Non-uniform compaction may cause the concrete to become:
Correct Answer: D. All options are correct
📚 Detailed Explanation: Consequences of Non-Uniform Compaction
Why D (All options) is correct: When compaction is applied unevenly, some zones get fully compacted while others remain with entrapped air. This creates spatially variable concrete with multiple simultaneous defects.
Effects of Non-Uniform Compaction
| Effect | Mechanism | Consequence |
|---|---|---|
| A. Porous | Air voids not expelled in under-vibrated zones | Permeable concrete; susceptible to chemical attack, carbonation, chloride ingress |
| B. Non-homogeneous | Aggregate distribution uneven; paste concentration varies | Inconsistent properties across the cross-section; weak planes |
| C. Reduced strength | Voids reduce load-bearing cross-sectional area | Actual strength < design strength; potential structural failure |
Visual Signs of Poor Compaction
| Defect | Appearance | Cause |
|---|---|---|
| Honeycombing | Visible voids with exposed aggregate on concrete surface | Severe under-compaction; concrete didn't flow around reinforcement |
| Cold joints | Visible horizontal line in finished concrete | Delay between layers; earlier layer partially set before new pour |
| Sand streaks | Vertical channels of washed-out paste | Excess water / vibration near formwork |
- Non-uniform compaction simultaneously causes porosity, non-homogeneity, and reduced strength.
- Vibrator must be inserted at regular intervals (not more than 450 mm apart) for uniform coverage.
- Each insertion should be ~600 mm deep (or full depth of layer) and withdrawn slowly at ~75 mm/sec.