Concrete workability is a broad term but refers to how easily fresh concrete can be mixed, placed, consolidated and finished with minimal loss of homogeneity. The workability of concrete has a direct relationship with the strength, quality and appearance on the concrete and its required application. The following factors affects concrete workability:

Water/cement ratio – A higher ratio of cement results in a stronger/compressive strength concrete, but an incorrect ratio of water to cement will result in poor strength development. However, too much water will make a very workable concrete, but this can cause segregation between the aggregates and cement. 

Aggregate size and shape – Smaller/finer aggregates have a higher surface area, which requires more cement paste to over the surfaces, which is less workable when compared with larger aggregates. Crushed aggregates are good as they provide a better bond between the cement and results in a workable concrete.

Admixtures – There are many types of admixtures, which can affect concrete workability and properties. Superplasticizers which are also referred to as high range water reduces, are used in high strength concrete. They improve the flow characteristics of the concrete mix and reduces the amount of water required in the mix without negatively affecting the workability of concrete.

The concrete workability directly correlates to the concrete slump class, and an incorrect ratio of concrete constituents in the mix can badly affect the finished concrete during construction, which may not be realized until after the concrete has set. This is why continuous testing of concrete is essential before, during and after construction. The slump test is an adequate indicator the concrete slump class.