WHAT IS CEMENT???  A cement is a binder, a substance that sets and hardens independently, and can bind other materials togetherbinder  It was 1 st introduced in England in 1824 by John Aspidin

INGREDIENTSPERCENTAGEUSES CaO50-60%Controls strength and soundness SiO220-25%Gives strength, excess quantity causes slow setting Al2O35-10%Quick setting, excess lowers strength MgO2-3%Color and hardness, excess causes cracking Fe2O31-2%Imparts color, helps in fusion of ingredients SO31-2%MAKES CEMENT SOUND

NATURAL 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 °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 WATER CALCAREOUS MATERIAL CRUSHED WET GRINDING IN WASH MILLS SLURRY CORRECTION AND STORAGE BASINS COAL PULVERISED ROTARY KILN CEMENT CLINKERS GYPSUM GRINDING 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 kiln ComponentPercentage 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)

WET PROCESS 1. 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 PROCESSWET 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.

It is usually done in the rotary kiln, which is a steel tube, about m in diameter and m 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

 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(in soluble)

 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

SRISHTI SINGH PREETI JAIN ANKITA CHOUDHARY BY 2013 EC BRANCH