U Box test on Fresh Concrete | Apparatus, Procedure & Result

In this article, we will discuss the U box test on fresh concrete.

  1. Introduction  

U Box test on fresh concrete is done to determine the filing and passing ability of self-compacting concrete with the use of a U shape box.

Generally, the Slump test is used to find the workability of high slump value concrete. Because of high fluidity, it is impossible to carry out this test for Self-compacting concrete.

  2. Apparatus  

1. U box of a stiff must be of non-absorbing material

2. Scoop

3. Trowel

4. Stopwatch

5. Spirit Level

  3. Procedure  

This takes 10 to 15 minutes and can be done easily and it is a very simple process.

1. At first place the apparatus on the leveled ground and check by Spirit level.

2. Nearly 20 liters of concrete is required to perform this test.

3. Don’t forget to apply dampness on the inner side of the apparatus before starting.

4. Now, start the test by filling concrete on the left container of the apparatus to the top without any compaction.

5. Remove the extra concrete from the apparatus.

6. Leave the apparatus for 1-2 minutes.

7. Now, open the gate and allow the concrete to flow to the right side of the container.

8. Measure the height of concrete in both sides of the container as H1 AND H2.

9. Substracting H1-H2 will provide you a filling height.

  4. Result  

Filling height = H1-H2

If the concrete moves as freely as water, at rest it will be horizontal, so H1-H2=0. The ‘filling height’ must be near zero for the better flow and passing ability of the concrete.