Before understanding the admixture, we need to know about concrete. Concrete is a mixture of cement, sand, aggregate, water and admixtures. Here we can see that admixture is an additional element of concrete mix to change the properties of fresh and hardened concrete.
In simple words, concrete admixtures are ingredients added to concrete mix before or during mixing to improve various properties like hydration, setting time, workability and dispersion in the fresh or hardened form.
Function of Admixtures in Concrete
Concrete admixtures have various functions and they are as given below
- To improve the workability of concrete without adding more water. For example, fly ash is a pozzolanic material which is used to improve the workability of concrete.
- To accelerate the setting time and develop high strength at an early time. For example, calcium chloride (Cacl2) is the most widely used accelerator.
- To increase durability of concrete
- To make concrete impermeable
- For purpose of integral waterproofing, crystalline waterproofing admixture also useful for integral waterproofing
- To retard the setting time of concrete. For Example, Best retarder is calcium sulphate, Gypsum (caso4).
Types of Admixture
Admixtures for concrete can be classified into several categories such as:
- Accelerators
- Retarders
- Plasticizers
- Superplasticizers
- Air Entraining Agent
- Waterproofing Admixtures
- Bleeding Agent
- Workability Agent
- Bonding Admixture
- Pozzolans
- Grouting Agent
- Colouring Agent
- Algicides
- Fungicides
Accelerators
Accelerators speed up the setting time of concrete and develop early strength. Accelerators are highly used in civil engineering construction.
Accelerators are used to stop leakage in swimming pools, pipelines and water tanks, emergency repair work such as highway, bridge, tunnel and airport runway repair.
Some examples of accelerators are given below.
- Calcium Chloride (CaCl2)
- Sodium Chloride (NaCl)
- Aluminium Chloride
- Potassium hydroxide
- Sodium hydroxide
Retarders
Retarders used to retard the setting time of concrete. Retarders are useful in hot environmental conditions. It reduces the setting time of concrete during hot weather conditions. It is also useful to boost compressive strength under freezing and thawing conditions.
Some examples of retarders are given below.
- Sugar
- Calcium Sulphate (CaSo4)
- Ferrous and ferric chlorides
- Ammonium
- Cellulose
- Starch
Plasticizers
Plasticizers are construction chemicals that are used to improve workability of concrete and achieve higher strength by reducing w/c ratio.
Some examples of organic plasticizers are,
- Carboxylic acid
- Lignosulphonates Salts
Super Plasticizers
Super plasticizers are an advancement of plasticizers that are used to make flowing concrete where it requires to be placed in a hard to reach portion or when it requires to be placed quickly.
Some examples of super plasticizers are,
- Modified Lignosulfonates
- Synthetic polymers
Air Entraining Agent
Air entraining agents increase the workability of concrete and weather resistance quality of concrete. It also reduced bleeding and segregation of concrete.
Some examples of Air Entraining Agent are,
- Calcium Lignosulfonates
- Natural wood resins
Waterproofing Admixture
Waterproofing admixture used to minimise the water penetration into the pores of concrete. It is classified in two categories such as water repellent materials and pore filling materials.
Water Repellent Materials : Soda, fat, wax, resin and vegetable oil.
Pore Filling Materials : alkaline silicates and aluminium and zinc sulphate
Colouring Agent
Colouring agents are a new trend in admixture for concrete. Concrete colour gives a nice look to your concrete construction projects. Concrete colouring is not only a beautiful design option but it is also economical and suitable with both old and new concrete.
Some examples of colouring agent are,
- Red (Red Oxide)
- Black (Ferrous oxide)
- Brown (Raw umber)
- Chromium oxide (Green)
FAQs on Admixture for Concrete
What are the 5 types of admixtures?
Five types of admixtures based on their functions. 1. Accelerating Admixtures 2. Retarders 3. Air Entraining Agent 4. Water Reducing Admixture 5. Plasticizer or Super Plasticizer
What is retarder admixture?
Retarders used to retard the setting time of concrete. Retarders are useful in hot environmental conditions. It reduces the setting time of concrete during hot weather conditions. It is also useful to boost compressive strength under freezing and thawing conditions.
What is plasticizer admixture?
Plasticizers are construction chemicals that are used to improve workability of concrete and achieve higher strength by reducing w/c ratio.
What is RCC slab code?
IS 456 : 2000 is the guideline design and construction of RCC structure.
What is another name for superplasticizer?
Super plasticizer is also known as high range water reducer.
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