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Tests on road aggregates
Short answer
Tests include aggregate crushing value (strength), Los Angeles abrasion (hardness), impact value (toughness), soundness (durability), flakiness/elongation (shape), specific gravity/absorption, stripping (adhesion) and grading. They ensure aggregate resists traffic loads, weathering and bitumen stripping; e.g. ACV ≤30% for wearing course, LA abrasion ≤30%.
What are the laboratory tests performed on road aggregates to judge their suitability in road construction? Describe their significance.
Road aggregates are tested in the laboratory for strength, hardness, toughness, durability, shape and bitumen affinity (IS:2386 and IRC/NRS 2070 specifications).
| Test | What it measures | Significance / typical limit |
|---|---|---|
| Crushing value (IS:2386 Pt IV) | Resistance to a gradually applied load | Strength; ACV not more than 30% for wearing course, 45% for base |
| Los Angeles abrasion | Resistance to wear and impact | Hardness/toughness; max 30-40% |
| Impact value | Resistance to sudden shock load | Toughness; AIV not more than 30% (wearing course), 45% (base) |
| Abrasion (Deval)/attrition | Wear by rubbing and traffic | Hardness; Deval abrasion not more than 3% by weight |
| Soundness | Weathering by sodium/magnesium sulphate cycles | Durability; loss not more than 12% (Na2SO4) or 18% (MgSO4) |
| Shape tests - flakiness & elongation | Proportion of flat and long particles | Combined FI + EI not more than 30-35%; flat or elongated pieces break and give poor interlock |
| Specific gravity & water absorption | Density and porosity | Porous aggregate is weaker and absorbs bitumen; absorption not more than 2% |
| Stripping / bitumen affinity (coating & stripping, water immersion) | Adhesion of bitumen to aggregate | Hydrophilic aggregates strip in the presence of water; retained coating at least 95% |
| Polished stone value (PSV) | Skid resistance (surface aggregate) | PSV not less than 55-60 for wearing course |
| Grading/sieve analysis | Particle size distribution | Mix stability and density |
Why these are needed
- Strength tests (ACV, AIV, LAA) make sure the aggregate does not break under rollers and traffic.
- Hardness/abrasion tests prevent early wear of the surface.
- Soundness ensures durability against rain, frost and chemical weathering.
- Shape tests help in good packing and compaction.
- Affinity tests make sure the bituminous layer does not strip in the presence of water.
✓ Answer checked by Claude Opus 5.5 (high effort)
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