Increased cohesiveness of concrete makes the mix:
Correct Answer: A. Less liable to segregation
📚 Detailed Explanation: Higher Cohesiveness Reduces Segregation Risk
Why A (Less liable to segregation) is correct: Cohesiveness is a mix property that reflects how strongly the cement paste holds all the constituents together. A more cohesive mix has a higher yield stress (paste is stiffer and stickier), which prevents the heavy coarse aggregate from settling or rolling away. Therefore, higher cohesiveness = less segregation.
Cohesiveness and Segregation Relationship
| Mix Property | High Cohesiveness | Low Cohesiveness |
|---|---|---|
| Paste yield stress | High; resists aggregate settlement | Low; aggregate sinks freely |
| Paste viscosity | High; aggregates suspended in thick paste | Low; aggregates fall through thin paste |
| Segregation risk | Low (less liable to segregation) | High (more liable to segregation) |
| Workability | Can still be workable if properly designed | May be highly fluid but unstable |
Ways to Increase Cohesiveness
| Method | How It Increases Cohesiveness |
|---|---|
| Lower w/c ratio | Less free water; thicker, more viscous paste |
| Add fine material (mineral admixtures) | Fly ash, silica fume, GGBS fill micro-voids; increase paste viscosity |
| Air-entrainment | Tiny air bubbles act as ball bearings; improve cohesion without adding water |
| Superplasticisers | Allow low w/c + high workability combination; more cohesive workable mixes |
| Proper aggregate gradation | Well-graded aggregate has less void space; more cohesive mix |
- Increased cohesiveness → less liable to segregation.
- Cohesion is one of the three components of workability (alongside mobility and stability/stability/compactability).
- Lean mixes (low cement, high water) are both less cohesive and more prone to segregation.