Bleeding is considered acceptable to a limited extent only when concrete is:
Correct Answer: C. Plastic
📚 Detailed Explanation: Bleeding Acceptable Only in Plastic State
Why C (Plastic) is correct: Bleeding is the upward migration of free water to the concrete surface, driven by the settlement of heavier solid particles (aggregate and cement). While the concrete is still in the plastic (fluid, not-yet-set) state, a small amount of bleeding is natural and can actually aid finishing. Once the concrete begins to stiffen, bleeding becomes problematic.
Bleeding at Different Stages
| Stage | Bleeding Effect | Acceptability |
|---|---|---|
| During transport | Water separates in transit mixer or truck; alters w/c ratio | Undesirable — causes quality inconsistency |
| During mixing | Excess water visible immediately; indicates over-watered mix | Undesirable — suggests too high w/c |
| Plastic state (freshly placed) | Thin water film appears; concrete still fluid and workable | Tolerable in small amounts; aids surface finishing |
| After initial set | Trapped bleed water creates capillary channels below aggregate | Undesirable — permanent permeability channels |
Causes of Excessive Bleeding
| Cause | Effect |
|---|---|
| High water-cement ratio (excess water) | More free water available to bleed to surface |
| Excessive troweling | Disturbs surface and drives water upward |
| Addition of calcium chloride (CaCl2) | Accelerates hydration and increases bleeding tendency |
| Highly fluid mix (high slump) | Less viscous paste cannot retain water |
Consequences of Excessive Bleeding
- Laitance: weak, dusty top layer of cement paste and fines that forms as bleed water evaporates.
- Reduced impermeability: capillary channels left by bleed water create pathways for water ingress.
- Reduced bond: water collects under reinforcement bars and coarse aggregate, creating weak interfaces.
- Rule: minor bleeding in the plastic state only is acceptable; excessive bleeding at any stage is harmful.