chapter 2 literature review - shodhganga : a...
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CHAPTER 2
LITERATURE REVIEW
2.1 GENERAL
Efforts are underway all over the world to develop environmentally
friendly construction materials, which make minimum utility of fast
dwindling natural resources and help to reduce greenhouse gas emissions.
Several research works carried out to examine the possibility of Geopolymer
concrete in construction applications as an alternative solution to this issue.
Many research works carried out to investigate the durability of Geopolymer
materials under different environmental conditions that are anticipated under
actual service conditions. In this connection, Geopolymers are showing great
potential. Researchers have critically examined the various aspects of their
viability as binder system and have proved its durability. In this chapter, some
of the literatures reviewed are presented.
2.2 PRECURSOR
Malhotra (1990) presented data on the durability of structural
concrete incorporating high volumes of low-calcium fly ash which have been
under study in CANMET since 1985. The durability aspects considered were
freezing and thawing, resistance to chloride ion permeability and the
expansion of concrete specimens when highly reactive aggregates were used
in the concrete. He indicated that concrete incorporating high volumes of fly
ash had excellent durability with regard to frost action, had very low
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permeability to chloride ions and showed no adverse expansion when highly
reactive aggregates were incorporated into the concrete.
Anjan Chatterjee (2011) has investigated into newer avenues of
bulk use of flyash produced in India, where generation of electricity has been
overwhelmingly dependent on the combustion of high-ash coal. The present
availability of fly ash had already exceeded 130 million tons, and its
generation would likely to reach 170 million tons by the coming years.
Although the gainful use of fly ash was close to 50% of the quantity
generated, a countrywide directive has been established to effectively use the
entire quantity generated in the years to come. To achieve this target, several
technological endeavours were in progress in India to enhance the quality and
reactivity of fly ashes through mechano chemical activation. He has realized
and worried about the regular and experimental technologies of comminution
and size classification which had not resulted in producing
submicrocrystalline or nanocrystalline particles from the crystalline fly ashes
to enhance their reactivity. Therefore, he insisted on the need for converting
the fly ash grains to submicrocrystalline particles which is critical if the
performance of fly ashes has to approach that of silica fume or silica gel.
2.3 GEOPOLYMERISATON
Joseph Davidovits (1988) proposed that an alkaline liquid could be
used to react with the silicon (Si) and the aluminium (Al) in a source material
of geological origin or in byproduct materials such as flyash and rice husk ash
to produce binders. He coined the name “Geopolymer” to represent these
binders because of the reaction that took place was a polymerisation process.
He also reported that Geopolymers were members of the family of inorganic
polymers similar to natural zeolitic materials.
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Joseph Davidovits (1994) proposed a controversial theory that
documented in a book and has since gained widespread support and
acceptance. He postulated that the great pyramids of Egypt were not built by
natural stones, but that the blocks were cast in place and allowed to set,
creating an artificial zeolitic rock with Geopolymerisation technology. He
collected a great amount of evidences which come from old ancient Egyptian
literatures and samples in sites to confirm his Geopolymerisation theory.
From then on, many experts began to focus their concerns on Geopolymer
studies. Davidovits (2008) firstly began to investigate the possibilities of
heavy metal immobilization by commercial Geopolymeric products in the
early 1990s. The leachate results for Geopolymerisation on various mine
tailings showed that over 90% of heavy metal ions included in the tailings
could be tightly solidified in 3D framework of Geopolymer.
Gourley (2003) experimentally investigated heat-cured low-
calcium fly ash based Geopolymer concrete. Low calcium fly ash (ASTM
Class F) would be preferred as a source material than high-calcium (ASTM
Class C) fly ash. He declared that the presence of calcium in high amounts
might be interfering with the polymerisation process and may alter the
microstructure.
Fernandez-Jimenez et al (2005) made a microscopic study of a set
of alkali-activated and thermally cured fly ash samples to establish a
descriptive model for the micro structural development of fly ash-based
cementitious Geopolymers. Class F fly ash which was mixed with 8M
solution of NaOH with 0.35 as the ratio of solution/ash and cured in an oven
at 850 C for 5 h, 24 h and 60 days. Based on the findings from the
microscopic study, it was emphasized that the presence of soluble silica in the
activating dissolution played an important role in the micro structural
development of the cementitious systems. The authors also confirmed that the
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conceptual model presented described the reactive process of fly ash if
soluble silica would exit in the system. It was also concluded that the
activation reaction rate and chemical composition of the reaction products
depended on several factors like particle size distribution, mineral
composition of fly ash, type and concentration of activator etc., but the
mechanisms controlling the general process of activation were independent of
those variables.
