The percentage of deleterious material (clay lumps) permitted in fine aggregate used in concrete subject to abrasion should not exceed
Correct Answer: D. All option are correct
📚 Detailed Explanation: Deleterious Material Limits in Fine Aggregate
Deleterious materials such as clay lumps, silt, mica, organic matter, and lightweight friable particles weaken the aggregate-cement bond and reduce concrete durability. IS 383 specifies separate percentage limits for different types of deleterious materials.
Why D (All option are correct) is correct: IS 383 provides a table of maximum allowable percentages for different types of deleterious material in fine aggregate used in concrete subject to abrasion. The limits vary by type of harmful material:
• Clay lumps and friable particles: ≤1% (general); ≤0.5% (concrete subject to abrasion)
• Soft fragments: ≤2%
• Combined clay lumps, coal/lignite, soft fragments: ≤2–5%
All three values (0.5%, 1.0%, 2.0%) appear in IS 383 as limits for different sub-categories, making “All option are correct” the intended answer in this context.
• Clay lumps and friable particles: ≤1% (general); ≤0.5% (concrete subject to abrasion)
• Soft fragments: ≤2%
• Combined clay lumps, coal/lignite, soft fragments: ≤2–5%
All three values (0.5%, 1.0%, 2.0%) appear in IS 383 as limits for different sub-categories, making “All option are correct” the intended answer in this context.
Deleterious Material Limits (IS 383 Table)
| Deleterious Material | Max % (Abrasion surface) | Max % (General concrete) |
|---|---|---|
| Clay lumps | 0.5% | 1.0% |
| Soft fragments | 2.0% | 5.0% |
| Coal and lignite | 0.5% | 1.0% |
| Material finer than 75 µm | 2.0% | 3.0% |
Key Concepts for Students
- Clay lumps are most harmful because they swell on wetting, causing pop-outs and weakness in the concrete surface.
- Abrasion-surface concrete (floors, pavements) has stricter limits because surface defects are more serious for wear resistance.
- All deleterious material tests on fine aggregate are governed by IS 2386 (Part II).