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Laboratory study of concrete produced with admixtures intended to inhibit corrosionOkunaga, Grant J January 2005 (has links)
Thesis (M.S.)--University of Hawaii at Manoa, 2005. / Includes bibliographical references (leaves 120-121). / xii, 282 leaves, bound ill. (some col.) 29 cm
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Solid-gel interactions in geopolymersLee, William K. January 2002 (has links) (PDF)
This is partly because the requirements for such an ultimate material change with people’s perception about its properties as well as its environmental impact. Thus, the once-believed ultimate Portland cement binder is now becoming unacceptable for a number of reasons including poor durability as well as severe environmental impact during production. Thus, an improved mineral binder is required by modern society to serve the same purposes as the existing Portland cement binder, as well as to reduce the current environmental impact caused by Portland cement production. / Geopolymerisation is such a ‘green’ technology capable of turning both natural ‘virginal’ aluminosilicates and industrial aluminosilicate wastes, such as fly ash and blast furnace slag, into mechanically strong and chemically durable construction materials. However, the source materials for geopolymer synthesis are less reactive than Portland cement clinkers and the chemical compositions of these source materials can vary significantly. Consequently, product quality control is a major engineering challenge for the commercialisation of geopolymers. / This thesis is therefore devoted to the mechanistic understanding of the interfacial chemical interactions between a number of natural and industrial aluminosilicates and the various activating solutions, which govern the reactivity of the aluminosilicate source materials. The effects of activating solution alkalinity, soluble silicate dosage and anionic contamination on the reactivity of the aluminosilicate source materials to produce geopolymeric binders, as well as their bonding properties to natural siliceous aggregates for concrete making, are examined. In particular, a new set of novel ‘realistic’ reaction models has been developed for such purposes. These reaction models have been further utilised to develop a novel analytical procedure, which is capable of studying geopolymerisation on ‘real’ geopolymers in situ and in real time. This novel procedure is invaluable for the total understanding of geopolymerisation, which is in turn vital for effective geopolymer mix designs.
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Freeze-thaw durability of high strength silica fume concreteKashi, Mohsen Gholam-Reza January 1988 (has links)
Specimens from 27 batches of concrete with water to cementitious (cement plus silica fume) ratio of 0.25 to 0.32, with and without entrained air, were tested for freeze-thaw durability in accordance with ASTM C666, procedure A (freezing and thawing in water). In addition, another set of similar specimens were moist cured for 28 days instead of 14 days and tested in accordance with ASTM C666 , Procedure A to determine the effect of curing time on the freeze-thaw durability of high strength concrete. Results show that non air-entrained high strength concrete with water cementitious ratio of less than 0.30, regardless of the length of curing time, is frost resistant. Non-air-entrained concrete with water-cement ratio of 0.32 is also durable if silica fume is not used. / Ph. D.
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Mechanical properties of fly ash/slag based geopolymer concrete with the addition of macro fibresRyno, Barnard 12 1900 (has links)
Thesis (MEng) -- Stellenbosch University, 2014. / ENGLISH ABSTRACT: Geopolymer concrete is an alternative construction material that has comparable mechanical
properties to that of ordinary Portland cement concrete, consisting of an aluminosilicate and
an alkali solution. Fly ash based geopolymer concrete hardens through a process called
geopolymerisation. This hardening process requires heat activation of temperatures above
ambient. Thus, fly ash based geopolymer concrete will be an inadequate construction material
for in-situ casting, as heat curing will be uneconomical.
The study investigated fly ash/slag based geopolymer concrete. When slag is added to the
matrix, curing at ambient temperatures is possible due to calcium silicate hydrates that form
in conjunction with the geopolymeric gel.
The main goal of the study is to obtain a better understanding of the mechanical properties of
geopolymer concrete, cured at ambient temperatures. A significant number of mix variations
were carried out to investigate the influence that the various parameters, present in the matrix,
have on the compressive strength of fly ash/slag based geopolymer concrete. Promising
results were found, as strengths as high as 72 MPa were obtained. The sodium hydroxide
solution, the slag content and the amount of additional water in the matrix had the biggest
influence on the compressive strength of the fly ash/slag based geopolymer concrete.
