What is workability of concrete?
A concrete is said to be workable if it is easily transported, placed, compacted, and finished without any segregation of concrete materials. And that ability is known as the workability of concrete.
Segregation is the separation of concrete materials like aggregate, sand, and water with each other while casting. It decreases the strength of concrete due to a nonhomogenous mixture of materials in different portions of structural members.
Factors affecting workability of concrete
It is very necessary to be workable concrete. Because it decides the quality of concrete. The workability of concrete depends upon the different factors given below.
Without the workability of concrete, we can not transport, place or finish the concrete properly after mixing all ingredients of concrete. The factors that affect the workability of concrete are given below.
- Water content in concrete
- Amount of Cement and its properties
- Aggregate Grading
- Nature of aggregate
- Concrete Admixture
Now let us describe all of them one by one in brief.
1) Water content in concrete:-
The workability of concrete increases as the water content in it increases but keep in mind the strength of concrete decreases.
Water added in concrete acts as a lubricant but too much water creates segregation in concrete because water creates gaps between the ingredients of concrete.
So, the right amount of water should be added to concrete to be a good workable concrete.
2) Amount of cement and its properties
The workability of concrete increases with increasing the amount of cement in it. The addition of water in concrete need more water for lubrication.
The finer cement increases the workability of concrete. The size of grains in types of cement decides the fineness of the cement. Some cement has small grains of cement which makes it finer than other cement.
3) Grading of Aggregate (Size of aggregate)
A properly graded aggregate is more workable because these types of aggregate create less void between the ingredients due to which the cement paste can reach everywhere. A well-graded aggregate decreases the segregation in concrete.
The different sizes of aggregate make the aggregate well graded for concrete to reduce the voids between aggregate in concrete.
For big-size aggregate, the total surface area to be wetted is less, so less amount paste is required for lubrication of the surface to reduce the internal friction. Hence for the given water content, the big size of aggregates provides more workability to concrete.
The presence of more “fines” (Sand and cement) in the mix improves the workability of concrete as well as decreases the segregation in concrete. This is because the fines act as a lubricant and fill all the voids making strong bonds as mortars.
Too much fine aggregate (Sand) decreases the quality of concrete because it affects the durability and impermeability of concrete after hardening.
So, a desirable quantity of fine aggregates should be used to prepare concrete.
4) Nature of aggregate (Shape, Surface Texture, porosity)
For a given water content round and cubical shape, aggregates are more workable than rough angular or flaky aggregate.
As round and cubical shape aggregate have a lesser surface area and lesser void, less amount of cement paste is required as a lubricant. In these types of aggregates, frictional resistance is also small and so less amount of lubricant is required. Hence river sand and gravel are more workable than crushed sand and gravel.
A rough surface aggregate has more surface area than a smooth one. So, smooth round aggregates are more workable.
Porous aggregate observes more water and makes the concrete less workable at a given water-cement ratio. As the porous aggregate observes more water, the water content in the concrete becomes less and makes concrete less workable.
5) Concrete admixture
There are different types of admixture having different functions that are used in concrete. The workability of concrete depends upon the types of admixture used in concrete.
Some of the admixtures are used to increase the workability whereas some of the admixtures are used to decrease the workability of concrete. Admixtures are used according to the required condition of construction sites.
For example, Plasticisers are used to achieve higher strength by reducing the water-cement ratio from the concrete as a result there is an increment of workability in concrete.
How do you measure the workability of concrete?
The workability of concrete can be measured by the following method given below.
- Slump Test
- Flow table test
- Vee-Bee Consistometer
- Compaction factor test
- Kelly Ball Test
In the next article, I will discuss the above process in detail.
I hope this article on “Factors affecting workability of concrete” remains helpful for you.
Happy Learning – Civil Concept