Joseph Davidovits (2005) reported that Geopolymers were
members of the family of inorganic polymers similar to natural Zeolitic
materials. He found out that Geopolymeric materials would have a wide range
of applications in civil engineering industries. He also found out that a low
Si:Al ratio normally 2 would be suitable for civil engineering industry.
Divya Khale and Rubina Chaudhary (2007) reviewed the
mechanism of Geopolymerisation and factors influencing its development.
The authors undertook the review to study the work carried out on the
development of Geopolymers, including the chemical reaction, the role and
effect of the source materials and the factors affecting the mix compositions
such as curing temperature, curing time, ratio of silica to alumina, alkali
concentration and water solid ratio. From the findings, the authors concluded
that the technology of Geopolymerisation, could be utilized to consume by-
products like fly ash, slag and kiln dust and also for immobilization of toxic
metal in the waste. It was also found that the Geopolymer materials needed
only moderate energy to produce and CO2 emissions got reduced by about
80% compared to that of ordinary Portland cement.
2.4 GEOPOLYMER GELS, MORTAR AND CONCRETE
2.4.1 Geopolymer Gels
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Ailar Hajimohammadi et al (2011) have investigated the effect of
seeded nucleation on the formation and structural evolution of one-part (‘‘just
add water’’) Geopolymer gels. Gel-forming systems were seeded with each of
three different oxide nanoparticles, and seeding was shown to have an
important role in controlling the silica release rate from the solid geothermal
silica precursor, and in the development of physical properties of the gels.
Nucleation had accelerated the chemical changes that took place during the
Geopolymer formation. The nature of the seeds affected the structure of the
growing gel by affecting the extent of phase separation, identified by the
presence of a distinct silica-rich gel in addition to the main, more alumina-
rich gel phase. Synchrotron radiation-based infrared microscopy (SR-FTIR)
has shown the effect of nucleation on the heterogeneous nanostructure
and microstructure of Geopolymer gels, and was combined with data obtained
by time resolved FTIR analysis to provide a more holistic view of the reaction
processes at a level of detail that had not previously been available. While
spatially averaged (ATR-FTIR) infrared results have shown similar spectra
for seeded and unseeded samples which had been cured for more than 3
weeks, SR-FTIR results have shown marked differences in gel structure as a
result of seeding.
Ross et al (2010) in their study have investigated methods for
determining the formulation for manufacturing Geopolymers made with fly
ash from coal-fired power stations. The accepted method of determining the
formulation of Geopolymers to get the desired matrix chemistry has used the
bulk composition of the feedstock materials. This formulation method had
been widely used in investigations using feedstock materials that almost
completely react during processing. It has been widely considered that
amorphous components of fly ash were the reactive components in the
Geopolymerisation reaction. However, quantification of the amorphous
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components was challenging and generally avoided with the concomitant
problem that the formulation was far from optimum.
For the work they have presented here, the composition of the
amorphous part was determined accurately and this information utilised to
synthesize Geopolymers. The bulk composition was first determined using
X-ray fluorescence spectroscopy (XRF) and then the amorphous
composition determined using XRF and quantitative X-ray diffraction
(QXRD). Formulating the mixture based on amorphous composition
produced samples with a significantly higher compressive strength than those
formulated using the bulk composition. Using the amorphous composition of
fly ash produced Geopolymers with similar physical properties to that of
metakaolin Geopolymers with the same targeted composition. They have
demonstrated a new quantitative formulation method that is superior to the
accepted method.
Van Jaarsveld and Van Deventer (1997) set out to study the
solidification effectiveness of Geopolymer manufactured from fly ash. The
bond mechanism between heavy metalions and Geopolymer matrix is also
simply explained on the basis of the XRD, IR, MAS-NMR and leaching
results.
Alvarez-Ayusoa et al (2008) have studied experimentally the
synthesis of Geopolymer matrixes from coal combustion fly ashes as the sole
source of silica and alumina in order to assess both their capacity to
immobilise the potentially toxic elements contained in these coal combustion
by-products and their suitability to be used as cement replacements. The
Geopolymerisation process had been performed using (5, 8 and 12M) NaOH
solutions as activation media and different curing time (6-48 h) and
temperature (40-800C) conditions. Synthesized Geopolymers had been
characterised with regard to their leaching behavior. In addition, Geopolymer
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mineralogy, morphology and structure have been studied by X-ray diffraction
(XRD), scanning electron microscopy (SEM) and Fourier transform infrared
spectroscopy (FTIR), respectively. It was found that synthesized Geopolymer
matrixes were only effective in the chemical immobilisation of a number of
elements of environmental concern contained in fly ashes, reducing
(especially for Ba), or maintaining their leachable contents after the
Geopolymerisation process, but not for those elements present as oxyanions.
