CEMENT

WHAT IS CEMENT???

A cement is a binder, a substance that sets and hardens independently, and can bind other materials together

It was 1st introduced in England in 1824 by John Aspidin

COMPOSITION OF CEMENT

INGREDIENTS PERCENTAGE USES

CaO 50-60% Controls strength and soundness

SiO2 20-25% Gives strength, excess quantity causes slow setting

Al2O3 5-10% Quick setting, excess lowers strength

MgO 2-3% Color and hardness, excess causes cracking

Fe2O3 1-2% Imparts color, helps in fusion of ingredients

SO3 1-2% MAKES CEMENT SOUND

CLASSIFICATIONNATURAL CEMENT

• Made by calcining naturally occurring argillaceous limestone by heating at high temp

• Has hydraulic properties ,quick setting, relatively lower strength

• Used in laying bricks and setting stones

PUZZOLANA CEMENT

• Consists of silicates of aluminum, iron and calcium

• Made by simply mixing and grinding natural puzzolana(deposits of volcanic ash) and slaked lime

• Has hydraulic properties, used by mixing with portland cement

SLAG CEMENT

• Made from blast furnace slag and hydrated lime

• Set more slowly than portland cement

• Have lower strength

• Poor in abrasion resistance

PORTLAND CEMENT

• Most important and reliable cementing material used for construction

• An extremely finely ground product obtained by calcining together at 1500̊C, an intimate and properly proportioned mixture of argillaceous (clay containing) and calcareous(lime containing)

PORTLAND CEMENT:MANUFACTURE

Raw materials required are:

1. Calcareous Materials, CaO (such as limestone, chalk, etc)

2. Argillaceous Materials, Al2O3 and SiO2 (such as clay, shale, slate, etc)

3. Powdered coal or Fuel Oil

4. Gypsum(CaSo4.2H2O)

PRODUCTION STEPS

Raw materials are crushed, screemed & stockpiled

Raw materials are mixed with definite proportions to obtain “raw mix”

They are mixed either dry (dry mixing) or by water (wet mixing)

Prepared raw mix is fed into the rotary kiln

As the materials pass through the kiln their temperature is rised upto 1300-1600 °C

The process of heating is named as “burning”;the output is known as “clinker”

Clinker is cooled & stored Clinker is ground with gypsum (3-6%)

to adjust setting time Packing & marketting

PRODUCTION STEPS

ARGILLACIOUS

MATERIAL

WATERCALCAREOUS MATERIAL

CRUSHED

WET GRINDING IN WASH MILLS

SLURRY

CORRECTION AND STORAGE BASINS

COAL

PULVERISED

ROTARY KILN

CEMENT CLINKERS

GYPSUMGRINDING IN BALL MILLS

AND TUBE MILLS

CEMENT

MANUFACTURE STEP1:MIXING OF RAW MATERIALS• DRY PROCESS

1. Raw materials are crushed then ground to fine powder(in ball mills/tube mills)

2. Powdered materials are mixed in required proportion to get dry ’raw mix’ stored in storage bins(called silos) and kept ready to be fed into rotary kilnComponent Percentage range by

mass

Lime (CaO) 60-69

Silica (SiO2) 17-25

Alumina (Al2O3) 3-8

Iron Oxide (Fe2O3) 2-4

Magnesium oxide (MgO) 1-5

Sulphur trioxide (SO3) 1-3

Alkali oxides (Na2O+K2O)

0.3-1.5

MANUFACTURE STEP1:MIXING OF RAW MATERIALS

• WET PROCESS1. Calcareous raw materials are crushed, powdered and stored in

big storage tanks(‘Silos’)

2. Argillaceous material(say clay) is mixed thoroughly with water in wash mills to remove any adhering organic matter, etc

3. The basin washed clay is also stored

4. Powdered limestone(from silos) and washed wet clay(from basins) are allowed to flow in a channel in right proportions

5. From the channel, the two raw materials are led to grinding mills where they are mixed intimately to form a paste, called ‘slurry’

6. The slurry is led to a ‘correcting basin’ where its chemical composition may be adjusted, if necessary ; the slurry contains about 30-40% water

7. The slurry is finally stored in storage tanks and kept ready for feeding to a rotary kiln

MERITS AND DEMERITS OF DRY AND WET PROCESSES

DRY PROCESS WET PROCESS

1. It is adopted when the raw materials are quite hard.

2. Fuel consumption is low.3. Process is slow.4. Cement produced is of

inferior quality.5. Cost of production of cement

is less .6. On the whole, the process is

costly.

