Why do cracks appear in concrete the day after it has been cast? What are the possible reasons?

Cracks appearing in concrete shortly after casting (typically the next day) can result from a combination of factors. Below are the main reasons and mechanisms behind this issue:

1. Plastic Shrinkage Cracking

• Cause: Occurs when water evaporates from the surface of the concrete faster than it is replaced by bleeding water.
• Factors:High temperature, low humidity, or windy conditions. Poor curing practices. Insufficient water content in the mix.

2. Thermal Cracking

• Cause: Temperature changes cause expansion and contraction, leading to cracks.
• Factors: Heat generated during the hydration process (exothermic reaction).Uneven cooling of the concrete surface and core.

3. Drying Shrinkage

• Cause: Loss of moisture as concrete cures and dries leads to volume reduction.
• Factors: High water-cement ratio. Inadequate curing.

4. Improper Curing

• Cause: Lack of proper moisture retention during the curing process.
• Factors: Failure to cover or water the concrete properly. Curing in a hot and dry environment without protection.

5. Settlement Cracking

• Cause: Differential settlement of concrete due to uneven subsurface conditions.
• Factors: Inadequate compaction. Uneven support from formwork or underlying soil.

6. Excess Water in the Mix (High Slump)

• Cause: Excessive water reduces the strength and increases the porosity of concrete.
• Factors: Overuse of water to make placement easier. Poor mix design.

7. Subgrade Movement or Settlement

• Cause: Movement of the soil or base beneath the concrete slab.
• Factors: Poor compaction of the subgrade. Inadequate support for heavy loads.

8. Premature Loading

• Cause: Applying loads on the concrete before it achieves sufficient strength.
• Factors: Early pedestrian or vehicle traffic.

Preventive Measures

• Use a proper mix design with an appropriate water-cement ratio.
• Protect concrete from rapid evaporation using curing blankets, water spraying, or curing compounds.
• Avoid casting during extreme weather conditions, or take precautions such as windbreaks and shade.
• Ensure even and proper compaction of the subgrade and concrete.
• Delay loading until the concrete has achieved adequate strength.

By addressing these factors during design, mixing, placement, and curing, you can significantly reduce the likelihood of early cracks in concrete. READ MORE

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