2.4.2 Geopolymer Mortar
Chindaprasirt et al (2007) studied and investigated the basic
properties like workability and strength of Geopolymer mortar made from
coarse lignite high calcium fly ash. The Geopolymer was activated with
sodium hydroxide, sodium silicate and heat. All Geopolymer mortars were
prepared with sand to fly ash ratio of 2.75, sodium silicate to NaOH ratios by
mass of 0.67, 1.00, 1.50 and 3.00 and three concentrations of NaOH being 10,
15 and 20M. In order to get workable Geopolymer mortar, they have a
minimum water content of 5% by mass.
Joseph Davidovits et al (1999) suggested that it shall be preferable
to mix the sodium silicate solution and the sodium hydroxide solution
together at least one day before adding the liquid to the solid constituents. He
also suggested that the sodium silicate solution obtained from the market
usually was in the form of a dimer or a trimer, instead of a monomer, and
mixing it together with the sodium hydroxide solution assisted the
polymerization process. When this suggestion was followed, it was found that
the occurrence of bleeding and segregation ceased and it was decided to
observe the following standard process of mixing in all further studies.
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2.4.3 Geopolymer Concrete
Hardjito et al (2005) conducted experiments to study the materials
and the mixture proportions, the manufacturing process and the influence of
various parameters on the properties of fresh and hardened Geopolymer
concrete. They have found out that fly ash-based Geopolymer concrete had
excellent compressive strength which might be suitable for structural
applications. It was found that fresh fly ash-based Geopolymer concrete could
be handled at least up to 120 minutes after mixing, without any sign of
setting, and without any degradation in compressive strength. With regard to
hardened concrete, the molar ratio of H2O-to-Na2O significantly influenced
the compressive strength of fly ash-based Geopolymer concrete. An increase
in this ratio decreased the compressive strength.
Other important factors that influenced the properties of hardened
fly ash-based Geopolymer concrete were the curing temperature and the
curing time. The higher the curing temperature, the higher was the
compressive strength. The fly ash-based Geopolymer concrete also showed
excellent resistance to sulphate attack, underwent low creep, and suffered
very little drying shrinkage.
Peter Duxson et al (2007) studied the role of inorganic polymer
technology in the development of “Green Concrete”. In this paper, issues
related to the distinction between Geopolymers synthesized for cement
replacement applications and those tailored for ceramic applications were
discussed. Attention was also paid to the role of free alkali and silicate in
poorly-formulated systems and its deleterious effects on concrete
performance, which necessitates a more complete understanding of the
chemistry of Geopolymerisation for the technology to be successfully applied.
More definitely the relationship between CO2 footprint and composition in
comparison with Portland base cements had been quantified. The paper
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briefly outlined the specific properties of Geopolymers which led to particular
suitability in each of these applications.
The development of “green concrete”, the key aim of the paper, the
composition range of much interest therefore was narrowed to include the
range from 1 < Si/Al < 5, and with Na/Al ratios not too dissimilar from 1. It
was finally advised that care must be taken when defining what is and what is
not a Geopolymer, as negative durability results obtained from poorly
formulated and/or poorly characterized systems were likely to be deleterious
on perceptions of the Geopolymeric materials as viable alternative to existing
cement technologies.
Lee et al (2004) have experimented and reported the micro
structure and the bonding strength of the interface between natural siliceous
aggregates and fly ash based Geopolymers. It was found that when the
activating solution that contained no or little soluble silicates, the compressive
strength of the Geopolymeric binders, mortars and concretes were
significantly weaker than those activated with high dosage of soluble silicates.
The presence of soluble silicates in the initial activating solution was also
effective in reducing alkali saturation in the concrete pore solution even when
a highly alkali-concentrated activating solution was used. They subsequently
promoted greater inter-particle bonding with in the Geopolymeric binders as
well as to the aggregate surfaces. It resulted in denser binders as well as
stronger aggregate/binder interfaces were formed with increasing soluble
silicate dosage. It was concluded that the interfacial bonding between the
aggregates and Geopolymeric binders was the critical factor in determining
the mechanical strengths of the Geopolymeric mortars and concretes.
Konstantinos Komnitsasa (2011) stressed that sustainable cities of
the future, apart from having low energy consumption and greenhouse gas
emissions should also adopt the “zero waste” principle. He revealed that
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Geopolymer concrete and construction components could be manufactured
from several wastes or by-products, including coal combustion ashes and
metallurgical slags, and construction and demolition wastes can be utilized for
the production of Geopolymer concrete and construction components. Also,
he outlined briefly the potential of Geopolymer technology towards green
buildings and future sustainable cities with a reduced carbon footprint and
declared that in contrast to Portland cement, most Geopolymer systems
rely on minimally processed natural minerals and industrial by-products or
wastes to provide binding agents, thus enabling noticeable energy and CO2
savings in the construction sector.
