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For producing high-quality concrete you should take control of problems which are commonly occurred during concreting. These problems mainly happen for improper mixing, placing and handling. Some problems also happen due to the weather effect and other reasons. These problems have a major impact on the strength and duration of concrete First you should know about the common problems of concrete.

The common problems are:

1- Segregation

2- Bleeding

3- Shrinkage cracking

4- Dusting

5- Laitance

6- Scaling, etc.

1- Segregation: Segregation is the tendency of separating concrete particles in fresh concrete. Due to segregation honeycomb, scaling, laitance, porous layers and bond failure at construction joint etc. can happen in concrete.
To avoid segregation following actions can be taken

1- Properly following concrete mix-design

2- Mixing concrete ingredients properly

3- Maintaining the water-cement ratio

4- Not dropping concrete from too high during placing

5- Avoid over vibrating of concrete

 

2- Bleeding: when concrete begins to set the mixing water come out from the concrete and evaporates. If the evaporation rate of water is not sufficient then water stays on the concrete surface. Normal Bleeding is a part of the concrete hardening process. But excess bleeding is harmful to concrete. It reduces the bond between reinforcement and concrete and also concrete particles with cement paste. As a result, it reduces the strength and durability of hardened concrete.
Bleeding can be avoided using the following technique 
1- Maintaining proper water-cement ratio
2- Using water reducing admixture with concrete mix
3- Using well-graded fine aggregates.
3- Plastic Shrinkage cracking: If the evaporation rate of mixing water of concrete is higher than the bleed water of concrete then this cracking occurs in the concrete surface. It happens due to hot weather.

4- Dusting: If the concrete surface bond is weak with the subsequent layer then the surface dusts under traffic.
The following measures can be taken to avoid this problem

1- Keep the water-cement ratio under a reasonable level

2- Use dust-free aggregates

3- Ensure proper hydration of concrete

4- Avoid concrete finishing work with bleed water. etc

5- Laitance: laitance is the bad effect of concrete bleeding and segregation. Due to bleeding and segregation, a thin layer of cement-sand particles appears on the concrete surface that is the laitance. It’s also harmful to concrete as it weakens the bond of subsequent layers of concrete.
The following measures can be taken to prevent the occurrence of concrete laitance

1- Remove the clay, dust, silt and other organic materials from concrete aggregate before mixing.

2- Don’t apply water on fresh concrete during finishing work.

3- Maintain proper water-cement ratio.

4- Using well-graded fine aggregates.

5- Using water reducing admixture with concrete mix.

Scaling: Scaling is the appearing of concrete aggregate on the surface due to flaking or peeling away mortar from the concrete surface. Same protective actions for laitance and dusting can be taken to protect concrete scaling.
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