Workability of Lightweight Concrete

Test for Workability of Cement

Slump test:- ( Unit –mm) The mould for the slump test is the frustum of a cone, as shown in the figure. Concrete is filled in three layers and the cone slowly lifted and the unsupported concrete will now slump. The decrease in the height of the center of the slumped concrete is called slump and measured in ―”mm”.

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Slump test is used to check hour to hour workability on site

Frustum of cone

Frustum of cone

Compaction factor test – The concrete is filled at the top hopper and allows falling in the lower cylinder passing through the middle hopper. The actual density of concrete in the cylinder is measured and the compaction factor is calculated as follows.

 Compaction\: factor=\frac{ Density\: actual \: achived\: in \:test}{max.density\: of\: the\: same\: concreate}

Test for Workability of Cement

Vee – Bee test (Unit-sec) it is a lab test in which using vibration, the time is calculated for change of state of concrete from cone to cylinder. This is a good test for dry concrete whose slump value can’t be determined.

Ball penetration test:- (Unit –mm) This test is the same as the slump test that can be used in the field. In this test, a metal hemisphere of 152mm diameter and 14kg weight sink in the concrete under its own weight, and sinking depth is measured

Flow table test:- This test is popular for concrete made with superplasticizers admixtures.

Table showing the degree of workability for different values of the slum, compaction factor, and Vee-bee time.

Degree of WorkabilitySlumpCompaction FactorVee-Bee timeUse
Very lowNone0.78 to 0.8010-20 secShallow Sections , Pavements Using Pavers
LowNone0.855-10 secMass concreting, lightly reinforced sections in slabs, beam-columns, canal lining, Strip footing.
Medium25 – 75 mm0.922-5 secHeavily reinforced sections in slabs, beams, walls, columns, pumped concrete.
High75-100 mm0.95Congested reinforcement, Insitu pilling, and where vibrators can’t be used.
  • Higher slump value, more workability. Higher compaction factor value more workability. Higher Vee – Bee time less workability
  • Workability is directly proportional to aggregate size , grading of aggregate, air in the mix and water content
  • Workability is inversely proportional to time of transit of mixture.

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