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For My Non Muslim Students :
"Success doesn't come to you unless you work towards achieving it
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REMINDER FOR MY MUSLIM STUDENTS
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HYDRATION PROCESSHYDRATION PROCESS
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OBJECTIVES OF LECTUREOBJECTIVES OF LECTURE
At the end of the lecture, students shouldAt the end of the lecture, students should
be able tobe able to
Define and explain the mechanism ofDefine and explain the mechanism of
hydration process in depthhydration process in depth
Explain the contribution of hydrationExplain the contribution of hydrationprocess towards concrete properties andprocess towards concrete properties and
its characteristicits characteristic
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INTRODUCTIONINTRODUCTION
Hydration is the chemical reaction that takesHydration is the chemical reaction that takes
placed when Portland cement and water areplaced when Portland cement and water are
mixed together.mixed together.
The heat generated when water and cementThe heat generated when water and cement
chemically react is called as heat of hydration.chemically react is called as heat of hydration.
Amount of heat generated dependent upon theAmount of heat generated dependent upon the
chemical composition of cement.chemical composition of cement. Rate of heat generation depends on fineness,Rate of heat generation depends on fineness,
chemical composition of cement and curingchemical composition of cement and curing
temperatures.temperatures.
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Chemical CompositionChemical Composition
Chemical Constituents OPC (%) Pozzolanic material(%)
Silicon Dioxide (SiO2) 20.2 43.6
Aluminium Oxide (Al2O3) 5.7 11.4
Ferric Oxide (Fe2O3) 3.0 4.7
Calcium Oxide (CaO) 62.5 8.4
Magnesium Oxide (MgO) 2.6 4.8
Sodium Oxide (Na2O) 0.16 0.39
Potassium Oxide (K2O) 0.87 3.5
Sulphur trioxide (SO3) 1.8 2.8
Phosporus Oxide ( P2O2) 0.87 3.5
Loss On Ignition (LOI) 2.70 18.0
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At the end of hydration process, the followingAt the end of hydration process, the following
components arecomponents area) Some unhydrated cementa) Some unhydrated cement
b) Lime crystals; Ca(OH)b) Lime crystals; Ca(OH)22c) Calcium Silicate Hydrate gel (Cc) Calcium Silicate Hydrate gel (C--SS--H)H)
d) Some minor componentsd) Some minor componentse) Residue of water filled spaces in fresh pastee) Residue of water filled spaces in fresh paste
CC--SS--H gel is main product of hydrationH gel is main product of hydration
process.process. Ca(OH)Ca(OH)22 is a non binder and vulnerable tois a non binder and vulnerable to
chemical attack.chemical attack.
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The engineering properties of concrete such asThe engineering properties of concrete such as
setting and hardening, strength & dimensionalsetting and hardening, strength & dimensionalstability depends primarily on Cstability depends primarily on C--SS--H gel.H gel.
Hydration process increase the amount ofHydration process increase the amount of
CC--SS--H gel leading to increment in the strengthH gel leading to increment in the strengthof concrete.of concrete.
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Calcium Silicate Hydrate gelCalcium Silicate Hydrate gel
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Calcium Silicate Hydrate gelCalcium Silicate Hydrate gel
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Calcium Hydroxide in hexagonal shapeCalcium Hydroxide in hexagonal shape
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Microstructure of hydrated cement pasteMicrostructure of hydrated cement paste
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Hydration ProcessHydration Process
Portland cement is not a simple chemicalPortland cement is not a simple chemical
compound.compound.
There is 4 main compounds in cement that is:There is 4 main compounds in cement that is:a) Tricalcium Silicate (Ca) Tricalcium Silicate (C33S)S)
b) Dicalcium Silicate (Cb) Dicalcium Silicate (C22S)S)
c) Tricalcium Aluminate (Cc) Tricalcium Aluminate (C33A)A)
d) Tetracalcium Alumino Ferite (Cd) Tetracalcium Alumino Ferite (C44AH)AH)
Tricalcium silicate hydrates fast and contributeTricalcium silicate hydrates fast and contribute
towards early strength developmenttowards early strength development
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Dicalcium silicate hydrates slower because it isDicalcium silicate hydrates slower because it is
less reactive and contribute towards belatedless reactive and contribute towards belatedstrength development.strength development.
