1 Chapter – 1 INTRODUCTION 1.1 General : Concrete is a widely used construction material around the world, and its properties have been undergoing changes through technological advancement. Numerous types of concrete have been developed to enhance the different properties of concrete. So far, this development can be divided into four stages. The earliest is the traditional normal strength concrete which is composed of only four constituent materials, which are cement, water, fine and coarse aggregates. With a fast population growth and a higher demand for housing and infrastructure, accompanied by recent developments in civil engineering, such as high-rise buildings and long-span bridges, higher compressive strength concrete was the need of time. At the beginning, reducing the water-cement ratio was the easiest way to achieve the high compressive strength. Thereafter, the fifth ingredient, a water reducing agent or super plasticizer, was indispensable. However, sometimes the compressive strength was not as important as some other properties, such as low permeability, durability and workability. Thus, high performance concrete was proposed and widely studied at the end of the last century. Currently, high-performance concrete is used in massive volumes due to its technical and economic advantages. Such materials are characterized by improved mechanical and durability properties resulting from the use of chemical and mineral admixtures as well as specialized production processes. HPC is used in massive volumes due to its technical and economical advantages. Such materials, so called the 21st century concrete, are distinguished by enhanced mechanical and durability properties due to use of chemical and mineral admixtures as well as specialized production processes. In the literature, different types of mineral admixtures in forms of binary, ternary or quaternary blended mortars have been used. Pozzolanic additives are the materials or admixtures that can improve concrete properties such as concrete strength, durability and impermeability. They are used either as partial substitutes of Portland cement or as an addition . The main component of pozzolanic additives is usually active SiO 2 in the amorphous phase. Pozzolanic reaction is a simple acid-based reaction between calcium hydroxide (Ca(OH) 2 ) and silicium acid (H 4 SiO 4 ) . Mechanism of pozzolanic reaction between microsilica and calcium hydroxide in water solution has been investigated particulary by Grutzeck. According to his study, during the first hour of getting in contact with water, gel is formed on the surface of microsilica particles that is rich in silicium and poor in calcium. In presence of water microsilica particles form agglomerates. After a while, the gel on the surface of microsilica particles dissolved and microsilica agglomerates started reacting with calcium hydroxide thus forming calcium hydrosilicates. In the presence of cement the above mentioned mechanism becomes more complicated. In this case, microsilica absorbs lime containing water, forms silicium-rich gel and consumes most of the available water. Gel particles clump together and fill the voids between the cement particles and agglomerates in bigger masses. Within the first 15 minutes up to one hour, calcium hydrosilicate particles that do not contain water are enclosed by microsilica gel. In case of ordinary concrete, approximately 3 hours later discrete calcium hydroxide crystals are formed in pores, however when pozzolanic admixtures are used such weak crystals are not formed because excess lime reacts with the surface of silicium-rich gel thus forming calcium hydrosilicates, which is a stronger binder phase than calcium hydroxide. The reactivity of pozzolans is closely linked to the silicate and alumosilicate content in the amorphous phase as well as to the fineness of the
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1
Chapter – 1
INTRODUCTION
1.1 General :
Concrete is a widely used construction material around the world, and its properties have
been undergoing changes through technological advancement. Numerous types of concrete
have been developed to enhance the different properties of concrete. So far, this development
can be divided into four stages. The earliest is the traditional normal strength concrete which
is composed of only four constituent materials, which are cement, water, fine and coarse
aggregates. With a fast population growth and a higher demand for housing and
infrastructure, accompanied by recent developments in civil engineering, such as high-rise
buildings and long-span bridges, higher compressive strength concrete was the need of time.
At the beginning, reducing the water-cement ratio was the easiest way to achieve the high
compressive strength. Thereafter, the fifth ingredient, a water reducing agent or super
plasticizer, was indispensable. However, sometimes the compressive strength was not as
important as some other properties, such as low permeability, durability and workability.
Thus, high performance concrete was proposed and widely studied at the end of the last
century. Currently, high-performance concrete is used in massive volumes due to its technical
and economic advantages. Such materials are
characterized by improved mechanical and durability properties resulting from the use of
chemical and mineral admixtures as well as specialized production processes. HPC is used in
massive volumes due to its technical and economical advantages. Such materials, so called
the 21st century concrete, are distinguished by enhanced mechanical and durability properties
due to use of chemical and mineral admixtures as well as specialized production processes.
In the literature, different types of mineral admixtures in forms of binary, ternary or
quaternary blended mortars have been used. Pozzolanic additives are the materials or
admixtures that can improve concrete properties such as concrete strength, durability and
impermeability. They are used either as partial substitutes of Portland cement or as an
addition . The main component of pozzolanic additives is usually active SiO2 in the
amorphous phase. Pozzolanic reaction is a simple acid-based reaction between calcium
hydroxide (Ca(OH)2) and silicium acid (H4SiO4) . Mechanism of pozzolanic reaction between
microsilica and calcium hydroxide in water solution has been investigated particulary by
Grutzeck. According to his study, during the first hour of getting in contact with water, gel is
formed on the surface of microsilica particles that is rich in silicium and poor in calcium. In
presence of water microsilica particles form agglomerates. After a while, the gel on the
surface of microsilica particles dissolved and microsilica agglomerates started reacting with
calcium hydroxide thus forming calcium hydrosilicates. In the presence of cement the above
mentioned mechanism becomes more complicated. In this case, microsilica absorbs lime
containing water, forms silicium-rich gel and consumes most of the available water. Gel
particles clump together and fill the voids between the cement particles and agglomerates in
bigger masses. Within the first 15 minutes up to one hour, calcium hydrosilicate particles that
do not contain water are enclosed by microsilica gel. In case of ordinary concrete,
approximately 3 hours later discrete calcium hydroxide crystals are formed in pores, however
when pozzolanic admixtures are used such weak crystals are not formed because excess lime
reacts with the surface of silicium-rich gel thus forming calcium hydrosilicates, which is a
stronger binder phase than calcium hydroxide. The reactivity of pozzolans is closely linked to
the silicate and alumosilicate content in the amorphous phase as well as to the fineness of the
2
material (surface area available for reaction). The influence of superplasticizer on the
performance of concrete is reviewed in this paper as well. Previously, the influence of
superplasticizer was studied by many authors . At present, superplasticizers play an important
role in concrete mix composition (especially in case of high and ultra-high strength concrete),
where reduction of water amount is necessary to obtain higher compressive strength. When
dry particles are mixed with small amount of water, the electric charges upon the solid
particles tend to cause their aggregation and prevent free distribution of the water between
solid particles, thus preventing ultimately an optimal repartition of the hydrates formed
between the particles. Originally the term pozzolan was associated with naturally formed
volcanic ashes and calcined earths, which react with lime at ambient temperatures in the
presence of water. The admixtures in the form of siliceous aluminous materials which, in
finely divided form and in the presence of water, will react chemically with calcium
hydroxide Ca(OH)2 to form compounds that possess cementitious properties. This
generalized definition covers waste products such as fly ash (FA), rice husk ash and silica
fume (SF). Portland cement, if fully hydrated, produces calcium hydrate (CH) which does not
make a significant contribution to strength and can be harmful to concrete durability. The
complete elimination (or) partial reduction of (CH) with the reaction of pozzolan results in
stronger and durable concrete. Because of these technical advantages over the last few
decades, there has been increasing and widespread utilization of FA, SF and natural zeolite in
concrete. The volume of industrial by products with pozzolanic properties, produced world
wide exceeds their current utilization and it is widely believed that their utilization will
increase with increasing realization of the environmental benefits associated with such use.
This will immensely help in the protection of environment and leads to sustainable
construction. There are therefore competing reasons, in the long term, to extend the practice
of partially replacing cement with waste by products and processed materials possessing
pozzolanic properties. Natural pozzolans in the form of calcined earths blended with lime
have been used to produce cementitious materials for thousands of years. The utilization of
calcined clay in the form of Metakaolin (MK) as a pozzolanic addition for mortar and
concrete has received considerable interest in recent years. Much of this interest has been
focused on removal of the CH, which is produced by the hydration of cement and which is
associated with poor durability. Reduction of CH makes the concrete and mortars more
resistive to sulphate attack and reduces the effect of alkali - silica reaction. This provides
enhanced strength which is derived from the additional cementitious phases generated by the
reaction of CH with MK. MK is processed from high - purity kaolin clay by calcination at
moderate temperature (6500C-800
0C). The silica and alumina in the MK reacts effectively
with the CH. The principal reasons for the use of clay-based pozzolans in mortar and concrete
have been due to availability of materials and durability enhancement. In addition, it depends
on the calcining temperature and clay type. It is also possible to obtain enhancement in
strength, particularly during the strength of curing. The very early strength enhancement is
due to a combination of the filler effect and acceleration of cement hydration. Consequently,
these effects are improved by the pozzolanic reaction between MK and the CH produced
during the hydration of cement.
