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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.