Different Admixtures added to cement concrete to change its properties

Certain materials if added to cement concrete impart certain specific properties to the concrete. Following are some of the admixtures.

1.Accelerators:- To accelerate the process of hydration of cement in cold weather concreting, admixtures known as accelerators are added. This has to be done to enable remove from work after reasonable time.

                                       Calcium chloride upto 1.5% by weight of cement is generally used as an accelerator. Accelerators increase shrinkage and decrease resistance of concrete to thawing and freezing. They increase the rate of hydration.

2.Air Entraining Agents:- These are such agents which when added to concrete, entrain air in form of small air bubbles. These agents increase workability of concrete and also increase the resistance to frost action. Due to increase workability w/c ratio is lowered which results in increase in the strength of the concrete. But this increased strength is compensated by decrease in strength due to air pores left in the concrete due to addition of this agent.

3.Water Reducing and Set Controlling Agents:- In hot weather, setting of concrete may start very soon. To gain time for mixing, transportation and placing before setting of the concrete may start, retarders are added in the concrete. Retarding agents keep concrete plastic for longer times.