Cement|Types|Composition and functions

Some of them are listed below:

●Cement slurry is used for filling cracks in concrete structures.

●Cement mortar is used for masonry work, plastering and pointing.

●Cement concrete is used for the construction of various structures like buildings, bridges

water tanks, tunnels, docks, harbors, etc.

●Cement is used to manufacture lamp posts, telephone posts, railway sleepers, piles, etc.

●For manufacturing cement pipes, garden seats, dust bins, flower pots, etc. cement commonly used.

●It is useful for the construction of roads, footpaths, courts for various sports, etc.

Types of Cement

i)Ordinary Portland cement (OPC)

-It is most common type of current

-It has medium rate has of strength development and heat generation

Initial setting time = 30 minute

- It can not withstand chemical attacks e,g. sulfate attack

ii) Rapid hardening cement (RHC)

it is modified OPC with high early strength

Early strength is obtained by increased lime content finer grinding

The quantity of C3 is greater than C₂S in this type of cement.

3 days strength of RHC= 7 days strength of OPC

Heat evolution is high so rapid hardening cement may be advantageous in colder

region

It is costly in comparison with OPC (Generally 10% more)

It is also known as high early strength cement

Initial setting time = 30 min, final setting = 10 hrs

iii) Extra- rapid hardening cement (ERHC)

It is obtained by grinding RHC & CaH₂

Addition of Cacl₂ should not exceed 2 % by weight of PHC

Concrete mix prepared by this cement should be transported, placed and compacted and finished within 20 minutes.

This cement should not be stored more than one month

- Its early strength is about 25% higher than RHC

- At 90 days, the strength is nearly equal to the OPC.

iv) Sulphate resistant cement (Portland)

In this cement percentage of C₁A is reduced & C₂S is increased

It is very effective in sulfate attack.

Initial setting time = 30 min & final setting time = 10 hours

v) Blast Furnace cement (Slag cement)

It is obtained by grinding the mixture of clinker, gypsum and granulated blast furnace slag in suitable proportions.

- The rate of hardening is slower than OPC.

 Heat evolution during hydration is low, hence It is used in mass concrete work such as dam, retaining walls, foundation, bridges abutment.

- This cement also solves environmental problems.

vi) Quick setting cement

- This cement is obtained by reducing gypsum content at the time of grinding of OPC clinker.

It sets very early.

- The setting action of cement starts within 5 minutes & it becomes stone - hard in less than 30 min.

- This cement is mostly used in underwater construction, grouting operation

vii) Super sulfate cement

- This cement is made by grinding a mixture of well granulated blast furnace mixture of well granulated blast furnace (80 to 85 %), calcium sulfate (10 to 15%) and ordinary cement (1 to 2%)

This cement is ground finer than OPC.

Heat evolution of this cement is low,

 hence most useful in mass concrete

- The water cement ratio for this cement should not be less than 0.5.

- Initial setting time 4hr and final setting time 4hr 30min.

- It is highly resistant to chemical attack & can be used in all cases where normal OPC are used except in very hot weather.

viii) Low heat cement

- This cement is obtained by lowering C3S & CA and increasing C₂A and increasing C₂S.

.

It was developed in the USA during 1930 for use in mass concrete construction such as dams.

-Hard slowly and produce low heat.

- Ultimate strength of this cement is the same as OPC.

- Initial setting time = 60 min, Final setting time = 10 hrs.

ix) High alumina cement

- It is manufactured by fusion of Bauxite & lime stone at a temperature of 1600°C. Bauxite consists of hydrated alumina, oxide of iron and titanium with a small quantity of silica.

- The strength gained by this cement in 24 hours is equal to the strength gained by OPC in 28 days.

It is highly resistant to sulfate because of the absence of Ca(OH)₂

- It is used for underwater construction and emergency repair.

- Initial setting time = 30 min & Final setting time = 10 hours.

x) Expansive cement

Expansive cement is obtained by mixing about 8 to 20 parts of  aluminate clinker with 100 parts of the OPC clinker & 15 parts of stabilizer.

- This cement suffers no overall change in volume on drying.

- Experienced and skilled manpower is required to use this cement.

- This cement is used for grouting anchor bolts or grouting machine foundation.

xi) Portland Pozzolana cement (PPC)

- It is obtained by grinding together a mixture of 60 - 80 % of Portland cement & 40 -20% of pozzolana. It may be natural active material such as volcanic ash or pumice or an artificial product such as burnt clay or shale containing siliceous & aluminum mineral Substance.

- It is highly resistant to chemical attack.

- It increases workability, lowers the heat of hydration and increases water tightness.

- It also decreases the manufacturing cost.

xii) Air entraining cement

- Made by mixing a small amount of an air entraining agent with OPC - clinker at the time of grinding.

- Examples of air entraining agents are alkali salt, wood resin.

- Synthetic detergent of the alkyl and sulfate

- This cement has better resistance against frost action.

xiii) Hydrophobic cement

- It is obtained by grinding OPC clinker with water repellant film - forming substance such as oleic acid,

satiric acid etc

- It is more costly than OPC.

Composition and Function of Cement Clinkers

Clinker is a small nodular (ball) shape of size between 3mm to 25 mm formed by sintering and partially fusion of raw material of cement. It is cement in composition but is ball shaped which is grinded to and gypsum salt is added to form cement.

The different compounds present in cement clinker are

Tricalcium silicate (3CaO SiO₂) (C3S):

(i) Generate heat more rapidly.

(ii). Hydrates more rapidly.

(iii) Possesses less resistance to chemical attack.

(iv) Develops early strength.

Dicalcium silicate (2CaOSiO₂) (C₂S):

(i) Imparts ultimate strength to the cement.

(ii) Offers more resistance to chemical attack.

(iii) Hardens more slowly.

(iv) Hydrates slowly.

Tricalcium aluminate. 

(i) Weak against sulfate attack.

(ii) Reacts fastly, generating a large amount of heat.

(iii) Does not contribute to developing strength.

(iv) Causes initial setting of cement

Tetra calcium aluminum ferrite 

(i) Poor cementing value

(ii)React slowly generating small amount of heat

(iii) Comparatively inactive.