North Carolina Building Contractor License Practice Exam

Concrete should reach at least what percentage of its design strength before post-tensioning cables are stressed?

1. 50 percent

2. 70 percent

3. 80 percent

4. 90 percent

The correct answer is: 80 percent

Concrete must reach at least 80 percent of its design strength before post-tensioning cables are stressed. This threshold is crucial because it ensures that the concrete has developed sufficient strength to handle the additional stresses induced by the tensioning of the cables. By achieving 80 percent of the design strength, the concrete is capable of withstanding the forces without risking damage or failure. This practice not only helps in maintaining the integrity and performance of the structural system but also minimizes the potential for cracking and deformations that can occur if the concrete is too weak at the time of stressing. The selection of this percentage is based on engineering standards and empirical evidence that indicate the safe and effective stress application to the concrete. The focus on achieving a specific strength before stressing contributes to the overall reliability and durability of the post-tensioned concrete structure.