2. cement composition and special cements - part 2

7/30/2019 2. Cement Composition and Special Cements - Part 2

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Typical composition

Compound Composition

C3S: 4560% C2S: 1530%

C3A: 612%

C4AF: 68%

Gypsum ~ 4%

Oxide Composition

CaO: 6067% SiO2: 1725%

Al2O3: 38%

Fe2O3: 0.56% MgO: 0.54%

Alkalis (as Na2O): 0.31.2%

SO3: 2.03.5% Loss of ignition - 2 %

Insoluble residue0.5 %

Additivesup to 5% 1


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Types of cements

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Cements are classified based on:

Chemical CompositionPhysical properties

Additives to the cement powder

Special purpose

ASTM Classification (ASTM C150)

Type I: General purpose (Type IA for air entrained cement)

Type II: Moderately sulphate resistant, and moderate heat of

hydration (Type IIA for air entrained cement)

Type III: High early strength

Type IV: Low heat of hydration

Type V: Sulphate resistant


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ompoun compos t on

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ASTM

TypeC3S (%) C2S (%) C3A (%) C4AF (%)

I 45-55 20-30 8-12 6-10II 40-50 25-35 5-7 10-15

III 50-65 15-25 8-14 6-10

IV 25-35 40-50 5-7 10-15

V 40-50 25-35 0-4 10-20

In general, in relation to Type I cement,

Type II has marginally lower C3S and C3A

Type III has marginally higher C3S, and a higher fineness

Type IV has lower C3S (lower than Type II) and C3A

Type V has lower C3A (lower than Type IV)

ASTM C 595 also classifies two blended cements

Portland Slag Cement (Type IS) consists of 2570% slag by mass

Portland Pozzolana Cement (Type IP) consists of 1540% fly ash


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BIS classifies cements into the following major categories:

Ordinary Portland Cement 33 gradeIS:269 (1989)

43 gradeIS:8112 (1989)

53 gradeIS:12269 (2004)

Portland Cement, Low HeatIS:12600-1989

Rapid Hardening Portland CementIS:8041-1978Portland-Pozzolana Cement (PPC)IS:1489-1976

Portland-Slag Cement (PSC)IS 455-1976

Sulphate Resisting CementIS 12330

OPC vs. PPC

1. Availability

2. Strength and durability of concrete

BIS Classification


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Expansive cements (Shrinkage compensating) ASTM 845-90

Expansion upon hydration

Alumino-sulphate additives that cause extensive ettringite

formation in the early stages of cement hydration.

Rapid setting cement

Mixture of Plaster of Paris or Calcium Aluminate Cement

with OPC

Setting within 1015 minutes is desired.

White cement (IS 8042)

low in Fe2O3 (Max. 1%), is used for architectural

purposes, and to make coloured concrete (by use of

pigments).

Cements for special purpose


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Oil Well Cements

Used for cementing steel castings to rock formationsduring oil drilling. The cement is pumped as slurry,

which needs to be fluid under service conditions, and

then harden quickly.

Reduced C3A and fineness, and sometimes retarders

are used for setting and accelerators for strength gain

Masonry cements (IS 3466)

Mixture of OPC clinker, gypsum, and limestone

powder, along with an air-entraining plasticizer.

Provide better applicability to masonry mortar.


C f i l


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Supersulphated cements (IS 6909, BS 4248:1974)

Based on blast furnace slag (80%), with a high amount

of gypsum (15%), along with a little PC clinker or limeas activators.

Fineness 400500 m2/kg

highly resistant to sulphate and marine environments

Slow hydration leads to very little heat (200 J/g).

Calcium aluminate cements (High Alumina Cement)

Prepared using limestone and bauxite as raw materials Resultant cement has CA as its main ingredient

highly resistant to acidic and sulphate environment

Major problem - loss of strength with age

CA cement is used in refractory linings for furnaces



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Hydrophobic Cement (IS 8043-1991)

Water repellent chemicals to OPC clinker at the grinding

stage

Can be stored under humid and damp conditions forprolonged periods

Film around cement grain breaks down when vigorously

mixed with aggregates.

Slightly longer mixing time for making concrete with

Hydrophobic Cement


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Phase systems

A molten mixture of the calcined feedstock can crystallizeinto various different compositions upon reachingequilibrium in the cooling process.

Based upon the starting composition of the raw materials,the final phase assemblage that forms will depend on thenumerous phase diagrams that exist within the CaO SiO2

Al2O3Fe2O3 system.

These include binary, ternary, and quaternary phasediagrams, depending on whether the system has two, three,or four components.

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Ternary phase systems Two primary systems exist for cement:

CaO-SiO2-Al2O3 and CaO-Al2O3-Fe2O3

The first system is composed of binary phases that

make up nearly 90% of Portland cementC3S, C

2S,

C3A, C12A7

Lime-rich portion of phase diagram significant for PC

The second system is composed of various solid

solutions; C4AF is also one

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C-S-A system

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12http://www.ce.berkeley.edu/~paulmont/165/expansive_cements.pdf


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Some basics of Phase Diagrams

Lets consider a simple system of sugar and water


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Oil Well Cement- Composition

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Oxide % Compound %

CaO 64 C3S 62

SiO2 22 C2S 15

Al2O3 3 C3A 1Fe2O3 5 C4AF + 2C3A 16

MgO 1

SO3 2.2LOI 0.60

IR 0.30

2. cement composition and special cements - part 2

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