The percentage of deleterious material (coal and lignite) permitted in fine aggregate used in concrete subject to abrasion should not exceed
Correct Answer: D. All option are correct
📚 Detailed Explanation: Coal and Lignite Limits in Fine Aggregate
Coal and lignite are organic materials that, when present in fine aggregate, can expand when wetted and cause pop-outs in hardened concrete surfaces. They also burn away over time (in fire exposure), leaving pores. IS 383 limits their presence through specific percentage thresholds.
Why D (All option are correct) is correct: Similar to Q83 (clay lumps), IS 383 provides tiered limits for coal and lignite in fine aggregate:
• For concrete subject to abrasion: ≤0.5% (most stringent)
• For general concrete: ≤1.0%
• In combination with other soft/friable materials: up to 2.0% combined
All three percentages (0.5, 1.0, 2.0) represent correct IS 383 limit values in their respective contexts. The question's answer key recognises all three as correct values from the standard.
• For concrete subject to abrasion: ≤0.5% (most stringent)
• For general concrete: ≤1.0%
• In combination with other soft/friable materials: up to 2.0% combined
All three percentages (0.5, 1.0, 2.0) represent correct IS 383 limit values in their respective contexts. The question's answer key recognises all three as correct values from the standard.
Coal and Lignite Limits (IS 383)
| Application | Max Coal/Lignite in FA |
|---|---|
| Concrete subject to abrasion | ≤0.5% |
| General structural concrete | ≤1.0% |
| Combined with other deleterious (soft fragments) | ≤2.0% |
Key Concepts for Students
- Coal and lignite in fine aggregate are identified by their low specific gravity (<2.0) and dark colour.
- They cause pop-outs (small conical spalls) in concrete surfaces as they swell and expand.
- Test: IS 2386 Part II — float the aggregate sample in liquid of specific gravity 2.0 (ZnCl2 solution); particles that float contain coal, lignite, or lightweight material.