What is Compaction of Concrete?
Compaction is the process of moulding concrete in the desired shape formwork and obtain homogeneous concrete without voids so that compaction of concrete improves quality of concrete
The amount of air trapped in the concrete depends on the workability of concrete or the hardness of the mixture
The Workability is inversely proportional to the voids (air) available in the concrete mix i.e. If lower the Workability than the amount of air present in the mix concrete is higher
For example, the stiff concrete mixture has a high amount of air voids and therefore, it should need higher compacting work otherwise chances of segregation or honeycombs
The density, strength and durability of concrete highly depend on the compaction quality
A Requirement of Compaction of Concrete
Necessary of Compaction becomes useful like
Condensation helps reduce internal friction between concrete material and between reinforcement and concrete and between formwork and concrete
The internal friction of particles available in the concrete mixture makes it difficult to form concrete
Friction also prevents the concrete from coming in close contact with the reinforcement, which becomes a cause of a poor bond between the reinforcement and the surrounding concrete
The air inside the concrete mix reduces the strength of concrete greatly
If I give an example in data then only 5 per cent Voids presence in hardened concrete left due to incomplete/improper compaction of concrete may decrease the strength of concrete by about 35 per cent and 10 percent voids reduce the strength by about 50 per cent
Therefore, 100 Percent compaction of concrete is of the topmost importance in the operation of compaction
Air voids available in the hardened concrete makes the concrete honeycombed and increase the permeability of concrete which is not allowable
Hence fully compaction is the first requirement and also an answer to why compaction of concrete is necessary
Purpose of Compaction of Concrete
The main importance of concrete compaction is to achieve a dense concrete without any air voids, to obtain the concrete to surround all reinforcement bars and to fill all conner of formworks
Poor compaction of concrete give poor structural strength and durability
- The best result achieved by the vibrator compaction method
- Rodding, spading and tamping is also an alternative way of removing voids from concrete and to compact, however, the best and effective method is a vibration but at some conditions, another method becomes useful due to some reason and we have done our work
Methods of Compaction of Concrete
- Hand compaction method
- Compaction by vibration method
- Compaction by pressure and jolting method
- Compaction by a spinning method
The choice of a particular method of compaction of green concrete depends upon the various because some are useful for one condition but in the same condition, others are inadequate compaction of concrete results in bad effect
So The choice of a particular method of compaction depends on various factors like
- Structure element type
- Different properties of concrete mixture, mainly its w/c ratio
- The desired properties of hardened concrete like strength, durability, water tightness etc
- Production process duration and rate of output in case of precast concrete elements
1. Hand Compaction
- Rodding
- Ramming
- Tamping
Compaction of concrete by hand is generally adopted for small and unimportant works and also adopted in a condition where a large quantity of reinforcement is used so that you cannot be compacted by mechanical methods
a. Rodding
- Rodding is nothing but concrete to be beaten with rods of about 2 meters in length and 16 mm in diameter
- A small piece of bamboo can also be used to stick/rodding concrete
- Concrete is packed between reinforcement and sharp corners and edges by rodding
- The thickness of the concrete layer is limited to about 15 cm to 20 cm
b. Ramming
- Ramming is typically done in unreinforced foundation concrete or surface/ground construction
- In the case of reinforced concrete or any upper floor construction, it should not be permitted
- To compact dry mix concrete, the concrete surface is rammed with the help of a heavy flat-bottomed rammer, until a small quantity of cement paste is visible on the surface, indicating that the concrete voids Are filled
c. Tamping
- Tamping is adopted in compacting roofs or floors or roads pavements where the thickness of the concrete casting is comparatively small and the surface is smooth and flat
- A wooden beam that is used for tamping which cross-section 10cm * 10cm
Compaction by hand, give satisfactory results but the strength of concrete will be lower due to the higher w / c ratio required for complete condensation
2. Compaction by Vibrator
Construction work where high strength is required, it is necessary to use hardened concrete with a low W/C ratio. To compact the hardened concrete, mechanically operated vibrators are used
