Bleeding of Concrete

Bleeding of Concrete

Definition:

• Bleeding: Movement of water to the surface of freshly placed concrete.

Causes:

1. Water Content: High water content in the mix leads to excess water rising to the surface.
2. Aggregate Grading: Poorly graded aggregates can contribute to bleeding.
3. Cement Fineness: Coarser cement particles can increase bleeding.
4. Mix Proportions: Incorrect mix proportions can exacerbate bleeding.
5. Water-Cement Ratio: High water-cement ratio is a major cause.

Effects:

1. Surface Weakness: Leads to a weak, porous surface layer.
2. Reduction in Strength: Overall reduction in concrete strength.
3. Settlement Cracks: Can cause cracks and promote segregation.
4. Surface Dusting: Creates a fine, dusty layer on the surface.

Prevention:

1. Water-Cement Ratio: Reduce the water-cement ratio.
2. Quality Gradation: Use properly graded and clean aggregates.
3. Cement Fineness: Opt for finer cement particles when possible.
4. Admixtures: Use admixtures to control bleeding, such as water-reducing agents or superplasticizers.
5. Mix Design: Ensure proper mix design with adequate proportions of materials.

Testing:

1. Slump Test: Helps in assessing the consistency and workability of concrete.
2. Bleed Tests: Specific tests to measure water gain and settlement in concrete.

These notes provide a concise overview of the phenomenon of bleeding in concrete, offering insights into its causes, effects, and preventive measures, along with methods used for detection and testing.