What is a common reason for using control joints in concrete?

Control joints are incorporated into concrete flatwork primarily to prevent cracking due to shrinkage. As concrete cures, it undergoes a natural process of drying and shrinking, which can lead to internal stresses. If these stresses exceed the strength of the concrete, cracks may occur.

By strategically placing control joints, the concrete is allowed to crack in a controlled manner along these predetermined lines, rather than random cracking that can compromise the structural and aesthetic integrity of the slab. This not only preserves the appearance of the concrete but also enhances its durability and longevity.

While decorative patterns and surface finishes can certainly enhance the overall look of concrete, they are not the primary purpose of control joints. Similarly, control joints do not play a role in load-bearing capacity directly or in improving adhesion for overlays or finishes. Their main function is to mitigate the effects of shrinkage, making option B the valid choice.