Therefore MK is a very effective pozzolan and results in enhanced early strength with no
detriment to the long-term strength. MK modifies the pore structure in cement paste, mortar
and concrete and makes the mixes more resistive to the diffusion of harmful ions and
penetration of water which lead to degradation of the matrix. Presently Metakaolin is more
expensive than Portland cement, as is Silica Fume, even though moderately low temperatures
are required for its processing and its overall production cost is significantly less than that of
Portland cement.
3
Metakaolin differs from other supplementary cementitious materials (SCMs), like fly ash,
silica fume, and slag, in that it is not a by-product of an industrial process; it is manufactured
for a specific purpose under carefully controlled conditions.
1.2 Objective of study
This study is conducted to accomplish some predefined objectives.
The objectives are:
1.To study the performance of concrete containing different percentages of metakaolin and to
identify the optimum replacement percentage.
2.To compare the performance of metakaolin blended concrete by micro-silica powder with
other cement replacement materials (CRMs).
1.3 Significance of the Study :
Concrete has been used in the construction industry for centuries. Many modifications and
developments have been made to improve the performance of concrete, especially in terms of
strength and durability.
The introduction of pozzolans as cement replacement materials in recent years seems to be
successful. The use of pozzolan has proven to be an effective solution in enhancing the
properties of concrete in terms of strength and durability. The current pozzolans in use are
such as fly ash, silica fume and slag. Development and investigation of other sources of
pozzolan such as kaolin will be able to provide more alternatives for the engineer to select the
most suitable cement replacement material for different environments.
Unlike other pozzolans, metakaolin is not a by-product which means its engineering values
are well-controlled. Therefore, using metakaolin should promise some advantages compared
to other cement replacement materials. In this case, it is needed to study the performance of
concrete using metakaolin, silica fume and it‘s blend. The performance of metakaolin-silica
fume concrete will be compared to the cost of production of metakaolin and silica fume to
determine whether it is worthy to be developed as a new cement replacement material.
1.4 Scope of Study :
This study focuses on the strength performance of concrete with metakaolin, silica fume and
its blend. Strength is the most important property of concrete since the first consideration in
structural design is that the structural elements must be capable of carrying the imposed
loads. Strength characteristic is also important because it is related to several other important
properties which are more difficult to measure directly. With regard to this matter, the
development of compression strength of metakaolin, silica fume and its blend concrete is
studied. Cement replacements by 5%, 10%, 15%, 20% with metakaolin, silica fume and its
blend are studied. Concrete tests are conducted on the concrete samples at the specific ages.
All the strength tests are limited to the ages of 28 days.
For the performance comparison study, the cement replacement materials used are silica
fume and metakaolin. These two cement replacement materials are chosen as they are the
most common replacement materials nowadays and will be good comparisons to metakaolin.
The comparison is made on the compressive strength performance of metakaolin, silica fume
concrete.
4
Chapter – 2
LITERATURE REVIEW
2.1. General :
Concrete is known to be a simple material in appearance but with a very complex internal
nature. In contrast to its internal complexity, versatility, durability, and economy of concrete
have made it the most frequently used construction material in the world. Concrete is a
mixture of cement, water, and aggregates, with or without admixtures. The cement and water
will form a paste that hardens as a result of a chemical reaction between the cement and
water. The paste acts as glue, binding the aggregates (sand and gravel or crushed stone) into a
solid rock-like mass. The quality of the paste and the aggregates dictate the engineering
properties of this construction material. During hydration and hardening, concrete will
develop certain physical and chemical properties, among others, mechanical strength, low
permeability and chemical and volume stability. Concrete has relatively high compressive
strength, but significantly lower tensile strength (about 10% of the compressive
strength).Concrete is used to make pavements, building structures, foundations, roads,
overpasses, parking structures, brick/block walls and bases for gates, fences and poles. Over
six billion tons of concrete are made each year, amounting to the equivalent of one ton for
every person on Earth
2.2. Review of literature of concrete containing pozzolanic materials such as silica fume
and metakaolin :
Many Researchers have studied the effect of replacement of Portland cement by Metakaolin
and also on fibre addition on the mechanical and durability properties of ordinary Portland
cement concrete. The literature being reviewed is given under three sections :
Review of literature of concrete containing pozzolanic materials such as Metakaolin.
Review of literature of OPCC, MKC & SFRC on exposure to elevated temperatures.
Review of literature of OPCC on compressive strength, split tensile strength, flexural
strength and modulus of elasticity when exposed to different thermal cycles.
Yogendran et al. (1987) made an attempt to modify the properties of concrete with respect to
its strength and other properties by using silica fume and chemical admixtures. They
concluded that optimum replacement of cement by silica fume for high strength is found to
be 15% for a water cementatious ratio of 0.34 at all age.
Alhozaimy, A.M., et al (1995) carried out experimental investigations on the effects of
adding low volume fractions (<0.3%) of calculated fibrillated polypropylene fibres in
concrete on compressive flexural and impact strength with different binder compositions.
They observed that polypropylene fibres have no significant effect on compressive (or)
flexural strength, while flexural toughness and impact resistance showed increased values.
They also observed that positive interactions were also detected between fibres and
pozzolans.
F.Curcio, B.A. De Angelis, and S.Pagaliolico (1998) in their investigation, super-plasticized
mortars containing Metakaolin (MK) as 15% replacement of cement and with a water/binder
ratio of 0.33 have been characterized with four commercially available MK samples have
5
been studied and compared to silica fume. Three out of four Metakaolin samples showed
improvement in compressive strength at early ages, when compared to SF, but at 90 days and
later the difference is reduced. The difference in the compressive strength between the
specimens with micro fillers and the control decreases after 28 days, because of a smaller
slow down of the hydration rate in the control. This can be related to the fineness of the
micro-filler in the specimens with Metakaolin. At 90 and 180 days Metakaolin and silica
fume specimens gave similar strengths.
F.Curcio and B.A. De Angelis (1998) in their investigation, cement pastes containing
Metakaolin have been studied with a co-axial cylinder rotational viscometer. They show a
dilatent behavior that is strongly dependent on the water /binder ratio, on the level of cement
replacement by Metakaolin and on the fineness of the latter. Dilatency is caused by angular
and plate like shape of MK particles. They concluded that dilatency is governed by water to
binder ratio , amount of metakaolin and its fineness. Finally, the dilatant properties can be
explained by considering the plate like and angular shape of MK particles in comparison with
SF.
Handong yan, Wei Sun, Husiu chen (1999) in their investigation, the impact and fatigue
performance of high-strength concrete (HSC), silica fume high-strength concrete
(SIFUHSC), steel fibre high strength concrete (SFR HSC), and steel fibre silica fume high-
strength concrete (SSF HSC) under the action of repeated dynamic loading were studied. The
mechanisms by which silica fume and steel fibres, reduce the damage were investigated.The
results indicate that, steel fibre effectively restrained the invitation and propagation of cracks
during the failure. The presence of steel fibres in high strength concrete was effective in
restoring the structure under fatigue and impact by delaying the damage process. Silica fume
effectively improved the structure of the inter-face, eliminated the weakness of the interfacial
zone, reduced the number and size of cracks, and enhanced the ability of steel fibres to resist
cracking and restrain damage. As a result, the incorporation of steel fibres and silica fume can
together increase greatly one performance of HSC subjected to impact and fatigues. The filler
effect of silica fume can reduce the number and size of the original cracks in the interfacial
zone and in the bulk of concrete and enhanced the interfacial effect. Steel fibres mainly
strengthen, toughen and resist cracking in HSC.
J.M. Kinuthia et al. (1999) An experimental investigation is made by the authors in studying
the workability of concrete incorporating combinations of pulverized fuel ash (PFA) and
Metakaolin (MK) as partial replacements for Portland cement (PC). The aim of the research
work is to explore the potential of using PFA and MK as blends with PC in terms of the flow
properties of the resulting concrete. Mixtures containing 0, 10, 20, 30 and 40% total
replacement of cement with combinations of Metakaolin (0-15%) and PFA (0-40% for
concretes with water-to-binders ratios of 0.4, 0.5 and 0.6 were prepared. Workability of the
concrete was measured by the slump, compacting factor and vee-bee time tests. The
following conclusions are made by the authors.
i). The workability of PC-MK concrete is substantially reduced with an increase in MK
content. The workability reduction caused by MK is attributed to its high chemical activity
and high specific surface, resulting in increased intake and hence greater water requirement.
