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Workability Requirements for Different Concrete Placement:

Requirement of concrete workability varies with different types of construction. Workability of concrete is decided by design engineers based on concrete strength requirements, durability requirements and ease of construction at site.

For a construction with use of large percentage of reinforcement, where the gap between reinforcement is less and compaction can not be done effective, highly workable concrete such as self compacting is recommended.

Since workability of concrete is achieved by more water, it reduces the strength of concrete. Thus it is recommended to use workability enhancing concrete admixtures such as air-entraining agents. But use of admixtures may also affect the strength of concrete. So, for critical components of building such as slab, beam and columns, and for structures where strength of concrete is of much importance, degree of workability recommended is very low. For mass concrete where and lightly reinforced concrete structures, low degree of workability can be used.

Mass Concrete Workability

The degree of workability is measured with slump test of concrete during mixing. The slump value recommended for each degree of workability for different placing conditions of concrete is given in table below:

DEGREE OF WORKABILITY FOR DIFFERENT PLACING CONDITIONS

Placing Condition

Degree of concrete workability

Slump (mm)

Binding concrete,

Shallow Sections

Pavement using pavers

Very low

Use compacting factor test as per IS: 1199

Mass concrete,

Lightly reinforced sections in slabs, beams, walls, columns, foors, hand placed pavements, canal linings, strip footings

Low

25-75

Heavily Reinforced sections in slabs, columns, walls, slipform work, pumped concrete

Medium

50 – 100, 75 – 100

Trench fill, in-situ piling

High

100 – 150

Tensile concrete

Very high

Use determination of flow test as per IS: 9103