Tricalcium Aluminate is an unavoidableTricalcium Aluminate is an unavoidable
content in cement & contribute slightly to earlycontent in cement & contribute slightly to early
strength.strength.
It reacts very fast and release high heat andIt reacts very fast and release high heat and
may lead to Flash Set, therefore Gypsum hasmay lead to Flash Set, therefore Gypsum has
been added to slow the reaction.been added to slow the reaction.
Tetracalcium aluminoferrite responsible to giveTetracalcium aluminoferrite responsible to give
colour to the cement.colour to the cement.
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Hydration ProcessHydration Process
Cement + HCement + H22O CO C--SS--H gel + Ca(OH)H gel + Ca(OH)22
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PozzolansPozzolans
Are siliceous or siliceous and aluminousAre siliceous or siliceous and aluminous
materials which in themselves possess little ormaterials which in themselves possess little or
no cementitious property BUT in finelyno cementitious property BUT in finely
divided form and in the presence of moisture,divided form and in the presence of moisture,
these materials can react with calciumthese materials can react with calcium
hydroxide of concrete at ordinary temperatureshydroxide of concrete at ordinary temperatures
to form compounds of cementitious properties.to form compounds of cementitious properties.
This reaction is called POZZOLANICThis reaction is called POZZOLANIC
REACTIONREACTION
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PozzolanicPozzolanic ReactionsReactions
Stage 1 : Hydration ProcessStage 1 : Hydration Process
Cement + HCement + H22O CO C--SS--H gel + Ca(OH)H gel + Ca(OH)22
Stage 2 :Stage 2 : PozzolanicPozzolanic ReactionReaction
SiOSiO22 + Ca(OH)+ Ca(OH)22 + H+ H22O CO C--SS--H gelH gel
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PozzolanicPozzolanic reaction would only take place afterreaction would only take place after
Calcium Hydroxide has been produced throughCalcium Hydroxide has been produced throughthe occurrence of hydration process.the occurrence of hydration process.
However, water is essential forHowever, water is essential for pozzolanicpozzolanic
reaction to occur & form secondary Creaction to occur & form secondary C--SS--H
gel.H
gel. Therefore, initial water curing is essential toTherefore, initial water curing is essential to
ensure faster hydration process to create a largeensure faster hydration process to create a large
amount of lime for the occurrence ofamount of lime for the occurrence of pozzolanicpozzolanic
reaction as well.reaction as well.
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Formation of additional CFormation of additional C--SS--H gel would fillH gel would fill
the existing voids in concrete thus creatingthe existing voids in concrete thus creatingdenser concrete.denser concrete.
Furthermore, reduction in amount ofFurthermore, reduction in amount of CaOHCaOH
that is vulnerable to aggressive environmentthat is vulnerable to aggressive environmentimproves the durability of concrete.improves the durability of concrete.
This finally increases the strength andThis finally increases the strength and
durability of this hardened material.durability of this hardened material. Amorphous silica reacts with Ca(OH)Amorphous silica reacts with Ca(OH)22 andand
alkalis generally more rapidly than does silicaalkalis generally more rapidly than does silica
in crystalline form.in crystalline form.
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Without POFA (left) : Internal structure More voidsWithout POFA (left) : Internal structure More voids
With POFA (right) : Denser internal structureWith POFA (right) : Denser internal structure
Concrete MicrostructureConcrete Microstructure
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Effect ofEffect of pozzolanicpozzolanic admixtureadmixture
Low early strengthLow early strength
Lower heat of hydrationLower heat of hydration
Higher ultimate strengthHigher ultimate strength
Less permeableLess permeable
Improves durability of concrete (Improves durability of concrete (SulphateSulphate, acid, acid
and ASR)and ASR)
Reduce costReduce cost
Increase workability (some of it)Increase workability (some of it)
Reduce waste ending at landfill (some of it)Reduce waste ending at landfill (some of it)
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POFA concrete is more resistant toPOFA concrete is more resistant to sulphatesulphate attackattack
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Does this find yourself in this kind of situation before this?????
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To be alive is a gift, So learn to appreciate it
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