The influence of MK on compaction and flow is reduced to the thixotropic nature of clay
suspension and to a reduction of void space due to the improved dispersal of the MK
particles.
6
ii). The workability of PC-PFA concrete without super plasticizer increases significantly with
increase in PFA content. For PFA contents above 10% PFA workability falls. The reduction
in workability is attributed to flocculation/coagulation at low PFA concentration and the
increase in workability at high concentration is attributed to neutralization of positive charges
on cement particles and their resultant dispersal. When super plasticizer is used as a
dispersing agent, no fall in workability is observed.
iii). Loss of workability due to the present of MK can be compensated for by the
incorporation of PFA. The degree of restoration of workability, provided by PFA, is
influenced significantly by the cement replacement level, the MK/PFA ratio and the W/b
ratio-dispersed mixture is a critical MK/PFA ratio at which the loss in workability imparted
by the MK is exactly compensated for by the gain in workability imparted by the PFA.
Kinuthia J.M. et al (2000) The contribution by the authors in this paper forms a part of an
ongoing investigation examining the potential of using Metakaolin, pulverized fuel ash (MK-
PFA) blended for cements in concrete. The investigation involves the examination of the
effect of the blends on the strength development and factors affecting durability including
chloride penetration, carbonation and water transport properties. The following conclusions
were made by the authors:
i) Although the early compressive strength of concrete is reduced by the incorporation
of PFA as a partial replacement for cement, pozzolanic action develops in the medium
term and up to 30% PFA may be used without detriment to the strength at 90 days.
PFA is particularly effective in this respect at the moderately low water-to-binder
ratios of 0.4 and 0.5.
ii) ii) Up to 15% partial cement replacement by Metakaolin results in considerable
enhancement in strength in both the short and the medium term. The strength
enhancement is obtained for all the water to binder ratios used (0.4-0.6).
iii) The contrasting roles played by PFA and Metakaolin in the strength development,
particularly at the early stages, can be compared to produce effective blends for
cement. At short curing times, only mixtures with low PC replacement levels and high
MK/PFA ratios achieve strength in excess of the control. However, after 90 days
curing, mixtures with high PC replacement levels and low MK/PFA ratios also
achieve strengths in excess of the control.
iv) The incorporation of small quantities of PFA, as partial cement replacement, results in
an acceleration of PC hydration, which in turn gives rise to increased strength.
M.Frias, M.I.Sanchez derojas, J.Cabrera (2000) In their experimental work, the influence
of the pozzolanic activity of the Metakaolin(MK) on the hydration heat has been studied in
comparison to the behaviors of other traditional pozzolanic materials such as flyash and silica
fume. The results revealed that MK mortars produce a slight heating increase when compared
to a 100% Portland cement mortar, due to the high pozzolanic activity of MK. With respect to
the hydration heat, MK-blended mortar showed closer behaviors to silica fume than to fly
ash.
Moises Frais, Joseph Cabrera. (2000) the authors shows the results of an investigation
focusing on the effect of Metakaolin (MK) on the micro-structure of MK-blended pastes.
Pastes containing 0%, 10%, 15%, 20% and 25% of MK were prepared at a constant
water/binder ratio of 0.55 and cured at 200c for hydration periods from 1 to 360 days. They
investigated total capillary and gel porosity evolution with the curing period and also
estimated the degree of hydration in the ordinary Portland cement and Metakaolin blended
pastes. The values of the degree of hydration are calculated from the amount of Ca(OH)2
7
present in the paste and from the data of differential thermal analysis (DTA)
thermogravimetry (TG). A good association between porosity and degree of hydration has
been established.
The total porosity decreases up to 28-56 days of curing time. They observed that, up to 28 to
56 days of curing the porosity is same for all the mixes. Beyond 56 days the porosity of all
the Metakaolin mixes increasing when compared with OPC mix. Similar phenomenon is
observed for capillary porosity. The best evidence of the influence of MK on the refineness of
the pore structure was detected in pores with radius smaller than 100 0A. Between 7-90 days,
the gel porosity of MK mixes increase, while the OPC mix remains practically constant. The
results show the necessity of obtaining important improvement in the porosity reducing the
average pore diameter and gel porosity. Measured lime contents show the total consumption
of MK (10% to 15%) at 90 days of hydration time. A good statistical relationship has been
found between the degree of hydration and the porosity.
Brooks et.al. (2000) after studying the effect of silica fume, Metakaolin, fly ash and ground
granulated blast furnace slag on setting times of high strength concrete, they concluded that
there was increase in the retarding effect up to 10% replacement of cement by Metakaolin
and as the percentage replacement is increased, the retarding effect is reduced.
Shannag (2000) designed and studied very high compressive strength of 69 to 110 MPa
along with incorporation of locally available natural pozzolana and silica fume. He concluded
that 15% replacement of cement with silica fume along with 15% natural pozzolan gave
relatively higher strength than without natural pozzolan.
A.Shvarzman, K.Kovler, G.S.Grader G.E.Shter (2001) The effect of heat treatment
parameters on the dehydroxylation/amorphization process of the kaolinite based materials
such as natural and artificial kaolin clays with different amounts of amorphous phase
(Metakaolin) was investigated by the above authors. The process of
dehydroxylation/amorphization of kaolinite were characterized by DTA/TGA with mass-
spectrometry and x-ray power diffraction. The influence of the heat treatment, temperature
and content of the amorphization phase on pozzolanic activity was studied. The results
obtained are important for an optimization of the process of the Metakaolin large scale
production and its use as a pozzolanic admixture. At the calcination temperature below 4500C
kaolin clays show relatively low level of the dehydroxylation degree, less than 0.18. In the
range from 4500C to 570
0C, the degree of dehydroxylation sharply increased to 0.95, and
finally at the temperature range between 570 and 700OC the kaolinite was fully
dehydroxylated since the only moderate change of degree of dehydroxylation was observed
in this range (from 0.95 to 1.0). It was found that the dehydroxylation is accompanied with
the kaolinite amorphization which affects the activity of additives. A method of qualitative
evaluation of amorphous phase content (APC) in treated materials was developed and applied
for characterization of the investigated samples. Therefore, even with the partial
dehydroxylation of kaolinite accompanied with approximately 55% ammorphization, the
material may be considered as very active pozzolanic admixture (according to ASTM 618).
This finding seems to be extremely important for reduced energy demand during the
production of Metakaolin.
K.A.Gruber, Terry Ramlochan, AndreaBoddy, R.D.Hooton, M.D.A.Thomas (2001) The
investigations carried out by the above authors revealed that the temperature rise in MK-PC
mortars (above 5% MK and up to at least 15% MK) is greater than that in equivalent PC
mortar (other than at very low MK levels). The increase in heat evolution during initial hours
8
of hydration was resulted from the combined effect of accelerated Portland cement hydration
and pozzolanic reaction. The temperature rise in PFA-PC mortars is less than that in
equivalent PC mortars, this is attributed to the dilution of the PC by the PFA coupled with the
latter‟s negligible pozzolanic activity during the reaction, both the rate of heat evolution and
the total heat evolved.
Xia Oquian and Zongjinli (2001) studied the stress–strain relationships of concrete
containing 0% to 15% of Metakaolin at an incremental rate of 5%. They concluded that
incorporation of Metakaolin up to 15% has increased the tensile and compressive strength
and also peak strain is increased at increasing rate of Metakaolin up to 15%. Incorporation of
Metakaolin has slightly increased the compressive elasticity modulus.
Poon et al (2001) investigated the rate of pozzolanic reaction of Meta kaolin in high
performance cement mortars. They studied the hydration progress of Metakaolin in terms of
its compressive strength, porosity and pore size distribution. They concluded that the higher
pozzolanic reactivity results in a higher rate on strength development and its pore structure
refinement for the cement pastes at earlier ages.
W.Aquino, D.A.Lange, J.Olek (2001) Attempt is made by the authors to study the influence
of SF (Silica Fume) and HRM (High Reactivity Metakaolin) on the chemistry of ASR (Alkali
Silica reaction) products. They observed that silica fume and high reactivity Metakaolin
reduce expansion due to ASR. Also they observed that the calcium content of ASR products
is increasing with time in all the samples without mineral admixtures and a lower level of
calcium was detected in samples containing mineral admixtures. In addition, X-26 ray micro-
analysis showed that calcium content increases with time in ASR products. It was found that
as ASR reaction proceeds, the calcium to silica reaction of the reaction products increases
following a linear trend. From the results it is suggested that calcium in gel products may be
responsible for expansion.
