hydration of cement
TRANSCRIPT
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HYDRATION OF CEMENT
Presented By,D.SARATHKUMAR.,B.E.,(710015813007)II-Year- M.E-Structural Engineering(Part Time)Anna University Regional Campus,Coimbatore-641 046
&
SPECIAL TYPES OF CEMENT
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CONTENTThe discussion is divided into
following sections.Hydration-IntroductionHydration Process or MechanismHeat of Hydration Factors Affecting HydrationSpecial Types of CementReferences
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HYDRATION- INTRODUCTION
Chemical reaction take place between cement and water is referred as hydration.
Hydration is the reaction(Series of chemical reactions) of cement with water to form the binding material(C-S-H Gel).
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Structure of 1.4 nm tobermorite, a sheet like silicate composed ofoctahedral layers and silicate chains. The silica tetrahedra can be replaced by hydroxil ions. If part the bridging tetrahedra (B) are replaced only paired groups remain explaining the dimer signal in NMR studies.
Structure of C-S-H gel
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Structure of C-S-H gel
x
c
Structural waterAdsorbed waterCapillary poreC-S-H layerC-S-H particleC-S-H gel models
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HYDRATION- INTRODUCTION
Name of the Compound
Formula Abbreviated Formula
Percentage
Tri-calcium Silicate
3CaO.SiO2 C3S 25-50
Di-calcium Silicate
2CaO.SiO2 C2S 20-45
Tri-Calcium Aluminate
3CaO.Al2O3 C3A 5-12
Tetra Calcium Aluminoferrite
4CaO.Al2O3.Fe2O3
C4AF 6-12
Bogue’s Compounds
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HYDRATION- INTRODUCTION
In presence of water, the silicates(C3S and C2S) and Aluminates(C3A and C4AF) form products of hydration which in time produce a firm(Solid) and hard mass - the hydrated cement paste
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HYDRATION PROCESS -CALCIUM SILICATE
(C3S & C2S)
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HYDRATION PROCESS-C3S
2(3CaO.SiO2)+6H2O 3 CaO.2SiO.3H2O + 3Ca(OH)2
OR
2C3S+6H
C3S2H3 + 3Ca(OH)2
Tri-calcium Silicate hydrates rapidly and forms earlier strength of the concrete .
C3S produce more amount heat during hydration process.
Cement with more content of C3S is better cold weather concreting.
Calcium Silicate Hydrates
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SEM micrographs of fractured C3S pastes (w/c = 0.4) in pure water at (A) 7 days, (B) 13 days, (C) 1 month of hydration
HYDRATION PRODUCTS
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HYDRATION PRODUCTS
Early Porous C-S-H gel (Eternite shingle, 2100x) Late dense C-S-H gel (Eternite shingle, 800x)
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HYDRATION PROCESS-C2S
2(2CaO.SiO2)+4H2O 3CaO.2SiO.3H2O + 3Ca(OH)2
OR
2C2S+4H
C3S2H3 + Ca(OH)2
Di-calcium Silicate hydrates slowly and it is responsible for progressive strength of the concrete.
C3S produce less amount heat during hydration process.
Responsible for major strength of concrete.
Calcium Silicate Hydrates
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The other products of hydration of C3S and C2S is Calcium Hydroxide.
Lack of durability of concrete, is on account of the presence of calcium Hydroxide.
Ca(OH)2 reacts with sulphates presents in soil or water to form Calcium Sulphate which further reacts with C3A and causes the deterioration of concrete. This reaction is known as the sulphate attack.
HYDRATION PROCESS- CA(OH)2
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HYDRATION PROCESS- CA(OH)2
The use of blending materials such as fly ash ,silica fume& other pozzolanic materials are steps to over come the sulphate attack.
Pozzolan + Calcium hydroxide+ water C-S-H (Gel)
Only advantage is that Ca(OH)2,being alkaline in nature maintain pH value around 13 in the concrete which resists the corrosion of reinforcements.
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HYDRATION PROCESS- CALCIUM ALUMINATE
HYDRATES (C3A&C4AF)
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HYDRATION PROCESS-C3A
3CaO.Al2O3+H2O 3CaO.Al2O3.6H2OOR
C3A + H
C3AH6
Tri-calcium Aluminate hydrates rapidly about 225o C.
C3A produce large amount heat during hydration process.
Hydrated aluminates do not contributes anything to the strength of concrete, but it will be give durability of concrete.
Calcium Aluminate Hydrates
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HYDRATION PROCESS-C4AF
4CaO.Al2O3.Fe2O3+H2O 3CaO.Al2O3.6H2O+CaO.Fe2O3.H2O
C4AF + H
ORC3AH6
The hydrates of C4AF show a comparatively higher resistance
to the attack of sulphates.
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HYDRATION PRODUCTS
Lathshaped AFm (sulfatefree) crystals (3900x) Ettringite (sulfatefree) crystals (1500x)
Hydrogarnets (1500x)
All images are from fiber concretesamples.
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w/c is 0.5 for (a)
a is 1.0 for (b)
Volume relationships
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Hydration mechanisms in Portland cement
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Hydration mechanisms in Portland cement
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HEAT HYDRATIONThe Hydration of cement with water
is exothermic.
Exothermic-An exothermic reaction is a chemical reaction that releases by light or heat.
The liberation of heat is called heat of hydration.
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HEAT HYDRATION Study and control of hydration becomes important
in mass construction(like dams.etc.,)
Heat evolution due to the reaction of solution of aluminates(C3S) and sulphates.(C3A)
Initial heat evolution ceases quickly when the solubility of aluminates is depressed by gypsum.
