L-Box (named for Greta M. Ljung and George E. P. Box) Test for Passing ability of Self Compacting Concrete
The L-box test is used to assess the passing ability of self-compacting concrete to flow through tight openings including spaces between reinforcing bars and other obstructions without segregation or blocking. (IS:1199 Part 6)
Principle of L box test
The L-box test is used to assess the passing ability of self-compacting concrete. There are two variations.
The two-bar test for less congested reinforcement
Three bar tests for more congestion.
Only the three-bar test is covered in this section, as it simulates more congested reinforcement. A measured volume of fresh concrete is allowed to flow horizontally through the gaps between vertical, smooth reinforcing bars. The heights of the concrete in the vertical section (H1) and at the end of the horizontal section (H2) are measured and the ratio H2/H1 determined. This ratio is a measure of the passing or blocking behaviour of self-compacting concrete. (IS: 1199 part 6)
Apparatus for L Box Test
L Box as shown with dimensions above.
Smooth steel bars at equal spaces shall be provided in box/
(Steel bars of 12 ± 0.2 mm diameter will provide a gap of 41 ± 1 mm. )
Test Procedure of L Box test for self-Compacting Concrete.
Place the L- Box on firm and levelled space and clean it out and manage it in wet dry conditions.
Close the gate between the vertical and horizontal sections.
Pour the concrete from the container into L-box, without any compaction.
Remove and level the concrete at top with straight edge and allow to stand for 60 ± 10 s.
Open the sliding gate to allow the concrete to flow into the horizontal portion of the L -Box apparatus.
Note the status of concrete when there is no flow.
At this time measure the drop in the vertical arm as DH1 (mean of several drop values)
H1 = height of vertical section – DH1
Find the DH2 value (mean of several DH2 readings)
H2 = height of vertical section at end – DH2
Measure of L-Box Test is calculated as pass ability ratio as given below:
PL = H2 / H1
where PL = passing ability, ratio measured by the L-box test
H1 = mean depth of concrete in the vertical section of the box, in millimetres
and H2 = mean depth of concrete at the end of the horizontal section of the box, in millimetres.
A minimum acceptable value of 0.8.
L- Bos Pass ability Test record format for Self-Compacting Concrete