2.5 STRUCTURAL APPLICATIONS OF GEOPOLYMER
CONCRETE
Angel Palomo et al (2004) demonstrated and revealed the details of
methodology to manufacture small sized pre-stressed Geopolymer concrete
monobloc sleeper for railway tracks made in a precast concrete plant. They
established that the Geopolymer concrete railway sleepers could easily be
produced using the existing current concrete technology without any
significant changes. The engineering performances of the products were
excellent and the drying shrinkage was small. Sleepers made by using this
process and installed for seven years on tracks belonging to the Spanish
railway network offered a series of specific advantages, including: They
ensured better final track geometry (essential for high speed) They were more
resistant to lateral stress on track. They provided very important allowances
that could be required in compliance with static, Fatigue and dynamic testing.
Chang Ee Hui (2009) has focused on the importance of shear and
bond behaviour of reinforced low calcium fly ash-based Geopolymer concrete
beams. For the study of shear behaviour of Geopolymer concrete beams, a
total of nine beam specimens were cast. The beams were 200 mm x 300 mm
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in cross section with an effective length of 1680 mm. The longitudinal tensile
reinforcement ratios were 1.74%, 2.32% and 3.14%. The behaviour of
reinforced Geopolymer concrete beams failing in shear, including the failure
modes and crack patterns, were found to be similar to those observed in
reinforced Portland cement concrete beams. It was also found that the
methods of calculations, including code provisions, used in the case of
reinforced Portland cement concrete beams shall be applicable for predicting
the shear strength of reinforced Geopolymer concrete beams.
2.5.1 Developments in Geopolymer Precast Concrete
Gourley and Johnson (2005) demonstrated and revealed the details
of methodology to manufacture Geopolymer concrete sewer pipes, railway
sleepers and wall panels made in a precast concrete plant. They also reported
the results of the tests on acid resistance of Geopolymers and Geopolymer
concrete. They had written that Geopolymer concrete was superior to OPC
concrete in terms of acid resistance as the weight loss was much lesser. But
they noticed some degradation in compressive strength of specimens after
acid exposure. The rate of degradation depended on the period of exposure.
Siddiqui (2007) demonstrated the manufacture of reinforced
Geopolymer concrete culverts in a precast concrete plant. A two-stage steam-
curing regime was used by him in the manufacture of prototype reinforced
Geopolymer concrete box culverts. It was found that steam-curing at 800C for
a period of four hours provided enough strength for de-moulding the culverts.
Test results revealed that two-stage steam-curing regime did not produce any
degradation in the strength of the products.
Thokchom et al (2009) prepared Geopolymer mortar samples using
equal proportions of fly ash and sand with varying Na2O %. Specimens
received white deposits on the surfaces during exposure to magnesium
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sulphate solution which gradually transformed from soft and flaky shape to
hard and rounded shape. No visible cracks were noticed on the specimen
though fine micro cracks were seen on a few specimens through optical
microscope. Exposure solutions recorded considerable increase in pH value
which can be attributed to migration of alkalis from specimen to solution.
Maximum increase in pH occurred in solution containing specimen with
highest Na2O content which suggests that more alkalis migrated from these
specimens. Geopolymer mortar specimen gains weight during exposure to
magnesium sulphate solution and such gain are related to Na2Ocontent of the
specimen. Specimen recorded extremely low gain in weight; the maximum
gain being noticed in the specimen with minimum Na2O content. Residual
compressive strength showed some fluctuations during the period of
exposure. Geopolymer mortar specimen manufactured with higher alkali
content performed better than those manufactured with lower alkali content.
Sumajouw and Rangan (2006) have investigated experimentally
reinforced Geopolymer concrete beams and columns manufactured from class
F flyash and activated by silicates and hydroxides of sodium and steam cured
at a temperature of 60oC for 24 hours. They have cast 12 beams of 200mm x
300mm x 3300mm long with four different percentage of reinforcement and
three different mixtures yielding nominal compressive strengths. They have
designated the three different mixtures as GBI, GBII and GBIII to yield
nominal compressive strengths of 40, 50 and 75 MPa respectively. Under
each mixture, four different percentage of tensile reinforcement ratio was
adopted as parameter. They have taken 0.64%, 1.18%, 1.84% and 2.69% of
tensile reinforcement ratio. The crack pattern, cracking moments, ultimate
flexural capacity and deflections were observed. They have noted and
declared that the design provisions contained in the draft Australian Standard
for concrete structures were applicable to reinforced Geopolymer concrete
beams. They have concluded that the crack patterns observed for reinforced
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Geopolymer concrete beams were similar to those reported in the literature
for reinforced Portland cement concrete beams. Also all beams failed in
flexure in a ductile manner accompanied by crushing of the concrete in the
compression zone.