D.M.Roy, P.Arjunan, M.R.Silsbee (2001) In their investigation, effects of aggressive
chemical environments were evaluated on the mortars prepared with low-calcium fly
ash/Metakaolin (MK)/silica fume (SF)/ordinary Portland cement (OPC) and at various
replacement levels. The natural adverse chemical environmental conditions were simulated
using sulphuric acid, hydrochloric acid, nitric acid, acetic acid, phosphoric acid and a mixture
of sodium and magnesium sulphates. They proposed resistance of the above mortars against
the chemical environment was in concurrence with compressive strength measurements.
The results show some interesting trends with respect to acid resistance. Substitution of SF,
MK, or FA under certain conditions has been shown to increase the chemical resistance of
such mortars over those with plain Portland cement. The mortar made from all three series
showed poor resistance to higher acid concentrations of 5% sulphuric acid, 5% acetic acid,
and 5% phosphoric acid environments. Chemical resistance increased in the order of SF to
MK to FA series and decreased as the replacement level is increased from 0-10% weight
replacement level to 15-30% weight level. They observed that compressive strength is
increasing in the order of fly ash to Silica fume to Metakaolin.
Megat Johari M.A. et al. (2001) In their investigation, the effect of Metakaolin (MK) on the
creep and shrinkage of concrete mixes containing 0%, 5%, 10% and 15% MK has been
studied. The outcomes showed that autogenous shrinkage measured from the time of initial
set at the early age of the concrete was decreased with the inclusion of MK, but the long –
term autogenous shrinkage measured for the age of 24 hrs was increased at 5% replacement
9
level, the effect of Metakaolin has increased the total autogenous shrinkage considering from
the time of initial set. While at replacement levels of 10% and 15% it reduced the total
autogenous shrinkage. The total shrinkage (autogenous plus drying shrinkage) measured from
24 hrs was reduced by the use of MK, while drying shrinkage was significantly less for the
MK concrete than for the control concrete. At higher Metakaolin replacement levels, the total
creep, basic creep as well as drying creep was significantly reduced. On overall, compared
with the control concrete, the greater part of the total shrinkage of the MK concrete is
constituted by autogenous shrinkage, the smaller part being drying shrinkage. Particularly at
higher Metakaolin replacement levels, drying creep, basic creep and total creep were greatly
reduced.
Jamal M.Khatib, Roger M.Clay (2003)74 in their investigation, the water absorption (WA)
by total immersion and by capillary rise of concrete containing Metakaolin (MK) is studied.
Cement was partially replaced with up to 20% MK. The results show that the presence of
Metakaolin is greatly beneficial in reducing the water absorption by capillary action. There is
a systematic reduction in water absorption by capillary action with the increase in Metakaolin
content in concrete. Between 14 and 28 days curing, there is slight increase in absorption by
total immersion and by capillary rise for all MK concretes. The partial replacement of cement
with MK reduces the water penetration in to concrete by capillary action. The water
absorption of concrete by total immersion, however is slightly increased in concrete
containing Metakaolin. WA decreases with duration of curing for all MK concretes up to 14
days. Between 14 and 28 days of curing, there is a slight increase in water absorption. After
28 days of curing there is little change in WA. An increase in the total pore volume leads to
an increase in water absorption.
Sabir, B.B. et al (2002) The authors reports the influence of the composition of Portland
cement, pulverized fuel ash and Metakaolin (PC-PFA-MK) binders on sorptivity and strength
development of Portland Cement – Pulverised Fuel Ash - Metakaolin concrete cured both in
water and in air and on carbonation depth, and relates this to measured changes in
absorptivity of the concrete. Concrete mixtures covering four different total cement
replacement levels (10%, 20%, 30% and 40%) for PC-PFA-MK concrete with various
MK/PFA proportions, water and air cured for upto 18 months were investigated. The change
in compressive strength and absorptivity with age at all cement replacement levels under both
water and air curing are compared with those of the control Portland cement concrete. The
results presented in this paper from part of an investigation in to the optimization of a ternary
blended cementitious system based on ordinary Portland cement, Pulverised Fuel Ash and
Metakaolin for the development of HPC. Increasing replacement of PC with PFA in PC-PFA
air (CO2 enriched) cured concrete increases carbonation depth where as systematically
replacing the PFA with MK in PC-PFA-MK concrete reduces carbonation depth.
Jain-Tong Ding and Zongjinli (2002) investigated the properties of concrete by
incorporating 0% to 15% cement replacement by Metakaolin (or) silica fume. They
concluded that by incorporation of Metakaolin and silica fume, they can reduce the free
drying shrinkage and restrained shrinkage cracking width. Also they can reduce the chloride
diffusion rate significantly.
Luccourard et al. (2003) studied the durability of mortars containing Metakaolin. The
studies on transport and chemical behaviors by means of chloride diffusion tests and sulfate
immersion were carried out. They concluded that 10% to 15% replacement of cement by
Metakaolin lead to low decrease of workability and best mechanical performance and
inhibition effect on chloride diffusion and sulfate attack for 20% Metakaolin.
10
T.Ramlochan, et al. (2003) the expansive behaviors of heat cured mortars containing
pozzolans and slag was investigated by the authors. In almost all the mortars, the addition of
any amount of pozzolans and slag to the mixture usually reduced the onset of expansion, the
rate of expansion, and long-term expansion. However, the efficiency of a particular pozzolan
(or) slag in controlling expansion may depend on its Al2O3 content. Metakaolin, which
contains a higher amount of reactive Al2O3, was the most effective at controlling expansion at
relatively low cement replacement levels. Slag and fly ash which are also sources of Al2O3
were also effective at suppressing expansion at higher replacement levels. Silica fume was
less effective at controlling expansion at conventional replacement levels, and even at higher
replacement levels expansion may be delayed.
Zongjin Li, Zhu Ding (2003) in their investigation, the physical and mechanical properties
of Portland cement (PC) containing Metakaolin (MK) or combination of MK and slag and the
compatibility between such materials and super-plasticizers were studied.
The following conclusions are made by the authors:
MK is a new active mineral admixture used in cement concrete products. It has a positive
effect on the mechanical properties of cement. However, MK blended cement has a poorer
fluidity compared to Portland cement under the condition which used the same amount of
super plasticizer. By the addition of ultra fine slag this can be improved. By incorporating
10% MK and 20% (or) 30% ultra-fine slag jointly into PC, not only the fluidity of blended
cements was improved, but above the 28-day compressive strength of the cements was
enhanced. Metakaolin is a high active pozzolanic mineral admixture. The formula can prompt
the hydration of PC, shorten the setting time of cement, increase the water requirement and
increase the fluidity losing of the fresh paste. However, slag can delay the reaction of cement
hydration and prolong the setting time of cement paste. Both MK and slag can react with CH
released by cement clinker hydration to produce secondary C-S-H gel inside the cement paste
matrix. Therefore the macroscopic property of cement was improved. XRD analysis indicates
that more Calcium Hydroxide was consumed after adding both mineral admixtures.
Jamal Khatib and Roger (2003) investigated the water absorption by total immersion and
by capillary rise of concrete containing Metakaolin up to 20% replacement level. They
concluded that water absorption of curing for all Metakaolin concretes up to 14 days and
between 14 and 28 days of curing there is a small variation in absorption.
E.Badogiannis, V.G.Papadakis, E.Chaniotakis, S.Tsivilis (2004) in their investigation, the
effect of Metakaolin on concrete, kaolin was thermally treated at defined conditions, and the
produced Metakaolin was superfine ground. For comparison, a commercial MK of high
purity was used and the strength development of Metakaolin concrete was evaluated using
the K - value (efficiency factor). The produced Metakaolin as well as the commercial one
imparted similar behaviour with respect to the concrete strength. Both conventional and
commercial Metakaolins demonstrate very high K-values (close to 3.0 at 28 days) and are
depicted as HR pozzolanic materials that may lead towards concrete production with an
exceptional performance.
Juenger et al. (2004) studied the alkali-silica reactivity of large silica fume derived particles.
They reported that under accelerated testing agglomerated silica fume decrease expansion
when used as a 5% replacement of reactive sand.
