What is the minimum length of the tamping rod required for concrete testing?

For concrete testing, particularly in procedures such as the slump test, the specifications require the tamping rod to be of adequate length to ensure effective compaction of the concrete sample being tested. The correct option states that the minimum length of the tamping rod should be at least 100 mm greater than the depth of the bowl used for the test. This is crucial because the tamping rod must extend sufficiently above the surface of the concrete to allow for effective tamping without interference from the bowl edges.

Having a tamping rod that is too short can lead to inadequate compaction, which can adversely affect the integrity of the test results. Therefore, ensuring that the rod exceeds the bowl depth by at least 100 mm helps to facilitate proper technique in tamping the concrete mix, allowing for a more accurate determination of its consistency and workability during testing.