IS 2386:1963 Part 1 is the Indian Standard (BIS) for methods of test for aggregates for concrete - part 1: particle size and shape. This standard prescribes the methods of test for determining the particle size distribution (sieve analysis) and shape characteristics (flakiness, elongation, and angularity) of aggregates. These properties are critical for determining the workability of fresh concrete and the durability of hardened concrete.
Covers methods for determining particle size and shape of aggregates, including grading and flakiness index.
Particle size & shape tests for concrete aggregates — sieve analysis, fineness modulus, flakiness, elongation.
| Reference | Value | Clause |
|---|---|---|
| Sample mass — coarse aggregate (40 mm) | 30 kg minimum | Cl. 2.2 (Table 1) |
| Sample mass — coarse aggregate (20 mm) | 10 kg | Cl. 2.2 (Table 1) |
| Sample mass — coarse aggregate (10 mm) | 5 kg | Cl. 2.2 (Table 1) |
| Sample mass — fine aggregate | 0.5 kg minimum | Cl. 2.2 (Table 1) |
| Sieve sizes — coarse aggregate | 80, 63, 40, 20, 16, 12.5, 10, 6.3, 4.75 mm | Cl. 3.1 |
| Sieve sizes — fine aggregate | 10, 4.75, 2.36, 1.18, 0.6, 0.3, 0.15 mm | Cl. 3.1 |
| Mechanical sieving duration | 10 minutes | Cl. 3.4 |
| Wet sieving — required when | > 5 % passing 75 μm | Cl. 3.6 |
| Fineness modulus formula | Σ (cumulative % retained) / 100 | Cl. 4.2 |
| Fineness modulus — fine aggregate (Zone I) | FM 2.71–3.50 | (IS 383 Table 4) |
| Fineness modulus — fine aggregate (Zone II) | FM 2.40–3.10 | (IS 383 Table 4) |
| Fineness modulus — fine aggregate (Zone III) | FM 2.10–2.90 | (IS 383 Table 4) |
| Fineness modulus — fine aggregate (Zone IV) | FM 1.71–2.61 | (IS 383 Table 4) |
| Flakiness index — definition | weight % with thickness < 0.6 × mean | Cl. 5.1 |
| Flakiness index — limit (general concrete) | ≤ 35 % combined with elongation | (IS 383) |
| Elongation index — definition | weight % with length > 1.8 × mean | Cl. 5.2 |
| Combined flakiness + elongation — pavement | ≤ 30 % | (IRC 37 / MORTH) |
| Angularity number — measurement | 67 − (% solid volume) | Cl. 6 |
| Angularity number — typical aggregate | 0–11 (lower = more rounded) | Cl. 6 |
| Required quartering before testing | to representative ≤ 1 kg sub-sample | Cl. 2.3 |
IS 2386 (Part 1) covers the particle size and shape tests for aggregates — sieve analysis (gradation), flakiness index, elongation index, and angularity. These are the gateway tests for any aggregate procurement, mix design, or quality acceptance for concrete.
IS 2386 has eight Parts in total — Part 1 (size and shape) is the most-cited because every batching plant runs it weekly:
Use Part 1 whenever you specify an aggregate for concrete or mortar — it is the gradation test that proves the aggregate matches your mix design.
1. Sieve analysis (Clause 2) - Sample size: 0.2-30 kg depending on max aggregate size (200 g for fine sand, 30 kg for 80 mm coarse) - Standard sieves: 80, 63, 40, 31.5, 25, 20, 16, 12.5, 10, 6.3, 4.75 mm (coarse) and 2.36, 1.18, 0.6, 0.3, 0.15, 0.075 mm (fine, IS 460 series) - Procedure: oven-dry sample, sieve through nest of sieves on mechanical shaker for 10 minutes, weigh fraction retained on each sieve - Report: cumulative percentage passing each sieve; plot grading curve - For fine aggregate, also compute fineness modulus = sum of cumulative % retained on 4.75 mm and the standard set (2.36, 1.18, 0.6, 0.3, 0.15 mm) divided by 100
2. Flakiness index (Clause 3) - A particle is *flaky* if its least dimension < 0.6 × mean sieve size - Use the BS thickness gauge (slot widths corresponding to 0.6 × mean sieve) - Result: mass of flaky particles / total mass × 100 = flakiness index (%)
3. Elongation index (Clause 4) - A particle is *elongated* if its greatest dimension > 1.8 × mean sieve size - Use the BS length gauge - Result: mass of elongated particles / total mass × 100 = elongation index (%)
4. Angularity number (Clause 5, less common) - A measure of how rounded vs angular the aggregate particles are; relevant for asphalt and pavement work, less so for concrete.
