Vacuum Concrete

Vacuum Concrete

In the thin section of concreting like slabs and walls, a fluid mix with a water-cement ratio of 0.50 to 0.65 is required to facilitate the placing and compaction. Such a mix will lead to relatively low strength and poor abrasion resistance. In such a situation, the vacuum treatment of concrete, involving the removal of excess water and air by using suction can be helpful. An arrangement for vacuum treatment of concrete using suction through a surface that connected to a vacuum to a vacuum pump.

The duration of treatment depends upon the water-cement proportion and the quality of water to be removed. It generally from 1 to 15 minutes for slabs varying in thickness from 25 mm to 125 mm. The effect of treatment is more pronounced in the beginning and falls off rapidly. Hence, it is of no advantage to prolong the periods of treatment beyond these values.

The vacuum treatment is not very effective for a water-cement ratio below 0.4. The suction pressure on the concrete is about one-third of the atmospheric pressure. The vibration of concrete before vacuum treatment can assist the process. The application of vibration simultaneously with vacuum treatment after initial vibration is very effective. Continued vibration beyond 90% may damage the structure of concrete, and hence the vibrations should be stopped beyond this period and the only vacuum needs to be applied for the remaining duration of the treatment.

The vacuum treatment has been found to considerably reduce the time of final finishing o floor and stripping of all forms. The strength of concrete and its resistance to wear and abrasion increase and total shrinkage is reduced. Vaccum-treated concrete provides a good band with the underlying concrete.

The vacuum-processed concrete has been extensively used for factory production of precast plain and reinforced concrete units, and another important construction of horizontal and sloping concretes slabs, such as floor slabs, road and airport pavements, thin load-bearing and partition walls. It can also be used in the resurfacing and repacing and repair of road pavement.

Advantages of vacuum concrete

1. The final strength of concrete is increased by about 25%.
2. Sufficient decrease in The permeability of concrete is sufficiently decreased.
3. 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.
4. This is of considerable economic value, particularly in a precast factory as the forms can be reused at frequent intervals.
5. The bond strength of vacuum concrete is about 20% higher.
6. The density of vacuum concrete is higher.
7. 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.
8. It bonds well to old concrete and can, therefore, be used for resurfacing road slabs and other repair works.