Hydration Process

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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