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

CONTENTThe discussion is divided into

following sections.Hydration-IntroductionHydration Process or MechanismHeat of Hydration Factors Affecting HydrationSpecial Types of CementReferences

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).

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

Structure of C-S-H gel

x

c

Structural waterAdsorbed waterCapillary poreC-S-H layerC-S-H particleC-S-H gel models

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

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

HYDRATION PROCESS -CALCIUM SILICATE

(C3S & C2S)

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

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

HYDRATION PRODUCTS

Early Porous C-S-H gel (Eternite shingle, 2100x) Late dense C-S-H gel (Eternite shingle, 800x)

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

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

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.

HYDRATION PROCESS- CALCIUM ALUMINATE

HYDRATES (C3A&C4AF)

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

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.

HYDRATION PRODUCTS

Lathshaped AFm (sulfatefree) crystals (3900x) Ettringite (sulfatefree) crystals (1500x)

Hydrogarnets (1500x)

All images are from fiber concretesamples.

w/c is 0.5 for (a)

a is 1.0 for (b)

Volume relationships

Hydration mechanisms in Portland cement

Hydration mechanisms in Portland cement

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.

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).

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

TEMPORAL EVOLUTION OF THE PRODUCTS

Temporal evolution of the hydration hydration products (Kurtis, )

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

FACTORS AFFECTING HYDRATIONChemical Composition of CementCement TypeSulfate Content Fineness of CementWater Cement RatioCuring TemperatureEffect of Admixtures

SPECIAL TYPES OF CEMENT

Acid Resistance CementBlast Furnace CementExpanding CementColoured CementHigh Alumina CementHydrophobic CementLow Heat CementOil Well CementIRS-T 40 Special Cement

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.

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.

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.

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.

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.

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.

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

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.

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.

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.

Queries?Thanking You