Which joint is designed to crack along a line?

• A. Control joint
• B. Isolation joint
• C. Construction joint
• D. Expansion joint

Answer: (A)

Cracking is controlled by creating a planned weak line where the concrete will crack. Concrete shrinks as it cures and moves with temperature changes, so without a preset path, cracks can appear randomly. A control joint is specifically placed to encourage cracking along a defined line, typically by forming or sawing a groove to a depth that makes that line the preferred crack path. This keeps cracks predictable, neat, and easier to seal or repair. Other joints serve different purposes: isolation joints separate slabs from structures to allow independent movement; expansion joints provide space and a filler to accommodate thermal expansion and contraction; construction joints mark where pours are stopped and later resumed, not where cracking is intended. So the joint designed to crack along a line is the control joint.