ACI Certification Practice Exam

Which of the following should not happen when rodding the top layer?

1. The rod should penetrate the top layer

2. You should add excess water

3. Concrete should be low

4. Additional concrete should be added

The correct answer is: You should add excess water

When rodding the top layer of concrete, it is vital to maintain the proper consistency and quality of the mix. Adding excess water at this stage can introduce several issues, adversely affecting the concrete's strength and durability. Too much water can lead to segregation, where the heavier aggregates settle at the bottom while the lighter cement particles rise to the surface, compromising the homogeneous nature of the mix. Additionally, excess water can increase the water-cement ratio, which is detrimental because a higher ratio often results in weaker concrete that is more susceptible to cracking and other structural problems. In this context, the other options represent actions that are generally acceptable during the rodding process. For instance, penetrating the top layer with a rod is essential for ensuring that the mix is compacted properly and any air bubbles are eliminated. Keeping the concrete low can help facilitate this process, ensuring that the proper amount of material is rodded effectively. Adding additional concrete may also be acceptable to achieve the desired level or to compensate for settling, as long as the overall properties of the mix remain intact.