Construction

Construction joints are provided

1. When the day’s work comes to an end
2. When there hasn’t been enough fresh concrete
3. When the concrete member is tall, i.e, IS 456 restricts the free fall of concrete to 1.2 m. This means that if a column is concreted, the form works are placed only to a height of 1.2m so that the free fall of concrete does not increase 1.2 m. Further extending of the form works after the concrete has been poured is a tedious process.

Construction joints should be avoided whenever possible. Monolithically cast sections perform better than sections with joints.

The reason why we don’t see construction joints in typical residential buildings is because

1. The slab is mostly cast in a single day
2. The lintel beams, beams are also mostly cast in a single day

Construction joints are found in columns, but they may not be prominent because of the workmanship. Columns are generally cast in stages to a height of 1.2 m each time. Between each session, bond is ensured by providing a rough surface on the older section. This ensures the bond between the new layer and the old layer.