2.6 CURING MODE OF GEOPOLYMER CONCRETE
Rangan et al (2005) has presented a study to develop a mixture
proportioning process to manufacture low-calcium fly ash- based Geopolymer
concrete and to identify and study the effect of salient parameters that affects
the properties of low-calcium fly ash-based Geopolymer concrete. It also
aimed to study the short-term engineering properties of fresh and hardened
low calcium fly ash-based Geopolymer concrete. In order to develop the
mixture proportioning, they had selected varied ranges of constituent
materials of Geopolymer concrete. The ratio of sodium silicate solution to
sodium hydroxide solution, by mass, was kept between 0.4 and 2.5. The
molarity of the sodium hydroxide solution varied in the range of 8M to 16M.
They concluded that the higher the ratio of sodium silicate to
sodium hydroxide by mass, the higher the compressive strength of fly ash-
based Geopolymer concrete. An increase in the curing temperature increased
the compressive strength of the fly ash-based Geopolymer concrete. A longer
curing time in the range of 96 hours (4 days), produced a higher compressive
strength of the fly ash-based Geopolymer concrete. However, the increase in
strength beyond 24 hours of curing was not significant.
Bakharev (2005b) has published in his paper the results of the
study of the influence of elevated temperature curing on phase composition,
microstructure and strength development in Geopolymer materials prepared
using Class F fly ash and sodium silicate and sodium hydroxide solutions. In
particular, the effect of storage at room temperature before the application of
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heat on strength development and phase composition was studied. X-ray
diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and SEM
were utilised in this study. He has given after findings that long precuring at
room temperature before application of heat was beneficial for strength
development. The main product of reaction in the Geopolymeric materials
was amorphous alkali aluminosilicate gel. However, in the case of sodium
hydroxide activator in addition to it, traces of chabazite, Linde Type A, Na-P1
(gismondine) zeolites and hydroxysodalite were also present. The type of
zeolite present and composition of aluminosilicate gel were dependent on the
curing history. Samples prepared with the sodium hydroxide activator had
traces of zeolite phases in addition to amorphous alkali aluminosilicate that
was the only phase present in fly ash activated by sodium silicate activator.
The composition of aluminosilicate gel depended on the treatment history. An
increase of temperature of heat treatment caused a decrease of Si/Al ratios in
aluminosilicate gel, and long curing at room temperature narrowed the range
of distribution of the Si/Al ratios.
2.7 DURABILITY OF GEOPOLYMER CONCRETE
2.7.1 Acid Attack
Bakharev (2005a) presented an investigation into the durability of
Geopolymer materials manufactured using class F fly ash and alkaline
activators when exposed to 5% solutions of acetic and sulfuric acids. The
evolution of weight, compressive strength, products of degradation and
microstructural changes were the main parameters in the investigation. The
paper presented a study of durability in the acid environment of three
Geopolymer materials utilizing class F fly ash activated by sodium silicate,
sodium hydroxide and a mixture of sodium and potassium hydroxides. The
resistance of materials to the acid attack was studied by the immersion of
cylindrical specimens of size 25 mm x 50 mm in 5% solutions of acetic and
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sulfuric acids. The testing media were replaced monthly with fresh solutions.
The compressive strength of cylinders was measured at 30, 60, 90, 120 and
150 days of exposure.
The test results were compared with that of cylindrical specimens
of the same size made of Portland cement paste and Portland cement paste
with 20% fly ash replacement. From the test results, it was concluded that
Geopolymer specimens had very small change in appearance after 5 month of
immersion in the acidic solutions, whereas in the case of OPC cement
specimens, severe deterioration was observed in appearance. Samples
activated by sodium hydroxide exhibited best performance in both tests and
had weight loss of 0.45% and 1.96% in acetic acid and sulfuric acid solutions
whereas OPC samples had weight gain of more than 40% but got deteriorated
more severely. Geopolymer specimens with fly ash exhibited strength loss of
38.3% after 6 months whereas OPC and OPC + FA samples showed 91% and
84% after 6 months of exposure. It was finally concluded that specimens
made of Geopolymer materials behaved better than OPC and OPC + FA
specimens when exposed to acidic environment.
Song et al (2005) have presented experimental data on the
durability of fly ash based Geopolymer concretes exposed to 10% sulfuric
acid solutions for up to 8 weeks. Class F fly ash based Geopolymer concrete
was initially cured for 24 hours at either 23°C or 70°C. The compressive
strength of 50mm cubes at an age of 28 days ranged from 53MPa to 62MPa.
