Sieve Analysis and Fineness Modulus: Solved Examples and IS 383 Grading

What is Sieve Analysis?

Sieve analysis (also called gradation test) is a laboratory test to determine the particle size distribution of an aggregate sample. By passing the aggregate through a series of sieves of decreasing aperture sizes, we can quantify what percentage of the aggregate falls in each size range. This data is essential for:

• Checking if aggregates meet IS 383 grading requirements
• Selecting appropriate aggregate proportions in concrete mix design
• Calculating the Fineness Modulus (FM)
• Checking for excessive fines or coarse particles

Procedure for Sieve Analysis

For Fine Aggregate (IS 2386 Part I):

Take approximately 1 kg of oven-dried fine aggregate sample. Arrange the sieves in descending order: 10 mm → 4.75 mm → 2.36 mm → 1.18 mm → 600 μm → 300 μm → 150 μm → pan. Pass the sample through the sieve set (mechanical shaker for 10 minutes or hand-sieving). Weigh the mass retained on each sieve. Calculate cumulative retained mass and cumulative % passing.

For Coarse Aggregate:

Take 5–10 kg sample. Sieves: 80 mm → 40 mm → 20 mm → 16 mm → 12.5 mm → 10 mm → 4.75 mm → pan. Same procedure.

Fineness Modulus – Definition and Formula

The Fineness Modulus (FM) is an empirical number that gives an index of the fineness or coarseness of an aggregate. It is calculated as:

Standard sieves used for FM calculation: 150 μm, 300 μm, 600 μm, 1.18 mm, 2.36 mm, 4.75 mm (for fine aggregate) and additionally 10 mm, 20 mm, 40 mm, 80 mm for combined/coarse aggregate.

Interpretation of FM:

• FM = 2.0–3.5 → Fine aggregate range
• FM ≈ 2.2–2.6 → Fine sand (Zone I, II)
• FM ≈ 2.6–2.9 → Medium sand (Zone II, III)
• FM ≈ 2.9–3.2 → Coarse sand (Zone III, IV)
• FM > 5.0–8.0 → Coarse aggregate range

Ideal FM for fine aggregate in concrete: 2.3–3.0. If FM < 2.3, the sand is too fine → excessive surface area → high water demand. If FM > 3.0, sand is too coarse → concrete may be harsh and bleed.

Solved Numerical Example

Problem: A sample of fine aggregate (1000 g) was sieved and the following masses were retained: 4.75 mm = 20 g, 2.36 mm = 60 g, 1.18 mm = 120 g, 600 μm = 250 g, 300 μm = 350 g, 150 μm = 140 g, Pan = 60 g. Calculate the Fineness Modulus.

FM = 249.0 / 100 = 2.49

Result: FM = 2.49 → The sand is a medium-fine sand, suitable for concrete (falls in the ideal range of 2.3–3.0). This corresponds to Zone II or Zone III fine aggregate as per IS 383.

IS 383 Grading Zones for Fine Aggregate

Zone II and Zone III are generally recommended for concrete. Zone I (coarse sand) needs more cement paste to fill voids. Zone IV (very fine sand) has high surface area requiring excessive water and cement.

🎯 Exam Tips (RTMNU)

✅ Key Takeaways

• Sieve analysis determines particle size distribution of aggregates.
• FM = (Sum of cumulative % retained on standard sieves) / 100.
• Ideal FM for fine aggregate in concrete: 2.3–3.0.
• IS 383 defines 4 grading zones for fine aggregate; Zone II and III preferred.
• Higher FM = coarser aggregate; Lower FM = finer aggregate.
• FM helps in mix proportioning and checking aggregate quality consistency.

📖 Related Reading: Aggregates: Classification and Properties | Bulking of Sand: Cause, Measurement and Effect

🔗 External Reference: IS 2386 (Part I):1963 – Methods of Test for Aggregates, Particle Size Distribution

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