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| Last Updated:13/02/2017

Thesis and Dissertation

THE EFFECT OF PROPERTIES OF FLY ASH ON STRENGTH AND MICROSTRUCTURE DEVELOPMENT OF MORTARS

 
By:
Ms. AMARPREET KAUR, PhD Thesis (2016), Indian Institute of Technology Delhi,

 

Abstract

Supplementary cementitious materials such as fly ash are currently used as clinker replacement to reduce costs and environmental pollution associated with the production of cement. The objective of this study was to understand the effect of physical and chemical properties of fly ash on strength development and hydration kinetics of mortars and cement pastes. Ten different fly ashes, collected from northern and central parts of India, were used. All the fly ashes and cements were characterised using X-ray diffraction (XRD) and X-ray fluorescence (XRF). The chemical composition of fly ashes shows that all the fly ashes fall under category Class F as per ASTM C-618 that have pozzolanic properties and react with water and calcium hydroxide produced by cement hydration. Two cements, obtained from two different cement plants, were used to eliminate effects that may be associated with one particular cement. The mortar mixes were prepared by replacing 25% of cement with fly ash, using three different water to binder ratios viz. 0.4, 0.45, 0.5, which were cured under water at a temperature of 27°C. The compressive strength of mortars was measured at 1, 3, 7, 28 and 90 days. The hydration kinetics were measured using isothermal calorimetry and chemical shrinkage. Sorptivity was measured on mortar discs after 90 days of hydration to study the effect of fly ash on the pore-structure. Advanced techniques such as scanning electron microscopy (SEM) were used to understand the effect of fly ash on the morphology of the cement paste. The results from experiments show that the early strength of mortars with fly ash is lower than cement mortar but most of the mortars recover strength by 28 days. Finer fly ashes show higher or equal strength as compared to OPC after 28 days. It is also observed from sorptivity and SEM (Scanning electron microscopy) images that the finer fly ashes improve the microstructure and porosity. A linear correlation was found between degree of hydration and strength. Modelling of the strength development on the basis of the particle size distribution was carried out. It was found that it is possible to predict the strength development of the mortars using only the particle size distribution of the fly ash as the input. It was found that for the fly ashes studied, there is little effect of the chemical composition of the fly ash on hydration and strength development. It was also found that the existing test for reactive silica in the Indian standard is not suitable to assess the reactivity of a fly ash.

Source: http://web.iitd.ac.in/~bishnoi/theses/AmarpreetKaurFullThesis.pdf


ENHANCING THE STRENGTH PROPERTIES OF FLY ASH BY ADDING WASTE PRODUCTS

 
By:
Alfred J. Susilo, Doctoral Dissertation(2016) University of Kentucky,

 

Abstract

For this study, the main material to be investigated is Class F fly ash that originates from the combustion of Appalachian coal. Alone, fly ash exhibits poor strength properties and is susceptible to liquefaction when subject to dynamic loading. This research is focused on investigating the effect of adding materials that would otherwise be considered as waste products to the fly ash. Materials to be considered include crumb rubber, shredded carpet and shredded paper. The benefits from this research are twofold. First, provide a method to stabilize fly ash. For large masses of fly ash such as those found at power plants and landfills, improved strength of the fly ash will make the mass safer and more reliable with respect to stability. Second, provide a use for waste materials that would otherwise be stockpiled or disposed of in landfills at a significant cost, which in turn will minimize the environmental impact. Using this approach, materials will be added to fly ash rather than using fly ash as an additive, which will increase the rate of fly ash usage and more directly address the issue the large volumes of fly ash that are being produced today. To perform this research, representative samples of Class F fly ash were tested to characterize the physical properties of the materials. Later, this Class F fly ash was mixed with specific percentage of three waste materials to evaluate the behavior and performance of the fly ash admixture. Using these reconstituted specimens, a suite of laboratory tests to assess the static and cyclic strength properties of each specimen was performed, as well as the dynamic properties of the specimens. The expectations were to develop correlations between mixture ratios and the various measured properties, and to identify mixture ratios that will optimize the strength characteristics of the specimens. In the end, crumb rubber was found to be the best additive to improve the properties of Class F fly ash compared to the other waste materials used. This conclusion can be used by power plant facilities to increase the safety factor against liquefaction at their impoundment facilities.

Source: http://uknowledge.uky.edu/ce_etds/44/


Study on Utilization of Fly Ash as a replacement of Cement and Fine Aggregates in Concrete.

