Correct option is D
Correct Answer: D) Slump test
Solution:
Workability of concrete is the property of fresh concrete that determines the ease with which it can be mixed, transported, placed, compacted, and finished without causing segregation or bleeding. It depends on factors such as water-cement ratio, aggregate size and shape, grading of aggregates, cement content, and the use of admixtures.
The Slump Test is the most widely used field test for determining the workability (consistency) of freshly mixed concrete. It is simple, quick, and economical, making it suitable for routine quality control at construction sites.
The test is carried out using a standard slump cone having:
· Height = 300 mm
· Bottom diameter = 200 mm
· Top diameter = 100 mm
The cone is placed on a rigid, non-absorbent surface and filled with fresh concrete in four equal layers. Each layer is compacted with 25 blows of a standard tamping rod. After filling and striking off the top surface, the cone is lifted vertically in 5–10 seconds. The concrete subsides due to gravity, and the difference between the original height of the cone and the highest point of the slumped concrete is measured as the slump.
The magnitude of the slump indicates the workability of concrete:
· Low slump: Indicates stiff concrete with low workability.
· Medium slump: Suitable for most reinforced concrete works.
· High slump: Indicates highly workable concrete, but excessive slump may lead to segregation and bleeding.
The slump test is most suitable for plastic and cohesive concrete mixes. It is not considered reliable for very dry mixes (which exhibit negligible slump) or very wet mixes (which may collapse completely).
Explanation of the other options:
· A) Consistency test: Consistency refers to the degree of wetness or fluidity of a mix. For fresh concrete, the slump test itself is the standard consistency/workability test. "Consistency test" is not the standard name of a separate test for concrete workability in this context.
· B) Water absorption test: This test is conducted on hardened concrete to determine its porosity, permeability, and durability. It has no relation to the workability of fresh concrete.
· C) Compression test: The compression test is performed on hardened concrete specimens (usually cubes or cylinders) to determine the compressive strength of concrete, not its workability.
Therefore, among the given options, the Slump Test is the standard test used to determine the workability of fresh concrete.
∴ Correct Answer: D) Slump test
