Plastic settlement cracking

The stability of the concrete mix can be considered in terms of its cohesion , which is a subjective term used to describe its ability to maintain a homogeneous appearance when subjected to applied stress. Lack of cohesion leads to segregation of the mix components into layers relevant to their densities. A further term associated with mix stability is that of bleeding , which is the movement of water to the surface of the fresh concrete. This phenomenon can occur either in isolation or as a manifestation of segregation. Bleeding in excess is normally considered to be undesirable because of the dangers of water runs at the shutter/concrete interface and cracking due to plastic settlements, and there is also the possibility of adverse effect on the concrete-reinforcement bond due to the collection of water beneath the steel. 

Plastic settlement and plastic shrinkage cracks - occur within a few hours of casting. 

It is important to remember that corrosion is not the only deterioration mechanism in reinforced concrete. Alkali-sillica reactivity (ASR), freeze-thaw, plastic shrinkage, thermal movement, settlement and other movement can all lead to cracking and spalling of concrete. 

Plastic Cracking. Cracking in concrete before it has set and hardened. Its cause may be differential settlement, or shrinkage. 

Examples of uncontrolled cracking are cracks resulting from plastic shrinkage, settlement or an overload condition. 

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