Vacuum Concrete - Equipments, Procedure, Advantages, Disadvantages, Applications

Introduction Of Vacuum Concrete

Vacuum Concrete was invented in the year 1935 by Billner in United States. It is a type of method in which excess water is removed with the help of vacuum pressure to increase the strength of concrete since the extra water used in the mixing does not react with cement, which does not lead to formation of heat of hydration.

The process of removal of water is done before settlement of the concrete. There are vacuum mat known as filter pads which are laid above the concrete, connected to  a vacuum pump which generates vacuum pressure resulting in removal of water. The duration of treatment depends on the w/c ratio and the amount of water to be removed which can generally take as long as 15-20 minutes depending on thickness of the concrete.

Why we use Vacuum Concrete

To react water to cement and produce heat of hydration, the water to cement ratio is required to be 0.38, but to maintain the workability the water to cement ratio is taken more. As we know that the more the water to cement ratio in concrete, the less the durability and strength we will recieve.

Just to overcome the problem Vacuum concrete is used so as to remove the extra water gaining high concrete strength and durability.

Equipment used in Vacuum Concrete

1. Vacuum Pump with hose pipe - It is a pump of 5 Hp to 10 Hp which generates vacuum through th hose pipe resulting in suction of water.
2. Water separator - Water of concrete " vacuum " is stored here.
3. Filter Pad - Laid above concrete for suction of water.
4. Screen Board vibrator - Known as beam vibrators normally for 3 m-4.5 m of length.
5. Power floater and Power trowels - These machines are used for finishing works. gives a shiny surface

Procedure of Vacuum Concrete

Firstly, the concrete is poured on the surface and is leveled properly with the help of skilled masons. After that with the help of Screen board vibrator the concrete if compacted properly. The weight of screen vibrator is considerably heavy so atleast two person are required to place and skit it on the surface of concrete. Once the concrete is compacted properly and gets little hard , than the Filter pads are laid on the top of the surface. These filter pads looks like mats and are attached to vacuum pump of 5 HP to 10 HP and water separator. The water is collected in separator and later discharged outside.

After the concrete almost acquire its setting stage floaters and trowels are used for finishing.

Note - We have to take care of laitance ( a white layer of cement or aggregate) which may get deposited from top surface or pump surface.

Advantages of Vacuum Concrete

• They increase the compressive strength of concrete upto 25% to 40% because of the low water content.
• Since they are well compacted and by reducing the water, the voids are been removed resulting in decrease of permeability to concrete.
• The bond strength is increase by 20%.
• Due to the lower water content, the final setting time is reduced to great extent.
• The density of vacuum concrete is high if compared to normal concrete.
• Formwork can be removed earlier.
  

Disadvantages of Vacuum Concrete

• The initial cost of this is high compared to conventional method.
• Requirement of skilled labours having experience with same work needed.
• Specific equipments are required for the work to be executed.

Area of applications

• Used in underground parking also known as 'Trimix'.
• Used in hydro power plants.
• Used in Cold storage's.