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CONTENTS Introduction Definition History Classification Grades Manufacture Characteristics Common applicationsAdvantages and disadvantages Conclusion
INTRODUCTION The word "cement" traces to the Romans, who used the term opus caementicium to describe masonry resembling modern concretethat was made from crushed rock with burnt lime as binder. The volcanic ash andpulverized brick additives that were added to theburnt lime to obtain a hydraulic binder were later referred to as cementum, cimentum, cäment, and cement.
DEFINITION Cements are materials thatexhibit characteristic properties of settingand hardening when mixed to a pastewith water. This makes them join rigidmasses into coherent structures. It ispowdery bonding material havingadhesive and cohesive properties. Chemically it is a finely groundmixture of calcium silicates andaluminates which set to a hard masswhen treated with water. These are calledas Hydraulic Cements (Portland Cement)and those setting in air are Non Hydrauliccements (Ordinary Lime).
HISTORY It is uncertain where it was first discovered that a combination of hydrated non-hydraulic lime and a pozzolan produces a hydraulic mixture, but concrete made from such mixtures was first used by the Ancient Macedonians and three centuries later on a large scale by Roman engineers. They used both natural pozzolans (trass or pumice) and artificial pozzolans (ground brick or pottery) in these concretes. Many excellent examples of structures made from these concretes are still standing, notably the huge dome of the Pantheon in Rome and the massive Baths of Caracalla. The vast system of Roman aqueducts also made extensive use of hydraulic cement. The technical knowledge of making hydraulic cement was later formalized by French and British engineers in the 18th century.Modern hydraulic cements began to be developedfrom the start of the Industrial Revolution (around1800). Cement was first made by Joseph Aspdin in 1824 in England.
CLASSIFICATION OF CEMENT•Natural Cement: Obtained bycalcinating and pulverizing naturalcement rock of argillaceous and claywith limestone. It does not havesufficient strength and is cheap andquick setting & have hydraulicproperties.•Pozzolana Cement: Volcanic ashcontaining silicates of calcium, iron andaluminum when mixed with lime andheated produces this cement.•Slag Cement: Mixture of blast furnaceslag (Ca and Al Silicates) and hydratedlime. Sometimes accelerators likeclay, salt, caustic soda are added tohasten hardening process.•Portland Cement: It consists ofcompounds of lime, silica, alumina andiron. When mixed with water it forms apaste which binds the rock, sand andgravel to form concrete.
GRADES OF PORTLAND CEMENT 33 grade –General Construction like plastering, finishing works etc, where strenth is not required. 43 grade –Useful for structural works, precast items etc, Strength development is faster than 33 grade. 53 grade–Used for multi-storey buildings, precast pre-stressed items, bridges, tall structures,etc. Develops very fast strength and speeds up construction.
MANUFACTURE OF PORTLAND CEMENT •Crushing •Mixing (Wet Process) •Mixing (Dry Process)•Grinding (Ball Mill and Tube Mill) •Storage of Ground Materials •Burning –Drying Zone –Calcination Zone –Clinkering Zone •Grinding –Retarder –Dispersing Agent –Water Proofing •Packaging
CRUSHINGThis is the first step in the manufacture of Portland Cement.Jaw crushers of various sizes areemployed for the crushing purpose.Raw materials are crushed by crushers tillthe size of the raw material reduces to ¾of an inch.It is than send for either Wet process orDry process. Wet process is universallyemployed.
MIXING PROCESS Wet processCalcareous materials are crushed, powdered and stored in bins.Argillaceous materials is mixed with water and washed. This removesany adhering organic impurities.Powdered Calcareous and Washed Argillaceous materials are mixed inproper proportions to get a slurry.Chemical composition is analyzed and corrected if necessary by additionof the deficient materials.This slurry is then fed into the rotary klin. Dry processHard raw materials like cement rock or blast furnace slag are first crushedto 50mm pieces in ball mill, then dried and stored.Crushing is done by gyratory crushers and drying is done by rotary driers.Separate powdered ingredients are mixed in required proportions to getthe raw mix which is then fed to rotary klins.
STORAGE OF GROUND MATERIALSThe ground materials containing 30 – 40% of water is storedin separate tanks equipped with agitators.This step is followed by process of burning.
BURNINGSlurry is burnt in rotary klin where actual chemical changes takes place.Klin is long steel cylinder 30-40 meter in length, 2-4 meter indiameter, lined by refractory bricks. It is inclined at gradient of 0.5-0.75inch and can be rotated at the desired speed.The material is introduced in the klin from the upper end as the klinrotates material passes slowly towards the lower end.Klin is heated by burning pulverized coal or oil and temperature ismaintained at about 1400-1500°C. At clinkering temperature actualchemical reactions takes place.
GRINDING Grinding can be done in two stages•Ball Mill–Consists of cast iron drum containing iron andsteel balls of different sizes. The principle used inball mill s impact and shear produced by largeno. of tumbling and rolling balls.•Tube Mill–Ball mill grinding is followed by tube millgrinding. Tube mill is conical at the discharge endwith separate inlet and outlet.–Slower is the feeding speed finer is the productcoming out of the tube mill.
GRINDING Clinkers are finally grinded in ball mill and tubemill to a fine powder. Additives added are as follows. Retarder: Gypsum or Plaster of Paris acts as retarder toprevent quick setting. After initial setting gypsum retardsthe dissolution of tricalcium aluminate by formingtricalcium sulphoaluminate. Dispersing Agent: Sodium salts and polymers of condensednapthlene or sulphonic acid are added to prevent theformation of lumps and cakes in the cement. Water proofing agents are also added.
PACKAGING The ground powder is packed by automatic machines in a bag. This is then dispatched to the markets where it is sold.
CHARACTERISTICS OF CEMENT When water is added to initiate dry mixtures of cement and sand, hydration of cement starts and it will binds sand particles as well as the surrounding surfaces of masonry and concrete. The proportion of cement and sand will decide the strength of mortar. A richer mix than 1:3 proportion is prone to shrinkage. Solid surface are provided by well proportioned mortar. A leaner mix is not able of closing the voids in sand.
COMMON APPLICATIONS OF CEMENT Building (floors, beams, columns, roofing, piles, bricks, mortar, panels, plaster). Transport (roads, pathways, crossings, bridges, sleepers, viaducts, tunnels, stabilization, runways, parkin g). Water (pipes, culverts, kerbing, drains, canals, weirs, d ams, tanks, pools). Civil (piers, docks, retaining walls, silos, warehousing, poles, pylons, fencing) .
ADVANTAGES AND DISADVANTAGES Advantages: Cement is very strong. It can create large structures quickly. It conforms to different shapes (arcs and circles, etc). It has high thermal mass (moderates temperature). Disadvantages: Cement is subjected to cracking. It is very difficult to provide idoneous curing conditions.It is not ideal for situation when settlement is expected.
CONCLUSION Cement is a binder, a substance that sets and hardens independently, and can bind other materials together. It was first made by Joseph Aspdin in 1824 in England. It is Classified as Natural Cement, Pozzolana Cement, Slag Cement, Portland Cement. Portland cement is most commonly used. Its manufacturing process consists of Crushing, Mixing (Wet Process), Mixing (Dry Process), Grinding (Ball Mill and Tube Mill), Storage of Ground Materials, Burning, Packaging and finally transporting to sell. It is most commonly used in building construction, civil, water carrying and storage, transportation and agriculture.