LIME AND CEMENT

Done BySaran.pNandha college of technology

What is Limestone?

Sedimentary rockMade up of the shells of millennia old dead sea creaturesLayers of these built up over millions of years, and were squashed together until they formed limestone

Limestone

Chalk(Soft)

Limestone (CaCO3)(Comparatively hard)

Marble(Hardest)

Lime mortar:•The paste is prepared by mixing lime and sand or surkhi in suitable proportions in addition to water. •If surkhi is to be added in lime mortar the equal proportions of sand and surkhi should be mixed with lime.•These mortars are inferior to cement mortars in strength as well as water tightness.•These mortars should not be used for underground works as they set in the presence of carbon dioxide and break up in damp conditions.•This type is used for construction work above ground level i.e. exposed positions.

In producing masonry mortars

Plaster mortars – sets slower than gypsum

White-wash

In production of masonry blocks – slaked lime + sand under pressure

Uses Of Lime

CEMENT

FUNCTIONS OF INGREDIENTS IN CEMENT :

1. Lime – most important ingredient of the cement . its proportion have to be carefully maintained; in excess it causes cement to expand and disintegrate, on the other hand, if lime is less then the strength of the cement is greatly decreased and it causes cement to set quickly.

2. Silica – it imparts strength to the cement due to the formation of dicalcium and tricalcium silicates. If silica is present in excess the strength increases but setting time is prolonged.

3. Alumina – it imparts quick setting properties to the cement, however in excess it weakens the cement. It also lowers the clinkering temperature.

4. Calcium sulphate – this ingredient increases the initial setting time of cement.5. Iron oxide – it imparts colour, hardness and strength to the cement.6. Magnesia – in small amount helps in hardness and colour but excess makes

cement unsound.7. Sulphur – only a very small quantity is allowable for strength.

Grades Of 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.

• 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

MANUFACTURE OF PORTLAND CEMENT

This is the first step in the manufacture of Portland Cement.

Jaw crushers of various sizes are employed for the crushing purpose.

Raw materials are crushed by crushers till the size of the raw material reduces to ¾ of an inch.

It is than send for either Wet process or Dry process. Wet process is universally employed.

CRUSHING

Wet process Calcareous materials are crushed, powdered and stored in bins. Argillaceous materials is mixed with water and washed. This removes any

adhering organic impurities. Powdered Calcareous and Washed Argillaceous materials are mixed in proper

proportions to get a slurry. Chemical composition is analyzed and corrected if necessary by addition of

the deficient materials. This slurry is then fed into the rotary klin.

MIXING PROCESS

Dry processHard raw materials like cement rock or blast furnace slag are first crushed to 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 get the raw mix which is then fed to rotary klins.

The ground materials containing 30 – 40% of water is stored in separate tanks equipped with agitators.

This step is followed by process of burning.

STORAGE OF GROUND MATERIALS

Slurry is burnt in rotary klin where actual chemical changes takes place. Klin is long steel cylinder 30-40 meter in length, 2-4 meter in diameter,

lined by refractory bricks. It is inclined at gradient of 0.5-0.75 inch and can be rotated at the desired speed.

The material is introduced in the klin from the upper end as the klin rotates material passes slowly towards the lower end.

Klin is heated by burning pulverized coal or oil and temperature is maintained at about 1400-1500°C. At clinkering temperature actual chemical reactions takes place.

BURNING

Grinding can be done in two stages

Ball Mill

Consists of cast iron drum containing iron and steel balls of different sizes. The principle used in ball mill s impact and shear produced by large no. of tumbling and rolling balls.

Tube Mill

Ball mill grinding is followed by tube mill grinding. Tube mill is conical at the discharge end with separate inlet and outlet.

Slower is the feeding speed finer is the product coming out of the tube mill.

GRINDING

PACKAGING

The ground powder is packed by automatic machines in a bag.

This is then dispatched to the markets where it is sold.

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.

Characteristics of cement

Building (floors, beams, columns, roofing, piles, bricks, mortar, panels, plaster).

Transport (roads, pathways, crossings, bridges, sleepers, viaducts, tunnels, stabilization, runways, parking).

Water (pipes, culverts, kerbing, drains, canals, weirs, dams, tanks, pools).

Civil (piers, docks, retaining walls, silos, warehousing, poles, pylons, fencing).

Agriculture (buildings, processing, housing, feedlots, irrigation).

Common applications of cement

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. 

Advantages and disadvantages

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