 
By:
MOHAMAD RKEIN, Fourth Year Bachelor of Engineering Thesis Topic (2015), Charles Darwin University Australia

 

Abstract

Concrete is a construction material that is mostly used across the world. It is a composite material made out of water, cement, fine aggregate (sand) and coarse aggregate (stones). However, the manufacturing process of raw materials used in concrete such as cement and aggregate causes environmental influences (emission of greenhouse gases and dust) and significantly consumes energy and natural resources. Aggregate normally accounts 70 to 80 % of the entire volume of concrete, while water and cement account 20 to 30 %. These percentages affect the mechanical properties of concrete. Replacing any of these materials by industrial waste material can have a positive impact on the environment as it diminishes the problem of waste disposal and reduces the intensive use of energy and natural resources (aggregate mining). In addition; it reduces the amount of emission of gases. There are plenty of industrial wastes that can be used in concrete as either replacement of aggregate or cement. Hence, this project has focused on evaluating the opportunity of using one of these waste materials which is the fly ash as a partial replacement material for cement and fine Aggregate. Fly ash is generally considered as a waste material that is produced as a by-product of coal combustion process. The physical and chemical properties of fly ash are similar to cement, which allows it to be used in concrete. The primary aim of this research is to determine the feasibility of using fly ash as a replacement of cement and fine aggregate in concrete and their effects on the mechanical properties of concrete. This Paper presents the results of an experimental investigation carried out to evaluate the mechanical properties (workability and compressive strength) of concrete mixtures in which fine aggregate (sand) and cement were partially replaced with Fly Ash. Both fine aggregate and cement were replaced with five percentages (10%, 20%, 30%, 40%, and 50%) of fly ash by weight. Tests were conducted for properties of fresh concrete (workability), and compressive strength was determined at 7, 28 and 56 days. Test results indicate significant improvement in the strength properties of plain concrete by the inclusion of fly ash as partial replacement of either fine aggregate (sand) or cement and can be effectively used in concrete structures.

Source: https://espace.cdu.edu.au/eserv/cdu:46192/Thesis_CDU_46192_Rkein_M.pdf


SHEAR STRENGTH PARAMETERS OF SAND FLY ASH CEMENT MIXTURES

 
By:
Oksana Nikolayevna Spears, degree of Master of Science in Civil Engineering (2014), UNIVERSITY OF NORTH FLORIDA

 

Abstract

According to a 2012 American Coal Ash Association Coal production Survey Report, US coal fired power plants produced more than 109 million tons of waste that year. Approximately half of this waste is the valuable by-product fly ash. There are three classes of fly ash: cementitious class C and non-cementitious classes F and N. Over half of the fly ash produced is used in the geotechnical/construction industries. Most geotechnical soil stabilization studies using fly ash are focused on controlling shrink-swell potential of clays. This study utilized the less desirable class F fly ash to assess the improvement of shear strength parameters of granular soils. Two mix designs were developed and tested using consolidated undrained, unconfined compression, and triaxial testing. Mix designs consisted of 15% fly ash with 0.5 or 1% cement, and poorly graded Ottawa sand compacted using a standard effort at 10 percent moisture content. Consolidated undrained testing on Mix 1, which included flushing and saturating the specimens, produced higher shear strength parameters than for the sand alone. However, the results were inconsistent with respect to the increase in shear strength parameters with time. Unconfined compression testing was then conducted on both Mix 1 and Mix 2 to assess strength gain with time. Results showed both mixes gained appreciable strength with time but doubling the cement did not double the unconfined compressive strength. Triaxial testing was then conducted on Mix 1 using specimens that were not flushed or saturated. This testing was used to determine if flushing destroyed the specimen soil fabric. The shear strength parameters from the triaxial testing were very similar to those determined from consolidated undrained testing. This demonstrated that flushing did not affect the shear strength parameters. Inconsistent triaxial test results from fly ash-cement-sand mixes have been previously reported in the literature.

