Testing self compacting concrete: L-box test || L Box test of Self Consolidating Concrete

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Testing self compacting concrete: L-box test || L Box test of Self Consolidating Concrete

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Testing self compacting concrete: L-box test || L Box test of Self Consolidating Concrete #concrete #concretetesting #construction #concretetechnology #practicaltraining #civilengineering
L-box test - Test on Workability of Self Compacting Concrete
Theory and Scope of L- Box Test
The L-Box test measures the filling (flowing) and passing capacity of self-compacting concrete to flow through tight openings, including gaps between reinforcing bars and other barriers without splitting or blocking. There are two differences; Two bar tests and three bar tests. The three-bar test simulates high-density reinforcement.
The new concrete is initially placed on the vertical side of the box. The sliding gate is opened between the vertical or horizontal parts of the box, allowing the concrete to flow into the horizontal area of the box through the gaps or gaps between the vertical and soft reinforcement bars. . The points 200 mm (T200) and 400 mm (T400) are recorded at the time of reaching the concrete in the horizontal part of the box.
After the concrete rests on the machine, the height of the concrete at the end of the horizontal section, H2, and at the beginning of the horizontal section, H1 are measured. The filling capacity or flow of self-compacting concrete is described in terms of the passing rate, H2 / H1.
Apparatus required for L- Box Test
· L-box of a stiff non-absorbent material
· Ruler
· Container or bucket
· Trowel
· Scoop and Stopwatch.
Description of Apparatus
This machine, consisting of a rectangular box made of steel, plastic or plywood, shall have an 'L' shaped, smooth, flat and hard construction with surfaces that are not easily hit or stained by cement paste. The vertical and horizontal sections are separated by a movable gate, the front of which is fitted with longitudinal reinforcement bars. The horizontal part of the box is marked as 200 mm and 400 mm from the gate. The vertical hopper may be removable for easy cleaning. With the gate closed, the size of the vertical hopper should be (12.6 to 12.8) liters.
Devices holding reinforcement bars shall have two soft bars with a diameter of 12 mm with a spacing of 59 mm for the two-bar test and three soft bars with a spacing of 41 mm for the three-bar test. These encounters are interchangeable. Locate the bars in the L-box so that they are perpendicular and across the width of the box. The general structure of the L-box is illustrated in the figure below and the dimensions can withstand ±1 mm. Instead of the steel mould, the mould and end grain built into the 12mm coated formwork plywood can be sealed.
Ruler graduated from 0−300 mm in intervals of 1.0 mm.
Container of capacity of more than 14 litres to hold the concrete sample.
The procedure of L- Box Test
Two operators are required if times are measured, and operator error is inevitable.
Step 1: Collect a representative sample of concrete of about 17 litres to perform the test using a normal sampling procedure.
Step 2: Set the apparatus on a level, firm horizontal base; ensure that the sliding gate can open freely.
Step 3: Moisten the inside surfaces of the apparatus and remove any surplus water.
Step 4: Close the sliding gate between the vertical and horizontal sections. Pour the concrete sample from the container into the hopper of the L-box to fill the vertical section of the apparatus; allow it to stand for 60 ± 10 seconds.
Step 5: Lift the sliding gate and start the stopwatch simultaneously.
Step 6: Allow the concrete to flow out into the horizontal section of the box and record T200 and T400, the times taken for the concrete to reach the 200 and 400 mm marks, respectively.
Step 7: When the concrete has stopped flowing, measure the depth of the concrete at the end of the horizontal portion of the L-box at three positions equally spaced across the width of the box. These three measurements are used to calculate the mean depth of concrete as H2 mm.
Step 8: The procedure of Step 7 is used to calculate the depth of concrete immediately behind the sliding gate as H1 mm.
Step 9: Calculate the passing ability, PA as PA = H2/H1 to the nearest 0.01.
The real test has to be performed within 5 minutes.
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