Vacuum concrete is a type of concrete that is produced by using vacuum technology during the mixing and casting process. This method aims to remove excess air from the concrete mixture, resulting in a more durable and higher-quality concrete.
The process typically involves placing the concrete mix in a vacuum chamber to reduce the pressure, which causes the air bubbles to expand and rise to the surface. By removing the excess air, vacuum concrete can have improved strength, durability, and resistance to freeze-thaw cycles.
What Is Vacuum Concrete?
Vacuum concrete is a type of concrete in which excess water is removed to increase its strength parameter before a hardening starts. This water is generally extracted by the use of vacuum mats connected to the vacuum pump. The amount of water mixed in concrete while making is not a necessity for the full hydration process.
In Vacuum Concrete excess water is removed from fresh concrete to increase its strength before hardening takes place. Vacuum Concrete is an equipment-oriented technique to extract surplus water after placing a highly workable concrete mix with the help of a vacuum.
Necessity of Vacuum Concrete
The high water-cement ratio is detrimental to the quality of concrete.
The hydration of cement is sufficed by the water-cement ratio of 0.38. Water in excess of this amount adversely affects the quality of concrete in terms of strength. However, a low water-cement ratio reduces the workability of concrete and renders its handling and compaction difficult.
As a result, high strength with higher workability is generally difficult to achieve simultaneously. The vacuum concrete fulfils this contradicting demand of attaining higher strength for workable concrete.
Properties of Vacuum Concrete
- Increase in strength to about 25%
- Increase in density
- Decrease in permeability
- Increase in durability
- Increase in abrasion resistance
- Increase in impact resistance by 10%
Advantages of Vacuum Concrete
The following are vacuum concrete advantages,
- Higher workability can be achieved along with a higher strength of concrete.
- The final strength of concrete is escalated to about 25 % (Both compressive and tensile strength of concrete are elevated.)
- Vacuum concrete improves the bonding strength of concrete to about 20% which facilitates easy bonding with underlying concrete.
- Formwork can be removed early since concrete stiffens rapidly. This enables its usage in other repetitive works. Additionally, this allows the structure to be put into use early.
- The curing period is reduced. 1 week curing period is reduced to 3 days and 4 weeks curing period can be brought down to 1 week.
- A Reduced water-cement ratio not only increases strength but also reduces the permeability of the concrete.
- The durability and density of vacuum concrete are both quite good, with a reduction in voids
- Final finishing of the floor of concrete can be achieved earlier
- Compaction is made easier and more effective
- The surface of vacuum concrete is pitting-free.
- The top layer has a very high resistance to abrasion, which makes it a suitable choice for the construction of structures in contact with water flowing at large velocities.
Equipment Required for Producing Vacuum Concrete
The following equipment’s required to produce vacuum concrete,
- Formwork
- Vacuum pump with hose
- Filtering pad
- Suction mat
- Double beam screed vibrator
- Power float
1. Formwork
Mostly MS channels are used for formworks. They perform a twofold function as in stopper & providing support to screed vibrator.
2. Vacuum Pump
It is small yet powerful. Normally, it is hosts electric motor of 5-10 horsepower.
3. Filtering Pad
A filtering pad constitutes a backing piece and a rubber seal. The seal has wrapped all-round the periphery around. Over this backing piece, an expanded metal sheet is placed, which a sheet of wire gauge covers.
The mat of minimum size 90 * 60 cm should be taken. Smaller mats are not effective in generating a vacuum.
4. Suction Mat
It consists of a large single PVC sheet. Nylon/muslin cloth is laid beneath to work as a fine filter. The top surface of mat houses a junction box and hose.
5. Power Trowel
During the suction of water, capillaries are formed in concrete when water is forced out of it. These capillaries are detrimental to the concrete and hence should be corrected. Power trowel does exactly that. It fills up the cracks through vibrations.
6. Power Float
It is used for grinding the surface. As a result, the surface attains wear resistance. It also helps in removing surface modulations so that the surface finishing can be achieved with ease.
7. Double Beam Screed Vibrator
It is a lightweight electrically driven vibrator weighing 128.5 kg.
Application of Vacuum Concrete
The following are vacuum concrete uses,
- Large scale production of precast PCC & RCC units in the factory
- Construction of horizontal & sloping concrete slabs
- Workshops & warehouse construction
- Canals
- Railway platforms
- Airport pavements & Docks
- Thin load-bearing walls
- Partition walls
- Parking lots & Basements
- Resurfacing & repair of road pavement (as it bonds well with the previously laid concrete)
- Hydropower plants
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