Source:  http://digitalcommons.unf.edu/cgi/viewcontent.cgi?article=1573&context=etd


Increased fly ash volume and internal curing in concrete structures and pavements

 
By:
De la Varga, Igor,  PhD Thesis (2013), Purdue University

 

Abstract

Fly ash, a by-product generated by the combustion of coal, has been broadly used in concrete applications over the last half century. Fly ash is typically used as either an addition or as a cement replacement. It is the replacement of cement with fly ash however that enables the fly ash to have sustainability benefits as it can efficiently reduce the clinker factor, and CO 2 production in concrete. Fly ash use in the US accounted for a 12% average replacement of cement in 2008, but it is frequently used in higher dosages for certain applications (e.g., mass concrete). In addition to its benefit in reducing the clinker content and embodied CO 2 per yard of concrete, fly ash is an industrial by-product that is able to be re-used thus preventing the need for it to be landfilled. The use of fly ash can also increase the long-term strength and durability of concrete. This is the reason why many producers and transportation agencies are investigating the use of higher volumes of fly ash. In this work concrete mixture designs have been developed with cement replacement levels of more than 40 % by volume. However, many hurdles exist to implementing this type of mixtures in practice, including: 1) potential incompatibilities among fly ash, admixtures, and cement; 2) strict limits on the maximum fly ash permitted and the time of the year that it can be used; 3) delays in set time and strength development that slow construction operations; and 4) concerns about providing enough and proper curing. This thesis examined potential solutions for items 2 through 4. This thesis develops a strategy for using high volumes of fly ash to replace cement in concrete (higher volumes than conventionally used). The work seeks to minimize potential issues associated with early strength development that occur when fly ash replaces part of the cement fraction by using a lower water-to-cementitious materials ratio ( w/cm ). While a lower w/cm would be beneficial in terms of improved mechanical and transport properties, it has been shown that these mixtures may be more susceptible to early-age shrinkage cracking and poor curing due to the slower reaction of the fly ash. This thesis evaluates the use of internal curing using pre-wetted lightweight aggregates to reduce autogenous shrinkage and cracking potential while enabling more of the fly ash to react by providing water curing for longer time periods. An extensive study that evaluates mechanical, shrinkage, hydration, and transport properties of low w/cm internally cured HVFA mortar mixtures is presented in this thesis. The HVFA mixtures performance is compared to that of the mortar fraction of a typical bridge deck concrete mixture design used in the state of Indiana (with w/c = 0.42). The main findings include similar early-age strength development and increased long-term strength in the low w/cm internally cured HVFA mixtures. These mixtures also have a reduced potential for autogenous and thermal shrinkage cracking. It is also shown in this thesis that while the transport properties of low w/cm High Volume Fly Ash mixtures (with or without  internal curing) are considerably reduced compared to a control w/c =0.42 mixture, internal curing provides similar transport properties in concrete with similar cementitious content. Two additional chapters are included in the thesis where the interpretation of electrical properties and fly ash reactivity of HVFA mixtures is discussed. The first of these two chapters explains the differences in the measured electrical conductivity between 100 % ordinary portland cement and high volume fly ash systems. The proper interpretation of these results becomes crucial when using electrical properties as long-term performance predictors. In regards to the study on fly ash reactivity, the results obtained allow determining the physical and chemical effects that high volumes of fly ash have on the cement hydration at both early and later ages. The results obtained in this thesis show that low w/cm internally cured HVFA mixtures provide additional benefits that should permit a larger use of fly ash and internal curing in concrete applications.

 

Source: http://search.proquest.com/docview/1477571584#top


Characterization and modeling of toxic fly ash constituents in the environment. 


By :
Zhu, Zhenwei,  PhD dissertation  (2011), University of Tennessee

 

Abstract
Coal fly ash is a by-product of coal combustion that has drawn renewed public scrutiny due to the negative environmental impacts from accidental release of this waste material from storage facilities. Historically, the leaching of toxic elements from coal fly ash into the environment has always been a major environmental concern. Despite extensive efforts into the characterization of coal fly ash, effective models for the fate and transport of toxic fly ash constituents have remained lacking, making it difficult to perform accurate environmental impact assessment for coal fly ash. To close this critical knowledge gap, the overall objective of this study was to develop a predictive model for the leaching of toxic elements from fly ash particles. First, physical properties of coal fly ash were characterized to evaluate their contribution to elemental transport. Unburned carbon was shown to contribute to the sorption of arsenic to fly ash, which slowed the release of arsenic from fly ash. In parallel, leaching properties of various elements were determined to differentiate species of varying leaching capacities, demonstrating that the majority of toxic elements were not mobile under environmentally relevant conditions. Subsequently, a mechanistic model for the dissolution of fly ash elements was developed and validated with batch kinetics studies. Furthermore, elemental dissolution was integrated with hydrodynamic modeling to describe the leaching of toxic elements from fly ash in dry disposal facilities, which was validated by column studies. The mechanistic model developed and validated in this research represents the first such model that successfully characterized the complex processes underlying the release and transport of toxic elements in coal fly ash, providing a valuable tool to predict the environment impact of coal fly ash and develop more effective management practices for both the industry and regulators.