The modulus of the elasticity of fly ash/slag based geopolymer concrete did not yield
promising results as the majority of the specimens, regardless of the compressive strength,
yielded a stiffness of less than 20 GPa. This is problematic from a structural point of view as
this will result in large deflections of elements. The sodium hydroxide solution had the most
significant influence on the elastic modulus of the geopolymer concrete. Steel and polypropylene fibres were added to a high- and low strength geopolymer concrete
matrix to investigate the ductility improvement. The limit of proportionality mainly depended
on the compressive strength of the geopolymer concrete, while the amount of fibres increased
the energy absorption of the concrete. A similar strength OPC concrete mix was compared to
the low strength geopolymer concrete and it was found that the OPC concrete specimen
yielded slightly better flexural behaviour. Fibre pull-out tests were also conducted to
investigate the fibre-matrix interface. From the knowledge gained during this study, it can be concluded that the use of fly ash/slag
based geopolymer concrete, as an alternative binder material, is still some time away as there
are many complications that need to be dealt with, especially the low modulus of elasticity.
However, fly ash/slag based geopolymer concrete does have potential if these complications
can be addressed. / AFRIKAANSE OPSOMMING: Geopolimeerbeton is ‘n alternatiewe konstruksiemateriaal wat vergelykbare meganiese eienskappe
met beton waar OPC die binder is, en wat bestaan uit ‘n aluminosilikaat en ‘n alkaliese oplossing.
Vliegas-gebaseerde geopolimeerbeton verhard tydens ‘n proses wat geopolimerisasie genoem word.
Hierdie verhardingsproses benodig hitte-aktivering van temperature hoër as dié van die onmiddellike
omgewing. Gevolglik sal vliegas-gebaseerde geopolimeerbeton ‘n ontoereikende konstruksiemateriaal
vir in situ gietvorming wees, aangesien hitte-nabehandeling onekonomies sal wees.
Die studie het vliegas/slagmentgebaseerde geopolimeerbeton ondersoek. Wanneer slagment by die
bindmiddel gevoeg word, is nabehandeling by omliggende temperature moontlik as gevolg van
kalsiumsilikaathidroksiede wat in verbinding met die geopolimeriese jel vorm.
Die hoofdoel van die studie was om ‘n beter begrip te kry van die meganiese eienskappe van
geopolimeerbeton, wat nabehandeling by omliggende temperature ontvang het. ‘n Aansienlike aantal
meng variasies is uitgevoer om die invloed te ondersoek wat die verskeie parameters, aanwesig in die
bindmiddel, op die druksterkte van die vliegas/slagmentgebaseerde geopolimeerbeton het. Belowende
resultate is verkry en sterktes van tot so hoog as 72 MPa is opgelewer. Daar is gevind dat die
sodiumhidroksiedoplossing, die slagmentinhoud en die hoeveelheid water in die bindmiddel die
grootste invloed op die druksterkte van die vliegas/slagmentgebaseerde geopolimeerbeton gehad het.
Die styfheid van die vliegas/slagmentgebaseerde geopolimeerbeton het nie belowende resultate
opgelewer nie. Die meeste van die monsters, ongeag die druksterkte, het ‘n styfheid van minder as 20
GPa opgelewer. Vanuit ‘n strukturele oogpunt is dit problematies, omdat groot defleksies in elemente
sal voorkom. Die sodiumhidroksiedoplossing het die grootste invloed op die styfheid van die
vliegas/slagmentgebaseerde geopolimeerbeton gehad. Staal en polipropileenvesels is by ‘n hoë en lae sterke geopolimeer beton gevoeg om die buigbaarheid
te ondersoek. Die die maksimum buigbaarheid het hoofsaaklik afgehang van die beton se druksterkte
terwyl die hoeveelheid vesels die beton se energie-opname verhoog het. ‘n OPC beton mengsel van
soortgelyke sterkte is vergelyk met die lae sterkte geopolimeerbeton en daar is gevind dat die OPC
beton ietwat beter buigbaarheid opgelewer het. Veseluittrektoetse is uitgevoer om die veselbindmiddel
se skeidingsvlak te ondersoek.
