What Is Consolidation of Concrete?
Consolidation of Concrete is the process of reducing or eliminating the volume of voids, air pockets, and entrapped air from the fresh concrete mix, usually accomplished by applying mechanical energy.
Concrete Consolidation is also related to a process of reducing the gap between aggregate and aggregate; between aggregate and reinforcement; and between aggregate and forms.
The main aim of the consolidation of concrete is to eliminate the air voids from concrete and increase its density of concrete.
As we know the higher density of concrete gives high compressive strength. Proper and close contact between reinforcement and concrete is ensured by proper consolidation.
Consolidation of concrete is significantly the ultimate strength of concrete and enhances the bond with reinforcement.
It also increases concrete durability and abrasion resistance decreases permeability and helps to minimize its shrinkage-and-creep characteristics.
Consolidation of concrete is done by a different method usually by vibration, centrifugation, rodding, tamping, or some combination of these actions.
Consolidation is essential because freshly mixed concrete generally has entrapped air in it which is become a reason for honeycombing in concrete.
If there does no applied consolidation then the concrete will become non-uniform, weak, porous, and poorly bonded to the reinforcement. It will also have a poor appearance and quality.
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Factors Affecting Concrete Consolidation:
Workability of concrete:
Workability it refers to its ease of mixing the ingredient, compacting, placing and consolidating the concrete and it plays a significant role in consolidation process of concrete.
Concrete with higher workability is generally easier to consolidate effectively.
Reinforcement and embedded item:
The presence of embedded item like electrical pipes, conduits and reinforcement bars can obstruct the movement of the vibrator, so that proper placement and positioning of this element is crucial for ensuring thorough consolidation.
Shape and Size of the Formwork:
The shape and size of the formwork used for casting the concrete element and it affect the consolidation process.
Thickness of Concrete Pour and Vertical Height:
The thickness of concrete pour and vertical height of pour can influence the consolidation process; higher vertical height or thicker concrete section may require special attention.
Concrete mix proportion:
The mix proportion and the properties of the concrete like shape and size of aggregate, water cement ratio and admixture can impact its consolidate ability and workability.
Equipment and techniques use:
The selection of appropriate consolidation equipment and techniques and it play a vital role in achieving proper consolidation technique.
Different consolidation method like external vibrators, internal vibrator or formwork may be more suitable for specific project requirements.
Ambient Temperature and Condition:
Ambient temperature condition includes the humidity and temperature and it can affect the initial setting time and final setting time, workability of concrete, higher temperature can accelerate the concrete setting process and it require faster and more efficient consolidation process.
Time Constrains and Construction Schedule:
The time constrain and construction schedule can affect the process of consolidation.
Concrete Consolidation Methods
The following are various methods of consolidation used for concrete,
- Hand Compaction
- By Rodding (ii ) By Ramming (iii ) By Tamping
- Compaction by Vibration
- Internal vibrator (Needle vibrator)
- Formwork vibrator (External vibrator)
- Table vibrator
- Platform vibrator
- Surface vibrator (Screed vibrator)
- Compaction by Pressure and Jolting
- Compaction by Spinning.
Let’s discuss each method in detail,
1. Hand Compaction
Hand compaction of concrete is generally employed where concrete quantity is small and for unimportant work.
Rodding:
This first method of hand compaction is Rodding. In this method, a rod of a minimum of 16 mm and a length of about 1m is used. Rodding is continuously inserted in concrete to compact concrete and remove air void from it.
Ramming:
The light ramming method is generally used for unreinforced foundation concrete or in-ground floor construction.
Tamping:
Tamping is mostly used in the case of pavement, and floor slabs where the thickness of concrete is comparatively less and the surface is finished smooth and level.
Tamping is done by continuously beating the concrete surface with the wooden crossbeam.
2. Vibration
In the case of high-strength concrete, the water-cement ratio is too low and the concrete is too stiff to compact by hand.
To compact such types of concrete, mechanically operated vibratory equipment must be used.
By use of a vibrator, we can complete compact 4cm slum value concrete in a closely spaced reinforced concrete work, whereas, for hand, compaction can use for only up to 12 cm slum value concrete.
Vibration reduces the friction between concrete ingredients and gives them time to settle down in a compacted mass of concrete.
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(i) Internal Vibrator
The internal vibrator is widely used on construction sites. It is also called a “Poker Vibrator” or “Needle Vibrator”. It generally consists of a power unit, a flexible shaft, and a needle.
Internal vibrators are used to compact concrete in beams, walls, columns, and slabs. There are many factors that affect the performance of the internal vibrator-like frequency, amplitude, and head dimensions of vibrators.
