The Sand Equivalent Test: Method and What the Result Means
Sand equivalent shows the ratio of sand to clay-like fines by a quick method. Learn the ASTM D2419 procedure, the calculation and the limits of interpreting it.
Quality and technical information
What Is the Fineness Modulus of Sand and How Is It Calculated?
Fineness modulus is a simple indicator of how coarse or fine a sand is. See the calculation with a worked example, ASTM C33 limits and its effect on mix design.
Fineness modulus is a number that sums up how coarse or fine a sand is. It does not replace the grading curve, but it is a simple, effective tool for comparing materials quickly and checking the uniformity of shipments.
Defining fineness modulus
Fineness modulus equals the sum of the cumulative percentages retained on the standard sieve series, divided by 100. The sieves used are 150, 300 and 600 µm and 1.18, 2.36, 4.75 and 9.5 mm, with larger sieves added for coarser materials.
The larger the number, the coarser the sand.
Worked example
The table below shows a hypothetical sample and is not a test result for any specific material.
| Sieve | Cumulative % retained |
|---|---|
| 9.5 mm | 0 |
| 4.75 mm | 2 |
| 2.36 mm | 13 |
| 1.18 mm | 30 |
| 600 µm | 52 |
| 300 µm | 78 |
| 150 µm | 96 |
| Total | 271 |
The fineness modulus of this sample is therefore 271 divided by 100, or 2.71.
Reference limits
ASTM C33 requires the fineness modulus of concrete fine aggregate to lie between 2.3 and 3.1. The same standard also sets passing limits for each sieve, so a sand with a suitable fineness modulus may still not satisfy the grading requirements on its own. For projects in Iran, Iranian National Standard 302 and the project specification are the main references.
Effect on mix design
Fineness modulus influences the proportions of sand and gravel in a mix:
- Finer sand has more specific surface and usually needs more cement paste and water.
- Coarser sand may produce a harsh mix with lower workability and a risk of bleeding.
More important than the absolute value is the stability of this number. If fineness modulus changes noticeably from one shipment to another, the mix design should be reviewed. ASTM C33 also limits how far the fineness modulus of fine aggregate from a given source may vary from its base value.
Control in practice
Fineness modulus is calculated from sieve analysis results (ASTM C136). Recording this number for every shipment is the simplest way to track changes in sand and gives early warning that a mix design needs correcting.
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