Bleeding in fresh concrete is defined as:
Correct Answer: A. Separation of water, sand, and cement from fresh concrete mix
📚 Detailed Explanation: Bleeding — Upward Separation of Water, Sand, and Cement
Why A is correct: Bleeding is defined as the upward migration of water (and fine particles of sand and cement) from freshly placed concrete. It results from the differential density between the mix constituents: coarse aggregate (≈2650 kg/m³) and cement (≈3150 kg/m³) settle down, while free water (1000 kg/m³) and fine sand particles migrate upward through the concrete mass.
Bleeding vs. Segregation — Key Distinction
| Property | Bleeding | Segregation |
|---|---|---|
| What separates | Water + fine particles (upward migration) | Coarse aggregate (separates laterally or settles) |
| Direction of movement | Upward (water rises to surface) | Lateral or downward (aggregates fall away from mortar) |
| Primary cause | Excess free water; gravity-driven settlement | Insufficient cohesion; high drop height; over-vibration |
| Visual indication | Water sheen on concrete surface | Aggregate-rich zones and paste-rich zones visible |
| Resulting defect | Laitance; capillary channels; reduced surface strength | Voids; honeycombing; non-uniform strength |
Effects of Bleeding on Concrete Quality
| Effect | Mechanism | Impact |
|---|---|---|
| Laitance formation | Cement + water film evaporates on surface | Weak, dusty top layer; must be removed before bonding layers |
| Capillary channels | Upward water paths remain as voids after evaporation | Increased permeability; reduced durability |
| Weak zones under rebar | Water accumulates under horizontal bars; weak interface | Reduced bond strength between concrete and reinforcement |
| Reduced surface strength | High w/c at the top surface | Reduced abrasion resistance and hardness |
- Bleeding = upward separation of water, sand, and fine cement particles from fresh concrete.
- This is driven by gravity: heavier aggregate and cement sink; lighter water rises.
- The surface water film (bleed water) forms laitance on evaporation — a classic quality defect.