Generally, the shape of the vibrator needle is cylindrical and has a needle diameter of around 2 to 12 cm.
As the needle diameter increases the effective actionable area of the needle also increases. For example, if the needle dia. is 4 cm then its effective area in concrete will be 15 cm and if the dia. of the needle is 8cm then its effective area in the concrete is about 45 cm.
Moreover, the correct method of using an internal vibrator is also important to achieve the best compaction. To avoid segregation defects in the concrete horizontal movement of the vibrator must be avoided. Effective compaction depth is about the length of the needle or 50 cm.
While using the needle vibrator in the slab, try to keep it in concrete this can be done by laying the needle horizontally or at an angle in concrete to use additional 1.5 times the radius action as the distance to guarantee overlap of the previously adjacent vibrated layer.
The needle must be kept in the same position for at least for 5-15 seconds to obtain desirable consolidation.
The time for which the needle is kept submerged in concrete generally depends on workability, the force of the vibrator, and the nature of the element that is being compacted.
When aggregate from the surface of concrete goes down and cement slurry comes up, then we can say that the compaction of concrete is done properly.
(ii) Formwork Vibrator (External Vibrator)
Formwork vibrators are mostly used where the depth of concrete members is too high and needle vibrators may not reach full the depth of members such as columns, thin concrete walls, and precast concrete members. This vibrator machine is clamped to the external surface of the formwork.
Formwork vibrator must be properly attached to forms otherwise energy will be lost because of improper attachments.
This type of vibrator is proven best choice in cases compacting concrete in thin and heavily congested forms, consolidating stiff mixtures, and supplementing external vibrators.
Formwork vibrators are played an important role in the manufacturing of pipes, masonry units, and other types of precast concrete.
The spacing of the form vibrator is also important to apply the transfer same amount of vibration inside the concrete member.
(iii) Table Vibrator
This is one type of formwork vibrator that is clamped to the table. They’re generally used for compacting concrete cubes and small concrete precast members.
(iv) Platform Vibrator
A platform vibrator is similar to a table vibrator, but its size is larger than it. This type of vibrator is generally used to consolidate big prefabricated concrete elements such as electric poles, railway sleepers, prefabricated roofing elements, etc.
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(v) Surface Vibrator
Surface vibrators are called “Screed Board Vibrators”. A small size vibrator fixed on a screed board is called a surface vibrator. Screen Board vibrator is proven effective for compaction and leveling of thin concrete members, such as floor slabs, roof slabs, and road surfaces.
(vi) Vibratory Roller
Generally, for compaction of very dry and lean concrete vibratory rollers are used.
Effect of Improper Compaction
If compaction or consolidation of concrete is done properly, then many defects can develop in concrete such as,
- Honeycomb
- Sand streaks
- Cold joints
- Subsidence cracking
- Placement lines
Conclusion:
In conclusion the consolidation of concrete is a critical step in the construction process which significantly impacts the quality, durability and strength of the concrete structure.
By effectively eliminating the air voids and achieving proper consolidation and enhance the overall performance and longevity of concrete.
Various type of Consolidation method such as external vibration, internal vibration, self-consolidating concrete(SCC), surface rodding and it provide construction professionals
Proper consolidation ensures that the concrete mixture is uniformly distributed, reducing the risk of cracking, shrinkage, and the formation of weak spots.
It minimizes porosity and permeability, thereby preventing the ingress of harmful substances and protecting against corrosion and structural damage.
Consolidation methods, such as internal vibration, external vibration, surface rodding, and self-consolidating concrete (SCC).
These all method improve the workability, adhesion, enhance bonding and it allow for construction in challenging condition. This Consolidation process is help to increase strength, reduced maintenance needs, improved durability.
FAQs:
What is the consolidation of concrete?
The consolidation of concrete refers to the process of compacting freshly poured concrete to remove trapped air voids and achieve maximum density and strength.
What are the common methods used for concrete consolidation?
The commonly used methods for concrete consolidation include internal vibration (using vibrating poker or needle), external vibration (using vibrating screed or formwork vibrators), and mechanical methods such as tamping or rodding.
What is self-consolidating concrete (SCC)?
Self-consolidating concrete is a highly flowable type of concrete that is able to consolidate under its own weight without the need for mechanical consolidation methods. SCC is useful in situations where traditional consolidation techniques may be challenging or impractical.
What are the mechanical methods used for concrete consolidation?
Mechanical methods of concrete consolidation include tamping and rodding. Tamping involves manually compacting the concrete using a handheld tamper, while rodding involves inserting a rod into the concrete and moving it vertically.
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