Retarders

Retarding admixtures:

                            

                             A retarded is an admixture that slows down the chemical admixtures and so that concrete remains plastic and workable for longer time than concrete without retarder.Retarder are used to overcome the accelerating effect of high temperature in hot weather concreting.

Action Of Retarders:

• Retarders delay the setting time of concrete cement.
• By forming a thin Coating on the cement particles and slowing down the resolution and reaction with water.By increasing the Intra molecular distances of reacting silicates and aluminates from water molecules by forming certain transcite compound in the system.
• Perhaps most commonly known as retarder sulphates.

          Ex:Sugar,starch,ferricor Ferrous Chloride,sodium Hexameta phosphate and sulphonic acid and their salts,carbonates and their salts.

Uses of Retarders

• Their Chief use of retarder in the hot weathering concreting which tends to reduce the setting time on account of high temperature and may allow completion of the concrete.
• Compassion finishing operations before initial set of the cement.
• In ready mix concrete where time element is involved in its transportation in mixing before it can be laid,compacted and finidhed.
• Use to obtain exposed aggregate look like concrete.Used in the growth of oil wells and concrete archs