Coarse aggregate gradation (per IS 383:2016 Table 4 for nominal max size 20 mm — single-size grading):
| Sieve (mm) | % passing | |---|---| | 25 | 100 | | 20 | 95-100 | | 12.5 | — | | 10 | 25-55 | | 4.75 | 0-10 | | 2.36 | 0-5 |
Fine aggregate gradation zones (IS 383:2016 Table 9):
| Sieve | Zone I (coarse) | Zone II (medium) | Zone III (fine) | Zone IV (very fine) | |---|---|---|---|---| | 10 mm | 100 | 100 | 100 | 100 | | 4.75 mm | 90-100 | 90-100 | 90-100 | 95-100 | | 2.36 mm | 60-95 | 75-100 | 85-100 | 95-100 | | 1.18 mm | 30-70 | 55-90 | 75-100 | 90-100 | | 600 µm | 15-34 | 35-59 | 60-79 | 80-100 | | 300 µm | 5-20 | 8-30 | 12-40 | 15-50 | | 150 µm | 0-10 | 0-10 | 0-10 | 0-15 |
Fineness modulus targets: - Zone I (coarse sand): ~3.2-3.7 - Zone II (medium): ~2.6-3.2 - Zone III (fine): ~2.2-2.6 - Zone IV (very fine): ~1.8-2.2
Most good-quality natural sand for general concrete falls in Zone II.
Flakiness + elongation limits (combined, per IS 383:2016 Clause 6.2.2): - General concrete: combined ≤ 35-40 % - Pavement / wearing course: combined ≤ 30 % - High-strength (M50+): combined ≤ 20 % (good practice)
1. Sieving wet aggregate. Moisture clogs fine sieves and gives false-low passing percentages on the 150 µm and 75 µm. Always oven-dry to constant mass at 110 ± 5 °C before sieving. 2. Insufficient sample size for the max aggregate size. A 1 kg sample for 40 mm aggregate is too small — particle-size scatter from a single oversize lump dominates the result. Follow IS 2386 Clause 2.2 sample-size table. 3. Skipping the 75 µm sieve on fine aggregate. The < 75 µm fraction is the *silt and clay content*. IS 383:2016 Clause 5.4 caps it at 3 % (uncrushed) / 15 % (crushed manufactured sand). Always sieve down to 75 µm and report. 4. Confusing fineness modulus with grading zone. FM is a single number; zone is a profile. Two sands can have the same FM but very different shapes. Always report both the zone and the FM, plus the curve. 5. Using flakiness gauge slot widths from BS instead of IS values. Verify the gauge slot widths match Clause 3.2. Mismatches give systematic error of 5-10 % in flakiness. 6. Combining flakiness and elongation by simple addition without de-duplication. A particle can be both flaky AND elongated (a long thin sliver). The standard requires you to test on separate splits of the sample, not on the same particles. Some labs are sloppy here. 7. Gap-graded crushed stone marketed as 'graded'. Some quarries supply nominal 20 mm with very little 12.5 mm material. The mix designer compensates with extra fines, raising water demand. Plot the grading curve every supply; reject if it sits outside the IS 383 envelope.
Source qualification (one-time per quarry / sand source): - Full IS 2386 Part 1-7 panel from a NABL lab - Grading curves for at least 5 samples spaced over a week of production - Petrographic report (Part 8) — especially for AAR-prone zones
Routine acceptance: - Each delivery (coarse): sieve analysis on a 30 kg composite sample - Each delivery (fine sand): sieve analysis + 75 µm wash-sieve on a 5 kg sample - Plot against IS 383 envelope; reject any out-of-zone delivery - Flakiness + elongation at the start of every new quarry shipment, then weekly
Frequency for ongoing supply: - Plant-on-plant high-volume RMC: per supply day - Site-batched concrete: per stockpile change-out - One sample = at least 3 sub-samples taken from different points of the stockpile (top, middle, base), composited and quartered
Documentation: retain grading curves and FM values; trend them. A drifting FM or zone change over weeks is an early signal of source quality drift before strength tests catch it.
| Parameter | IS Value | International | Source |
|---|---|---|---|
| Standard Sieve Series (Coarse) | 80, 63, 40, 20, 10, 4.75 mm | 75 (3"), 50 (2"), 37.5 (1.5"), 25 (1"), 19 (3/4"), 9.5 (3/8"), 4.75 mm (No. 4) | ASTM C136 / C136M |
| Flakiness Criterion | Thickness < 0.6 × mean sieve size | Particles passing through slots of a bar sieve with opening D/2 (where D is sieve size) | BS EN 933-3 |
| Elongation Criterion | Length > 1.8 × mean sieve size | Ratio of length to width > specified value (e.g., 3:1); value is not fixed by the standard. | ASTM D4791 |
| Separator for Fine/Coarse Aggregate | 4.75 mm IS Sieve | 4.75 mm (No. 4) Sieve | ASTM C136 / C136M |
| Sieving Time (Mechanical Shaker) | Not less than 2 minutes. Sieving is complete when no more than 1% of residue passes a sieve in 1 minute. | No specific time, but sieving is complete when no more than 0.5% by mass of the total sample passes any sieve during 1 minute. | ASTM C136 / C136M |
| Shape Test Apparatus | Thickness Gauge (for flakiness) and Length Gauge (for elongation). | Proportional Caliper Device. | ASTM D4791 |
| Basis of Calculation (Shape) | Index is the mass of flaky/elongated particles as a percentage of the total mass tested. | Percentage by mass or by particle count of particles exceeding a specified dimensional ratio. | ASTM D4791 |