On "Cold Joint"

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Cold joint is a specific word used to describe a process in concrete casting.
In standard conditions, a piece of concrete needs to be cast in one shot in order to ensure its cohesive strength, however, when it is cast in a few batches where the time between each batch is too long, it will cause "cold joint", which is a phenomenon in which the two separate batches do not join together well and result in a "layered" look between the two pieces. This affects the strength of the casted concrete and is to be avoided whenever possible.

Nevertheless, different storeys and sections of a building are usually "cold joined". In these cases, various measures needs to be taken to ensure the integrity of the joint pieces. For example, ribars are to connect between the joints, edges are to be roughened to improve connectivity and bonding agents are used.

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