What is the Workability of Fresh Concrete?
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Workability is a property of freshly mixed concrete. Concrete is a mixture of cement, aggregates, water, and admixtures. The properties of concrete, whether in the fresh state or hardened state, are affected by its ingredients and their proportions.
An understanding and knowledge of the workability are the most important for making a well-designed concrete mix which can be easily placed and compacted with minimum effort.
Workability is a purely physical property of freshly mixed concrete. Workability of concrete simply means the ability to work with concrete. Fresh concrete is said to be workable if it can be easily transported, placed, compacted, and finished without any segregation. The ease of placing, compacting, and finishing of concrete in the desired manner is called its workability.
Concrete must be workable so that it achieves maximum density with a reasonable amount of compaction effort. If concrete is not workable or relatively less workable, it will not be compacted to its desired density resulting in less strength and porosity ultimately. If concrete is not workable, one will not be able to place it well.
Adequate compaction of concrete is necessary; if it is not done properly there will be voids. The presence of voids will greatly reduce its strength. Voids in Concrete are either bubbles of entrapped air or spaces left after excess water has evaporated. This phenomenon happens when the non-workable concrete has been placed in the structure. Even 2 percent of air voids may lower the strength by as much as 8-10 percent and 5 percent voids can lower the strength by much as 25-30 percent. Further, the voids will lead to leakage, too.
Workability Depends on Following Factors:
- Water-cement ratio (W/C ratio)
- Fine Aggregate to coarse aggregate ratio (FA/CA)
- Cement to aggregate ratio
- Admixtures- Admixtures increase the workability of fresh concrete without increasing water-cement ratio and affecting the strength of the concrete structure.
We have also discussed the factors affecting the workability of concrete.
Elaborating More a Concrete is Said to be Workable If:
- It can be placed without loss of homogeneity. i.e. concrete ingredients never get dispersed while placing and remain uniformly distributed across cross section.
- It can be handled without segregation. i.e. concrete ingredients never get separated during transport or placing.
- It can be compacted with specified effort. i.e. with a normal vibrator or even rodding with bamboo or a rod.
- It can be finished easily.
Thus, concrete with poor workability will result in either segregated concrete or concrete with voids, both resulting in leakage and poor strength. Further it will require a lot of efforts in handling, placing and compacting. Workability of concrete measured by the slump test. To know more about the slump test of concrete.