2.8:
Expansion and Contraction in Masonry Walls
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.
2.8:
Expansion and Contraction in Masonry Walls
Masonry walls are subject to slight expansion and contraction due to variations in temperature and moisture. Thermal movement in masonry is relatively straightforward to measure and plan for. On the other hand, moisture movement poses more of a challenge. New clay masonry units typically absorb water and expand over time under normal environmental conditions. Conversely, new concrete masonry units tend to shrink as they lose the excess moisture acquired during their production process.
To accommodate these movements without causing damage to the structure, buildings must incorporate specific types of joints. Expansion joints are crucial as they are designed to open or close, allowing the material room to expand or contract in response to changes in moisture and temperature. These joints are often sealed with flexible materials to prevent the infiltration of air and water. Control joints, another essential feature, are intentionally incorporated as planes of weakness within the masonry. These joints are designed to open and manage shrinkage, particularly during the initial curing phase of the masonry.
Both expansion and control joints should be strategically placed in the structure. Common locations include points of geometric discontinuity like corners, changes in the wall's height or width, and near openings.