Vacuum concrete is the type of concrete in which the excess water is removed for improving concrete strength. The water is removed by use of vacuum mats connected to a vacuum pump.
In the usual manner a concrete mix with good workability is pace in the form-works. As fresh concrete contains continues system of water-filled channels, the application of a vacuum to the surface concrete results in a large amount of a vacuum to the surface of the concrete. This results in a large amount of water being extracted from a certain depth of the concrete. The vacuum is applied through porous mats connected to a vacuum pump. The final water cement ratio before setting is thus reduced and as this ration largely controls the strength, vacuum concrete has a higher strength and also density a lower permeability and a greater durability.
Advantages of Vacuum Concrete
Vacuum Concrete has several advantages over normal concrete. Some of the advantages are given below.
- The final strength of concrete is increased by about 25%.
- Sufficient decrease in The permeability of concrete is sufficient decreased.
- Vacuum concrete stiffens very rapidly so that the form-works can be removed within 30 minutes of casting even on columns of 20 ft. high.
- This is of considerable economic value, particularly in a precast factory as the forms can be reused at frequent intervals.
- The bond strength of vacuum concrete is about 20% higher.
- The density of vacuum concrete is higher.
- The surface of vacuum concrete is entirely free from pitting and the uppermost 1/16 inch is highly resistant to abrasion. These characteristics are of special importance in the construction of concrete structures which are to be in contact with flowing water at a high velocity.
- It bonds well to old concrete and can, therefore, be used for resurfacing road slabs and other repair works.
- A text Book of Engineering Materials by Dr. M.A. Aziz