 

Source: http://trace.tennessee.edu/utk_graddiss/1152

 

Evaluation of fly-ash based artificial zeolite formation as treatment for salt-laden process water from eastern Montana coal operations 

 

By: Dudley, Sean P., M.S., Dissertation (2011) (Graduate Work), MONTANA TECH OF THE UNIVERSITY OF MONTANA


Abstract: 
Montana has roughly 120 billion tons of coal reserves, more than any other state in the U.S. However, Montana ranks low among coal-producing states. Various factors including coal quality, mining conditions, resulting economics, transportation costs, taxation and environmental regulation contribute to Montana's lag. A major factor that has historically limited the market for certain Montana coal reserves is high-sodium content and resulting degradation of combustion systems. The issue is compounded by the increased focus on control of minor pollutants, including sodium, in industrial effluents and the already limited capacity of major coal reserve areas such as the Powder River Basin (PRB) to absorb increased salt presence. This thesis presents the work related to coal development for eastern Montana, specifically focusing on wastewater issues associated with the processing and removal of sodium from coal matrices. A variety of means exist to remove sodium from process waters, but most options are economically disadvantaged and still produce waste streams for subsequent disposal. This work focuses on a technology that, if applicable, has the propensity to combine waste streams and produce a by-product that is not only beneficial but saleable. Artificial zeolite formation was evaluated as the primary means to treat effluent, hoping to capitalise on the characteristic aluminosilicate structure of fly-ash by product and the ability of sodium, to not only act as a structure formation director, but be included in those structures effectively combining waste streams, cleaning process water, and producing a by-product that is a benefit to operations. Results indicated that process variables are still widely not understood, but formation of a zeolite phase (or conversely a geopolymer) favours conditions of high pH, moderate sodium solution concentration, low solid to liquid ratios, and low temperatures

 

Source: http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&res_dat=xri:pqdiss&rftvalfmt=info:ofi/fmt:kev:mtx:dissertation&rft_dat=xri:pqdiss:1491987


Fluid Extraction of Metals from Coal Fly Ash:  Geochemical Simulation of Natural Leaching

 

By Ann Gallagher Kim, PhD Thesis (2002), UNIVERSITY OF PITTSBURGH

 

Abstract
The objective of this study was to develop data that are broadly applicable to the release of trace metals from fly ash, and to quantify the rate of release as a function of the composition of the ash. Thirty-two samples of Class F fly ash from pulverized coal combustion boilers were leached with seven leaching solutions simulating natural fluids. The leachate was analyzed for 21 cations that were major, minor, or trace constituents of the ash. The rate at which metal ions are released from fly ash is a complex function of the alkalinity of the ash, the distribution of elements in various chemical compounds or minerals, and characteristics of the leachant solution, particularly its pH. In this experiment, the release of cations is defined as a solubility function with respect to the volume of leachant solution. During the first leaching interval, the ashes alkalinity is neutralized, and the release of metal ions, except for Ca, is relatively low. At some point, the release of metal ions increases by one or more orders of magnitude, and remains at that level, until the readily soluble ions are released. Then the elemental release decreases, again by one or more orders of magnitude. 

The solubility of an element is defined by the three volumetric functions and the median volumes for those functions. The N LF (neutralization leaching function) is describes the release of cations until the sample is neutralized (dMN /dVN , meq/L). The RLF (rapid leaching function) rate is the average slope of cumulative curve between inflection points (dML /dVL , meq/L). The TLF (terminal leaching function) is the average slope of cumulative curve after 2nd inflection point (dMT /dVT , meq/L). In a natural setting, if the infiltration rate is known (L/d), the time dependent release of the elements can be estimated. The results of this study show that most cations in fly ash are only slightly soluble, that elements, other than arsenic, tend to be most soluble in acid solutions, and that non-silicates tend to be more soluble than silicates.

 

Source: http://d-scholarship.pitt.edu/7825/1/dissertationagk.pdf


CONCRETE MIX DESIGN WITH FLY ASH

 

By Barton K. Benson, MSc Dissertation (1986) University of Arkansas

 

ABSTRACT

The effects of substituting Class C fly ash for a portion of the portland cement in both Class S and Class S(AE) concrete were studied. The percentage of substitution ranged from 25% to 65%. Multiple samples were made and tested for compressive strength at ages of 7 days to 6 months, rapid freeze-thaw durability, and resistance to deterioration due to the action of deicing chemicals. The same tests were conducted on control specimens using the same mix designs without fly ash to provide a comparison basis. The results indicate that, for nonair-entrained concrete, up to 65% of the portland cement can be replaced with Class C fly ash as produced locally with no severe adverse effect on those characteristics examined in this study. For air-entrained concrete, replacement of up to 25% was found to have no adverse effects, and replacement of up to 65% adversely affected only the resistance to deicing chemicals.

