What is the difference between construction joint and cold joint ?

Cold joints are formed primarily between two batches of concrete where the delivery and placement of the second batch has been delayed and the initial placed and compacted concrete has started to set. The full knitting together of the two batches of concrete under vibration to form a homogeneous mass is therefore not possible, unlike the compaction of two fresh workable batches of concrete. This could be a potential plane of weakness.

Construction Joints

Construction joints (figures7-36,7-37,7-38, and7-39) are made where the concrete placement operations end for the day or where one structural element is cast against previously placed concrete. These joints allow some load to be transferred from one structural element to another through the use of keys or (for some slabs and pavement) dowels. Note that the construction joint extends entirely through the concrete element.

Figure7-36.-Vertical bulkhead in wall using keyway.

Figure7-37.-Keyed wall construction joint.

Figure7-38.-Construction Joint between wail and footing with a keyway.

Figure7-39.-Types of construction Joints.