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An air content test is required for checking air entrained concrete. The method of testing is given in BS EN 12350-7, which replaces BS 1881: Part 106.
Method A outlines the principle of the test. A sample of concrete is placed in the cylinder of an air meter in three layers, each being fully compacted by hand or by vibration. The cylinder is filled level with the top. The cover, which has a sealed graduated cylinder fitted, is clamped to the cylinder. The assembly is filled with water and any air is allowed to escape through a valve. The valve is closed and an air pump is used to increase the internal pressure. As the pressure rises the concrete becomes compressed and the water level in the graduated cylinder falls. When the pressure has reached a specified level, the reading of the water level is recorded. The pressure is then released and the water level rises. The difference in the two levels is the apparent air content. Various adjustments are made to give the true air content.
Method B works on a similar principle but the apparatus is generally easier to operate. Note that, once the test has been carried out, the concrete should be discarded and should not be used for any other test, such as slump.
Acknowledgement: The Concrete Society
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