As per IS 2386 (1963), the aggregate crushing value is calculated by using a single sized aggregate, which is:
Correct Answer: A. Passing 12.5 mm and retained on 10 mm
🧱 Detailed Explanation: Why the 10–12.5 mm Fraction Is Used for the ACV Test
The Aggregate Crushing Value (ACV) test, under IS 2386 (Part IV): 1963, is designed to evaluate how much an aggregate resists gradual compressive loading. Using a precisely defined single-sized aggregate fraction is essential for reproducibility: different sizes pack differently, so mixing sizes would yield inconsistent results across laboratories.
The 10–12.5 mm fraction is the IS standard because it:
Why option A is correct — Passing 12.5 mm, retained on 10 mm:
This narrow 10–12.5 mm fraction provides a uniform packing in the 150 mm diameter test cylinder. Particles are large enough that individual grain strength governs the result (rather than interparticle friction of very fine material), yet small enough to fit the cylinder without bridging. Options B (4.75–2.36 mm) uses fine aggregate; option C (20–40 mm) is too large for the test mould; option D (10–20 mm) mixes two size ranges and is not a single-sized fraction.
This narrow 10–12.5 mm fraction provides a uniform packing in the 150 mm diameter test cylinder. Particles are large enough that individual grain strength governs the result (rather than interparticle friction of very fine material), yet small enough to fit the cylinder without bridging. Options B (4.75–2.36 mm) uses fine aggregate; option C (20–40 mm) is too large for the test mould; option D (10–20 mm) mixes two size ranges and is not a single-sized fraction.
Option-by-Option Analysis
| Option | Fraction | Verdict |
|---|---|---|
| A. Passing 12.5 mm, retained 10 mm | 10–12.5 mm (IS standard) | ✅ Correct — IS 2386 Part IV |
| B. Passing 4.75 mm, retained 2.36 mm | 2.36–4.75 mm | ❌ Fine aggregate; not used for ACV |
| C. Passing 40 mm, retained 20 mm | 20–40 mm | ❌ Too large for the 150 mm test cylinder |
| D. Passing 20 mm, retained 10 mm | 10–20 mm (mixed) | ❌ Not single-sized; two size ranges |
Key Concepts for Students
- The single-sized fraction (10–12.5 mm) is mandatory for reproducibility. A mix of sizes would give variable packing density and inconsistent ACV results.
- Post-crush sieving is done on a 2.36 mm sieve — material passing it is the “crushed fines” used to calculate ACV.
- The test mould is a 150 mm diameter × 130 mm deep steel cylinder; 40 tonnes is applied over 10 minutes in three equal layers (tamped 25 times each).
- An ACV below 30% is “good”; above 45% the aggregate is unsuitable for concrete.