Construction Supervisor License Practice Exam

When control joints are required in basement concrete floors (3½" thick) on grade, what is their minimum depth?

1. 1/4 slab thickness, not less than 1" deep

2. 1/3 slab thickness, not less than 1" deep

3. 1/2 slab thickness, not less than 1 1/2" deep

4. 1/2 slab thickness

The correct answer is: 1/4 slab thickness, not less than 1" deep

In the context of basement concrete floors that are 3½ inches thick, control joints are essential for minimizing cracking due to shrinkage as the concrete cures and dries. The minimum depth of control joints should be appropriately scaled to the thickness of the slab to ensure effective performance. Choosing a minimum depth of 1/4 of the slab thickness establishes both a practical and effective guideline. Since the slab is 3½ inches thick, 1/4 of that thickness is approximately 0.875 inches. However, the requirement states that the minimum depth should not be less than 1 inch, which ensures that the control joint is adequately formed and can fulfill its purpose in controlling cracking. This standard acknowledges that while the approximate depth is based on the slab thickness to ensure the joint is effective, a minimum depth of 1 inch will provide the necessary depth to create a durable joint that allows for movement and alleviates stress within the concrete. It is important to follow these guidelines to maintain the integrity and longevity of the concrete structure, especially in areas prone to movement or environmental changes.