Different types of 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 patchwork. In the cold weather, accelerators were used to achieve 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 the reader is opposite to the accelerator. The retarder increases 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 were used in Ready mix concrete. The chemical is,
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 property.
The plasticizer is the admixture that was added in fresh concrete to increase its workability. Three main types of 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)
The extreme workability of concrete was achieved by the use of superplasticizer. The reduction, the water-cement ratio was done without loss of workability. The use of superplasticizer leads to the reduction of the overall cost.
For extreme workability, the electrochemical activities were responsible. The increase of the mobility of concrete the concrete starts to flow without segregation.
Superplasticizer enables the saving in the cement and makes the concrete ideal for pumping, Casting heavily reinforced concrete members and precast elements of concrete.
This type of admixture was added in concrete to make the structure waterproof. These chemicals react with lime, which is present in cement to form inorganic salts that block the pores and capillaries, thereby reducing moisture penetration.
Waterproofers may be obtained in liquid and in powder form and consist of pore-filling or water- repellent materials.