Different types of the admixtures are used in concrete construction.
Setting time was reduced by the use of the accelerator and generally produce an early setting of concrete repair and patch work. In the cold weathers accelerators was used to achieve the early strength.
The calcium chloride (CaCl2) is the most common accelerator which was used in the plain cement concrete work. The quantity of calcium chloride is limited in a concrete mix is about 1%-2% by weight of cement.
The Main properties of accelerator were
1: Shortening setting time
2: Increase early strength
3: Aids, cold weather concreting
The function of reader is opposite to the accelerator. The retarder increase the setting time of concrete. By the use of retarder the water cement ratio was reduced.
Usually by the use of this admixture the water was reduced at about 10%. Various types of water, reducing agents and set-retarding admixtures was used in Ready mix concrete.The chemical are,
1: Lignosulphonic Acid and their salts.
2: Hydroxylated carboxylic acid and their salts.
3: Sulphonated melamine.
4: naphthalene formaldehyde.
They also have a detergent like properties.
The plasticizer is the admixture which was added in fresh concrete to increase it’s workability. Three main types of the plasticizers were used such as
1: Finely divided minerals (Either cementitious or pozzolanic)
2: Air-entertaining agents (Produces discontinuous air bubbles)
3: Synthetic derivatives (Produce soapy action)
Extreme work ability of concrete was achieved by the use of superplasticizer. The reduction, water cement ratio was done without loss of work ability. The use of superplasticizer leads to the reduction of overall cost.
For extreme work ability the electrochemical activities were responsible. The increase of the mobility of concrete the concrete starts to flow without segregation.
Superplasticizer enable the saving in the cement and make the concrete ideal for pumping, Casting heavily reinforced concrete members and precast elements of concrete.
This type of admixtures was added in concrete to make the structure water proof. These chemicals react with lime, which is present in cement to form inorganic salts which blocks the pores and capillaries, thereby reducing moisture penetration.
Waterproofers may obtained in liquid and in powder form and consist of pore filling or water- repellent materials.
The chief material for a pore – filling are
1: Alkali silicated.
2: Notably silicates.
3: Zinc sulfates..
4: Chlorides of aluminium and calcium.
6: Miscellaneous Admixtures:
Many other chemical admixtures were used in concrete to achieve results such as
1: Gas-Forming and Expansive chemicals
2: Corrosion-Inhibiting Chemicals
4: Antifungal admixtures
5: Curing compounds
8: Floor coating
9: Guniting Aids
7: Mineral Admixtures:
To modify the concrete properties, mineral admixtures was used under the permits of IS: 456-2000. Those are
1: Fly Ash
2: Silica Fume
3: Rice Husk Ash
5: Ground Granulated Blast Furnace slag.
The following materials may added in concrete either as a admixture or as a part of cement.