11
Fabien Lagier, Kimberly E.Kurtis (2007) in their investigation, the research on two
Metakaolins which vary principally in their surface area, and Portland cements of varying
composition were examined via isothermal calorimetry for pastes at water cementitious
materials ratio of 0.50 containing 8% cement replacement by weight of Metakaolin. The
following preliminary conclusions are made by the authors:
i). The Metakaolins examined appear to have a catalyzing effect on cement hydration, leading
to acceleration in the reaction rates, an increased in cumulative heat evolved during early
hydration and for some cements apparently an increased intensity in heat evolved during
certain periods of each hydration. The surface area of the Metakaolin also seems to influence
these early hydration behaviors, with the higher surface area material producing a greater rate
of heat evolution, greater cumulative heat, and greater intensity during early hydration. It is
proposed that the Metakaolin may act to enhance dissolution of cementitious phases and or
by providing nucleation, in addition to increasing the solubilized aluminium in the system at
early ages.
ii). Strongly exothermic reactions appear to occur between the cements and Metakaolin
examined, particulars in the first 24 hours, and these reactions seem to be most closely allied
with the ―Third Peak‖ experiential in calorimetry related to the reaction of calcium aluminate
phases.
iii). The reaction of MK appears to be quite sensitive to variation in total alkali content in the
cement. When the alkali content increases the beginning of MK appears to result in
amplification of the third peak viewed during calorimetry. It is proposed that an increasing
rate of Metakaolin dissolution with increasing cement alkali-content may accelerate (or)
intensify the reaction of C3A phase.
David G. Snelson et al. (2008) investigated the effect of using Metakaolin and flyash as
partial replacements with cement on the rate of heat evolution during hydration. It was
observed that adding flyash to Portland cement enhanced the Portland cement hydration in
the very early stages of hydration, but at extended periods an increase in flyash replacement
causes a systematic reduction in heat output. When combining Metakaolin and flyash in
ternary blending, the Metakaolin has a dominant influence on the heat output versus time
2.3 Effect of silica fume on strength
High compressive is normally the first property associated with silica fume concrete.The
relationship between tensile, flexural and compressive strengths in silica fume concrete is the
same as those for ordinary strength concrete. Increase in compressive strength by using silica
fume also results an increase in the tensile and flexural strength. This plays an important role
when silica fume concrete is used in bridging, flooring, and roadway projects. Increased
tensile strength causes a possible reduction in slab thickness while maintaining high
compressive strengths. Hence, it reduces the overall slab weight and cost .
The stronger concrete is more brittle and silica fume concrete is no exception to this
rule. Modulus of elasticity does not follow the pattern of tensile strength, but only displays
slight increase compared to the compressive strength. Thus, high and ultra-high strength
concrete can be used for tall structures without loss of ductility .Silica fume concrete has a
very finer phase and good bonding to substrates compared to the ordinary concrete. Studies
have shown that the aggregate-cement interface changes in the presence of silica fume . By
using silica fume, the bonding to the steel fibres is significantly increased. This is particularly
12
useful in the steel fibre-silica fume modified shotcrete which is commonly used in
Scandinavia.
Short microfibers, such as glass, carbon, polypropylene, steel, and other fibres are used
as an admixture in concrete to improve the tensile and flexural properties and reduce the
drying shrinkage. Effective use of the fibres, which is consumed in very small quantities such
as 0.5% by weight of cement in the case of carbon fibres, needs good dispersion of the fibres.
The addition of untreated silica fume to microfibers reinforced cement enhances the degree of
fibre dispersion, due to the fine silica fume particles which help the mixing of the
microfibers. Silica fume also increases the structure of the fibre-matrix interface and
decreases the weakness of the interfacial zone and also the number and size of cracks .
2.4 Effect of silica fume on chemical
The reaction of calcium hydroxide with carbon dioxide in the atmosphere results
efflorescence, which is a whitish haze. Primary stage of efflorescence occurs while concrete
becomes hard. Secondary efflorescence is resulted from the weathering of the hardened
concrete. It does not only increase the aesthetic quality of the structures but it can also give an
increase in permeability, porosity, and ultimately weaker and less durable concrete. Research
has shown that addition of silica fume decreases efflorescence due to the refined pore
structure and increased consumption of the calcium hydroxide. The addition of untreated
silica fume to steel reinforced concrete enhances the corrosion resistance of the reinforcing
steel. Besides that, it also increases the concrete chemical attack resistance, whether the
chemical is acid, chloride, and sulphate. These cause reduction in the permeability .
According to the literature review , for equal strengths and any concrete strength below 40
MPa, carbonation is higher in silica fume concretes. Concrete above 40 MPa gives a
reduction in carbonation rate, but this concrete can be affected by corrosive damage due to
the reinforcement. Silica fume concrete is normally utilised when the compressive strength is
above 40 MPa .It is an issue as to whether carbonation is a serious risk. Concrete curing
procedures are necessary to ensure the optimum performance of the silica fume concrete .
Silica fume decreases bleeding significantly, because free water is used in wetting of the
large surface area of the silica fume. In addition, silica fume blocks the pores in the fresh
concrete and stops water from permeate the surface of the concrete.
2.5 Effect of silica fume on durability
The durability of silica fume concrete to freeze thaw is normally satisfactory at silica fume
content of less than 20%. Freeze-thaw durability is related to the ability to withstand changes
between temperatures above 0◦C and those below 0
◦C . Due to the presence of water, which
undergoes freezing and thawing and also in turn causes changes in volume, concrete shows a
tendency to decrease upon such temperature cycling. Air voids which are called air
entrainment are utilised as cushions to accommodate the changes in volume, thereby
improving the freeze-thaw durability. The addition of silica fume to mortar enhances the
freeze-thaw durability in spite of the poor air void system. Hence, the use of air entrainment
is still recommended. The permeability of chloride ions in concrete reduces by the addition of
untreated silica fume. In this regard, there is reduction in the water absorbance. These effects
are the cause of the microscopic pore structure which produces calcium silicate hydrate from
the pozzolanic reaction of silica fume with free lime within the hydration of concrete .
13
2.6 Effect of silica fume on temperature
Concrete with low thermal conductivity is useful for the thermal insulation of buildings. On
the other hand, concrete with high thermal conductivity is useful for decreasing temperature
gradients in structures. The thermal stress that is resulted from temperature gradients may
cause mechanical property reduction in the structure. Bridges are among the structures that
tend to encounter temperature differentials between their top and bottom surfaces. In contrast
to buildings which encounter temperature differentials; bridges do not require thermal
insulation Hence, concrete of high thermal conductivity is in demand for bridges and related
structures. The thermal conductivity can be reduced by the addition of untreated or silane
treated silica fume due to the interface between silica fume particles and cement which act as
an obstacle against heat conduction.
2.7 Effect of metakaolin on workability
Workability of concrete decreases as percentage of metakaolin or silica fume increases from
5% to 11% at intervals of 2% by replacement in OPC .By adding 10 % activated flyash in
both the mixes of silica fume and metakaoline workability is improved.
2.8 Effect of metakaolin on strength:
Calcium hydroxide accounts for up to 25% of the hydrated Portland cement, and calcium
hydroxide does not contribute to the concrete‘s strength or durability. Metakaolin combines
with the calcium hydroxide to produce additional cementing compounds, the material
responsible for holding concrete together. Less calcium hydroxide and more cementing
compounds means stronger concrete. Metakaolin, because it is very fine and highly reactive,
gives fresh concrete a creamy, nonsticky texture that makes finishing easier. Metakaolin
aggressively consumes calcium hydroxide, acid staining concrete with metakaolin added to it
might lead to disappointment. Acid stain needs the calcium hydroxide to react, and without
enough of it in the concrete, the acid stain color might not develop enough, or even not
develop at all.
2.9 Concrete deterioration caused by external agents
Concrete is inherently porous although with ‗good‘ concrete the permeability to gases and
liquids is very low. However, the outer ‗skin‘ of concrete cast against shuttering or trowelled
in some way is cement and water rich and is more porous than the body of concrete. The skin
may be quite thin—less than 1mm Agents which are aggressive to cements, e.g. acids and
sulphates, can only penetrate concrete when dissolved in water and even aggressive gases
only react with the cement hydrates in the presence of water. Two agents associated with the
deterioration of concrete are carbon dioxide and chlorides. They do not attack concrete as
such (although very high concentrations of chloride may do so) but they promote the
corrosion of embedded metals and will be dealt with . It should be pointed out that carbon
dioxide (CO2), which causes carbonation, is in practice positively beneficial to concrete since
carbonated concrete is stronger and more resistant to penetration by aggressive agents. The
confusion arises because excessive carbonation is associated with poor concrete and the
benefits of carbonation are not sufficient to turn it into good concrete.
