CEMENT

CEMENT

Definition:Cement is a crystalline compound of calcium silicates and other calcium compounds having hydraulic properties (Macfadyen, 2006).

Another Definition:Cement is a powdery substance made by calcining lime and clay, mixed with water to form mortar or mixed with sand, gravel, and water to make concrete.

History:Lime and clay have been used as cementing material on constructions through many centuries.

Best known surviving example is the Pantheon in Rome

In 1824 Joseph Aspdin from England invented the Portland cementThe word "cement" can be traced back to the Roman word termed as Caementicium,

CEMENT INDUSTRY In Pakistan :The annual production of the cement at the time of the creation of Pakistan was only 300000 tones per year.Pakistan has inexhaustible reserves of limestone and clay, which can support the industry for another 50-60 years. At present there are more than 28 cement plants in Pakistan with installed capacity of over 19.5 million tonnes per annum. The present demand for cement in Pakistan is around 9.5 million tonnes per annum.

CEMENT INDUSTRY In Pakistan :ProvinceNo. of UnitsCapacity(Mil.Ton)Sindh83.364Punjab12 7.894KPK54.351Baluchistan20.723Islamabad10.990 Total2817.312

Cement production in the World

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PORTLAND CEMENTPortland cementis the most common type of cementin general use around the world, used as a basic ingredient of concrete, mortar, stucco(plaster), and most non-speciality grout.

SOURCE ROCKS

Calcareous Rocks(Limestone) Argillaceous Rocks(Clay)

RAW MATERIALS:Lime or calcium oxide, CaO: from limestone, chalk, shells, shale or calcareous rock

Silica, SiO2: from sand, old bottles, clay or argillaceous rock

Alumina, Al2O3: from bauxite, recycled aluminum, clay

Iron, Fe2O3: from from clay, iron ore, scrap iron and fly ash

Gypsum, CaSO4.2H20: found together with limestone

GYPSUM

The materials, without the gypsum, are proportioned to produce a mixture with the desired chemical composition and then ground and blended by one of two processes - dry process or wet process. The materials are then fed through a kiln at 2,600 F to produce grayish-black pellets known as clinker.

The alumina and iron act as fluxing agents which lower the melting point of silica from 3,000 to 2600 F. After this stage, the clinker is cooled, pulverized and gypsum added to regulate setting time. It is then ground extremely fine to produce cement

Decomposition of raw materials - Reactions at temperatures up to about 1300 CIt includesWater evaporation in the raw feed, if any.Loss of carbon dioxide from the limestone (ie: calcining).Decomposition of the siliceous and aluminosilicate fractions of the feed.Formation of a sulfate melt phase.The decomposition products react with lime to form intermediate compounds which in turn form other compounds as clinkering proceeds.

CaCO3 CaO + CO2The calcium oxide is thenspent(slaked) mixing it with water to make slaked lime (calcium hydroxide):CaO + H2O Ca(OH)2Once the excess water is completely evaporated (this process is technically calledsetting), the carbonation starts:Ca(OH)2+ CO2 CaCO3+ H2O

Chemical Composition of Portland Cement:Portland cement is composed of four major oxides (CaO, SiO2, Al2O3, Fe2O3 90%) & some minor oxides. Minor refers to the quantity not importance.The proportions of these oxides determine the proportions of the compounds which affect the performance of the cement.

Compound Composition of Portland Cement: Oxides interact with eachother in the kiln to form more complex products (compounds). Basically, the major compounds of P.C. can be listed as:

Name Chemical Formula AbbreviationsTri Calcium Silicate 3CaO.SiO2 C3SDi Calcium Silicate 2CaO.SiO2 C2STri Calcium Aluminate 3CaO.Al2O3 C3ATetracalcium Aluminoferrite Ca4Al2Fe2O10 C4AF

Tricalcium aluminate, C3A:-It liberates a lot of heat during the early stages of hydration, but has little strength contribution. Gypsum slows down the hydration rate of C3A. Cement low in C3A is sulfate resistant.

Tricalcium silicate, C3S:-This compound hydrates and hardens rapidly. It is largely responsible for portland cements initial set and early strength gain.

Dicalcium silicate, C2S:-C2S hydrates and hardens slowly. It is largely responsible for strength gain after one week.

Tetracalcium Aluminoferrite :-This is a fluxing agent which reduces the melting temperature of the raw materials in the kiln (from 3,000o F to 2,600o F). It hydrates rapidly, but does not contribute much to strength of the cement paste..

Types of Cement Manufacturing Processes Wet Process Dry Process

Manufacturing Process of Cement: Quarry Grinding Burning Grinding Storage Packing Dispatch

THE CEMENT MANUFACTURING PROCESS1. BLASTING : The raw materials that are used to manufacture cement (mainly limestone and clay) are blasted from the quarry.

