Pycnometer, wire mesh bucket and water are used to calculate which characteristic property of the coarse aggregate?
🧱 Detailed Explanation: Pycnometer and Specific Gravity of Aggregates
Specific gravity (relative density) is the ratio of the mass of a material to the mass of an equal volume of water. For coarse aggregates, it is determined using a pycnometer (or wire mesh basket submerged in water) as specified in IS 2386 (Part III): 1963. The specific gravity value is essential for mix design — it determines how much volume a given mass of aggregate will occupy in the concrete.
Test procedure (wire mesh basket method, IS 2386 Part III):
1. Saturate the aggregate in water for 24 hours.
2. Surface-dry the aggregate to SSD condition (damp cloth).
3. Weigh in SSD condition → mass W1.
4. Place in wire mesh basket, submerge in water, weigh → mass W2 (= W1 minus weight of displaced water).
5. Oven-dry at 100–110°C and weigh → mass W3.
Specific gravity (SSD basis) = W1 ÷ (W1 − W2)
Water absorption (%) = (W1 − W3) × 100 ÷ W3
Crushing strength (A) requires a compression machine; attrition (B) is measured in a Los Angeles or Deval machine; impact value (C) uses a drop-hammer machine. None require a pycnometer or water-immersion setup.
Apparatus to Property: Matching Table
| Apparatus | Property Tested | IS Code |
|---|---|---|
| Pycnometer / wire mesh basket + water | Specific gravity and water absorption | IS 2386 Part III |
| Steel cylinder + compression machine | Aggregate Crushing Value | IS 2386 Part IV |
| Drop-hammer apparatus | Aggregate Impact Value | IS 2386 Part IV |
| Los Angeles drum + steel balls | Abrasion Resistance | IS 2386 Part IV |
Key Concepts for Students
- Normal-weight aggregates (granite, basalt, limestone) have specific gravity of 2.6–2.8. Values below 2.0 indicate lightweight aggregate; above 2.8 indicate heavyweight aggregate.
- Specific gravity is used in mix design to calculate volume yield: knowing mass and SG, you can find the volume each ingredient occupies in the fresh mix.
- The SSD condition is the mix-design reference state: aggregate pores are saturated but the surface is dry, so the aggregate neither absorbs from nor releases water into the mix.
- Specific gravity alone does not indicate strength — a dense stone can still be weak if it has fracture planes or high porosity in certain directions.