The self compaction concrete is the high fluidity concrete. It is used where the location is congested by reinforcement and no possibility of compaction of concrete by mechanically or manually. 


We have already discussed the L box test, which is used to determine the workability of Self-compacting concrete.

What is the U Box Test?

The test used to find the filling and passing ability of freshly mixed Self-compacting concrete with the help of a U shape box is called the U box test.

Why do we need to conduct a U Box Test?

Generally, slump tests are used to find the workability of high slump value concrete, but here the slump test is not suitable for SCC because of its high fluidity. So the U box test is used to find the workability.

Apparatus Required

U Box Test Apparatus

  • A stainless steel U shaped box divided into two compartments, which consist of sliding gates. At the bottom of the box, three 12mm dia steel bars placed at a spacing of 35mm to 50mm, and the spacing of the bar can be adjustable. 
  • Stopwatch
  • Trowel
  • Spirit level


It is a simple and easy method, and the total test can be completed within 5 to 10 minutes. 

test apparatus e1592377654156

  • Place the apparatus horizontally and ensure by the spirit level.
  • Apply dampness to the inner surface of the apparatus.
  • Now fill the concrete into the left compartment of the apparatus up to the top without compaction and remove the excess concrete. 
  • Then leave it to stand the apparatus up to 1 minute.
  • Now lift the gate and allow the concrete to flow to the right side of the compartment.
  • After completion of the concrete flow, measure the height from the concrete surface at both compartments as H1 and H2.
  • The difference between H1 and H2 is called the filling height.


Filling height = H1 – H2

The flow and passing ability of the concrete is good when the filling ratio is near to zero. Do the test at least 3 times and average the value as workability of Self-compacting concrete.

The filling concrete can be cleaned by rotating the box upside down.

Video Illustration

Happy Learning 🙂


Bala is a Planning Engineer & he is the author and editor of Civil Planets.

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