What are the requirements for the tamping rod in the air content test method?

The requirement that the tamping rod must be at least 100 mm longer than the bowl's depth is crucial for ensuring that the rod can adequately reach all areas of the contents being tested. The additional length allows the operator to effectively tamp the concrete sample within the bowl, reaching the bottom and ensuring uniformity in compaction. This is particularly important in obtaining an accurate air content measurement, as any inconsistencies in the sample can lead to erroneous results. The longer rod also facilitates proper handling and manipulation during the testing process, helping to maintain a consistent level of pressure and tamping necessary for reliable results.

The other choices—such as the material (wood), color, or cross-section—do not directly influence the effectiveness of the tamping rod in terms of fulfilling the requirements of the air content test.