What is the purpose of expansion joints in concrete slabs?

• A. To accommodate movement due to temperature changes and shrinkage and to prevent random cracking.
• B. To accommodate movement due to temperature changes.
• C. To prevent any movement in slabs.
• D. To change the color of the slab.

Answer: (B)

Expansion joints are placed so the concrete can move freely as it changes temperature and as it loses moisture (shrinkage). When concrete heats up it expands; when it cools or dries, it contracts. If movement is restrained, internal stresses cause cracks to form in unpredictable places. By giving slabs a planned gap, these joints relieve that stress and prevent random cracking. They aren’t meant to stop all movement or to change color; they simply provide a controlled space for movement, often filled with a flexible material to absorb the motion.