Cement – Basic & Technical Specification - Construction & Infrastructure

The cement is a fine powered material used in construction as binding material. Cement is a product obtained by burning a well proportioned mixture of Silicious, Argillaceous and Calcareous materials and crushing the same into a fine powder. Cement usually means OPC (Ordinary Portland Cement) in civil engineering.

Ingredients in cement :

Lime – 60-67%

Silica – 17-25%

Alumina – 3-8%

Iron Oxide – 0.5-6%

Magnesia – 0.1-4%

Soda & Potash – 0.2-1%

Sulphur Trioxide – 1-2.5%

Free lime – 1%

Alkalies – 0.5%

Role of Ingredients :

1. Lime :

i) Lime provides strength to cement.

ii) Excess lime results in objectionable expansion.

2. Alumina :

i) Alumina makes cement quick setting.

ii) Excess alumina lowers the strength.

3. Iron Oxide :

i) Iron Oxide provides colour to cement.

ii) It also imparts strength and hardness.

4. Magnesia :

i) Magnesia provides hardness and colour.

ii) Excess magnesia affects soundness of cement.

5. Alkalies :

i) Excess alkali cause alkali aggregate reaction, efflorescence and staining of concrete and brickwork.

Compounds in Cement :

1. Tricalcium Silicate (C₃S) or Alite :

i) The presence of Tricalcium Silicate in cement is 30-50%.

ii) It is responsible for early strength of concrete.

iii) Cement with more Tricalcium Silicate is better for cold weather concreting.

2. Dicalcium Silicate (C₂S) or Belite :

i) The presence of Dicalcium Silicate in cement is 20-45%.

ii) It’s presence in cement possesses the property of hydrating less rapidly.

iii) It provides strength after a duration of 7 days.

iv) The quality of product obtained in hydration of C₂S is better than that produced in hydration of C₃S.

v) Presence of C₂S in cement possesses more resistance to chemical attacks than C₃S.

3. Tricalcium Aluminate (C₃A) or Celite :

i) The presence of Tricalcium Aluminate in cement is 8-12%.

ii) Reaction of C₃A with water is very fast, this leads to flash set. Thus, to prevent flash set gypsum is added at the time of grinding the cement clinker.

4. Tetracalcium Alumino Ferrite (C₄AF) or Felite :

i) The presence of Tetracalcium Alumino Ferrite in cement is 6-10%.

ii) It does not provide any strength.

iii) Hydrates of C₄AF shows a comparatively higher resistance to attack of sulphates than the hydrates of calcium aluminate.

Types of Cement :

1. Ordinary Portland Cement (OPC) :

i) This cement is a commonly used material in construction industry.

ii) It has adequate resistance to dry shrinkage and cracking but has less resistance to chemical attack.

iii) It should not be used for construction work exposed to sulphate attacks.

2. Rapid Hardening Portland Cement :

i) This cement is lighter and gains higher strength earlier than OPC.

ii) It is used where the construction is done in cold weather conditions and where the form work is to be removed at the earliest.

iii) It is generally used in construction of pavements where early high strength is required.

3. Low Heat Portland Cement :

i) This cement contains less lime compared to OPC.

ii) This cement possesses less compressive strength.

iii) This cement is widely used in retaining walls.

iv) This cement should not be used for thin concrete structures.

v) This cement contains low percentage of tricalcium silicate which hydrates quickly and higher percentage of dicalcium silicate which hydrates slowly.

4. Sulphate Resisting Portland Cement :

i) This cement is used for structures which are likely to be damaged by alkaline conditions like canal linings, culverts, piers etc.

ii) This cement consists of tricalcium aluminate (<5%), which results in the increase in resisting against sulphate attacks.

5. High Alumina Cement :

i) This cement gains early high strength.

ii) It is used for structures which are constructed in sea water, chemical plants and furnaces.

iii) This cement consist of 35% of alumina.

6. Blast Furnace Slag Cement :

i) This cement is made by intergrinding of OPC clinker and granulated blast furnace slag.

ii) This cement develops low heat of hydration and has less early strength.

iii) It is cheaper than OPC.

7. Coloured Cement :

i) This cement is prepared by adding 5-15% of colour pigment before cement is finally grounded.

ii) This cement is widely used for finishing floors, external surfaces etc.

8. Pozzolana Cement :

i) This cement is obtained by adding about 30% of pozzolanic material in OPC.

ii) It is used for hydraulic structures such as dams, weirs etc.

Important Note :

1. Specific Gravity of Cement = 3.15.

2. Density of Cement = 1440kg/m3.

3. Initial Setting Time of Cement = 30 minutes.

4. Final Setting Time of Cement = 10 Hrs.

5. About 70-80% of cement is contributed by C₃S and C₂S.

Tags : types of cement, uses of cement, properties of cement, specific gravity, density, setting time.