ACI Concrete Field Testing Technician - Grade I Practice Exam

When rodding a standard 6 by 12 in [150 mm by 300 mm] cylinder, how many times must each layer be rodded?

1. 15 times

2. 25 times

3. 35 times

4. 45 times

The correct answer is: 25 times

When rodding a standard 6 by 12 inch cylinder, the correct process involves rodding each layer of concrete precisely to ensure proper consolidation and to minimize air pockets. Each layer of concrete should be thoroughly compacted through careful rodding. For a cylinder of this size, the accepted standard practice is to rod each layer 25 times. This number is based on procedures outlined in ASTM specifications, which dictate the testing and preparation methods for concrete samples. Rodding is done in a specific manner—uniformly distributing the strokes in a way that effectively compacts the concrete while not disturbing the layers previously placed. The rationale behind the importance of this specific number of roddings is to achieve a uniform density in the specimen, which is critical for accurate measurement of the concrete's properties later in testing. If too few roddings are performed, the concrete may not be adequately compacted, leading to unreliable test results. Therefore, performing 25 roddings for each layer strikes the right balance for effective consolidation in the creation of the concrete cylinder, ensuring the integrity of the test is maintained.