ACI Concrete Field Testing Technician - Grade I Practice Exam

When rodding the bottom layer, how should the tamping rod be positioned?

1. Vertical

2. Slightly inclined

3. Horizontal

4. Perpendicular

The correct answer is: Slightly inclined

When rodding the bottom layer, the tamping rod should be positioned slightly inclined. This angle allows for the most effective compaction of the concrete mix without causing segregation of the aggregates. When the rod is inclined, it creates an effective motion that helps in displacing the air pockets trapped in the concrete, ensuring a denser and more homogenous sample. Using a perfectly vertical or horizontal position might not achieve the same level of effectiveness in compaction. A vertical rod could lead to ineffective penetration into the mix, while a horizontal rod would not allow for the necessary movement to consolidate the concrete properly. The slight inclination strikes a balance, enabling better interaction with the concrete and achieving the desired density.