Contraction joints are designed to control cracking due to shrinkage.

• A. To transfer loads
• B. They control cracking due to shrinkage
• C. To seal joints
• D. To remove air

Answer: (B)

Contraction joints are placed to create a planned breaking plane in a concrete slab as it shrinks during drying and curing. When concrete loses moisture and experiences temperature changes, it tends to shrink and develop tensile stresses. Without control, cracks can form randomly and be wide or jagged. By introducing contraction joints at predetermined locations, cracks are encouraged to occur along the joint, producing a predictable, neater crack pattern and helping preserve the slab’s strength and appearance. This function is distinct from transferring loads, sealing joints, or removing air, which are not the primary purpose of contraction joints.