A cold joint in common is an undesired discontinuity between concrete layers that occur when a concrete layer is allowed to cure before pouring the rest of the concrete into what is supposed to be a single solid mass. The discontinuity occurs between the layers due to the inability of the newly poured wet concrete to mix and bind properly to the hardened concrete. Such discontinuity is often the result of logistical issues such as a contractor’s work schedule or an unexpected material shortage.
Problems associated with cold joints range from relatively small to very serious. At the less serious end of the scale, a cold can commonly result in a visual cost estimation discontinuity that appears on the surface when the concrete has hardened. This type of aesthetic defect can easily be hidden instead of being repaired.
A more serious problem associated with a cold in common is the possibility that moisture penetrates the concrete section. If water settles in the joint, it can lead to decomposition of the concrete under certain environmental conditions. For example, as water expands when it freezes and then contracts when it melts, water trapped in a cold joint can cause cracking or erosion of the material. Moisture can also damage anything beyond the concrete pulp, if it is able to sip all the way through it.
In addition, a cold in common is an area of reduced strength. Concrete is remarkable for its high strength during compression, but it is much weaker under tension. A cold in common is even weaker under tension, and it is sensitive to shear during discontinuity.
When possible, these joints should be avoided in concrete by filling the entire pour for a given section in a session. This allows the entire section to solidify in a continuous solid mass. If this is not possible, several measures can be taken to reduce the more serious problems.
Specialized sealant joint compound can be applied to the joint to make it waterproof and thus protect against potentially harmful moisture intrusion. A special surface preparation can be applied to the cured layer prior to application of a new layer of concrete. This will strengthen the ties between the two layers. Another way to increase the strength of the cold joint is to insert reinforcement bar or reinforcement iron into the first layer before pouring the next layer. This will better help tie them together and increase the tensile strength of the joint. It is also sometimes possible to locate the weakened joint in an area that is not critical to supporting a high load.