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U Box Test Method for Self Compacting ConcreteU box test was developed by the Technology Research Centre of the Taisei Corporation in Japan. Some time the apparatus is called a “box shaped” test. U Box test is used to measure the filing ability of self compacting concrete. The apparatus consists of a vessel that is divided by a middle wall into two compartments; an opening with a sliding gate is fitted between the two sections. Reinforcing bar with nominal diameter of 134 mm are installed at the gate with centre to centre spacing of 50 mm. this create a clear spacing of 35 mm between bars. The left hand section is filled with about 20 liter of concrete then the gate is lifted and the concrete flows upwards into the other section. The height of the concrete in both sections is measured.
Assessment of U Box testThis is a simple test to conduct, but the equipment may be difficult to construct. It provides a good direct assessment of filling ability. This is literally what the concrete has to do, modified by an unmeasured requirement for passing ability. The 35 mm gap between the sections of reinforcement may be considered too close. The question remains open of what filling height less than 30 cm is still acceptable.
Equipment for U Box Test
- U box of a stiff non absorbing material
Fig: U box test Apparatus