2.9.1. Acid attack
Hydrated cement is alkaline and reacts with acids (Harrison, 1987). The effect is generally to
dissolve the cement hydrates as calcium salts. For example, hydrochloric acid (HCl) is used
14
in the chemical analysis of hardened concrete to dissolve the cement completely, the products
being soluble calcium chloride, iron and aluminium chlorides and silicic acid. All cements
except HAC are equally susceptible. However, there are a number of mitigating
circumstances and in practice acid attack is only a problem in industrial processes, in sewers
and in circumstances where the concrete is exposed to rapid flows and considerable volumes
of acid. Concrete made with insoluble aggregates, i.e. most of those used other than
limestones, exposes progressively less cement hydrate to the acid as acid attack proceeds and
the aggregate is exposed. Also the silica in the cement is dissolved as silicic acid but this
readily polymerizes to form silica gel which is insoluble and ‗clogs up‘ the pores in the
hydrated cement, thus inhibiting further ingress of acid. The aggressiveness of the acid
depends on the solubiility of its calcium salt. Thus hydrochloric acid dissolves the cement to
form calcium chloride which is very soluble and is consequently very aggressive. In contrast,
a natural acid present in acid soils, humic acid, forms calcium humate which has a low
solubility and hence the acid is not very aggressive. Oxalic acid forms insoluble calcium
oxalate and is totally non-aggressive. The surfaces of the paste exposed to the acid, becomes
coated with the insoluble salt so that reaction ceases.
Sulphuric acid forms calcium sulphate which has a limited solubility but when the water
containing sulphuric acid has a vigorous flow, as may occur in sewers, the calcium sulphate
can be physically removed by scouring as well as dissolution and considerable attack can take
place. Sulphuric acid can beformed in sewers by biological processes acting on neutral
sulphates. Sulphate attack does not appear to occur in acid conditions. Because the acid is
neutralized when it reacts the effect is usually limited to the surface but if sufficient acid is
present the reaction is progressive so that in extreme cases the concrete is eventually
completely destroyed. However, the calcium salts formed may be absorbed into the concrete
and give rise to other deterioration mechanisms. For example, hydrochloric acid may leave
high concentrations of calcium chloride in the unattacked concrete which can promote
corrosion of the reinforcement. A special case of acid attack can be caused by dissolved
carbon dioxide in soft water which behaves as a solution of ‗carbonic acid‘ H2CO2. This
forms not insoluble calcium carbonate but relatively soluble calcium bicarbonate. Attack is
only significant with high flows of soft water saturated with carbon dioxide and is generally a
surface effect since precipitation of silica gel as a result of cement hydrate dissolution inhibits
further attack. Indeed cases have been observed where such waters acting on limestone
aggregate concrete have dissolved the aggregate without significant attack on the cement
paste. When a finite quantity of acid is involved the use of limestone aggregate is beneficial
since it is itself dissolved by acids and gives extra neutralizing power. There is also a more
uniform loss of surface compared with the rough exposed aggregate surface left with
insoluble aggregates. However, with continuous flows, attack is more pronounced.
2.9.2. Sulphate attack
Two of the components of cement paste, calcium hydroxide and calcium aluminate hydrates,
react with sulphate ions in solution. The solid reaction products have larger volumes than the
initial compounds so that disruption of the paste occurs. The reaction of calcium hydroxide
with dissolved sulphate ions depends on the nature of the sulphate. Chemical reactions are
written as equations with the left-hand side of the equation being the reactants and the right-
hand side the products. The two sides are connected by an ‗arrow‘ denoting the direction of
change. However, most ionic reactions do not always go to completion but achieve an
‗equilibrium state‘ and can then proceed in either direction. This is exemplified by the
reaction between calcium hydroxide and sodium sulphate:
15
Ca(OH)2+Na2SO4 = CaSO4 + 2NaOH
The reaction goes from left to right until the concentration of sodium hydroxide (NaOH)
builds up sufficiently to stop the reaction. If further NaOH is formed the reaction can then go
from right to left. Thus the efflorescence on some clay bricks is caused by the reaction of
NaOH from cement hydration reacting with insoluble gypsum (CaSO4) in the brick to form
soluble sodium sulphate which can then migrate to the brick surface and, on drying,
crystallize. Equation above denotes the ‗equilibrium‘ condition; for example, if the
concentration of sodium sulphate is 2% only about one-fifth of the sulphate forms calcium
sulphate (Lea, 1970). In contrast, the equation with magnesium sulphate
Ca(OH)2+MgSO4 = CaSO4 + Mg(OH)2
goes wholly from left to right, because magnesium hydroxide is very insoluble and therefore
the reaction from right to left is insignificantly slow. As a result magnesium sulphate
solutions react completely with the calcium hydroxide. When the reaction goes to
completion, as with magnesium sulphate, all the free calcium hydroxide may be changed to
calcium sulphate. Calcium silicate hydrate gel (C-S-H) is only stable in the presence of
calcium hydroxide and so it partially decomposes to give more calcium hydroxide and
hydrated silica. Thus with strong solutions of magnesium sulphate not only is there a
disruption caused by the physical forces of expansion but there can also be a progressive
breakdown of the silicate structure. Ammonium sulphate, usually only encountered in
industrial or agricultural environments, is also particularly aggressive because its reaction
with calcium hydroxide goes to completion. The ammonium hydroxide formed is
continuously evolved as ammonia gas and water. It is clear that calcium sulphate cannot react
with calcium hydroxide in a significant manner because both sides of the equation will be the
same. This reaction with the calcium hydroxide is an important part of sulphate attack and is
the primary reason why magnesium sulphate (and ammonium sulphate) is so much more
aggressive than sodium sulphate and calcium sulphate. The theoretical expansion in changing
from solid Ca(OH)2 to solid Ca(SO4) is about 2.2 times.
Carbonation of hydrated cement will be discussed more fully but the effect is to convert
calcium hydroxide to insoluble calcium carbonate, with very little volume change. Calcium
carbonate does not participate in reactions with neutral sulphate solutions and thus carbonated
concrete is not susceptible to this part of sulphate attack. The better resistance of ‗real‘
concrete to sulphates compared with that expected from consideration of laboratory
experiments is probably due to the existence of a carbonated layer at the surface. It is also
likely that the presence of dissolved carbonates in seawater makes it less aggressive than its
sulphate content would suggest. In a competition for reaction with calcium hydroxide
between sulphate and carbonate, the latter will win because of the insolubility of calcium
carbonate. The other major reaction involving sulphates is with the calcium aluminate
hydrates. Controlled amounts of calcium sulphate are added to Portland cements to control
their setting and early behaviour by moderating the rate of reaction of the C3A with water.
When excessive amounts of sulphate are incorporated in the fresh concrete the reaction with
C3A may be continued after the cement has set and begun to harden. If the expansion caused
is greater than the tensile strength of the paste, disruption occurs; the disruption will be
extensive because of the wide dispersal of the sulphate. However, if the paste can cope with
the forces, expansive or shrinkage-compensated properties can be achieved. When external
sources of sulphate are in contact with hardened concrete they can react with the outer
surface, but if the concrete is porous they may be absorbed to react further into the body of
16
the concrete. In practice, therefore, sulphate attack from external sources is manifested as a
progressive weakening and disintegration of the surface. With very porous materials it is
possible for the sulphate to be absorbed to such an extent that disruption takes place more
generally but such a mechanism is normally only observed in laboratory experiments. As a
consequence, concrete which has been damaged by contact with sulphates can be repaired by
removal of the outer weakened layers until sound concrete low in sulphates has been reached.
2.9.3. Chlorides attack
The passive oxide film formed on steel surfaces in the presence of hydroxide ions can be
destroyed by high levels of ions which form soluble iron compounds. Chlorides are abundant
and are the most common cause of such depassivation. The C3A phase in Portland cement
reacts with the sulphate in the cement to form sulphoaluminates .
Chloroaluminates can also be formed and the chloride in these is rather insoluble in pore
liquid. Cements containing high levels of C3A can therefore ‗bind‘ some chloride into an
insoluble and therefore non-reactive form. Some of the chloride incorporated in fresh
concrete as an admixture or from an unwashed marine aggregate can therefore be
immobilized to some extent if there is sufficient C3A hydrate present. It appears, however,
that if sulphate and chloride are competing for reaction with C3A, the sulphate is more likely
to win. Carbonation of chloroaluminates releases the bound chloride into a free mobile form.
