Plastic shrinkage cracking (as shown below) is caused by the rapid drying of the concrete surface. They can occur at any time of the year, from cooler low-humidity weather conditions, in particular, to warmer weather conditions that include either one or a combination of high temperatures, low humidity, and wind.
These types of cracks occur when the concrete is bleeding and during finishing work. Fresh concrete may be exposed to the elements for a considerable period of time during these stages, causing the concrete to dry out on the surface and shrink before it has any strength to resist the shrinkage forces.
Concrete cracks just like clay soil.
1. erecting temporary wind breaks
High wind velocities can greatly affect the rate of water evaporation from the concrete being laid. This in turn will result in plastic shrinkage cracking of the concrete. Therefore, to reduce the wind velocity on the concrete surface, put a temporary wind break.
2. provide sunshade
In case of concrete slab construction, it is very effective to provide a sunshade over the concrete slab and thereby control the surface temperature of the slab.
3. proper placement time
In very hot weather conditions, concrete should not be laid in the afternoon, as this can cause plastic shrinkage cracks on the concrete due to lack of water. It is therefore a good practice to set a concrete spot early in the morning or in the evening. This way we can have better control over the temperature of the concrete.
4. fog spray use
In very hot and dry periods the air is very hot. So use the fog spray to spray the fog into the air over the concrete surface and in the air opposite to the direction of the wind blowing. The use of fog spray reduces the rate of evaporation from the concrete surface.
5. reduce subgrade
During construction of concrete pavement in hot and dry weather, moisten the subgrade which is responsible for water absorption from the concrete. But remember that the subgrade should not be overly wet. Formwork and reinforcement should also be reduced.
6. using evaporator
Spray an evaporation retardant such as aliphatic alcohol on the surface of the freshly screed concrete. The surface may dry out prematurely if the rate of evaporation exceeds the rate of bleeding. These products form a film on the surface which reduces the rate of water evaporation, thus giving all the bleed water time to rise to the surface. In extreme situations, reapplication of evaporator retarder may be necessary both before and during troweling. These products do not affect the strength or performance of concrete and can act as a finishing aid.
7. start treatment immediately
Start treatment as soon as possible after you finish. Spray the surface with liquid membrane curing compound or cover the surface with wet burlap or begin water curing after concrete placement.
8. quick setting time of concrete
Use some sort of chemical admixture in the concrete to speed up the setting time of the concrete and avoid the large temperature difference between the concrete and the air temperature.
9. Adding Polypropylene Fiber to the Concrete Mix
Polypropylene fibers can be added to the concrete mix to reduce the incidence of plastic shrinkage cracking. The fibers bind the concrete surface together and provide some strength to the plastic concrete to resist shrinkage forces.
10. be ready
Have the proper manpower, equipment and supplies on hand so that concrete can be placed and finished quickly.