2.8 : 砌体墙的膨胀和收缩

Consider a brick wall exposed to continuous rain; the brick absorbs moisture and tends to expand slightly. In the absence of space to expand, compressive stresses develop in the wall, leading to the formation of cracks in the wall.

A continuous opening in the wall, called an expansion joint, has to be provided to allow the expansion in the masonry. 

In the case of a newly constructed concrete masonry wall, as the mortar dries, the wall undergoes shrinkage, which induces tensile stresses.

If these stresses exceed the tensile strength of the wall, shrinkage cracks appear.

These random cracks can be confined along a control joint, an intentionally created weak joint that runs continuously along the wall.

Expansion and control joints are provided where the walls intersect a column or opening and locations where the wall changes its direction, height, and thickness.

Vertical joints are built into the walls when bricks are laid. These joints are often filled with a backer rod and sealed with elastic joint sealers to prevent moisture and air from entering the room.