This field guide focuses on sieve sizes, percent passing, and curve shape. For other properties, use the broader aggregate, sand, and gravel testing guide.
What Does ASTM C136 Sieve Analysis Measure?
Sieve analysis separates a prepared dry aggregate sample by particle size and measures the mass in each fraction. Under ASTM C136/C136M, the stack runs from larger openings at the top to smaller openings below. Retained mass, cumulative retained percentage, and percent passing are then calculated, with the mass balance checked.
Percent passing is the portion smaller than an opening; confusing it with retained percentage reverses the interpretation. Material type, nominal size, and intended use define the series and envelope for aggregate testing.
Which Aggregate Sieve Sizes Are Commonly Used?
Coarse aggregate uses larger millimetre or inch openings, while finer fractions use numbered sieves selected by the governing specification. The following table is a reading aid, not a mandatory series or acceptance envelope for every sample.
| Opening | ASTM designation | Typical place in series |
|---|---|---|
| 37.5 mm | 1½ in. | Large coarse aggregate |
| 25.0 mm | 1 in. | Coarse aggregate |
| 19.0 mm | ¾ in. | Coarse aggregate |
| 12.5 mm | ½ in. | Smaller coarse fraction |
| 9.5 mm | ⅜ in. | Coarse transition |
| 4.75 mm | No. 4 | Common coarse/fine dividing point |
| 2.36 mm | No. 8 | Fine/transition fraction |
| 1.18 mm | No. 16 | Fine aggregate |
| 0.600 mm | No. 30 | Fine aggregate |
| 0.300 mm | No. 50 | Finer sand fraction |
| 0.150 mm | No. 100 | Very fine fraction |
| 0.075 mm | No. 200 | 75-μm fines boundary |
“No. 8” and “No. 200” are designations, not millimetre diameters. Compare actual openings and confirm the project-required sieves are present.
How Is Percent Passing Calculated and Checked?
Percent passing equals 100 percent minus cumulative percent retained through the sieve being read. The technician weighs each fraction, converts it to a share of the original test mass, and accumulates retained values from the top downward.
Check original and recovered mass plus the column headings. Mass loss, transposed retained/passing values, or early rounding can distort the curve.
How Do You Read a Gradation Curve Against the Envelope?
Plot sieve opening on the horizontal axis and percent passing on the vertical axis, then compare every sample point with the project-supplied upper and lower boundaries. The line makes the particle distribution visible; the envelope supplies the acceptance context.
- Match the sample ID, source, nominal size, and intended use to the material under review.
- Confirm that the envelope belongs to the same layer or mix and that the specification edition is identified.
- Check every required sieve rather than accepting a curve because most of it lies inside the band.
- Use curve shape as a diagnostic clue, separate from the contractual compliance decision.
The project may invoke ASTM C33 for concrete aggregate or an applicable SASO or MOT requirement. None creates one universal envelope for all materials. When the aggregate feeds a mix, connect the finding with the relevant concrete testing or asphalt testing plan; aggregate compliance alone does not approve the complete mix.
What Do Well-, Poorly-, and Gap-Graded Mean?
These terms describe particle-size distribution, but they do not replace the project envelope. A continuous or well-graded material contains a connected range of sizes. A uniform or poorly graded material is concentrated in a narrow range. A gap-graded material has a noticeable shortage of intermediate sizes.
A progressive curve suggests continuity; a sharp change can show size concentration, while a flat stretch can reveal a gap. These clues support investigation but cannot alone establish cause or reject a delivery.
What Is Fineness Modulus Used For?
Fineness modulus is a single index summarising the relative coarseness of fine aggregate, not a substitute for the gradation curve. It is calculated by adding cumulative percentages retained on the sieve series specified by the reference and dividing the sum by 100.
Similar modulus values can hide different curves. Use the index against project requirements and source trends while retaining the full table and curve.
Why Does Material Finer Than 75 μm Matter?
The fraction passing the 0.075 mm sieve can affect water or binder demand, adhesion, and workability, so it should be measured clearly where the specification requires it. ASTM C117 determines material finer than 75 μm by washing and is included in the aggregate service content where requested.
Dry No. 200 sieving may differ because fines can adhere to larger grains. The percentage alone does not prove the fines are clay or harmful.
How Should Sampling and Reduction Preserve Gradation?
A representative sample remains traceable and is reduced without changing particle-size proportions. Record source, lot or stockpile, date, type, nominal size, and use. Do not scoop only the surface, select convenient particles, or pour away half; follow the project plan and laboratory instructions.
Which Site Mistakes Most Often Distort the Result?
The worst errors precede the graph: biased sampling, a wrong reference, and retained/passing confusion. Other mistakes include mixing deliveries, omitting nominal size or use, comparing different sieve series, ignoring the pan or No. 200, and judging without the actual envelope.
What Should the Report Contain, and When Should You Test?
A useful report connects sample identity, method, sieve table, curve, and supplied comparison reference. It records source, lot, type, use, condition, test mass, retained or passing values, and scoped comparison.
Test when qualifying or changing a source or size, monitoring deliveries, or investigating segregation. Send the specification edition and envelope with type, source, nominal size, use, and sample count to the aggregate gradation laboratory. One sample does not automatically qualify an entire supply.