North Carolina Building Contractor License Practice Exam

Which method is used to place concrete underwater?

1. Dump truck delivery

2. Vacuum pumping

3. Using a tremie

4. Manual pouring

The correct answer is: Using a tremie

The method used to place concrete underwater is utilizing a tremie. A tremie is a specialized pipe system that allows concrete to be poured underwater without causing it to segregate or lose its integrity. This method works by placing the lower end of the tremie pipe below the water surface and allowing the concrete to flow through it directly into the underwater forms or excavation. The weight of the concrete helps to push it down through the pipe, and because it flows from the bottom up, it minimizes turbulence and prevents the mixing of water and cement. This is particularly important in underwater construction, such as in marine environments or deep foundations, where maintaining the quality and consistency of the concrete is critical for structural integrity. Other methods listed do not provide the same level of effectiveness for underwater placement. Dump truck delivery involves surface placement, while manual pouring would also be ineffective as it would likely wash away or become contaminated. Vacuum pumping can be used for other types of materials, but it is not applicable for the direct placement of concrete underwater. Therefore, the tremie is the specialized solution designed for this specific challenge in construction.