Which of the following methods is NOT used for measuring air content in fresh concrete?
Correct Answer: A. Blaine air permeability method
📚 Detailed Explanation: Blaine Test Measures Cement Fineness, NOT Concrete Air Content
Why A (Blaine air permeability method) is correct (NOT used for air content): The Blaine apparatus is a device that measures how easily air permeates through a bed of dry, compacted cement powder. The result is expressed as specific surface area (cm²/g or m²/kg) — a measure of cement fineness. It has nothing to do with the air content of fresh concrete.
What the Blaine Test Actually Measures
| Aspect | Detail |
|---|---|
| Standard | IS 4031 (Part 2) — Fineness of hydraulic cement |
| What is measured | Specific surface area of dry cement (cm²/g) |
| Sample used | Dry cement powder in a cylindrical cell |
| Result indicates | Fineness of cement; finer cement = higher reactivity |
Standard Methods for Air Content in Fresh Concrete (IS 1199)
| Method | Principle | Suitable For |
|---|---|---|
| Gravimetric method | Compare actual density with theoretical air-free density; air % = difference | All concrete types |
| Pressure method | Apply pressure in calibrated vessel; Boyle's Law relates pressure change to air volume | Normal density concrete; quick and widely used |
| Volumetric method | Fill vessel with water; measure volume displaced by air | Lightweight aggregate concrete (where pressure method is unreliable) |
| Blaine air permeability | Air permeability through dry cement bed | Cement fineness only — NOT air content in concrete |
- Blaine test = cement fineness; NOT used for air content of fresh concrete.
- Air content methods: Gravimetric, Pressure, and Volumetric (all per IS 1199).