 

Source: http://arkansastrc.com/TRC%20REPORTS/TRC%2086.pdf


Synthesis and characterization of geopolymers for infrastructural applications

 

By Jian He, PhD Theis (2012), Louisiana State University

 

Abstract:

In this study, the synthesis process, composition, and microstructure as well as mechanical  properties of geopolymers generated by 3 different kinds of raw materials (i.e., metakaolin,  mixture of red mud and fly ash, mixture of red mud and rice husk ash) was explored. For  geopolymers from identical raw materials, variable parameters involved in the synthesis were examined to investigate the extent and degree of geopolymerization. Uniaxial compression  testing was used to examine the mechanical properties (i.e. compressive strength, stiffness, and  failure strain). Then the composition and microstructure were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM) as well as energy-dispersive X-ray spectroscopy (EDXS). The results demonstrates that the geopolymeric products are not  geopolymer binders, but geopolymeric composites, which generally comprise pure geopolymer  binder as the major matrix, a small amount of unreacted source materials and nonreactive  crystalline phases (e.g., quartz, anhydrite, and hematite) from parent materials as inactive fillers.  Moreover, the study also shows that geopolymeric products can be used as a cementitious  material to replace Portland cement in certain engineering applications, such as roadway  construction, which brings environmental and economic benefits.

 

Source: http://etd.lsu.edu/docs/available/etd-06292012-003727/unrestricted/He_Diss.pdf

 

Fly Ash Applicability in Pervious Concrete

 

By: Na Jin, MSc Thesis  (2010), The Ohio State University

 

Abstract: 

Pervious concrete has been used in the United State for over 30 years. Because of  its high porosity, the most common usages have been in the area of stormwater  management, but have been limited to use in pavements with low volume traffic because  of its low compressive strength compared to conventional concrete. Fly ash has been shown in numerous post studies to increase the strength and durability of conventional concrete. In this study, six batches of pervious concrete with different amounts of aggregate, cement, and fly ash were prepared to find the mix that generated high compressive strength and study the effect of fly ash on the compressive strength and permeability of pervious concrete. Materials used in this study were selected based on literature reviews and recommendations from local sources. Unconfined compressive strength tests were carried out on pervious concrete specimens with fly ash contents of 0%, 2%, 9%, 30%, 32% by weight of the total cementitious materials. Falling head permeability tests were carried out on specimens having 2% and 32% fly ash.

 

Source: https://etd.ohiolink.edu/!etd.send_file?accession=osu1279136103&disposition=inline

 

Studies on Aluminum–Fly-Ash Composite Produced

 

By: Impeller Mixing M.Tech. Dissertation (2009), NIT Rourkela By Shuvendu Tripathy 

ABSTRACT 

Metal matrix composites (MMCs) constitute an important class of design and weight-efficient structural materials that are encouraging every sphere of engineering applications. There has been an increasing interest in composites containing low density and low cost reinforcements. Among various discontinuously dispersed solids used, fly ash is one of the most inexpensive and low density reinforcement available in large quantities as solid waste by-product during combustion of coal in thermal power plants. Hence, composites with fly ash as reinforcement are likely to overcome the cost barrier for wide spread applications in automotive and small engine applications. To produce Al matrix cast particle composites, wettaility of the ceramic particles by liquid Al is essential. To improve wettabilty, elements such as Mg and Si are added into Al melt to incorporate the ceramic particles. The present investigation has been focused on the utilization abundant available industrial waste fly ash in useful manner by dispersing it into aluminium/aluminium-magnesium/aluminium-silicon matrix to produced composites by liquid metallurgy route. Wide size range (0.1-100μm) fly ash particles were used. These composites were observed with the help of optical micrography, x ray micro analysis, x ray diffraction, wet chemical analysis, and image analysis. The dry sliding wear behavior of the composites in the cast conditions was studied at different loads and different sliding velocities with the help of Pin-On-Disc wear test machine. The worn surfaces and wear debris were analyzed using optical microscope and scanning electron microscope. The mechanical properties such as hardness and tensile strength have been investigated.

 

Source:  http://ethesis.nitrkl.ac.in/1499/1/207mm103.pdf