True or False: Slabs at isolation joints must be free to move horizontally but not vertically.

True or False: Slabs at isolation joints must be free to move horizontally but not vertically.

• A. True
• B. False
• C. Both directions
• D. Neither

Answer: (B)

Isolation joints are meant to relieve movement between concrete elements, so they must allow the slabs to move freely as conditions change. That movement isn’t limited to sliding side to side; vertical displacement can occur from settlement, loading, or subgrade changes, and the joint needs to accommodate that too. If vertical movement were restrained, stresses would build in the slabs and the joint area, leading to cracks or spalling. The filler in the joint is chosen to be compressible and maintain a gap while permitting movement in both directions. So the statement is false because slabs at isolation joints should be free to move horizontally and vertically.

Isolation joints are meant to relieve movement between concrete elements, so they must allow the slabs to move freely as conditions change. That movement isn’t limited to sliding side to side; vertical displacement can occur from settlement, loading, or subgrade changes, and the joint needs to accommodate that too. If vertical movement were restrained, stresses would build in the slabs and the joint area, leading to cracks or spalling. The filler in the joint is chosen to be compressible and maintain a gap while permitting movement in both directions. So the statement is false because slabs at isolation joints should be free to move horizontally and vertically.