What Is Cement| Composition Of Cement| Bogue Compounds| Types of Cement| Storage Of Cement| Test on Site| Setting of Cement|

Cement

Cement  is a binding material which is obtained by mixing together at high temperatures calcareous, siliceous and argillaceous raw materials mixed in different proportion and crushing the resulting clinkers to a fine powder.

Portland Cement

• Ordinary cement is usually called ordinary Portland cement.
• The ordinary cement after setting resembles in color to a stone quarried near Pordand  a place in England and hence called Portland cement.
• Cement was first introduced in use by a Leeds brick layer named Joseph Aspidin in 1824.

Chemical Composition of cement

• Silica, lime and alumina are the three basic raw material of cement
• Iron oxide,sulphur trioxide and other alkalies,are also present in the cement  but in very small proportions.
• All these materials are intimately mixed and burnt st al clinkering temperature of about 1400⁰c

The Chief Ingredients And Their Proportions In Ordinary Portland Cement Are

Lime(CaO)	60-67%
Silica(SiO2)	17-25%
Alumina(Al2O3)	3-8%
Calcium Sulphate	3-4%
Iron oxide	3-4%
Magnesia (MgO)	0.1-4%
Sulphur	1-3%
Alkalies	0.2-1%

 Brief Description of Each Ingredient Is As Follows

• LIME

It is the important constituent so its proportions needs to be examined very carefully. Excess lime makes the cement unsound while as its deficiency reduces its strength and causes cement to set quickly

• SILICA

This constituent gives strength to the concrete due to formation of silicates. Excess silica increases strength of concrete but prolongs its setting time

• ALUMINA

It gives quick setting to the cement its presence in excess weakens the cement

• GYPSUM

Its addition in small quantity is responsible for delaying the initial setting of the cement

• IRON OXIDE

It gives colour strength and hardness to the cement

• MAGNESIA

It gives colour strength and hardness to the cement but excess amount makes the cement unsound.

• SULPHUR

Small amount is good but in excess it makes cement unsound

• ALKALIES

These are mostly carried away by flue gases during heating.Excess of alkalies causes number of troubles such as efflorescence, alkali aggregate reaction

Composition

Analysis Percent	Rapid Hardening Cement	Normal Cement	Low Heat Cement	Sulphate Resisting Cement
Lime	64.5	63.1	60	64
Silica	20.7	20.6	22.5	24.4
Alumina	5.2	6.3	5.2	3.7
Iron Oxide	2.9	3.6	4.6	3

Bogue Compounds

During burning and fusion all the ingredients undergo chemical combination and form what are known as bogue compounds in the finely ground cement.

Name Of Bogue Compound	Abbreviation
Tricalcium Silicate(3cao,SiO2)	C3S
Dicalcium Silicate(2CaO,SiO2)	C2S
Tri Calcium Aluminate(3CaO,Al2o3)	C3A
Tetra Calciumalumino Ferrite(4CaO, Al2O3,Fe2O3)	C4AF

Tricalium Silicate and Dicalcium Silicate are the compounds most responsible for the strength characteristics of the cement

Tricalicium Silicates

• Tricalicium Silicates hydrates and is responsible for most of early strength of concrete
• Strength acquired during first 7 days  is mostly due to hydration of Tricalcium Silicate

Dicalcium Silicate

• Dicalcium Silicate reacts with water at a very slow  rate and hence,strength of concrete after 7 days is mainly due to hydration of this compound
• Dicalcium Silicate starts contributing strength after7 days of its placement and continues for about one year

Tricalcium Aluminate

• After Addition Of Water In Cement Tricalcium Aluminate Generates Considerable Heat Which May Be Responsible For Undesirable Properties Of The Concrete.
• It is Not Contributing Any Strength to the Concrete.It Is Mainly Responsible for Setting Action of the Cement.

Tetra Calcium Alumino Ferrite

Tetra-Calcium Alumino Ferrite is more or less inactive compound and does not play any role in setting properties or hardening properties of the cement.

       Percentage of Bogue compounds

Name  of Compound	Rapid Hardening Cement	Normal Cement	Low Heat Cement	Sulphate Resisting Cement
Tri-Calcium Aluminate	9	11	6	5
Tri-Calcium Silicate	50	40	25	40
Di-Calcium Silicate	21	30	45	40
Tetra-Calcium Alumino Ferrite	9	11	14	9

Types of cement

• Ordinary Portland cement

• Rapid hardening cement

• Low heat cement

• White & Coloured cement

• Quick setting cement

ORDINARY PORTLAND CEMENT

This cement is also known as normal setting cement. It is used in all types of structures like pavements, reinforced concrete buildings, tanks culverts and all such structures where heat of hydration will not cause any defect.

RAPID HARDENING CEMENT

This cement is also known as high early strength Portland cement. Strength attained by this cement in 3 days and 7 days is almost the same as that attained by ordinary cement in 7 and 28 days respectively. It is used for high way slab which is to be opened for traffic at the earliest possible moment.

LOW HEAT CEMENT

In the case for mass concrete structures such as dams, retaining walls, bridge abutments, rate of loss of heat of hydration is much lower than that generated leads to rise in temperature inside the mass of concrete and may develop thermal and shrinkage crack. Under such circumstances low heat cement can be advantageously used

WHITE & COLOURED CEMENT

It is an ordinary Portland cement having pure white colour. Strength of this concrete is less than that of ordinary cement but it is 4 to 5 times costlier than ordinary cement

QUICK SETTING CEMENT

When concrete has to be laid under water this type of cement can be used.the setting action of this cement starts within five minutes and it becomes stone hard in less than half an hour.

STORAGE OF CEMENT

• Cement should be stored in specially constructed stores having damp proof floors, waterproof walls and leak proof roofs.
• Cement stakes stakes should be raised leaving a clear distance of 30 cm from the walls of the store.
• Height of the stake should not exceed the height of 15 bags.
• Width of the stake should be limited to 3m.

Testing of Cement on Construction Site

Color test

Color of the cement should be uniform grey

Presence of lumps

Cement should be free from lumps presence of lumps indicates the moisture in it and hence cement should be rejected

Adulteration test

Take some cement with your and start rubbing between fingers When you rub cement between finger you should fell smoothness

Temperature test

When you insert your hand into cement bag you should feel cool

Float test

Put some cement into a bucket of water before it settles down it should float for sometime

Setting test

Make a thick paste of cement by adding water on a glass plate and keep this glass plate with cement paste in water for 24 hours and after 24 hours in water  get it out from the water the paste should be free from cracks it should get set.

Date of packing

No cement can be used after 3 months from the date of manufacture

Initial setting of cement

The time at which cement starts loosening its plasticity is called initial setting of cement for ordinary Portland cement the initial setting time is 30 minutes

Final setting of cement

The time at which cement completely loses its plasticity is called final setting of cement for ordinary Portland cement the final setting time is 600 minutes