Chlorides in the outer carbonated zone of concrete can therefore be washed away or
alternatively washed into the uncarbonated concrete. Chloride entering concrete from an
external source is to some extent analogous to carbonation. If water with a high concentration
of chloride is in contact with concrete saturated with chloride-free water diffusion of chloride
ions into the concrete will take place in an attempt to produce a uniform chloride
concentration in the water. With concrete saturated with seawater, for example, the chloride
concentration of the internal water will be lower, because of reaction with the C3A, than that
of the body of water external to the concrete and chloride diffusion into the concrete will take
place. Of course if concrete saturated with seawater is in contact with fresh water then free
chloride ions will diffuse out of the concrete. The diffusion of chloride will be through the
water in the capillary pores and, the finer and less continuous the pores, the slower will be the
diffusion rate. In practice the ingress of chloride into concrete by diffusion is a relatively slow
process and cycles of drying followed by saturation is a much more potent mechanism for the
ingress of chloride. Overall, dense concrete of high alkalinity and low permeability can carry
higher levels of chlorides without the occurrence of corrosion than permeable carbonated
concrete. The risk of reinforcement corrosion associated with carrying levels of chloride
content in both uncarbonated and carbonated concrete .
17
Chapter – 3
MATERIALS AND METHODOLOGY
3.1 Introduction:
Cements may be defined as adhesive substances capable of uniting fragments or masses of
solid mater to a compact whole (Lea, 1970). Portland cement was invented in 1824 by an
English mason, Joseph Aspdin, who named his product Portland cement because it produced
a concrete that was of the same color as natural stone on the Isle of Portland in the English
Channel. Raw materials for manufacturing cement consist of basically calcareous and
siliceous material. The mixture is heated to a high temperature within a rotating kiln to
produce a complex group of chemicals, collectively called cement clinker (Neville, 1987).
Cement is distinct from the ancient cement. It is termed hydraulic cement for its ability to set
and harden under water. Briefly, the chemicals present in clinker are nominally the four
major potential compounds and several minor compounds. The four major potential
compounds are normally termed as tricalcium silicate (3CaO.SiO2), dicalcium silicate
(2CaO.SiO2), tricalcium aluminate (3CaO.Al2O3) and tetracalcium aluminoferrite (4CaO.
Al2O3.Fe2O3).
The American Society for Testing and Materials (ASTM) Standard C 150, Specification for
Portland cement, provides for the following types of Portland cement:
Type I General Portland cement
Type II Moderate-sulfate-resistant cement
Type III High-early-strength cement
Type IV Low–heat-of-hydration cement
Type V High-sulfate-resistant cement 9
Type I Portland cement is a general cement suitable for all uses where special properties of
other cements are not required. It is commonly used in pavements, building, bridges, and
precast concrete products.
Type II Portland cement is used where precaution against moderate sulfate attack is important
where sulfate concentrations in groundwater or soil are higher than normal, but not severe.
Type II cement can also be specified to generate less heat than Type I cement. This moderate
heat of hydration requirement is helpful when placing massive structures, such as piers,
heavy abutments, and retaining walls. Type II cement may be specified when water-soluble
sulfate in soil is between 0.1 and 0.2%, or when the sulfate content in water is between 150
and 1500 ppm. Types I and II are the most common cements available.
Type III Portland cement provides strength at an early age. It is chemically similar to Type I
cement except that the particles have been ground finer to increase the rate of hydration. It is
commonly used in fast-track paving or when the concrete structure must be put into service
as soon as possible, such as in bridge deck repair.
Type IV Portland cement is used where the rate and amount of heat generated from hydration
must be minimized. This low heat of hydration cement is intended for large, massive
structures, such as gravity dams. Type IV cement is rarely available.
Type V Portland cement is used in concrete exposed to very severe sulfate exposures. Type V
cements would be used when concrete is exposed to soil with a water-soluble sulfate content
of 0.2% and higher or to water with over 1500 ppm of sulfate. The high sulfate resistance of
Type V cement is attributed to its low tricalcium aluminate content.
18
3.2 Cement Replacement Material
With the extensively use of cement in concrete, there has been some environmental concerns
in terms of damage caused by the extraction of raw material and CO2 emission during cement
manufacture. This has brought pressures to reduce the cement consumption in the industry.
At the same time, there are getting more requirements for enhancement in concrete durability
to sustain the changing environment which is apparently different from the old days.
With the development in concrete technology, cement replacement materials (CRM) have
been introduced as substitutes for cement in concrete. Several types of materials are in
common use, some of which are by-products from other industrial processes, and hence their
use may have economic advantages. However, the main reason for their use is that they can
give a variety of useful enhancements or modifications to the concrete properties. All the
materials have two common features (Malhotra, 1986):
i) Their particle size range is similar to or smaller than that of Portland cement.
ii)They are pozzolan material. 3.2.1 Pozzolanic Behavior
A common feature of nearly all CRM is that they exhibit pozzolanic behaviour. Pozzolanic
materials the materials which contains active silica (SiO2) and is not cementitious in itself but
will, in a finely divided form and in the presence of moisture, chemically react with calcium
hydroxide at ordinary temperatures to form cementitious compounds (Malhotra, 1983).
3.2.2 Types of Cement Replacement Material
The main cement replacement materials in use world-wide are:
Fig.3.1 Silica fume powder fig.3.2 scanning electron microscope
micrograph of silica fume particles at
20000 x
3.2.2.1 Silica fume
Silica fume, also referred to as microsilica or condensed silica fume, is a byproduct material
that is used as a pozzolan This byproduct is a result of the reduction of high-purity quartz
with coal in an electric arc furnace in the manufacture of silicon or ferrosilicon alloy. Silica
fume rises as an oxidized vapor from the 2000°C (3630°F) furnaces. When it cools it
condenses and is collected in huge cloth bags. The condensed silica fume is then processed to
remove impurities and to control particle size. Condensed silica fume is essentially silicon
19
dioxide (usually more than 85%) in noncrystalline (amorphorous) form. Since it is an
airborne material like fly ash, it has a
spherical shape. It is extremely fine with particles less than 1 μm in diameter and with an
average diameter of about 0.1 μm, about 100 times smaller than average cement particles.
Condensed silica fume has a surface area of about 20,000 m2/kg (nitrogen adsorption
method). For comparison, tobacco smoke‘s surface area is about 10,000 m2/ kg. Type I and
Type III cements have surface areas of about 300 to 400 m2/kg and 500 to 600 m2/kg
(Blaine), respectively. The relative density of silica fume is generally in the range of 2.20 to
2.5. Portland cement has a relative density of about 3.15. The bulk density (uncompacted unit
weight) of silica fume varies from 130 to 430 kg/m3 (8 to 27 lb/ft3).Silica fume is sold in
powder form but is more commonly available in a liquid. Silica fume is used in amounts
between 5% and 10% by mass of the total cementitious material. It is used in applications
where a high degree of impermeability is needed and in high strength concrete. Silica fume
must meet ASTM C 1240. And ACI 234 (1994) and SFA (2000) provide an extensive review
of silica fume. It is very fine no crystalline silica manufactured by electric arc furnaces as a
by-product of the production of metallic silicon or ferrosilicon alloys. The raw materials are
coal, quartz, and woodchips . The smoke that produced from furnace operation is stored and
sold as silica fume rather than being land filled. As the silica fume powder particles are
hundred times finer than ordinary Portland cement, there might be problems arise when deals
with silica fume, such as dispensing consideration, transportation, and storage that must be
taken into account. To overcome some of these difficulties, the material is commercially
divided in various forms. The difference between these forms is the size of the particle which
do not significantly affect the chemical make-up or reaction of material. This difference has
effect on the different purposes of use. Thus, careful consideration is needed when choosing
the type of silica fume for specific application. The properties of silica fume depend on the
type of producing and the process used for its manufacture. It is in form of spherical particle
shape. It is a powder with particles having diameters 100 times smaller than Portland cement
particles . Silica fume comes in three forms of powder, condensed, and slurry. Its colour
varies from light to dark grey which depends on the process in the manufacturing and is
influenced by some parameters such as wood chip composition, furnace temperature, ratio of
wood chip to the coal used, exhaust temperature, and type of metal produced.
For undensified silica fume, bulk density is in range of 200-350 kg/m3. Due to the low bulk
density, this form is considered impractical to be utilised in normal concrete production .
Undensified silica fume is commonly used in refractory products and formulated bagged
material such as mortars, grouts, protective coatings, and concrete repairs system.
