What is Workability of Concrete?
Workability of cement is defined as ease or difficulty to work with concrete is handled, transported and placed between the forms with minimum loss of homogeneity. In other word “Workability is the property of concrete by virtue of which it can be mixed, transported, placed, compacted and finished”.
Factors Affecting Workability –
The factors helping concrete to have more lubricating effect to reduce internal friction for helping easy compaction, these are as follows.
- Water content – The higher the water content per cubic meter of concrete, the higher will be the fluidity of concrete not affect the workability however, it reduces its strength due to high in its water-cement ratio. Hence, in order to increase the workability cement content is also increase in proportion with water content such that water- cement ratio remains constant.
- Mix Proportions – Higher the aggregate- cement ratio, the leaner the concrete and lesser the workability. Lower aggregate- cement ratio gives cohesive and fatty mix with better workability.
- Size and Shape of Aggregates – The bigger the size of aggregate, higher will be the workability up to an extent as smaller area is to be lubricated in this case. Angular, elongated or flaky aggregate makes the concrete very harsh compared to rounded or cubical aggregates.
- Surface Texture – A rough surface aggregate will have more surface area than a smooth round textured aggregate. Smooth textured aggregates contribute to higher workability.
- Grading of Aggregate – Well graded aggregates with less void content, as more is the availability of free cement paste for lubrication for same surface, gives higher workability.
- Use of Admixtures – Admixture may increase workability. Air entrained concrete is more workable. It is so because air forms bubbles, on which the aggregates slide past each other increasing the workability
Test for Measurement of workability
- Compaction factor test – Preferable for very low workability. Higher compacting factor means high workability.
- Slump Test – Preferable for low, medium, and high. Its value varies from 25mm (Low) to 150mm (High).
- Vee-Bee Test – This test is used to find workability of slump concrete less than 50mm. Higher value of time means low workability.
- Flow Test – This is performed for the concrete which possess very high workability.
- Kelly Ball Test –
There are five degree of workability as per IS-Code –
Consistency is a general term to indicate the degree of fluidity or degree of mobility. A concrete which has more consistency and which is more mobile, need not be of right workability for particular job. Every job requires a particular workability –
Values Of Workability for Different Placing Condition –
|Sl. No.||Degree of Workability||Slump (mm)||Compacting Factor||Vee-Bee Degree (sec)||Placing Condition|
|Small Apparatus||Large Apparatus|
|1||Very Low||–||0.78||0.80||>20||Highway construction; Blind concrete; Shallow sections;|
|2||Low||25-75||0.85||0.87||12-20||Mass concreting (like, dam construction); light reinforced section in slab, beams, column, walls; Floors; Footing;|
|3||Medium||50-100, 75-100||0.92||0.935||6-12||Heavily reinforced section of slab, column, beams, and when pumping of concrete is required, Slipform work.|
|4||High||100-150||0.95||0.96||3-6||In-situ piling, Trench fill|
|5||Very High||–||–||–||0-3||In-situ piling using tremie pipe|