- Vacuum concrete is concrete which includes high water content during the mixing to facility the mixing process and to improve the workability to enable it to be handled, placed into complicated moulds or around extensive reinforcement.
- Vacuum Concrete made by using steam to produce a vacuum inside a concrete mixing truck to release air bubbles inside the concrete, is being researched.
- Vacuum concrete was first invented by billner in United States in 1935.
- Reducing the final water-cement ratio of concrete before setting, to control strength and other properties of concrete.
- When the steam condenses into water it will create a low pressure over the concrete that will pull air from the concrete. This will make the concrete stronger due to there being less air in the mixture.
Need for Vacuum Concrete
- The chemical reaction of cement with water requires a water-cement ratio of less than 0.38.
- Vacuum concrete is the effective technique used to overcome this contradiction of opposite requirements of workability and high strength.
- Workability and high strength don’t go together as their requirements are contradictory to each other.
- But it is always taken more than 0.38.
- Workability is also important for concrete.
Technique for Vacuum Concrete
- The main aim of the technique is to extract extra water from concrete surface using Vacuum dewatering. As a result of dewatering, there is a marked reduction in effective water-cement ratio and the performance of concrete improves drastically. The improvement is more on the surface where it is required the most.
Equipment for Vacuum Concrete
- Vacuum pump
- Water separator
- Filtering pad
- Screen board vibrator
- With the help of screed vibrator the surface is vibrated.
- About 3% reduction in concrete layer depth takes place.
- By the use of power trowel and power floater the surface is given a hard and smooth finish.
- Vacuum pump is a small but strong pump of 5 to 10 HP.
- The mats are placed over fine filter pads.
- Water from concrete is vacuum and stored in water separator.
Applications of Vacuum Concrete
- Industrials floor sheds like cold storages
- Hydro power plants
- Bridges ports and harbor
- Cooling towers
Advantages of Vacuum Concrete
- Increase of final strength of concrete by about 25%.
- Early removal of wall forms.
- Due to dewatering through the vacuum, both workability and strength of concrete are achieved.
- Durability and density of vacuum concrete are very high.
- Sufficient decrease in permeability of concrete.
- Appreciable reduction of time for final finishing.
- As concrete is resistant to wind and water, it is very useful in storm shelters.
- Increase of about 20% bond strength of concrete.
Disadvantages of Vacuum Concrete
- Need power consumption
- Need specific equipment
- High initial cost
- Need trained labor
- The porosity of the concrete allows water, oil and grease to seep through, consequently weakening the concrete.
- Durability of the floor can be increased.
- 15-25% of water can be extracted out.
- Good quality of floors and pavements can be obtained.
- The compressive strength can be increased by 25-45%.