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Sieve Analysis and Fineness Modulus of Aggregates: Step-by-Step Guide

parag21pal@icloud.com09 mins





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 ξm → 300 ξm → 150 ξm → 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.

Sieve Analysis Setup – Sieve Stack (Fine Aggregate) 4.75 mm Sieve 2.36 mm Sieve 1.18 mm Sieve 600 ξm Sieve 300 ξm Sieve 150 ξm Sieve Pan (Collection) ← Coarse particles retained ← Medium-coarse ← Medium ← Medium-fine ← Fine ← Very fine ← Dust/fines collected
Figure 1: Sieve Stack Arrangement for Fine Aggregate Sieve Analysis

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:

FM = (Sum of cumulative % retained on all standard sieves) / 100

Standard sieves used for FM calculation: 150 Ξm, 300 Ξm, 600 Ξm, 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 Ξm = 250 g, 300 Ξm = 350 g, 150 Ξm = 140 g, Pan = 60 g. Calculate the Fineness Modulus.

Sieve Size Mass Retained (g) % Retained Cumulative % Retained Cumulative % Passing
4.75 mm 20 2.0 2.0 98.0
2.36 mm 60 6.0 8.0 92.0
1.18 mm 120 12.0 20.0 80.0
600 Ξm 250 25.0 45.0 55.0
300 Ξm 350 35.0 80.0 20.0
150 Ξm 140 14.0 94.0 6.0
Pan 60 6.0 — —
Total 1000 100.0 249.0 —

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

Sieve Size Zone I (Coarse) % Passing Zone II % Passing Zone III % Passing Zone IV (Fine) % Passing
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 ξm 15–34 35–59 60–79 80–100
300 ξm 5–20 8–30 12–40 15–50
150 ξm 0–10 0–10 0–10 0–15

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.

ðŸŽŊ Exam Tips (RTMNU)

  • FM calculation is a guaranteed 8–10 mark numerical in RTMNU exams — practice at least 3 solved examples.
  • The six sieves used for FM of fine aggregate are: 150 Ξm, 300 Ξm, 600 Ξm, 1.18 mm, 2.36 mm, 4.75 mm — always list these when stating the FM formula.
  • FM is NOT % passing or % retained — it is the sum of cumulative % RETAINED divided by 100.
  • Ideal FM for concrete = 2.3–3.0 — this range must be stated in your answer.
  • Zone II and Zone III are recommended for concrete — stating Zone I or Zone IV with reasons for avoidance earns marks.
  • Draw the grading curve (% passing vs sieve size on semi-log scale) for full marks in 10-mark questions.

✅ 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

❓ FAQs

Q1. What sieves are used for fineness modulus of fine aggregate?

The six standard sieves used are: 150 Ξm, 300 Ξm, 600 Ξm, 1.18 mm, 2.36 mm, and 4.75 mm. FM = (sum of cumulative % retained on these sieves) / 100.

Q2. What is the ideal fineness modulus for concrete?

The ideal FM for fine aggregate in concrete is 2.3 to 3.0. Below 2.3 means excessively fine sand (high water demand); above 3.0 means coarse sand (harsh concrete, bleeding).

Q3. What is a grading curve?

A grading curve (or particle size distribution curve) is a graph of cumulative % passing (Y-axis) vs sieve size on a logarithmic scale (X-axis). A well-graded aggregate has an S-shaped curve; a gap-graded aggregate shows a flat horizontal portion.

Q4. What does “well-graded” aggregate mean?

A well-graded aggregate has particles distributed across a wide range of sizes with no significant gaps. It produces a dense, compact packing with minimal voids, requiring less cement paste to fill gaps, leading to stronger, more economical concrete.

Q5. How does FM affect concrete mix design?

FM is used to determine the proportion of fine to coarse aggregate in mix design (as per IS 10262 and ACI 211). When FM of available sand is higher than the design value, more fine aggregate is added; when lower, less is added. A consistent FM ensures mix consistency batch-to-batch.

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