Daar kan tot die gevolgtrekking gekom word dat, alhoewel belowende resultate verkry is, daar steeds
sommige aspekte is wat ondersoek en verbeter moet word, in besonder die styfheid, voordat
geopolimeerbeton as ‘n alternatiewe bindmiddel kan optree. Volgens die kennis opgedoen tydens hierdie studie, kan dit afgelei word dat die gebruik van
vliegas/slagmentgebaseerde geopolimeerbeton, as 'n alternatiewe bindmiddel, nog 'n geruime tyd weg
is, as gevolg van baie komplikasies wat gehandel moet word, veral die lae elastisiteitsmodulus. Tog
het vliegas/slagmentgebaseerde geopolimeerbeton potensiaal as hierdie komplikasies verbeter kan
word.
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Industrial dispersing aids based on bark and wood extracts.Kaspar, Hanno Rolf Erich. January 1994 (has links)
A dissertation submitted to the Faculty of Science
University of the Witwatersrand, Johannesburg
for the degree of Master of Science / The object of this dissertation is to develop a cost effective plasticiser/water-reducer from
tannin extracts which does not retard initial strength development. Model compounds of
tannins indicated the suitability of substiuued phenols for this purpose, Catechol with
adjacent hydroxide groups gave a good combination of improved workability with
compressive strengths equivalent to the control. Combinations with ammonia and
torrnaldehyde resulted in some greatly improved performances, but also reduced stability
of the additives. Urea and metabisulphite did provide some improvements ai!1ddid not
adversely affect shelf life.
Some of the tannin extracts tested on their own gave considerate improvements in
workability and some strengths. To improve the stability of extract solutions, tannins
were modified with urea, metabisulphite, small amounts of potassium hydroxide and a
alcohol mixture used for pretreatment. Only the first two listed were consistently effective
without producing any disadvantages. They even further improved the concrete
performance of condensed tannins in particular. Small additions of TEA or its acetate salt
resulted to better one day strengths of the modified tannins.
Analytical techniques such as infrared and nuclear magnetic resonance were used to
monitor some; modifications of the tannins and their result. A test representing early
hydration conditions and X-ray diffraction provided clues to the additives mechanism in
its interaction with cement. The additives performance was evaluated by comparison with
a leading plasticiser/water-reducer, an independent concrete testing laboratory and
conduction calorimetry by a research and testing council. A tannin based plasticiser made
largely from local raw materials was quickly accepted during a recession by brick and
precast manufactures . / Andrew Chakane 2018
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Accelerated curing of concrete with high volume pozzolans - resistivity, diffusivity and compressive strengthUnknown Date (has links)
This investigation presents results of the temperature effect on durability properties (resistivity and diffusivity) and compressive strength of concrete with pozzolans, and the effect of pozzolanic admixtures on microstructure and chemical compositions of concrete pore solution. ... Temperature dependence of electrical resistivity and chloride diffusivity was studied by dynamic temperature tests. Accelerated curing regimes involving curing concrete specimens in 35À C lime water with different durations were tested. Compressive strength test, resisivity measurement and rapid chloride migration (RCM) tests were performed. A leaching method was used to measure pH and conductivity of concrete pore solution. ... The accelerated curing regimes were found to increase the compressive strength and resistance to chloride ion penetration at short-term and long-term. With the developed correlation between resistivity and migration coefficients, it is possible to employ the resistivity measurement as an alternative or replacement of the RCM test to evaluate resistance of chloride ion penetration of concrete. Pozzolanic admixtures were found to decrease both pH and conductivity of concrete pore solution as the replacement ratio increased. Moreover, the migration coefficients were found to be greatly correlated to the microstructure properties of concrete, such as porosity, formation factor and tortuosity. / by Yanbo Liu. / Thesis (Ph.D.)--Florida Atlantic University, 2012. / Includes bibliography. / Mode of access: World Wide Web. / System requirements: Adobe Reader.
