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What Is Workability of Concrete?
The term workability indicates the ease or difficulty with which the concrete is handled, transported and placed.
The amount of water present in concrete should be in the proper ratio. Generally, a higher water-cement ratio is required for good workability.
The actual function of water is to lubricate the concrete. The concrete which is easy for handling and placing is workable concrete.
There are various tests to measure the workability of the concrete mixture. Tests such as flow test, compacting test, Vee-Bee test, and slump cone test are done to determine the workability of the concrete mixture.
Types of Workability
- Low Workable Concrete
- Medium Workable Concrete
- High Workable Concrete
Low Workable Concrete
Low-workable concrete may also say harsh concrete. Concrete with a little amount of water is known as low workable concrete.
It is tough to mix this concrete by hand. Its water-cement ratio is below 0.4, and the compaction factor for this concrete is about 0.85.
Low workable concrete has high aggregate segregation due to a lack of cement paste lubrication to stick with aggregates.
Maintaining the homogeneity of such concrete is tough and required significant effort for compaction.
Medium Workable Concrete
Medium workable concrete is useful for nearly all construction work. This type of concrete allows simplicity in mixing, transportation, placing, and compaction without losing homogeneity.
This concrete doesn’t show much segregation. The compaction factor of such concrete is about 0.92, and the water-cement ratio is 0.4 to 0.55. This type of concrete is suitable for less dense reinforcement construction work.
High Workable Concrete
This type of concrete provides greater simplicity in mixing, transportation, placing, and compaction.
This concrete is useful for such construction work where adequate compaction is not possible.
This type of concrete flows smoothly and settles down without extra effort, but there is a strong possibility of segregation and loss of homogeneity in this situation. The water-cement ratio for this concrete is more than 0.55.
Due to the high water-cement ratio, coarse aggregate tends to settle down, and concrete paste comes up.
This concrete is suitable where the density of reinforcement is high, and concrete vibration is not possible. Self-compacting concrete (SSC) is an example of high workable concrete.
Factors Affecting The Workability of Concrete
- Water Content
- Size of Aggregate
- Shape of Aggregate
- Grading of Aggregate
- Surface Texture of Aggregate
- Amount of Cement
- Admixtures
Water Content
If the water content is more, it will result in an increase in the workability of concrete, If the water content is less than required, it will result in difficulty to handle the concrete and place it in the proper place. So water is added to the concrete according to the water-cement ratio.
The ratio of the amount of water to the amount of cement by weight is termed the water-cement ratio. The strength and quality of concrete depend on this ratio.
The quantity of water is usually expressed in litre per bag of cement. if water required for one bag of cement is 30 litres, the water-cement ratio is equal to 30/50 = 0.6.
The water-cement ratio should be such that it should impart a reasonable degree of workability to concrete, excess water affects the durability and strength of the concrete.
A lesser water-cement ratio makes the concrete unworkable while the excess water-cement ratio is liable to segregation. keeping the quality and quantity of ingredients the same, it is the water-cement ratio that determines the strength of concrete.
Size of Aggregate
If the size of aggregate is small that means more is the surface area which required more water as well as more cement paste or vice versa. So the bigger size of aggregates for the given quantity of water and cement paste will give higher workability.
Shape of Aggregate
The workability of rounded or cubical size aggregate is more than angular or flaky aggregates. As angular or flaky aggregates give the concrete very harsh.
Due to the round size of aggregates, the frictional resistance between the aggregates is greatly reduced.
So, as well as possible the aggregates should not be angular or flaky in the shape for getting more workable concrete.
Grading of Aggregate
If aggregates are well graded, that means less will be the void content and higher will be the workability, so as well as possible, the aggregate should be well-graded.
Surface Texture of Aggregates
If the surface of the aggregates is smooth or glassy texture, it will produce less surface area and will give better workability.
The frictional resistance between the smooth particle is reduced and which will produce higher workability. So this is an important factor for workability.
Amount of Cement
Cement content much affects the workability of concrete. If we increase the cement quantity, more will be the cement paste to cover the surface of the aggregate and for void filling.
It helps in reducing the friction between aggregates resulting in smooth movement of aggregates in transporting, placing, and compacting concrete.
For a specified water-cement ratio, an increase in cement quantity will increase the amount of water for concrete per unit volume, hence growing the concrete workability.
Admixtures
Admixture plays a vital role in improving the properties of concrete. Superplasticizers and plasticizers much enhance the workability of concrete with a low water-cement ratio.
They are also known as water-reducing admixtures. They help in reducing the quantity of water required for the same slump value.
Air entraining admixture also greatly increases the workability of concrete. It helps in reducing friction between aggregates by creating numbers of air bubbles that act as rollers between aggregate particles.
Conclusion
I hope now you understood the workability of concrete. If you found this information helpful, please be sure to share it with your friends.
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