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 the 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 the 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 combinations of these actions.
Consolidation is essential because freshly mixed concrete generally has the entrapped air in it which is become a reason for honeycombing in concrete.
If there if do not apply consolidation then the concrete will become non-uniform, weak, porous, and poorly bonded to the reinforcement. It will also have poor appearance and quality.
Concrete Consolidation Methods
The following are various types of consolidation used for concrete
(1) Hand Compaction
(i ) By Rodding (ii ) By Ramming (iii ) By Tamping
(2) Compaction by Vibration
(i) Internal vibrator (Needle vibrator)
(ii) Formwork vibrator (External vibrator)
(iii) Table vibrator
(iv) Platform vibrator
(v) Surface vibrator (Screed vibrator)
(vi) Compaction by Pressure and Jolting
(vii) Compaction by Spinning.
Lets discuss each method in details,
1. Hand Compaction
Hand compaction of concrete is generally employed where concrete quantity is small and for unimportant work.
i) Rodding: This first method of hand compaction is Rodding. In this method, a rod of dia minimum of 16 mm and length of about 1m is used. Rodding is continuously inserted in concrete to compact concrete and remove air void from it.
ii) Ramming: Light ramming method is generally used for unreinforced foundation concrete or in-ground floor construction.
iii) Tamping: Tamping is mostly used in case of pavement, floor slab where the thickness of concrete is comparatively less and the surface to be finished smooth and level. Tamping is done by continuous beating the concrete surface by the wooden crossbeam.
- In the case of high-strength concrete, the water-cement ratio is too low and 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 ingredient give them time to settle down in a compacted mass of concrete.
i) Internal Vibrator
The internal vibrator is widely used on a construction site. It is also called “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 internal vibrator-like frequency, amplitude, and head dimensions of vibrators.
Generally, the shape of the vibrator needle is cylindrical and has a needle diameter around 2 to 12 cm. As the needle diameter increases the effective actionable area of the needle also increase. For example, if the needle dia. is 4 cm then it an 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 also important to achieve the best compaction. To avoid segregation defects in concrete horizontal movement of vibrator must be avoided. Effective compaction depth is about the length of the needle or 50 cm.
While using needle vibrator in the slab, try to keep it into concrete and this can be done by laying needle horizontally or at an angle in concrete to use addition 1.5 times the radius action as the distance to guarantee overlap 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 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 come 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 member is too high and needle vibrator may not reach to full the depth of members such as column, thin concrete wall and precast concrete members. This vibrator machine clamped to the external surface of formwork.
Formwork vibrator must be properly attached to forms otherwise energy will be lost because of improper attachments. This types of the vibrator are proven best choice in case compacting concrete in thin and heavily congested forms, consolidating stiff mixtures, and supplementing external vibrators.
Formwork vibrator is played an important role in the manufacturing of pipes, masonry units, and other types of precast concrete. The spacing of form vibrator is also important to apply transfer same amount of vibration inside the concrete member.
iii) Table Vibrator
This is one type of formwork vibrator which is clamped to the table. They’re generally used for compacting concrete cube and small concrete precast members.
iv) Platform Vibrator:
Platform vibrator is similar to 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.
Read More: 17+ Uses Of Concrete In Construction
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 proved effective for compaction and leveling of thin concrete members, such as floor slabs, roof slabs, and road surface.
vi) Vibratory Roller
Generally, for compaction of very dry and lean concrete vibratory roller are used.
Effect of Improper Compaction
If compaction or consolidation of concrete is done properly, then are many defects can develop in concrete such as,
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