Usually, the slump test is used to find the workability of fresh concrete at the site. There are other tests used to find concrete workability, such as kelly ball test, Flow table test & Vee Bee Test.
But those tests are not suitable for high fluidity concrete.
The self-compacting concrete is the high fluidity concrete used where the reinforcement is congested, and vibrating is not possible at all.
What is the L Box Test?
The test used to find the passing ability of freshly mixed self-compacting concrete in the reinforcement is known as the L box test.
It is conducted at a site or lab to find the passing ability of fresh concrete used in underwater construction work in Japan. The L box test is done as per BS EN 12350-10, not by Indian Standard.
L Box Test Apparatus
- L box – It contains a vertical hopper & horizontal flow tank. A small gate placed at the bottom of the vertical hopper for concrete flowing.
- There are two or Three bar (12mm dia & 40mm spacing) obstacles placed in the horizontal flow tank. The spacing of rods is 3 times greater than the larger size of aggregate.
- Stop Watch
- Measuring Scale
The L box should be free from dust & other impurities. Dampness will be applied inside the box.
- Step 1 – Ensure the horizontal level of the box by spirit level.
- Step 2 – Fill the concrete into the vertical hopper up to the top & level it by the trowel.
- Step 3 – After 1 minute, open the gate and allow the concrete flowing to the horizontal tank.
- Step 4 – When the concrete flow is completed, note down the measurement, as shown in the picture.
- After the concrete flow was completed, measure the height of concrete settlement in both vertical and horizontal portions of the box.
- The measurement has to be taken at 3 places in both sections.
- The average depth of the upright portion is H1 & the average depth of the horizontal portion is H2.
The ratio between the concrete depth of horizontal and vertical portion is the passing ratio of the SCC concrete.
Concrete Passing Ratio = H2/H1.
Generally, the recommended blocking ratio of self-compacting concrete is 0.8 to 0.85. The flowing of the concrete at the end of the horizontal portion is having proper segregation.
Video Courtesy – Rakib Hasan
Happy Learning 🙂