1. It can be used for any type of raw materials.

2. Fuel consumption is higher.3. Process is comparatively

faster.4. Cement produced is of

superior quality.5. Cost of production of cement

is somewhat higher.6. On the whole, the process is

cheaper.

MANUFACTURE STEP 2:BURNING

• It is usually done in the rotary kiln, which is a steel tube, about 2.5-3.0 m in diameter and 90-120m in length

• The kiln is laid slightly inclined resting on roller bearings, capable of rotating about its longitudinal axis

• Burning fuel(usually powdered coal or oil) and air are injected at the lower end

• A long hot flame is produced heating the interior of the kiln up to a maximum temp of about 1750°C

• ‘Raw mix’ or ‘corrected-slurry’ is injected into the kiln at the upper end and flames are forced from the lower end

• Due to the slope the materials are fed in move continuously towards the hottest end

CHEMISTRY

In the upper part, temp is 400°C, most of the water in the slurry gets evaporated(DRYING ZONE)

In the central part, temp is 1000°C, limestone of dry mix or slurry undergoes decomposition to form quick lime and CO2 which escapes out

Material forms small lumps called nodules(CALCINATION ZONE)CaCO3 CaO +CO2(g)

CHEMISTRY

In the lower part the temp is around 1500 to 1700°C, here lime and clay(nodules) undergo chemical fusion yielding calcium aluminates and silicates(CLINKERING ZONE)

The aluminates and silicates fuse to form hard, grayish stones called clinkers

2CaO +SiO2 CaSiO4 (Dicalcium silicate C2S)3CaO +SiO2 Ca3SiO5 (Tricalcium silicate C3S)3CaO +Al2O3 Ca3Al2O6 (Tricalcium aluminate

C3A)4CaO +Al2O3+Fe2O3 Ca4Al2Fe2O10 (Trialcium

aluminoferrite C4AF)

3CaO +Al2O3 Ca3Al2O6 (Tricalcium aluminate C3A)

4CaO +Al2O3+Fe2O3 Ca4Al2Fe2O10 (Trialcium aluminoferrite C4AF)

CLINKERS

These clinkers are very hot The rotary kiln base is provided with

another small rotary kiln In this, hot clinkers fall and cool air

admitted from opp direction Air counter blast cools the clinkers Hot air so produced is used for burning

powdered coal The cool clinkers are then collected in

small trolleys

CHEMISTRY

MANUFACTURE STEP 3:GRINDING

The cool clinkers are ground to a fine powder in tube mills

During final grinding small quantity of powdered gypsum so that the resulting cement does not set very quickly

3CaO.Al2O3+xCaSO4.7H2O 3CaO.Al2O3.xCaSO4.7H2O(insoluble)

SETTING OF CEMENT

WHEN MIXED WITH WATER THE SETTING TAKES PLACE TO GIVE A HARD MASS

THIS IS DUE TO THE HYDRATION OF THE CONSTITUENTS AND REARRANGEMENT

IT IS AN EXOTHERMIC PROCESS GYPSUM IS ADDED TO DELAY THE PROCESS

SO THAT IT GETS SUFFICIENTLY HARDENED

GYPSUM

USES

Cement is a commodity of national necessity for any country

It is next to iron and steel Used in plastering Building of bridges, dams and

buildings Used in concrete and reinforced

concrete

THANK YOU

SRISHTI SINGH

PREETI JAIN

ANKITA CHOUDHARY

BY

2013 EC BRANCH