The compaction of concrete improves:
Correct Answer: D. All options are correct
📚 Detailed Explanation: Compaction Improves Density, Strength, and Durability
Why D (All options correct) is correct: These three properties are interconnected. Compaction removes air voids — this single action simultaneously increases density, strength, and durability because all three are inversely related to void content.
How Compaction Improves Each Property
| Property | Mechanism of Improvement | Quantitative Impact |
|---|---|---|
| Density | Air expelled → mass per unit volume increases | Density rises from ~2200 kg/m³ (uncompacted) to ~2400 kg/m³ (fully compacted) |
| Strength | Fewer voids = more solid load-bearing area per cross-section | Each 1% air removed ≈ +5% strength |
| Durability | Reduced capillary porosity = less ingress of water, chlorides, sulfates, CO2 | Properly compacted concrete has 3–5× greater service life in aggressive environments |
The Interconnection
All three improvements stem from the same fundamental change: reduced void content. The void content determines how much of the concrete cross-section carries load (strength), how closely packed the matrix is (density), and how easily aggressive substances penetrate (durability).
- Compaction improves all three: density, strength, and durability.
- Fully compacted concrete achieves ~2400 kg/m³ density and 100% design strength.
- Bond to reinforcement also improves with proper compaction (concrete fills around bars).