After immersion in 10% sulfuric acid solution, samples were tested at 7, 28,
and 56 days. The results confirmed that Geopolymer concrete was highly
resistant to sulfuric acid in terms of a very low mass loss, less than 3%.
Moreover, Geopolymer cubes were structurally intact and still had substantial
load capacity even though the entire section had been neutralized by sulfuric
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acid. Also, they have reported that Geopolymer binder possessing good acid
resistance property could be well applicable to manufacture sewer pipe.
Wallah et al (2006) discussed the following long – term properties
of low-calcium fly ash based Geopolymer concrete such as creep behavior
under sustained load, drying shrinkage behavior, sulphate resistance and
resistance to sulfuric acid. Fly ash based Geopolymer concrete cured in the
laboratory ambient temperature conditions gained compressive strength with
age. The 7th day compressive strength of ambient cured specimens depended
on the average ambient temperature during the first week after casting. The
higher the average ambient temperature, the higher was the compressive
strength. Heat-cured fly ash-based Geopolymer concrete underwent low
creep. The heat-cured fly ash-based Geopolymer concrete underwent very
little drying shrinkage in the order of about 100 micro strains after one year.
This value was significantly smaller than the range of values of 500 to 800
micro strains for Portland cement concrete.
Acid resistance of fly ash-based Geopolymer concrete was studied
by soaking concrete and mortar specimens in various concentrations of
sulfuric acid solution up to one year and by evaluating the behavior in terms
of visual appearance, change in mass and change in compressive strength
after exposure. Fly ash was used for all concrete and mortar specimens. The
test specimens were cured at 60oC for 24 hours. The sulfuric acid solution
was stirred every week and was replaced every month. The visual appearance
of the Geopolymer concrete specimens after soaking in various concentrations
of sulfuric acid solution for a period of one year were compared with the
specimen without acid exposure and left in ambient conditions of the
laboratory. It was seen that the specimens exposed to sulfuric acid underwent
erosion of the surface. The damage to the surface of the specimens increased
as the concentration of the acid solution increased. The severity of the damage
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and the distortion of the shape of specimens depended on the concentration of
the solution.
The tests on heat-cured Geopolymer mortar specimens indicated
that the degradation in the compressive strength due to sulfuric acid attack
was mainly due to the degradation in the Geopolymer matrix rather than the
aggregates. The degradation in compressive strength of mortar specimens was
larger than that of concrete specimens due to the larger Geopolymer matrix
content by mass of mortar specimens. When exposed to sulfuric acid solution,
the surface of heat-cured Geopolymer concrete test specimens got damaged
and caused a mass loss of about 3% after one year of exposure. The severity
of the damage depended on the acid concentration. The sulfuric acid attack
also caused degradation in the compressive strength of heat-cured
Geopolymer concrete. The extent of degradation depended on the
concentration of the acid solution and the period of exposure. However, the
sulfuric acid resistance of heat-cured Geopolymer concrete was significantly
better than that of Portland cement concrete as reported in earlier studies.
Suresh Thokchom et al (2009) investigated and expressed that fly
ash based Geopolymer mortar specimens manufactured with varying alkali
content showed varying degree of deterioration when exposed to sulfuric acid.
Though mortar specimens revealed no visible signs of structural
disintegration, surface deterioration was clearly visible under an optical
microscope and these appeared to be severe in specimen manufactured with
lesser alkali content. Loss in weight though observed in all specimens, those
with higher alkali content recorded higher weight loss. There was a sudden
loss in weight for the specimens at 3 weeks. Geopolymer mortar specimen
experienced loss in strength which was highest in the specimen manufactured
with minimum alkali content strength measured was 29.4% micrographs
showed different microstructures of mortar specimens before and after
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exposure in sulfuric acid solution. Microstructure of specimen appeared to be
denser after exposure due to formation of light colored.
