What is the role of control joints?

• A. To create predicted crack lines and control where cracks occur
• B. To increase thermal expansion
• C. To improve finish
• D. To remove moisture

Answer: (A)

Control joints give concrete a planned place to crack, directing the natural shrinkage and movement of the material into predictable lines. As concrete cures it shrinks and as temperatures change it expands and contracts, creating tensile stresses. If there are no control joints, cracks tend to form randomly across the surface, which can be unsightly and undermine strength in unpredictable ways. By introducing a controlled groove or joint, you create a weak plane where cracking is expected to occur, so cracks stay narrow, align with the joint, and occur in a way that’s easier to repair and maintain.

They don’t change how much the material expands with temperature, they don’t directly improve the surface finish, and they don’t remove moisture. Instead, their purpose is to manage movement and cracking in a controlled, predictable manner.