The resistance of an aggregate to the effects of cement hydration and weathering is called:
Correct Answer: A. Soundness
📚 Detailed Explanation: Soundness is Resistance to Weathering and Hydration Effects
Why A (Soundness) is correct: The term “soundness” in aggregate engineering specifically refers to the ability of an aggregate to resist disintegration from weathering (freeze-thaw, wet-dry cycles, temperature variation) and to remain stable under the chemical influences of cement hydration. A “sound” aggregate does not undergo harmful volume changes, crack, or break down under these influences.
Aggregate Properties: Definitions
| Property | Definition | Test Method (IS 2386) |
|---|---|---|
| A. Soundness | Resistance to weathering (freeze-thaw, chemical action of cement) and volume stability | IS 2386 Part 5: Sodium/Magnesium sulphate immersion cycles |
| B. Crushing strength | Resistance of aggregate particles to compression; load bearing capacity of the rock | IS 2386 Part 4: Aggregate Crushing Value (ACV) test |
| C. Abrasion resistance | Resistance of aggregate surface to mechanical wear by attrition and abrasion | IS 2386 Part 4: Los Angeles, Deval, or Dorry test |
| D. Impact value | Resistance to sudden impact (dynamic) loads; toughness | IS 2386 Part 4: Aggregate Impact Value (AIV) test |
Soundness Test (IS 2386 Part 5) Procedure
| Step | Detail |
|---|---|
| Reagent | Sodium sulphate (Na2SO4) or Magnesium sulphate (MgSO4) solution; concentration: saturated |
| Cycles | 5 immersion-drying cycles; each cycle: 18h immersion + 6h oven drying at 105°C |
| Principle | Sulphate solution enters pores; on drying, sulphate crystals form and exert expansive pressure; simulates freeze-thaw expansion of water |
| Result | Weight loss percentage; breakdown of particles; visual inspection for cracking/friability |
| Limits (IS 2386) | Loss ≤12% with Na2SO4; ≤18% with MgSO4 for concrete aggregate |
- Soundness is the resistance of aggregate to weathering and the effects of cement hydration.
- Crushing value, impact value, and abrasion tests measure different mechanical properties — not soundness.