2.7.2 Sulphate Attack
Bakharev (2005) has investigated and presented this paper about
the durability of Geopolymer materials manufactured using class F fly ash
and alkaline activators when exposed to a sulphate environment. Three tests
were used to determine resistance of Geopolymer materials. The tests
involved immersions for a period of 5 months into 5% solutions of sodium
sulphate and magnesium sulphate, and a solution of 5% sodium sulphate+5%
magnesium sulphate. The evolution of weight, compressive strength, products
of degradation and microstructural changes were studied. In the sodium
sulphate solution, significant fluctuations of strength occurred with strength
reduction of 18% in the 8FASS material prepared with sodium silicate and
65% in the 8FAK material prepared with a mixture of sodium hydroxide and
potassium hydroxide as activators, while 4% strength increase was measured
in the 8FA specimens activated by sodium hydroxide. In the magnesium
sulphate solution, 12% and 35% strength increase was measured in the 8FA
and 8FAK specimens, respectively; and 24% strength decline was measured
in the 8FASS samples. The most significant deterioration was observed in the
sodium sulphate solution and it appeared to be connected to migration of
alkalis into solution. In the magnesium sulphate solution, migration of alkalis
into the solution and diffusion of magnesium and calcium to the subsurface
areas was observed in the specimens prepared using sodium silicate and a
mixture of sodium and potassium hydroxides as activators. The least strength
changes were found in the solution of 5% sodium sulphate+5% magnesium
sulphate. The material prepared using sodium hydroxide had the best
performance, which was attributed to its stable cross-linked aluminosilicate
polymer structure.
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2.7.3 Water Absorption
Anurag Mishra et al (2008) have presented results of an
experimental study on the absorption characteristics of Geopolymer concrete.
The experiments were conducted on fly ash based Geopolymer concrete by
varying the concentration of NaOH and curing time. Totally, nine mixes were
prepared with 8M, 12M, and 16M NaOH concentration and curing time
varied as 24 hours, 48 hours and 72 hours. Compressive strength, water
absorption and tensile strength tests were conducted on each mix. They have
concluded that Geopolymer concrete was more environmental friendly and
had the potential to replace ordinary cement concrete in many applications
such as precast units. Results of the investigation indicated that there was an
increase in compressive strength with increase in NaOH concentration.
Sathia et al (2008) have investigated the water absorption property
of fly ash based Geopolymer concrete. The Geopolymer concrete was
prepared with varying fly ash content of 350, 450 and 550 Kg/m3 and
activators solution to fly ash ratio varied between 0.4 and 0.5. They have
declared that similar to Portland cement concrete, the water content in the mix
played an important role in the strength achievement of Geopolymer concrete.
The reaction occurring in the case of Geopolymer concrete was also different
from that of Portland cement concrete. In case of Geopolymer concrete, water
was required to improve workability, but was expelled during curing at
elevated temperature, increasing the porosity of concrete. It can be inferred
from the results that the absorption characteristics, which indirectly reflects
the permeability, have shown that the initial 30 minutes absorption values for
all the concretes was lower than the limits specified for “good concrete” by
Concrete society.
Wongapa et al (2010) revealed that the water permeability of
Geopolymer concrete made with flyash and rice husk ash activated by
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silicates and hydroxides of sodium depends on mix proportions, alkaline
solution to flyash ratio and the paste to aggregate ratio. They also showed that
water permeability was significantly related to compressive strength.
2.8 OPC MORTAR AND CONCRETE
2.8.1 Sulphate Attack on OPC Mortar and Concrete
Young-Shik Parka et al (1999) investigated through various
laboratory tests to assess the damage of chemical attack by magnesium
sulphate and sodium sulphate on normal and high strength concretes. The
selected solutions were pure water and 10% sulphate solutions (sodium and
magnesium), which were determined by consideration of the soil environment
in Korea. The parameters in the experimental programs were water-binder
ratio, silica fume content, and the compressive strength of concrete. Observed
differences in the characteristics between normal and high strength concretes
were discussed, and a scheme for maximizing the resistance of high strength
concrete against various kinds of sulphates was also suggested. They declared
that although the high strength concrete with silica fume was the most
efficient against sodium sulphate attack, its resistance to magnesium sulphate
attack was decreased as the content of silica fume was increased. The
specimens that contain at least 10% silica fume (HSC-S10 and HSC-S15)
have shown lesser strength than the specimens that used less than 10% silica
fume (HSC-S0 and HSC-S5) after 270 days. In higher silica fume mixes,
lesser linear expansion had occurred in the sodium sulphate solution, but more
linear expansion had occurred in the magnesium sulphate solution. They have
also reported that the weight variation of the specimens at an age of 90days
was negligibly small in pure water and in sodium sulphate solution regardless
of the silica fume content. However, the weight of the specimens in
magnesium sulphate solution was significantly decreased in particular mixes
with 15% silica fume content.
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Manu Santhanam et al (2002) have reported the results of an
investigation on the effects of sodium and magnesium sulphate solutions
on the expansion and microstructure of different types of Portland cement
mortars. The effects of using various sulphate concentrations and of using
different temperatures were also reported. They suggested from the results got
that the expansion of mortars in sodium sulphate solution had followed a two-
stage process. In the initial stage, Stage 1, there was little expansion followed
by a sudden and rapid increase in the expansion in Stage 2. Microstructural
studies have shown that the onset of expansion in Stage 2 corresponded to the
appearance of cracks in the chemically unaltered interior of the mortar.
