written by: Engr Sami Ullah (www.civilglobal.com)
what is workability of concrete:
Workability is one of the physical parameters of concrete which depend on the water. With water process it increase and decrease the strength and durability of concrete and also cost of labor.
The workability of concrete can be defined as the property of fresh concrete mix that will meet the diverse requirements of mixability, stability, transportability, placeability, mobility, compactability and Finishability of the fresh concrete. This property of the concrete is composite in nature.The workability of concrete increase with the addition of water, But it reduce the strength of concrete.Concrete could be workable when it is easily placed and compacted homogeneously without bleeding or Segregation
When the water amount is maximum then it loss the strength but its easy in placing and also it is too much easy for labor to take to one place to another. If the water amount is less in concrete so the concrete can gain the strength but it not easy to place and compact during concreting.
There for the concrete workability depend on the water cement ratio. If the water percentage is maximum in the concrete so the concrete become segregate and making bleeding during the placing of concrete.
Use of aggregate which are round and have a smooth surface so it is increase the workability of concrete.
keep the cement, aggregate .ratio in the same value. If the quantity of course aggregates is increased then the workability of concrete will improve.
There for slum test gives us the idea of workability of wet concrete or fresh concrete. The workability of concrete is the best determined by compaction factor test.
Factor effecting of work ability
- Water content
- Aggregate or cement ratio
- Size of aggregate
- Shape of aggregate
- Grading of aggregate
- Surface or texture of aggregate
- Used of admixture
Workability of concrete increases and decrease workability of concrete. If we use more water in the concrete it’s make disadvantages to aggregate .
- Increased quantity of water may cause bleeding in concrete.
- Cement slurry also escapes through the joints of formwork
- Strength of concrete may reduced.
Aggregate or Concrete ratio.
.The use of higher aggregate or cement ratio makes the concrete resulting poor workability for the concrete. So we have to use normal aggregate and cement ratio.
Size of Aggregate
Bigger size aggregates make the concrete workable and also it gives the strength to concrete. size of aggregate is also depend on the workability of concrete.
Shape of Aggregate.
Workability of aggregate is also affected by the shape of aggregate. These are the given following
- Angular aggregate
- Flaky aggregate
- Elongated aggregate
- Rounded aggregate
- Sub-rounded aggregate
- Cubical aggregate etc.
Grading of Concrete
Grading of aggregate is also the maximum influence on workability.. When total void are less, excess paste is available to give better lubricating effect.
Surface or Texture Of Aggregate
Surface or Texture of Aggregate is also effect of workability when Porous and non-saturated aggregate will be require more water than a non-absorbant aggregate. For same degree of workability latter will require less water.
Use Of Admixture
Air-entraining admixtures are used to purposely and introduce stabilize microscopic air bubbles in concrete.
written by: engr Sami Ullah (www.civilglobal.com)