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Plastic Shrinkage Crack is developed during the initial stage itself i.e. before hardening. It is caused by a rapid loss of water from the surface of the concrete before it has been set.
This crack generally occurs on horizontal surfaces than on vertical.
✔ When the concrete is in the plastic state, before hardening, it contains enough water. Eventually, the water gets evaporated before setting; leaving behind voids between the aggregate particles. The voids or the empty spaces thus formed weaken the concrete increasing the possibility of cracking.
1. Causes of Plastic Shrinkage Crack
✔ Plastic shrinkage crack is caused by a rapid loss of water from the surface of the concrete before it has been set.
✔ The condition exists when the rate of evaporation of surface moisture exceeds the rate at which rising bleed water can replace it.
Water receding below the concrete surface forms menisci between the particles of cement and aggregate causing a tensile force to develop in the surface layers.
If the concrete surface has started to set and has developed sufficient tensile strength to resist tensile forces, cracks do not form.
The main causes of plastic shrinkage crack can be listed as follows:
1. Low relative humidity.
2. High ambient temperature.
3. High wind velocity.
2. Prevention of Plastic Shrinkage Crack
The various precautions that must be taken for preventing plastic shrinkage crack are mentioned below:
1. If a harsh climatic condition exists at the site such as high wind velocity, or hot temperature; the placement must be done at an appropriate time such as late evening or early night.
2. In very hot or dry conditions, fog sprays must be used. Fog spray reduces the rate of evaporation of water.
3. Proper workmanship, equipment, and materials must be ensured.
4. The concrete must be covered with wet burlap or polyethylene sheets between finishing operations.
Read Also: Types of Concrete
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