Beyond this point, the expansion had proceeded at an almost constant rate
until the complete deterioration of the mortar specimen. In the case of
magnesium sulphate attack, expansion had occurred at a continually
increasing rate. Also, out of the microstructural studies, they clearly noticed
that a layer of brucite (magnesium hydroxide) on the surface had formed
almost immediately after the introduction of the specimens into the solution.
The attack was then governed by the steady diffusion of sulphate ions across
the brucite surface barrier. The ultimate failure of the specimen had occurred
as a result of the decalcification of the calcium silicate hydrate (C-S-H) and
its conversion to magnesium silicate hydrate (M-S-H), after prolonged
exposure to the solution. The effects of using various admixtures, and of
changing the experimental variables such as the temperature and
concentration of the solution, have also been summarized in this paper.
2.8.2 Structural Properties of OPC Concrete
Seong-Tae Yi et al (2007) have considered the importance of the
effect of member size when estimating the ultimate strength of a concrete
flexural member and presented it in this paper. In this study, the size effect of
a RC beam was experimentally investigated. For this purpose, a series of
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beam specimens subjected to four-point loading was tested. RC beams with
three different effective depths were tested to investigate the size effect. The
shear-span to depth ratio and the thickness of the specimens were kept
constant to eliminate the out-of-plane size effect. The test results were curve
fitted using Levenberg-Marquardt’s Least Square Method (LSM) to obtain
parameters for Modified Size Effect Law (MSEL) by Kim et al. The analysis
results have shown that the flexural compression strength and ultimate strain
decreased as the specimen size increased. Comparisons with existing research
results considering the depth of neutral axis were also performed. They also
show that the current strength criteria-based design practice should be
reviewed to include member size effect.
ZHOU et al (2011) have studied the importance of considering
simultaneously the strength and deformability in the flexural design of
reinforced concrete (RC) beams. In the current design codes, the design of
strength has been separated from deformability, and the evaluation of
deformability was independent of some key parameters, like concrete
strength, steel yield strength and confinement content. Hence, provisions in
the current design codes might not provide sufficient deformability for beams,
especially when high-strength concrete (HSC) and/or high-strength steel
(HSS) were used. In this paper, influences of key factors, including the degree
of reinforcement, concrete strength, steel yield strength, compression steel
ratio, and confining pressure, have been studied based on a theoretical
method. An empirical formula for direct evaluation of deformability has been
proposed. Interrelations between the strength and deformability were plotted
in charts. Based on the empirical formula and charts, a new method of beam
design called “concurrent flexural strength and deformability design” that
would allow both strength and deformability requirements to be considered
simultaneously has been developed. The method would provide engineers
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with flexibility of using high-strength concrete, adding compression steel or
adding confinement to increase deformability of RC beams.
Girija and Devdas Menon (2011) presented the results of 15
experimental tests on rectangular slender reinforced concrete (RC) beams.
The results revealed the limitations in existing theoretical formulations to
estimate the failure moment capacity and mode of failure. An improved
theoretical formulation has been proposed here to predict the critical buckling
moment including effects related to nonlinearity and cracking of concrete.
Also, following the trends in steel design, an improved measure of
slenderness ratio has been proposed. Based on a study of 72 test results, it was
shown that there was an interaction between flexural tension and instability
modes of failure in moderately slender beams. To avoid lateral instability
failure, it was suggested that the slenderness ratio be limited to unity. A
‘moment reduction factor’ was also proposed to account for slenderness
effects in RC beams.
2.9 CONCLUSION ON LITERATURE REVIEW
Based on the above literatures, it is observed that the Geopolymer
mortar and concrete exhibit very good properties when compared to Ordinary
Portland cement counterparts. On the durability aspect, Geopolymer concrete
cubes have shown good performance and reinforced Geopolymer concrete
elements have performed well in structural behavior also. Observing the
positive aspects of Geopolymer concrete over Ordinary Portland cement
concrete from the literature tour, experimental research work has been taken
on low calcium class F fly ash based Geopolymer concrete elements.
Moreover, it is obvious from the available literature sources, no such work
has been done on Indian flyash and other constituents. The methodology
adopted in Research Reports GC 1, GC 2 and GC 3 is found to be useful in
the initial stages of work. Tracing the long literature track, it is also found out
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that steam curing has been adopted as the single mode of curing the
Geopolymer concrete elements worldwide. Considering the above and to be
unique, it is decided to take up research on Geopolymer concrete and planned
to cure the Geopolymer concrete elements using Dry Heat curing, the other
possible way of curing. The results of the various tests are discussed in the
subsequent chapters and the adaptability of Geopolymer concrete in structural
applications to Indian context is verified.