How do control joints differ from expansion joints in masonry walls?

• A. They are the same and serve identical purposes.
• B. Control joints relieve moisture; expansion joints relieve heat.
• C. Control joints accommodate movement; expansion joints relieve tensile stresses.
• D. Control joints relieve tensile stresses due to shrinkage and temperature changes; expansion joints accommodate movement between joined sections or floor levels.

Answer: (D)

In masonry walls, joints are used to manage movement caused by drying shrinkage, temperature changes, and structural shifts. The best description distinguishes the two types by their function.

Control joints provide a planned weak plane where cracks can form in a controlled location. They relieve tensile stresses that arise from shrinkage and temperature fluctuations, guiding cracking to a predictable line so the overall appearance and performance of the wall stay better controlled.

Expansion joints, on the other hand, are gaps that allow movement between joined sections or between wall and floor levels. They accommodate expansion, contraction, and other movement without transferring it into the masonry, often using flexible filler so water stays out while the two sides can slide relative to one another.

So the correct statement aligns with control joints relieving tensile stresses due to shrinkage and temperature changes, and expansion joints accommodating movement between sections or floor levels. The other options mix up the purposes or give incorrect attributions (such as moisture or heat relief or identical functions).