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Use of hybrid Rice Husk Ash-Fly Ash mixtures as sustainable supplementary materials for concrete in the marine environmentUnknown Date (has links)
This paper presents the comparison of shrinkage and corrosion characteristics of optimized hybrid Rice Husk Ash (RHA)/Fly Ash (FA)-modified Concrete, with those of normal concrete in the marine environment. Uses of both FA and RHA have numerous environmental benefits. Shrinkage performance was determined by subjecting the mixes to restrained shrinkage testing per ASTM C1581. The time to cracking of the specimens improved an average of 18% with the hybrid mixes. Corrosion testing of reinforced columns was performed in a simulated tidal cycle Marine Environment. Corrosion potential improved by as much as 35% for the mix with the highest FA/RHA replacement, and corrosion activity as measured with potentiostat equipment improved by an average of 34% . These results indicate a clear performance improvement of the modified concrete that is proportional to the percent replacement of cement. / by Diana Arboleda. / Thesis (M.S.C.S.)--Florida Atlantic University, 2010 / Includes bibliography. / Electronic reproduction. Boca Raton, Fla., 2010. Mode of access: World Wide Web.
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Design of systems for time delayed activated internal release of chemicals in concrete from porous fibers, aggregates of prills, to improve durabilityDry, Carolyn Minnetta 22 May 2007 (has links)
Incorporation of chemicals into the internal matrix of cement or concrete, with later release occurring upon stimulation, alters the matrix parameters from those at the initial set. Permeability is reduced, for example, and therefore durability enhanced. The advantages of these designs would be the ability to reduce maintenance and repair costs in the initial building configuration and to delay the time of eventual repair. The components and the structure could take greater environmental abuse also.
Permeability is significantly reduced by release of a polymer from wax-coated porous fibers upon heating to temperature of polymerization. Freeze/thaw damage is somewhat reduced by the timed release of linseed oil or antifreeze from porous aggregates due to the freezing action itself. These example designs using timed release mostly gave improved durability performance when compared to conventional treatments for durability or environmental distress. Concerns that significant strength reduction would occur due to heating or fiber loading were shown to be unfounded by our test results; indeed, heating and fiber inclusion increased strength. An adequate amount of wetting of the samples could be obtained with 2.75% volume of fibers; however, above a 2.75% volume of fibers, fibers do reduce the strength. Results were analyzed by the method of comparing results in the samples with factors varied to results in samples without variable factors, that is, by comparing to the controls.
This research shows that timed internal release of chemicals into cement can be accomplished; it appears feasible and is potentially useful.
Long-term tests need to be performed on such factors as chloride ion intrusion/ corrosion tests. Filled fiber, aggregate or prill manufacture, storage, and placement need to be researched and assessed for cost. Design of components using only targeted areas for release in the component and the use of time released fibers in reinforced cement laminates should be evaluated. / Ph. D.
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The role of alumina in the mitigation of alkali-silica reactionWarner, Skyler J. 13 March 2012 (has links)
The use of fly ash as a supplementary cementitious material (SCM) has increased in the
last century due to its various environmental benefits as a recycled product. Within the
last 60 years, it has been found that it can be used to effectively control damage
induced by Alkali-Silica Reaction. However, it is not completely understood how to
properly assign a dosage of fly ash to control the reaction. This depends greatly on the
fly ash characteristics (e.g. composition, particle size, and reactivity), the reactivity of
the aggregate (e.g. high to low reactivity level) and the environmental exposure
conditions. The characteristics of the fly ash depend on the coal source being burned
and the burning conditions that result in the fly ash formation. A major concern when
supplementing cement with fly ash for ASR mitigation is the effect of the alkali
contribution of the fly ash to the concrete pore solution. Current test methods cannot
accurately determine the alkali contribution of fly ashes and there is no standardized
test method to doing so.