The next heat evolution is on account of formation of ettringite and reaction of C3S.
Ettringite-Calcium Aluminate tri-sulphate Hydrates(C6AS3H32).
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HEAT EVOLUTION DURING PORTLAND CEMENT HYDRATION
III
III
time (hours)
heat
evo
lutio
n ra
te W
/kg
Induction (dormant) period0 10 20 30
preinduction period
acceleration period
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TEMPORAL EVOLUTION OF THE PRODUCTS
Temporal evolution of the hydration hydration products (Kurtis, )
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HEAT EVOLUTION AND HYDRATION REACTIONS I
C3A hydrationFormation of ettringite
Ettringite coating retards further aluminate hydration
Ettringite to monosulfate transformation and further aluminate hydration
Relationship between reactions and heat evolution
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FACTORS AFFECTING HYDRATIONChemical Composition of CementCement TypeSulfate Content Fineness of CementWater Cement RatioCuring TemperatureEffect of Admixtures
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SPECIAL TYPES OF CEMENT
Acid Resistance CementBlast Furnace CementExpanding CementColoured CementHigh Alumina CementHydrophobic CementLow Heat CementOil Well CementIRS-T 40 Special Cement
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ACID RESISTANCE CEMENT
This Cement composed as following,1.Acid-Resistance Aggregate – Ex:
Quartz2.Additive- Ex: Sodium Fluosilicate (Na2 SiF6)3.Aqueous Solution of sodium silicate or
soluble glass. Na2 SiF6 - Accelerates the hardening and
increase the resistance of cement to acid. Binding Material of acid resistance
cement is soluble glass.
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BLAST FURNACE CEMENT For this cement Slag obtained from
blast furnace is used. The slag is waste product in the
manufacturing process of pig iron and it contains.
It contains alumina, lime and silica. This cement more or less same as
Ordinary Portland Cement. Its strength in early days is less and
hence is requires longer curing period.
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EXPANDING CEMENT This cement produced by adding an
expanding medium like Sulpo-aluminate. About 8-20 parts of the Sulpo-aluminate
clinker are mixed with 100 parts of Portland cement and 15 parts of stabilizer.
Use of expanding cement requires skill and experience.
This cement used in Water retaining Structures and repairing damaged concrete surface.
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COLOURED CEMENT Coloured cement will be obtained by mixing
of pigments with ordinary Portland cement. The amount of coloring material may vary
from 5 to 10 %. If this percentage exceeds 10 % the strength
of cement is affected.SI .No Pigment Colour
1 Chromium Oxide Green2 Cobalt Imparts Blue3 Iron Oxide in different
proportionBrown, Red, Yellow
4 Manganese Dioxide Black or Brown
oColoured cement are widely used Finishing Interior exterior, Flooring and artificial marble.
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HIGH ALUMINA CEMENT This cement produced by grinding clinkers
formed by bauxite and lime. The bauxite is an aluminum Oxide(Al2O3).
In this cement alumina content should not less then 32%.
Ratio of weight of alumina to the lime should not be between 0.85 to 1.30.
It can stand high temperature. It sets quickly and attains higher ultimate
strength short period. It is not suitable for mass construction as it
evolves great heat.
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HYDROPHOBIC CEMENT This type of cement contains admixtures which
decrease the wetting ability of cement grains. The usual hydrophobic admixtures are acidol,
naphthenesoap, oxidized petrolatum, Oletic acid and Stearic acid.
Above substance formed water repellent film around each cement grains.
This film protects them form the bad effect of moisture during storage and transportation.
The film is broken out when the cement and aggregate are mixed together at the mixer exposing the cement particles to normal hydration.
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LOW HEAT CEMENT Formation of cracks in large body of concrete
due to heat of hydration. So, concrete technologists produce a kind of
cement which produces less heat during hydration process.
This cement will be used in mass construction.
Low heat evolution is achieved by reducing the contents of C3S C3A.SI. No
Days Heat produced by low heat cement
(cal/gm)
Heat produced by OPC (cal/gm)
Cal-Calories
1 Calories = 4.2 joules
1 7 Not more than 65 89-902 28 Not more than 75 90-100
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OIL WELL CEMENT Oil well are drilled through sedimentary rocks
through a great depth of in search of oil. That oil or gas may escape through the space
b/w steel casing and rock formation. This cement may resist corrosive condition
from sulphur gases or water contains dissolved salts.
It will be used in 175oC temperature and 1300 kg/m2 pressure.
This cement obtained in two ways:i.Adjust cement compounds or adding Retarders.
ii. Adding workability agents.
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IRS-T 40 SPECIAL CEMENT This cement is manufactured as per
specification laid down by ministry of Railways under IRS-T40: 1985.
It is Very fine cement with high C3S content for high early strength.
It will be used to manufacture of concrete sleepers for Indian Railways.
This cement also used in prestressed concrete elements, high rise buildings, high strength concrete.
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REFERENCES M S Shetty, Concrete Technology Theory and Practice, S Chand
& Company Pvt Ltd,2011. Dr M L Gambir, Concrete Technology Theory and Practice, Tata
McGraw Hill Education Pvt Ltd, 2015. P Kumar Mehta, Paulo J M Monteiro, Concrete Micro Structures,
Properties and Materials, Tata McGraw Hill Education Pvt Ltd, 2008.
S C Rangwala, Engineering Materials(Material Science), Charotar Publishing House Pvt Ltd, 2009.
PPT from, Hydration of Cement, Institut de Mineralogie et Petrographiem University de Fribourg.
Dr.Abbas Oda Dawood, Concrete Technology, Lecture Notes, Department of Civil Engineering-Misan University.
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Queries?Thanking You