Construction Joints

Construction joints are otherwise called as cold joints. It is used in the normal concrete or the lightweight concrete. Concrete like the other materials has the tendency to expand and contract because of the climatic or different changes and may be because of concrete strain. This change of volume will create the cracks in the hardened concrete, until unless it is controlled by concrete sealers. By arranging provisions for changes in the volume at the selected place, the stress forces that produce cracks can be prevented. These provisions are called control relief joints. This joint will reduce the random cracks on the surface by the stress forces produced by moisture and temperature changes. It will be very effective, if the control relief joint is installed properly. Construction joint is the plain surface between the two elements of the concrete surface. Construction joint is hardened to a level that vibration cannot affect the surface.

Occurring of Cracks

The concrete is mixed to the specified proportions to produce the standardized mixture. During the initial state this mixture will occupies the maximum volume. Then the concrete is dried and looses the uncombined water via evaporation. As said earlier, the moisture loss will produce concrete contraction and reduction in length. Unless the change in volume are restricted by placing the provisions (control relief joint), cracks will occur. When the concrete is restrained or controlled from the contraction, cracks can develop.

Methods of Drying Shrinkage

• The ratio of water cement should be reduced to attain the suitable position and vibration consolidation.
• According to the design of structures, the aggregates that are used should be proper, clean and suitable grade.
• In the placement of concrete, low slump should be used.

The concrete should be properly merged. The concrete that is cured soon after the concrete finishing will have the greater strength.

Construction Joints on Concrete Slab

• Construction joints are formed by using bulkheads that are made of wood, steel, plastic, or precast concrete. There are five types of construction joints available they are, overlap joint, butt joint, lap joint, mortise and Tenon joint, and dovetail joint.
• Construction joints must work into the overall join plan, where the construction joints can also function as contraction joints.
• In case of equipment breakdown, an unexpected shortage of materials or bad weather, construction joints should be used. If that’s not possible, the odd section may later have to be removed.

Questions:

• What is construction joint?
• How do cracks occur?