The workability of concrete is defined as the property of freshness that determines the ease and symmetry with which concrete can be mixed, placed, compacted, and finished.
It is a parameter in which the type of work, distance of transport, loss of deceleration, method of placing, section thickness, method of compaction, mixture design, etc. must be specified properly.
Workability of fresh concrete is a complex system involving numerous parameters such as flow capability, mobility, stability, pump capacity, compatibility, elimination capacity, and isolation bleeding.
Workability of fresh concrete is a complex system of two essential parameters.
Consistency: The ability of fresh concrete to circulate constantly.
Homogeneity: Homogeneity means uniform and stable distribution of materials such as cement, aggregates and water and provides resistance to separation.
Types of Workability of concrete:
An unworkable concrete is typically known as harsh concrete that includes a very small amount of water.
The hand mixing of such concrete is difficult, such concrete has excessive separation of aggregates and it is extremely difficult to maintain the homogeneity of the concrete mixture.
Medium Workable concrete:
Medium workable concrete is used in most construction works.
This separation is comparatively easy to combine, transport, place and compact without much segregation and lack of homogeneity.
Highly Workable Concrete:
This type of concrete could also be very simple to mix, transport, place and compact used where environment-friendly compaction of concrete will not be possible.
The problem is that there are extreme possibilities of segregation and lack of homogeneity in extremely workable concrete.
factors affecting workability of Concrete:
The higher the amount of water per m3 of concrete, the higher the fluidity of concrete which affects the workability.
High water content can lead to increased bleeding and separation of aggregates, resulting in poor quality of concrete.
Aggregate / cement ratio is an important factor affecting the workability.
The higher the aggregate/cement ratio, the leaner is the concrete.
Lower aggregate /cement ratio implies more paste is offered to make the mix cohesive and gives greater workability.
Size of Aggregate:
For aggregates of larger size, the surface area is less therefore less amount of water and cement paste is required to cover the surface area.
Therefore to a certain extent, larger aggregate gives more practical concrete.
The shape of Aggregates:
The angular elongated or flaky aggregate makes the concrete much stiffer than the rounded aggregate.
Round aggregates will give more workable concrete.
Round aggregates will reduce the abrasion resistance while increasing the workability of the concrete.
Surface Texture of Aggregate:
Rough surface particles require more cement paste than smooth surface particles.
Smooth surface particles provide high workability.
Grading of Aggregates:
A well-graded aggregate has a lower ratio and provides better smoothing effects and greater workability.
Use of Admixture:
The use of an air-entraining agent reduces internal friction between particles and gives high practicality.
Similarly, fine glass pozolanic materials to enhance the surface provide better lubrication effect to give better functionality.
Ways to improve the workability of concrete:
These are some of the ways to increase the practicality of concrete as follows:
- By increasing the water / cement ratio.
- By using a large aggregate.
- Using well-rounded and smooth aggregates rather than irregular shapes.
- By enhance mixing time and temperature.
- Using non-porous and saturated aggregates.
- With the addition of air-entraining admixtures.
- Adding a suitable mixture to the concrete.
A workable concrete will have a uniform color, the aggregates shall be lubricated with sufficient cement paste so that the concrete can be easily poured and filled with voids and corners of the formwork.