SLUMP TEST - Measurement of Workability of Concrete

SLUMP TEST - Measurement of Workability of Concrete

Slump Test is also known as Test for Consistency of Concrete. The object of this test is to study the Workability of the concrete mix. Workability means the ease with which mixing, handling and placing of concrete can be done. Depending on the nature of work and site condition, the concrete mixture may be made either stiff or wet. For uniform concrete work, the same consistency must be maintained throughout.

Workability is affected by the factors, viz., 1. Mix Proportions, 2. Aggregate Properties, 3. Time, 4. Environmental Conditions and 5. Adding Admixtures. [Admixtures are additional fine materials like powdered earth, fly ash, hydrated lime, etc., used in concrete. Admixtures improve workability, reduce segregation and accelerate setting and hardening of concrete.]

SLUMP TEST

Slump Test is conducted to measure the workability of concrete and to decide the required quantity of water. Fig. 8(a) shows a Hollow Truncated Cone of sheet metal with top and bottom open. Actually, the slump cone is a ‘mould' that can be lifted vertically after filling with concrete. Height of the cone is H₁ = 30 cm.

Samples from ready-mixed concrete heaps are taken and poured into the cone. Filling the slump cone with concrete is done in layers of thickness of 8 cm. After laying each layer, it is compacted with 25 strokes using a rod. After filling the cone with concrete, it is gently lifted and carefully removed.

See Fig. 8(b). 

The concrete is allowed to subside. Now, Height of concrete (H2) is measured. Slump of concrete is the decrease in the height of the highest point of the slumped concrete. i.e., Slump = H = H₁ - H₂.

For stiff consistency, subsidence will be less and for plastic consistency, subsidence will be more. Normal consistency is denoted by a slump of 2.5 cm. Addition of 10% water will give a slump of 10 cm and 25% water will give a slump of 15 cm.