Compaction done by vibration has many advantages compared to hand compaction which is as follows
- A concrete of stiff consistency with the slump of around 4 cm can be placed in forms which containing closely spaced reinforcement structure design, while hand compaction required much higher consistency about maybe 12 cm slump
- If you use the vibrator compaction method then allows less water usage. Hence concrete of higher strength and better quality can be achieved with a given cement content because less mixing water can be used
- Lower w/c ratio and lower cement content can produce equally strong concrete more economically than by hand compaction
- In the case of congested reinforcement or inaccessibility of the concrete in the formwork, hand compaction methods are not practicable. In such situations concrete can be compacted by a vibration more effectively
- The increased bond strength between reinforcement and concrete
- Decreased time of compaction and subsequent savings in labour cost etc
Types of Vibrator in Civil Engineering
- Internal vibrator
- External vibrator
- Table vibrator
- Surface vibrator
3. Compaction by Pressure and Jolting
- In this method, stiff concrete is subjected to external pressure from the top and vibration from the bottom along with a series of jolting actions
- Excess water added during mixing exits due to large pressure
- By using great pressure, a concrete of which has a very low w/c ratio can be compacted to yield very high strength
- This method is used to compact hollow blocks, cavity blocks, and concrete blocks
4. Compaction by Spinning
- Compaction by Spinning is also called centrifugation
- This method Compaction by Spinning is used in the manufacture of concrete pipes, concrete lamp posts etc.
- It consists of feeding concrete into a slow spinning horizontal mould
- The spinning speed is increased after the pre-determined concrete is fed into the mould
- Water is extracted from the mixture. At the end of the spinning process, the speed gradually decreases and the dry cement is sprinkled in small quantities
- The initial w/c ratio of 0.35 to 0.40 reduced to about 0.30 after spinning
Patented products such as spun pipes and Hume pipes are compacted by the spinning process
FAQ 1: What is Compaction of Concrete?
We can define the compaction of concrete in simple words in this wayCompaction is the process of moulding concrete in the desired shape formwork and obtain homogeneous concrete without voids so that compaction of concrete improves quality of concreteThe amount of air trapped in the concrete depends on the workability of concrete or the hardness of the mixtureThe Workability is inversely proportional to the voids (air) available in the concrete mix i.e. If lower the Workability than the amount of air present in the mix concrete is higherFor example, the stiff concrete mixture has a high amount of air voids and therefore, it should need higher compacting work otherwise chances of segregation or honeycombsThe density, strength and durability of concrete highly depend on the compaction quality
FAQ 2: A Requirement of Compaction of Concrete
Necessary of Compaction becomes useful likeCondensation helps reduce internal friction between concrete material and between reinforcement and concrete and between formwork and concreteThe internal friction of particles available in the concrete mixture makes it difficult to form concreteFriction also prevents the concrete from coming in close contact with the reinforcement, which becomes a cause of a poor bond between the reinforcement and the surrounding concreteThe air inside the concrete mix reduces the strength of concrete greatlyIf I give an example in data then only 5 per cent Voids presence in hardened concrete left due to incomplete/improper compaction of concrete may decrease the strength of concrete by about 35 per cent and 10 percent voids reduce the strength by about 50 per centTherefore, 100 Percent compaction of concrete is of the topmost importance in the operation of compactionAir voids available in the hardened concrete makes the concrete honeycombed and increase the permeability of concrete which is not allowableHence fully compaction is the first requirement and also an answer to why compaction of concrete is necessary
FAQ 3: Purpose of Compaction of Concrete
1. The best result achieved by the vibrator compaction method.2. Rodding, spading and tamping is also an alternative way of removing voids from concrete and to compact, however, the best and effective method is a vibration but at some conditions, another method becomes useful due to some reason and we have done our work.
FAQ 4: Methods of Compaction of Concrete
Hand compaction methodCompaction by vibration methodCompaction by pressure and jolting methodCompaction by a spinning method
FAQ 5: Types of Vibrator in Civil Engineering
Internal vibratorExternal vibratorTable vibratorSurface vibrator
