U-Box for Self Compacting Concrete


U-box test measures the filling ability of self-compacting concrete. The U-box test originally developed in Japan and is sometimes referred to as the box-shaped test. Like other workability tests for self-compacting concrete, the U-box test is also applicable to highly flowable concretes and underwater concretes.


The apparatus consists of a  U-shaped box. Concrete is placed in the left side of the box. The apparatus features a flat bottom instead of a curved bottom. Ideally, the box should be made of clear plastic to permit the observation of the concrete in the box. To start the test, the door dividing the two halves of the box is opened and concrete  is allowed to flow from the left half of the box into the right half. Reinforcing bars are placed at the location of the door. The most common arrangement is 13 mm diameter bars with a clear spacing of 35 mm. The time from the opening of the door until the concrete ceases to flow is recorded. The height of the concrete in each side of the box is measured. A truly self-leveling fluid will rise to the same height on each side of the box. Concrete with good filling ability should reach a height of at least 30 cm on the right side of the box.


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