CEMENT

INTRODUCTION Cement is a commonly

used binding material in construction.

It is obtained by burning a mixture of calcareous(calcium) and argillaceous materials at very high temperature and grinding the product(clinker) to a fine powder.

HISTORY Cement was first produced

by Joseph Aspidin, a mason from England. He patented it in 1842 as Portland cement, as its colour resembled a variety of sandstone found in Portland, England, after it was set. The first cement factory in India was established in Chennai, Tamil Nadu, in 1904 by South India Industry Limited.

Today India has more than hundreds of large cement plants and hundreds of smaller ones. In 2011 Aditya Birla Group boasted a capacity to produce 52 million tonnes of cement pr annum in the country.

LEARNING OBJECTIVES

Chemical composition and chemistry of hydration of cement.

Manufacture of ordinary Portland cement in detail.

Chemical and physical properties of good cement and methods to test the same.

Varieties of cement. Methods of Storage and uses of cement.

CHEMICAL COMPOSITION OF RAW

MATERIALS OF OPC INGREDIENT

CONTENT(%)

RANGE(%)

Lime CaO

62 60 – 67

Silica SiO2

22 17 – 25

Alumina Al2O3

5.5 3 – 8

Iron Oxide Fe2O3

3 0.5 - 5.0

Calcium Sulphate CaSO4 3.5 3 – 4

Magnesia MgO

2 0.1 - 3.0

Sulphur trioxide SO3 1 1 - 3.0

Alkalis 1 0.4 - 1.3

Lime impart strength to cement. But if added in excess it makes cement unsound and causes disintegration.

Cement strength increases when more silica is added to it. This prolongs its setting time.

Alumina imparts a quick setting property, but when used in excess weakens the cement.

Iron oxide imparts colour and strength. Calcium sulphate in the form of gypsum,

increases the initial setting time. Magnesium and Sulphur are added in small

quantities to produce good quality cement. Alkalis, if used in excess, cause efflorescence and

staining.

SETTING & HYDRATION OF

CEMENT When water is added to cement, a

chemical reaction known as hydration takes place. Cement starts loosing its plasticity because of this. The time taken from the stage that water is added till the time cement starts loosing its plasticity is known as the initial setting time. The final setting time is the intervening time between adding water to cement, till the complete loss of plasticity. During hydration a lot of heat is given out. Hydration period extend to over a year. As hydration takes place, cement binds its own particles as well as any inert materials like sand and jelly around it. Finally its set into a hard mass quite resistant to pressure.

COMPONENTS IN OPC

There may be small quantities of impurities such as calcium oxide(CaO) and magnesium oxide(MgO2)

Tricalcium silicate 40%

Dicalcium silicate 30%

Tricalcium aluminate 11%

Tetracalcium alumino ferrite 11%

CHEMICAL PROCESS IN HYDRATION

When water is added to cement, tricalcium aluminate (C3A) is first to react and set. It generates a lot of heat. Tricalcium silicate (C3S) hydrates early and develops strength in first 28 days. It also generates heat. Dicalcium silicate(C2S) hydrates slowly and is responsible for increase in ultimate strength. Tetracalcium alumino ferrite(C4AF) is a comparatively inactive compound.

BALL MILL FOR GRINDING CYLINDERS

TUBE MILL

PHYSICAL REQUIREMENTS

1. Fineness: Measured in terms of percentage of weight retained on a sieve after sieving, it should be more than 10%.

OR Surface area of cement in square

centimetres per gram of cement, it should not be less than 2250cm/gm.

2. Setting Time: The minimum initial setting time is 30 min and maximum final setting time is 600 min.

3. Soundness: There should not be any volumetric change after concrete hardens. If so it is said to be unsound.

4. Compressive strength: 1 part of cement and 3 parts of standard sand should show a minimum compressive strength of 16N/mm after 3 days and 22N/mm after 7 days of curing.

TYPES OF CEMENT

Many varieties of cement ,each for different requirements

DIFFERENT TYPES OF CEMENT ARE :

PORTLAND POZZOLANA CEMENT(PPC): Volcanic powder found in Italy .it can be processed from shales and clay too . Pozzolana imparts higher degree of sulphur resistance and property of water-tightness to cement.

BLAST FURNACE SLAG CEMENT: Slag is a waste product obtained during manufacture of pig iron . This type of cement is produced by grinding cement clinkers with 60-65% slag . Its durable, but gains strength slowly . Properties sim~ OPC , but is cheap .

HIGH ALUMINA CEMENT : Manufactured by calcining a mixture of lime and bauxite .It develops almost full strength within 24 hours of adding water . Its used for under water concrete works.FLY ASH BLENDED CEMENT: A by-product in coal –based thermal plants. Highly efficient in resistance to weathering action .Though their gain of strength is slow ultimate strength=OPC. Popular brands are Birla Plus and Birla Star .

LOW-HEAT CEMENT : In mass concreting works like construction of dams, heat producing during the hydration of cement cannot disperse easily giving rise to cracks . Here, this type of cement containing 5%(C3A) and 46%(C2S)supports.

EXPANDING CEMENT: Expansion occurs as it sets.Addition of sulpho-aluminate imparts

this property .Used for filling cracks in concrete structures .

RAPID HARDENING CEMENT : Produced by increasing lime content and burning at hightemperatures Grinding to finersize is also necessary . Cementhardens and gains strength rapidly . Used for road and multi-storey building construction .QUICK SETTING CEMENT : Starts setting within 5 minutes after adding water .Property gained by reducing gypsum and adding aluminum sulphate. Under water or under slow running water concreting purpose.

WHITE CEMENT AND COLOURED CEMENT

If oxides of iron or manganese and chlorines are avoided and during manufacture oil fuel is used instead of coal ,

White cement is produced.For Colored cement : Adding CHLORIDE OXIDE (GREEN)Co OXIDE (BLUE)IRON OXIDE (BROWN ,RED , YELLOW)Mn OXIDE (BROWN OR BLACK)Both used for ornamenting ,flooring ,even walls and roofs .

ACID-RESISTANT CEMENT AND

SULPHATE-RESISTANT CEMENT

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ARC: This type of cement are produced by adding acid-resistant aggregates such as quartz, quartzite and sodium

silicate. It is commonly used in chemical factories .SRC: This cement is produced by keeping the percentage of tricalcium aluminate below 5% .It is used to construct

structures that are likely to be damaged in alkaline conditions

Such as canals and culverts .

USES OF CEMENT

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1.CEMENT SLURRY FOR FILLING CRACKS IN

CONCRETE STRUCTURES .2.CEMENT MORTAR FOR

BUILDING, PLASTERING AND PAINTING MASONRY

STRUCTURES.3.CONSTRUCTION WORKS OF BUILDINGS ,BRIDGES , LAMP

HOLDERS , DUST BINS , GARDEN SEATS , ROADS AND

FOOT PATHS ETC

By Amina, Reshma & Nilopher