Durability of concrete is proportional to:
Correct Answer: D. Cement-aggregate ratio
📚 Detailed Explanation: Durability Proportional to Cement-Aggregate Ratio
Why D (Cement-aggregate ratio) is correct: Durability is the property that allows concrete to remain serviceable for its intended design life without significant deterioration. It is directly proportional to the cement-aggregate ratio — a higher ratio means more cement binder, denser paste, fewer capillary pores, and less permeability, all of which improve durability. However, durability is also strongly influenced by permeability (which relates to w/c ratio).
How Cement-Aggregate Ratio Affects Durability
| Factor | Higher Cement-Aggregate Ratio | Effect on Durability |
|---|---|---|
| Paste content | More paste fills voids between aggregate | Denser concrete, lower permeability |
| Hydration products | More C-S-H gel and Ca(OH)2 produced | Better void-filling; stronger matrix |
| Permeability | Reduced capillary porosity | Less ingress of water, chlorides, CO2 |
| Strength | Higher compressive and tensile strength | More resistant to mechanical attack |
Factors Influencing Durability of Concrete
| Factor | Increasing Durability | Decreasing Durability |
|---|---|---|
| w/c ratio | Lower w/c → less permeable | Higher w/c → more porous |
| Cement content | Richer mix → denser paste | Lean mix → more permeable |
| Curing | Longer curing → more hydration | No curing → porous, weak |
| Compaction | Full compaction → no air voids | Poor compaction → honeycombing |
| Chemical exposure | Dense concrete resists attack | Acids, sulfates, chlorides degrade |
- Durability is directly proportional to cement-aggregate ratio.
- To enhance durability: low w/c ratio, high cement grade, extended curing, concreting at low temperatures, full compaction.
- Permeability is the most critical factor governing concrete durability in aggressive environments.