Isolation joint material must be:

Isolation joint material must be:

• A. Compressible
• B. Rigid
• C. Porous
• D. Non-porous

Answer: (A)

Isolation joints need a filler that can give way as concrete expands or contracts. The material in the joint must be compressible so it can be squished to accommodate movement between slabs, keeping the gap open and preventing stresses from transferring into adjacent sections. If the filler were rigid, it would resist movement and cause cracking, spalling, or other damage as the concrete moves with temperature changes, shrinkage, or loads. Porosity is not the defining factor here—compressibility is. A compressible joint filler, like foam or similar backer materials, allows the slabs to move independently while staying separated, which is the essential purpose of an isolation joint.

Isolation joints need a filler that can give way as concrete expands or contracts. The material in the joint must be compressible so it can be squished to accommodate movement between slabs, keeping the gap open and preventing stresses from transferring into adjacent sections. If the filler were rigid, it would resist movement and cause cracking, spalling, or other damage as the concrete moves with temperature changes, shrinkage, or loads. Porosity is not the defining factor here—compressibility is. A compressible joint filler, like foam or similar backer materials, allows the slabs to move independently while staying separated, which is the essential purpose of an isolation joint.