Types of Joints in Concrete Construction
Joints are used in concrete structure for various reasons such as relieving the stresses resulting from the increase of concrete structure length due to temperature. There are four types of joints in concrete structures.
- Construction joint: for large structures such as a long slab it is challenging to place concrete at one time. Therefore the concrete pouring is divided into stages. The boundary between these concrete pours is known as construction joints. The location of construction joints should be predetermined before begin with the casting process. Construction joint shall be roughened and cleaned to ensure a proper bond with next pour. Shear keys should also be added to improve shear resistance.
- Expansion joints: the purpose of forming an expansion joint in concrete is to accommodate the volume change of concrete structures. Expansion joints are essential for a large concrete structure. In bridge industry expansion joints are used widely. A gape to accommodate the volume change of the structure is formed at a specified location. There are many types of expansion joints, such as an asphaltic plug, elastomeric, and modular expansion joint.
- Contraction joint: contraction joint is sawed or formed in concrete to regulate the location of cracks resulted from the dimensional change of concrete structure. Uncontrolled cracks could expand and cause rough surface and allows the water infiltration in concrete. Contraction joints are used mainly in concrete pavement.
- Isolation joints: the purpose of this type of joint is to isolate a structural member from other parts of the structure. Isolation joints can be used to separate a drainage pipe from the slab. Also, it can be used to isolate a column or wall from the slab. If the column is designed to transfer the loads to a separate footing, then it should be isolated from the slab or other members. So the purpose of isolation joint is to separate two members that designed to function differently.