Fill Box Test for Self Compacting Concrete for Workability

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Fill Box Test Method for Self Compacting Concrete

Fill box test is also known as ‘Kajima test’ is used to measure the filling ability of self compacting concrete with a maximum aggregate size of 20 mm. The apparatus consists of a container (transparent) with a flat and smooth surface. In the container are 35 obstacles are made of PVC with a diameter of 20mm and a distance centre to centre of 50mm, see figure. At the top side is a put filling pipe (diameter 100mm height 500mm) with a funnel (height 100mm). The container is filled with concrete through this filling pipe and difference in height between two sides of the container is a measure for the filling ability.

Assessment of Fill Box Test

This is a test that is difficult to perform on site due to the complex structure of the apparatus and large weight of the concrete. It gives a good impression of the self compacting characteristics of the concrete. Even a concrete mix with a high filling ability will perform poorly if the passing ability and segregation resistance are poor.

Equipment for Fill Box Test

• Fill box of a stiff non absorbing material
• Scoop 1.5 to 2 liter
• Ruler
• Stopwatch

Fig.: Detail of fill box empty and filled with concrete

Procedure for Fill Box Test Method

About 45 liter of concrete is needed to perform the test, sampled normally. Set the apparatus level on firm ground, ensure that the sliding gate can open freely and then close it. Moisten the inside surface of the apparatus, remove any surplus water, fill the apparatus with the concrete sample. Fill the container by adding each 5 seconds one scoop with 1.5 to 2 liters of fresh concrete into the funnel until the concrete has just covered the first top obstacle. Measure after the concrete has come to rest, the height at the side at which the container has filled on two places and calculate the average (H1). Do this also on opposite side (H2). Calculate the average filling percentage: average filling percentage F= {(H1+H2)/2*H1}*100%. The whole has to be performed within 8 minutes.

Interpretation of the result

If the concrete flows as freely as water, at rest it will be horizontal, so average filling percentage = 100%. Therefore the nearest this test value, the filling height’, is to be 100%, the better self compacting characteristics of the concrete.