Quarry face

1. BLASTING

2. TRANSPORT3. CRUSHING AND TRANSPORTATION : The raw materials, after crushing, are transported to the plant by conveyor. The plant stores the materials before they are homogenized.

quarry

3. CRUSHING & TRANSPORTATION

2. TRANSPORT : The raw materials are loaded into a dumper.

crushing

conveyor

Next

dumper

storage at the plant

loader

THE CEMENT MANUFACTURING PROCESS1. RAW GRINDING : The raw materials are very finely ground in order to produce the raw mix. 1. RAW GRINDING

Raw grinding and burning

2. BURNING2. BURNING : The raw mix is preheated before it goes into the kiln, which is heated by a flame that can be as hot as 2000 C. The raw mix burns at 1500 C producing clinker which, when it leaves the kiln, is rapidly cooled with air fans. So, the raw mix is burnt to produce clinker : the basic material needed to make cement.

conveyorNext

Raw mix

kiln

cooling

Backpreheating

clinker

storage at the plant

Raw mill

THE CEMENT MANUFACTURING PROCESS1.GRINDING : The clinker and the gypsum are very finely ground giving a pure cement. Other secondary additives and cementitious materials can also be added to make a blended cement.1. GRINDING

Grinding, storage, packing, dispatch

2. STORAGE, PACKING, DISPATCH 2. STORAGE, PACKING, DISPATCH :The cement is stored in silos before being dispatched either in bulk or in bags to its final destination.Back

clinker storage

Gypsum and the secondary additives are added to the clinker.

silos

Home page

dispatch

bags

Finish grinding

Manfacturing Process :

TYPES OF CEMENT:Rapid hardening cement:The initial and final setting times of this cement are same as those of ordinary cement. But it attains high strength in early days. It contains high percentage of tricalcium silicate C3S to the extent of about 56%.Sulphate resisting cement:In this cement, the percentage of tricalcium aluminate C3A is kept below 5 percent and it results in the increase in resisting power against sulphates.

TYPES OF CEMENT:Rapid hardening cement:The initial and final setting times of this cement are same as those of ordinary cement. But it attains high strength in early days. It contains high percentage of tricalcium silicate C3S to the extent of about 56%.Sulphate resisting cement:In this cement, the percentage of tricalcium aluminate C3A is kept below 5 percent and it results in the increase in resisting power against sulphates.

TYPES OF CEMENT:Coloured cement:

The cement of desired colour may be obtained by intimately mixing mineral pigments with ordinary cement.These types of coloured cement are widely used for finishing of floors, external surfaces, artificial marble, window sill slabs, textured panel faces, stair treads, etc.White cement is prepared from such raw materials which are practically free from colouring oxides of iron, manganese or chromium. It is white in colour and is used for floor finish, plaster work, ornament work, etc.White cement:

TYPES OF CEMENT:Low heat cement:The considerable heat is produced during the setting of cement. In order to reduce the amount of heat, this type of cement is used. It contains lower percentage of tricalcium aluminate C3A of about 5% and higher percentage of dicalcium silicate C2S of about 46%.Pozzolana cement:Pozzolana is a volcanic powder. It is found in Italy near Vesuvius. This type of cement is used to prepare mass concrete of lean mix and for marine structures. It is also used in sewage works ad for laying concrete under water

The difference between ordinary cement and white cementsThe amount of chromium, manganese, iron compounds is significantly less in white cement in comparison to gray cement

Production of white cement consumes significantly more energy in comparison to gray cement.

Field Tests of Cement:Date of Manufacturing: As the strength of cement reduces with age, the date of manufacturing of cement bags should be checked.

Cement Color: The color of cement should be uniform. It should be typical cement colour i.e. grey colour with a light greenish shade.

Whether Hard Lumps are Formed: Cement should be free from hard lumps. Such lumps are formed by the absorption of moisture from the atmosphere.

Field Tests of Cement:Temperature Inside Cement Bag: If the hand is plunged into a bag of cement, it should be cool inside the cement bag. If hydration reaction takes place inside the bag, it will become warm.Smoothness Test: When cement is touched or rubbed in between fingers, it should give smooth feeling. If it felt rough, it indicates adulteration with sand.

Water Sinking Test:. If a small quantity of cement is thrown to the water, it should float some time before finally sinking

USES OF CEMENT:Cement is a very useful binding material in construction. It is used in mortar for plastering, masonry work, pointing, etc.

It is used for making joints for drains and pipes.

It is used for water tightness of structure.

It is used in concrete for laying floors, roofs and constructing lintels, beams, stairs, pillars etc.

USES OF CEMENT:It is used for precast pipes manufacturing, piles, fencing posts etc.

It is used in the construction of important engineering structures such as bridges, culverts, dams, tunnels, light houses etc.

It is used in the preparation of foundations, water tight floors, footpaths etc.

It is employed for the construction of wells, water tanks, tennis courts, lamp posts, telephone cabins, roads etc.

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