When contributed by the implementation of a SCM, alumina has been found to play a
role in the ability of an SCM to mitigate ASR-induced damage. It has been observed that
fly ashes containing higher levels of alumina (18-25%) tend to improve concrete
durabilty more effectively when compared to fly ashes with lower levels of alumina.
Additionally, the use of metakaolin, which is composed of 45-50% alumina, has been
found to lessen expansion with a lower percentage of cement replacement than would
be required if fly ash is used. Furthermore, the use of fly ash with another SCM
material, a high quality ultra-fine fly ash or alumino-siliceous metakaolin, in ternary
blends may improve the performance of fly ash resulting in a broadening of the
spectrum of SCMs usable for ASR mitigation.
For successful use of SCMs, it is important to develop an understanding of the alkalisilica
reaction and the ability of such SCMs to control expansion. This report provides an
overview of alkali-silica reaction and the use of fly ash and metakaolin as SCMs to
mitigate expansion due to the reaction, with an emphasis on the role of alumina when
contributed from the two materials. / Graduation date: 2012
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Multi-scale investigation of tensile creep of ultra-high performance concrete for bridge applicationsGaras Yanni, Victor Youssef 10 November 2009 (has links)
Ultra-high performance concrete (UHPC) is relatively a new generation of concretes optimized at the nano and micro-scales to provide superior mechanical and durability properties compared to conventional and high performance concretes. Improvements in UHPC are achieved through: limiting the water-to-cementitious materials ratio (i.e., w/cm < 0.20), optimizing particle packing, eliminating coarse aggregate, using specialized materials, and implementing high temperature and high pressure curing regimes. In addition, and randomly dispersed and short fibers are typically added to enhance the material¡¦s tensile and flexural strength, ductility, and toughness.
There is a specific interest in using UHPC for precast prestressed bridge girders because it has the potential to reduce maintenance costs associated with steel and conventional concrete girders, replace functionally obsolete or structurally deficient steel girders without increasing the weight or the depth of the girder, and increase bridge durability to between 75 and 100 years. UHPC girder construction differs from that of conventional reinforced concrete in that UHPC may not need transverse reinforcement due to the high tensile and shear strengths of the material. Before bridge designers specify such girders without using shear reinforcement, the long-term tensile performance of the material must be characterized.
This multi-scale study provided new data and understanding of the long-term tensile performance of UHPC by assessing the effect of thermal treatment, fiber content, and stress level on the tensile creep in a large-scale study, and by characterizing the fiber-cementitious matrix interface at different curing regimes through nanoindentation and scanning electron microscopy (SEM) in a nano/micro-scale study.
Tensile creep of UHPC was more sensitive to investigated parameters than tensile strength. Thermal treatment decreased tensile creep by about 60% after 1 year. Results suggested the possibility of achieving satisfactory microstructural refinement at the same temperature input despite the maximum temperature applied. For the first time, the presence of a 10 Ým (394 micro inch) wide porous fiber-cementitious matrix interface was demonstrated by nanoindentation and SEM for non-thermally treated UHPC only. Tensile creep at 90 days increased by 64% and 46% upon eliminating fibers for thermally and non-thermally treated UHPC, respectively. Increases in creep upon reducing the fiber content suggested that fibers carry part of the sustained load and thus reduce creep. Tensile creep strain was proportional to the stress applied up to 60% of the ultimate strength. No tensile creep failure occurred for a period of 1 year for pre-cracked UHPC under stress level of 40%. Also, no tensile creep failure occurred for a period of 90 days under stress level of 60%. Tensile creep failure occurred at stress levels of 70% and 80%. This study showed that fibers cannot be accounted for as shear reinforcement in lieu of stirrups unless micro-defect-free fiber-matrix interface is achieved.
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