Water is a key ingredient in the concrete mix, which gives it a fluid texture. But adding the right amount of water is critical. While a water-to-cement ratio of 0.38 initiates the chemical reaction, a ratio of 0.40 to 0.60 makes the mix easier to work with. For this, vacuum emerges as a solution that strikes a balance between these two needs and boosts strength. To explore this further,todays Brick & Bolt’s blog will shed light on vacuum concrete’s applications, procedures, and benefits. Keep reading.
What is Vacuum Concrete?
Vacuum concrete is a type of concrete that involves dewatering from freshly placed concrete using vacuum pressure before hardening. Vacuum pumps and mats are used to remove excess water from the concrete. After achieving the desired workability, excess water should be removed so that the concrete can enhance its durability and strength.
Components Required for Vacuum Dewatering of Concrete
Vacuum dewatering of concrete refers to the process of removing surplus water content from the surface of the concrete using vacuum pressure. The following are the major components required:
Vacuum Pump
Typically, a vacuum pump with a capacity of 5-10 HP is used. It creates controlled vacuum conditions to generate pressures and extract water from the concrete surface.
Water Separator
It is used to separate extracted water from air, preventing water re-entry into the vacuum system.
Filtering Pad
A filtering pad usually consists of porous fabric like muslin cloth and flexible sheet. It prevents debris, aggregates, and contaminants from entering the vacuum system. Moreover, it ensures cement and fine particles are not removed with water. The filtering pad must be at least 90 cm wide and 60 cm long.
Screed Board Vibrator
It supports the process by creating vibration which allows water removal, and further consolidates the mix to ensure levelling of concrete mix. This device has a 4.2-meter steel bar, spaced 250 mm apart, with a water-protected motor.
Procedure of Vacuum Concrete
The vacuum concrete process involves several key steps, which are described below:
- The basic ingredients of concrete are mixed together to achieve a slurry texture, just like in normal concrete. This mixture is then transferred to the formwork.
- Next, a screed vibrator is used to create vibration and compaction in the concrete, allowing water extraction to occur.
- After surface vibration, filter pads are placed on the fresh concrete, leaving approximately 4 inches of concrete exposed on all sides.
- A suction mat top cover is then positioned over the filter pads, covering the concrete completely.
- The vacuum pump is connected to the top cover via a suction hose, and once activated, generates a vacuum of approximately 0.08 MPa.
- As the pump operates, a vacuum is created between the top cover and filter pads, compressing the concrete and squeezing out excess water.
- This process reduces the water content in the concrete by 15-20% and decreases the concrete layer depth by up to 3%.
- The dewatering process typically takes around 1-1.5 minutes per cm of concrete thickness, with the pump running for 15-20 minutes.
- Once dewatering is complete, the concrete is levelled and smoothed using a power trowel and power floater machine.
- The resulting concrete now has enhanced strength and is ready to set.
Advantages of Vacuum Concrete
- A key benefit of vacuum concrete is that workability and strength can be achieved simultaneously.
- The reduced water-cement ratio increases compressive strength by 10% to 15%.
- Vacuum concrete is highly durable compared to normal concrete.
- As excess water is removed, it becomes highly resistant to corrosion attacks.
- Due to its high compressive strength, vacuum concrete prevents water infiltration through the concrete in the future.
- Being void-free, vacuum concrete minimises shrinkage issues.
- Additionally, cement sets faster, allowing for quicker formwork removal.
- The finished floor is level, smooth, and has an even surface.
- Vacuum concrete exhibits high wear and tear resistance.
- Overall, vacuum concrete provides superior durability, it’s one of the high density concrete compared to normal concrete.
Disadvantages of Vacuum Concrete
- Vacuum concrete needs special machines and trained workers, which can be expensive.
- The vacuum process uses a lot of energy which increases electricity costs.
- Vacuum concrete is very dense, making it hard to add reinforcement.
- Vacuum concrete can shrink and crack if not done correctly.
- Vacuum concrete is not suitable for complex or irregular shapes, it is mostly
suitable for flat surfaces.
- The process generates noise and vibrations, potentially disturbing nearby areas.
- Specialised formwork may be needed to achieve desired shapes.
- Vacuum equipment needs regular maintenance, adding costs and repairing damaged vacuum concrete also requires special techniques.
- Vacuum concrete requires longer curing times due to its density.
Application of Vacuum Concrete
Vacuum concrete has a wide range of applications, some of which are listed below.
Structural Components
High-strength buildings and bridges benefit from vacuum concrete’s enhanced compressive strength, ensuring structural integrity.
Water-Resistant Constructions
For water-resistant constructions such as water tanks and swimming pools, vacuum concrete is the preferred material.
Industrial Flooring
Vacuum concrete’s durability minimises maintenance costs for industrial floors in warehouses and factories.
Precast Components
Precast building components, including walls and roofs, rely on vacuum concrete’s precision and durability, ensuring a long lifespan.
Marine Infrastructure
Marine structures, like seawalls and docks, are protected from seawater corrosion with vacuum concrete.
Heavy Foundations
Specialised foundations for heavy machinery require vacuum concrete’s high load-bearing capacity, providing stability.
Architectural Designs
Complex architectural designs and curved shapes can be achieved with vacuum concrete’s precise forming capabilities, allowing creative freedom.
Infrastructure Repair
Vacuum concrete’s long-lasting properties extend the lifespan of repaired infrastructure, including roads and bridges.
Pavements
Vacuum concrete is suitable for pavements, supporting heavy vehicle traffic in parking lots and other high-traffic areas.
Conclusion
Vacuum concrete is the optimal choice, offering workability and high compressive strength. Although its applications are limited, it provides the best solution for construction projects. By utilising efficient energy, vacuum concrete optimises concrete’s strength, water resistance, and durability, ensuring building structures last longer.
Vacuum concrete can be more expensive than traditional concrete due to specialised equipment and processing.
Vacuum concrete is stronger, denser, and more durable than normal concrete due to reduced water and air content
Tests such as slump tests, compressive strength tests, and density measurements are taken to check the quality of vacuum concrete.
It usually takes 12-24 hours but it depends on mixture and environmental conditions.