Construction joints in RCC beams and columns are required when the concreting has to be stopped for the day or more than 30 minutes. In such case, typical construction joints shall be provided so that bond is maintained between set concrete and fresh concrete.
Below are some images showing correct method of construction joints to be provided in columns, beams and beam-column junction. To know about what is construction joint, read Joints in Concrete Construction.
1. Construction Joints in Column
Following figure shows correct method of providing construction joint in column. Construction joint in column shall not be provided with smooth surface or inclined surface. The top surface of the column should be rough with parts of coarse aggregates being seen.
Fig: Typical Construction Joint in RCC Column
2. Construction Joints in Beams and Beam-Column Joint:
Following figure shows the typical construction joint to be provided in beams and beam column joints.
Fig: Typical Construction Joint in Beams and Beam-Column Joint
The arrow symbol shows the direction of concreting, tick mark shows the correct method of providing construction joint while cross-mark shows the wrong method.
From the figure it can be seen that construction joint in the beams should be provided at 1/4 the span of beam from the face of the column and should not be provided on the column.
For a beam column joint, the construction joint for the column should be provided after construction of some length of column above beam level, and for the beam, it should be provided at a span of 1/4th from the face of the column.