Segregation in concrete can be defined as the tendency of:
Correct Answer: B. Coarse aggregate to separate from the mortar
📚 Detailed Explanation: Segregation — Coarse Aggregate Separating from Mortar
Why B is correct: Segregation is defined as the tendency of the constituent materials of concrete to separate. Specifically, it is the separation of coarse aggregate from the cement-sand mortar. This is because the coarse aggregate (density ≈2650 kg/m³) is the heaviest and most discrete constituent; it is most prone to rolling away or settling out when the mortar cannot hold it in suspension.
Segregation vs. Other Concrete Defects
| Defect | Definition | What Separates |
|---|---|---|
| Segregation | Loss of homogeneity due to coarse aggregate separating from mortar | Coarse aggregate from cement-sand mortar |
| Bleeding | Free water rises to surface | Water + fine particles (upward) |
| Laitance | Weak surface layer formed by bleed water | Fine cement + water (surface deposit) |
| Honeycombing | Voids left by coarse aggregate not surrounded by mortar | Result of severe segregation + poor compaction |
Root Causes of Segregation
| Cause | Why It Causes Segregation |
|---|---|
| High w/c ratio (wet mix) | Low paste viscosity; cannot suspend heavy aggregate |
| Dropping concrete >1.5 m | Impact energy causes aggregate to bounce away from mortar |
| Over-vibration | Liquefies mix; aggregate sinks under gravity |
| Poorly graded aggregate | Single-size or gap-graded; high void content; poor suspension |
| Large maximum aggregate size | Heavier particles; settle faster (Stokes' Law: V ∝ d²) |
- Segregation = tendency of coarse aggregate to separate from the mortar.
- IS 456:2000: maximum drop height for concrete placement = 1.5 m to prevent segregation.
- Segregation causes voids: 5% voids → 30%+ strength reduction.