIP Model. Basic and hybrid rheological viscoelastic models have also been used in order to generate the material behavior response. A study has been developed in order to understand the applicability of various viscoelastic models for obtaining the material response of real materials. An analytical model for predicting the Flexural Behavior of FRC under sustained creep loads is presented at the end. This model helps generate the stress strain and Moment Curvature response of FRC beams when subjected to creep loads post initial cracking
The Creep Testing Experimental Methodology is divided into three main parts which includes: (1) The Pre-cracking Partial Fracture Test; (2) Creep Test; (3) Post Creep Full Fracture Test. The magnitude of load applied to a specific specimen during creep testing was based on the results of average residual strength (ARS) tests, determined using EN14651. Specimens of the synthetic FRC mixture were creep tested at loads nominally equivalent to 30% and 50% of the FR1 value. The creep tests are usually continued until a steady Time versus CMOD response was obtained for the specimen signifying its presence in the secondary stage of creep. The creep recovery response is generated after unloading the specimen from the creep set up and later a full fracture test is carried out to obtain the complete post creep response of the beam under flexure.
The behavior of the Creep Coefficient versus Time response has been studied using various existing models like the ACI 209-R 92 Model and the CEB-FIP Model. Basic and hybrid rheological viscoelastic models have also been used in order to generate the material behavior response. A study has been developed in order to understand the applicability of various viscoelastic models for obtaining the material response of real materials. An analytical model for predicting the Flexural Behavior of FRC under sustained creep loads is presented at the end. This model helps generate the stress strain and Moment Curvature response of FRC beams when subjected to creep loads post initial cracking
ContributorsGohel, Megha Rajendrakumar (Author) / Mobasher, Barzin (Thesis advisor) / Dharmarajan, Subramaniam (Committee member) / Neithalath, Narayanan (Committee member) / Arizona State University (Publisher)
Created2017
Description
Sustainable materials and methods have achieved a pivotal role in the research plethora of the new age due to global warming. Cement production is responsible in contributing to 5% of global CO2 emissions. Complete replacement of cement by alkaline activation of aluminosilicate waste materials such as slag and fly ash is a major advancement towards reducing the adverse impacts of cement production. Comprehensive research has been done, to understand the optimized composition and hydration products. The focus of this dissertation is to understand the multiscale behavior ranging from early age properties, fundamental material structure, fracture and crack resistance properties, durability responses and alternative activation methods to existing process.
The utilization of these materials has relied primarily on the dual benefits of reduced presence in landfills and cost. These have also proven to yield a higher service life as opposed to conventional ordinary portland cement (OPC) concrete due to an enhanced microstructure. The use of such materials however has not been readily acceptable due to detrimental early age behavior. The influence of design factors is studied to understand the reaction mechanism. Silicon polymerization at the molecular level is studied to understand the aluminosilicate interactions which are responsible for prevention of any leaching of ions. A comparative study between fly ash and slag binders is carried out to evaluate the stable states of sodium, aluminum and silicon in both these binders, since the likelihood of the sodium ions leaching out is high.
Compressive and flexural strength have been reported in previous literature, but the impact of crack resistance was unevaluated from an approach of characterizing the fracture process zone. Alternative routes of activation are explored with an intent to reduce the high alkalinity by use of neutral salts such as sodium sulfate. High volume OPC replacement by both class C and F fly ash is performed to evaluate the differences in hydration phase formation responsible for its pore refinement and strength. Spectroscopic studies have also allowed to study the fundamental material structure. Durability studies are also performed on these samples to understand the probability external sulfate attacks as opposed to OPC mixes.
The utilization of these materials has relied primarily on the dual benefits of reduced presence in landfills and cost. These have also proven to yield a higher service life as opposed to conventional ordinary portland cement (OPC) concrete due to an enhanced microstructure. The use of such materials however has not been readily acceptable due to detrimental early age behavior. The influence of design factors is studied to understand the reaction mechanism. Silicon polymerization at the molecular level is studied to understand the aluminosilicate interactions which are responsible for prevention of any leaching of ions. A comparative study between fly ash and slag binders is carried out to evaluate the stable states of sodium, aluminum and silicon in both these binders, since the likelihood of the sodium ions leaching out is high.
Compressive and flexural strength have been reported in previous literature, but the impact of crack resistance was unevaluated from an approach of characterizing the fracture process zone. Alternative routes of activation are explored with an intent to reduce the high alkalinity by use of neutral salts such as sodium sulfate. High volume OPC replacement by both class C and F fly ash is performed to evaluate the differences in hydration phase formation responsible for its pore refinement and strength. Spectroscopic studies have also allowed to study the fundamental material structure. Durability studies are also performed on these samples to understand the probability external sulfate attacks as opposed to OPC mixes.
ContributorsDakhane, Akash (Author) / Neithalath, Narayanan (Thesis advisor) / Rajan, Subramaniam D. (Committee member) / Mobasher, Barzin (Committee member) / Marzke, Robert (Committee member) / Das, Sumanta (Committee member) / Arizona State University (Publisher)
Created2016