For this type of silica fume, bulk density is in range of 500 -650 kg/m3.In the densification
process the ultra fine particles become loosely agglomerated which makes the size of
particles larger. Hence, the powder becomes easier to be used, with less dust compared to the
intensified forms. This material is commonly used in those processes that utilise high shear
mixing facilities such as concrete roof tile works, pre-cast works, and ready mixed concrete
plants with wet mixing units .
Silica fume is produced during a high-temperature reduction of quartz in an electric arc
furnace when the main product is silicon or ferrosilicon. The chemical process is complex
and it depends on the temperature of the producing. The Si formed, initially plays important
intermediate roles.
At temperatures > 1520 0C
SiO2 + 3C = SiC+2CO
20
At temperatures > 1800 0C
3SiO2+2SiC = Si+4SiO+2CO
The unstable gas diffuses in the furnace where it reacts with oxygen to give the silicon
dioxide
4SiO+2O2 = 4SiO2
With the addition of silica fume, the slump loss with time is proportionally increased in
concrete mix. Due to the high surface area of silica fume particles in the concrete mix,
workability and consistency of concrete decrease . These are restraints against the suitable
utilisation of silica fume concrete. However, the consistency of silica fume mortar is
significantly increased by either using silane treated silica fume, i.e., silica fume which has
been coated by a silane coupling agent prior to incorporation in the mix, or utilising silane as
an additional admixture .
Vibration reduction is useful for structural stability, hazard mitigation, and structural
performance improvement. Effective vibration reduction requires both stiffness and damping
capacity. Silica fume is effective for increasing both damping capacity and stiffness. Sound
or noise absorption is helpful for numerous structures, such as noise barriers and pavement
overlays. The addition of silica fume to the concrete increases the sound absorption ability .
3.2.2.2 METAKAOLIN
Fig.3.3 Metakaolin powder fig.3.4 scanning electron microscope
micrograph of calcined clay particles
at 2000x
Calcined clays are used in general purpose concrete construction much the same as other
pozzolans. They can be used as a partial replacement for the cement, typically in the range of
15% to 35%, and to enhance resistance to sulfate attack, control alkali-silica reactivity, and
reduce permeability. Calcined clays have a relative density of between 2.40 and 2.61 with
Blaine fineness ranging from 650 m2/kg to 1350 m
2/kg. Calcined shale may contain on the
order of 5% to 10% calcium, which results in the material having some cementing or
hydraulic properties on its own. Because of the amount of residual calcite that is not fully
calcined, and the bound water molecules in the clay minerals, calcined shale will have a loss
on ignition (LOI) of perhaps 1% to 5%. The LOI value for calcined shale is not a measure or
indication of carbon content as would be the case in fly ash. Metakaolin, a special calcined
21
clay, is produced by low temperature calcination of high purity kaolin clay. The product is
ground to an average particle size of about 1 to 2 micrometers. Metakaolin is used in special
applications where very low permeability or very high strength is required. In these
applications, metakaolin is used more as an additive to the concrete rather than a replacement
of cement typical additions are around 10% of the cement mass. Natural pozzolans are
classified by ASTM C 618 (AASHTO M 295) as Class N pozzolans ACI 232 (2000)
provides a review of natural pozzolans.
Metakaolin is classified as a new generation of supplementary cementitous material.
Supplementary cementitious materials (SCMs) are finely ground solid materials that are used
to replace part of the clinker in a cement or cement in a concrete mixture. Use of metakaolin
Where , fck = Characteristics Compressive Strength at 28 days
K = Statistical value for risk factor
S = Standard Deviation
Fck = 40 + (1.65 × 5) = 48.25 N/mm2
2. Selection of Water-Cement ratio:
So, Assumed W/C = 0.4 (As per IS 456 – 200)
W/C As per IS 20262 we have 0.38 from graph.
Therefore, Considering W/C =0.4
3. Selection of Water & Sand content:
W/C = 0.4
Taking Cement upto 400 kg/m3
As per IS 456 for M40 grade minimum cement content is 360 kg/m3
Therefore as Weight of Cement taken is 400 kg/m3 .
Weight of water = 0.4 × 400
= 160 kg water
Assumed 1kg = 1 liter, Hence Water requirement is 160 liters.
Now for M40 as per IS Maximum cement content is 180 kg which is greater than calculated
hence ok.
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4. Calculation of C.A & F.A
V = [(W + C/SC) + (1/P × F.A/SF.A)] × 1/1000
and
V = {(W + C/SC) + [1/(1-P) × C.A/SC.A]} × 1/1000
Now as per IS – 20262, 2% is considered as air entrapment
V = 1- 0.2
= 0.98
Therefore, Weight of F.A = 680 kg
Weight of C.A = 1160 kg
Hence, Cement : F.A : C.A = 1 : 1.7 : 2.9
And W/C = 0.4
3.10 Experimental Investigation for Durability concepts regarding Acid Attack on
Concrete:
The materials used for this purpose is as listed above in and tested as per the code provisions
made in the above clauses (4.1 – 4.4)
Even the mixes and mix proportion made according to the requirement is also mentioned in
the above clause (4.5). BIS code procedure as per IS: 10262-1982 was followed for finding
the mix proportions of all the concrete specimens.
Water binder ratio was considered as 0.4 to the optimum.
The characteristics, physical and chemical properties of basic materials are listed in table 4.5.
The concrete mix used is of grade M40 whose mix proportions are as followed :
Concrete grade
Materials required in per m3 of concrete Water requirement
(litres) Cement
(kg)
Fine aggregates
(kg)
Coarse
aggregates (kg)
M40 400 680 1160 160
3.10 Testing methods for durability assessment :
The assessment of blended concrete in acidic environment was made based on the
performance from visual assessment, mass loss and strength deterioration factor.
38
3.11.1 Visual assessment :
Cubical specimens of 150x150 mm were casted for visual assessment and the prepared
specimens were cured in water for 28 days and were immersed in 5% HCl solutions for next
30 days. The specimens were positioned so that all sides were in contact with the solutions.
The pH5 of the solution was regularly monitored and adjusted to keep constant by replacing
the consumed solutions by fresh solutions. The visual observation of acid attack was made as
per the performance scale mentioned in Table 4.6 followed by Al-Tamimi. Table 3.6 Scale of visual deterioration level of concrete specimens immersed in acidic solution
Scale Deterioration level
0 No Attack
1 Very slight attack
2 Slight attack
3 Moderate attack
4 Severe attack
5 Very severe attack
6 Partial disintegration
3.11.2 Mass loss
The concrete cubes of 150 mm size were cast for finding the mass loss due to the acid attack.
The prepared cubes were cured in water for 28 days and were immersed in 5%HCl solutions
for next 30 days. The initial mass and the mass of concrete specimens after the immersion
period of 2, 4 weeks were measured for finding the mass loss due to the deterioration of
concrete specimens. The average value of three specimens was considered for assessment.
3.11.3 Strength deterioration factor (SDF)
The deterioration of concrete cube specimens was investigated by measuring the strength
deterioration factor expressed in percentage and it was calculated by using the equation -
Where, fcw is the average compressive strength of concrete cubes cured in water and fca is
the
average compressive strength of cubes immersed in acid solutions.
The compressive strength test was carried out for each specimen in both the solutions after 4
weeks of immersion period. In each test period, the average value of three specimens were
tested and reported.
39
Chapter – 4
RESULTS AND DISCUSSION OF EXPERIMENTAL WORK
4.1 Introduction
Results of fresh and hardened concrete with partial replacement of silica fume and
metakaoline in combination are discussed in comparison with those of normal concrete.
For the combinations of concrete mixes three cubes were being casted each for varying
curing days 3,7,28 days. Test for the same being conducted under compressive testing
machine of capacity 2000KN.
4.2 Result of concrete testing for cubes casted :
Result of 3days strength of concrete
Table 4.1 Strength of plain Concrete (3 days)
Sr. No. Area 3 days strength of cubes
Load
(KN)
Strength
(N/mm2)
Avg. Strength
(N/mm2)
1.
22500
688.18 30.586
30.855 2. 680.602 30.249
3. 713.925 31.73
Table 4.2 Strength of 10% Metakaoline Replacement (3 Days)
Sr. No. Area 3 days strength of cubes
Load
(KN)
Strength
(N/mm2)
Avg. Strength
(N/mm2)
1.
22500
661.95 29.420
29.770
2. 675.29 30.013
3. 672.232 29.877
Table 4.3 Strength of 10% Silica Fume Replacement (3 days)