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What is Admixtures | Admixture Type, Use, Advantage & Limitation

In this article we briefly learn about What is Admixtures | Admixture Type, Use, Advantage & Limitation, Classification, Advantage, adverse effect many more so read the whole article and join for more learning

What is Admixture?

Chemical Admixture is material which defined as use to modified some property of cement concrete in the fresh or hardened position to improve quality and workability of Concrete etc to gain specific results by adding properties to concrete

What is admixtures | Admixture type, use, advantage & limitation

Admixture is not a basic ingredient, The basic ingredients of concrete are cement, sand and aggregate

They should not affect any kind of property of concrete. Admixtures are no substitute for good concrete practices

Admixtures primarily use to reduce the cost of concrete construction project

Also Read: Measures to Prevent Extra Cost in Construction

Now you clear about What is admixtures now lest go to Admixture use

Why Admixtures Used in Concrete?

Admixture in concrete use for the modification of setting time of concrete, Workability of concrete, air-entrainment dispersion etc

In recent times the development increased on an extremely large scale, so we started using high strength concrete for bridge construction projects and high rise buildings like skyscrapers

So makings concrete manually on-site by labour’s is not possible so the use of ready mix concrete has really promoted and use of RMC has really promoted the use of concrete admixtures

In the market various types of admixtures used in concrete available like accelerators, retarders, air-entraining agents, pozzolanic materials, waterproofing admixture etc which are used in practice by civil engineer constructors in the construction industry

The admixture dosage in concrete normally used in small quantities like 0.005 to 2% by the weight of cement

But plasticizers and superplasticizers (water reduces) are widely used in recent times. They are specially invented in japan and Germany around 1970

Most of the admixture used in concrete are provided in ready-to-use liquid form and are added into the concrete at the construction site

Types of Admixtures Used in Concrete

  1. Chemical admixtures
  2. Mineral admixtures

Classification of Chemical Admixtures based on functions

IS CODE: 9103-1999 has covered main five types of admixtures which as given below

Air-entraining Admixtures

Small bubbles of air formed uniformly throughout the concrete mixture to increase cohesion and resistance to freeze-thaw durability of concrete

Create more workable concrete

  • Workability is high
  • The high degree of durability
  • Reduce the cycles of wetting and drying
Increased the cohesiveness of cement concrete

Accelerating Admixtures (Accelerators)

To reduce the time of early strength development of concrete also decrease the time of concrete curing
Increase the rate of early strength development in concrete

Retarding Admixtures (Retarders)

To increase the setting time of fresh concrete to make sure it workable
Slow down the setting rate of concrete in hot weather condition

Water reducing Admixtures (Workability admixtures)

It helps to decrease the quantity of water content required to reach a required concrete slump 
Low cement contain result in a low rate of CO2 emission
Reduce the water contain demand by 5 to 10%

Super-plasticizing Admixtures

It has the ability to decrease the water content to 12-25% to create highly fluid
Reduce the water demand by 12 to 30%

The other types of admixtures are :

Corrosion Inhibiting Admixtures

For reducing the rate of corrosion of reinforcement in concrete
Frequently used in marine structures, bridges and others that will be exposed to high levels of chloride
Slow down the corrosion of reinforcement

Other types of admixtures are 

Pozzolana Admixtures
Grouting Admixtures
Waterproofing Admixtures
Air-detraining Admixtures
Bonding Admixtures
Gas forming Admixtures
Colouring Admixtures
Alkali-aggregate expansion inhibiting admixtures
Fungicidal, Germicidal, Insecticidal admixtures

Classification of Mineral Admixtures based on functions

Admixture IS code 456:2000 give the guidelines for construction for the use of mineral admixtures
The various mineral admixture of concrete used with cement is
  • Fly ash IS CODE 3812
  • Silica fume IS CODE 15388
  • Blast furnace slag IS CODE 12089
  • Surkhi
  • Rice husk ash etc

What are the Advantages of Admixtures in Concrete?

Why we use admixtures in concrete is the most common question in now day

The list advantages of the use of admixtures in concrete are as following

Proposed of admixture used in concrete

  • To increase the strength of concrete/mortar
  • To accelerate the initial setting time of cement concrete
  • To retard the initial setting time of concrete
  • To improve the Workability of concrete
  • To increase the durability of concrete
  • To reduce heat during hydration
  • To produce lightweight concrete
  • To reduce the permeability of fina concrete
  • To control the alkali-aggregate expansion
  • To improve  the resistance to sulphate attack
  • To increase the bond capacity between old and new concrete
  • To increase the bond between concrete and reinforcements steel bar
  • To reduce the segregation of concrete
  • To decrease the bleeding of concrete
  • To give colour to concrete (mortar)
  • To control the corrosion of concrete

Adverse Effect of Excessive Use of Admixtures

Extreme use of admixture in concrete create Harmful effects for the property of concrete

Following are the adverse effects of excessive use of admixtures in concrete

  • One of the common plasticizers generally used is lignosulphonate acid in the form of calcium or sodium salt. At higher dosages, it may cause retardation in setting time
  • A higher dosage of Super-plasticizer affect the shrinkage and creep properties of concrete
  • A higher dosage of plasticizer may cause segregation and premature stiffening under certain conditions
  • A higher dosage of Super-plasticizer may increase the rate of loss of workability in concrete
  • Perhaps the most commonly known retarder is calcium sulphate (gypsum). The addition of an excess amount of gypsum may cause undesirable expansion and indefinite delay in the setting of concrete
  • Excess use of accelerators causes more heat evolution and there are chances of cracks in the concrete
  • In the case of air-entrained concrete strength decreases in proportion to the amount of air. It is observed that 1% of entrained air reduces  strength by about 5.5%
  • The optimum air content is ranging from 3 to 6 per cent
FAQ 1: What is Admixture?

Chemical Admixture is material which defined as use to modified some property of cement concrete in the fresh or hardened position to improve quality and workability of Concrete etc to gain specific results by adding properties to concrete

FAQ 2: Why Admixtures Used in Concrete?

Admixture in concrete use for the modification of setting time of concrete, Workability of concrete, air-entrainment dispersion etc In recent times the development increased on an extremely large scale, so we started using high strength concrete for bridge construction projects and high rise buildings like skyscrapers So makings concrete manually on-site by labour’s is not possible so the use of ready mix concrete has really promoted and use of RMC has really promoted the use of concrete admixtures In the market various types of admixtures used in concrete available like accelerators, retarders, air-entraining agents, pozzolanic materials, waterproofing admixture etc which are used in practice by civil engineer constructors in the construction industry The admixture dosage in concrete normally used in small quantities like 0.005 to 2% by the weight of cement But plasticizers and superplasticizers (water reduces) are widely used in recent times. They are specially invented in japan and Germany around 1970 Most of the admixture used in concrete are provided in ready-to-use liquid form and are added into the concrete at the construction site

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