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What is concrete?

Concrete: Concrete is a specific mixture of binder, aggregates, water and admixture, which is used to builtup of a building structure. 

Concrete=Binding material +Fine aggregates +Coarse aggregates +water+Admixture

Types of concrete : Concrete is divided in to three major categories on the basis of use and there properties which are on the basis of binding material, on the basis of proportion and bulk density. We will explain it following. 

I. On the basis of binding material:

1. Cement concrete

2. Lime concrete

3. Mud concrete

II. On the basis of proportion:

III. On the basis of place of cast.

1. In situ concrete

2. Precast concrete 

IV On the basis of bulk density :

Manufacturing process of concrete:

1. Baching: In this stape find the weight of raw content which are going for mixing.For construction of small scale raw content weight by volume. For large scale construction raw content weight by weight wise

2. Mixing: Mixing process performed by hand mixing, machine mixing and RMC plant. In hand mixing process 10 extra cement added as Compared to machine mixing. 

Mixing chamber rotate atleast 2 to 3 minutes or almost 20 revolution in each bach. Otherwise, segregation will occur.

3. Transporting: Transporting of fresh concrete must between 30 minutes.

Transporting tools: Pan, power, buggies and elevators, tower crane, boam pressure, chute pipe(galvanize Iron)

4. Placing: Free fall limit of concrete as per IS-456 should not be more than 1.5 meter. 

5. Compaction: Compaction removes the voids and produced a uniform concrete. If 1% voids remains in concrete then it reduced 5% strength of concrete.

Compaction tools:

Hand steel rod. 

Mechanical vibrator- Which are 35mm to 60mm dia. 

Foam vibrator. 

Surface vibrator- For pavement compaction.

Methods of concrete curing:

Water is one of the most important ingredient of concrete. Water cause the chemical reaction with cement which called 'Hydration reaction’.The Hydration reaction cause the concrete to set and develop strength.

It takes time for the complete development of strength around 28 days.It is essential that water has to remain in the concrete till it attains it's full strength.When the formwork for the RCC members are removed the concrete gets exposed to the air. The water from the concrete starts to evaporate to the atmosphere.

The Hydration reaction is an exothermic reaction due this heat the temperature of concrete rises and cause evaporation of the water inside the concrete.Hence there can be loss of water due to two reasons.Exposure to the atmosphereDue to heat generated by Hydration.

It therefore necessary to cure concrete.To prevent evaporative losses and to keep control on the temperature of concrete.Period of curing is 7 to 10 days.Tempreture should be 5° C to 32° C during curing period.

Methods of curing:

Ponding.

Spraying.

Fogging.

Covering with plastic sheet.

Curing compound.

Steam curing.

1. Ponding: Ponding means providing a thin layer of water on the top of the concrete surface. This method is used for curing slabs in this method bunds of mortar are spreaded around the perimeter of the slab and the portion in between is kept filled with a thin layer of water.

2. Spraying: Wateris continuously sprayed on the surface of exposed concrete.The water tends to evaporate quickly in hot and dry climate.Hence the surface is covered with jute cloth which is kept wet.

3. Fogging: Inested of continuously spraying water on the surface, a continuous mist is created around the concrete members.

4. Covering the surface with plastic sheet: The freshly cast slab in covered by a plastic sheet. This prevent evaporative losses.

5. Curing compound:Special compound in liquid state are brushed on the surface of concrete.They from a water proof film Which does not allow moisture to escape from the surface.

6. Steam curing:

Used for precast RCC members.

Members kept in a steam chamber for curing.

It is very fast method of curing.

Finishing of concrete:

1. Screeding: Striking of extra concrete is known as screeding. In this work we removes the extra concrete after removing of foam work.

2. Floating: In this method a wooden or aluminium flater is used to placed the concrete uniformly.

3. Troweling: It somethens the surface with steel conical members.

Compressive strength test of concrete: Generaly we tests the compressive strength of concrete by cube test. For this topic read the next blog. 

Workability test of concrete: To the find the workability of concrete test performed by slump cone test. For this topic read the next blog.

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