Testing guide
Sieve analysis and fineness modulus for washed concrete sand
Sand that changes makes block that changes. A sieve analysis tells you how much of your sand lands on each size, and the fineness modulus (FM) boils that down to one number you can log and chart. Here's how to run the test, check it, do the math, and use the result back at the plant.
Bubba, Buckley and Mandie are AI-generated animated characters. Created with Grok.
Read the transcript
Slide 1: Howdy, Bubba Here
Well, howdy, y'all! Bubba here, the animated presenter for Conrady Consulting and Technology. Today we're shakin' some sand: sieve analysis, and the number that comes out of it, fineness modulus.
Now, FM ain't a radio station. Though a good sand does have a nice ring to it.
Slide 2: Why Gradation and FM Matter
Gradation tells you how much of your sand lands on each size. Fineness modulus boils it down to one number. Bigger number, coarser sand. Smaller number, finer sand.
Why care? Sand that changes makes block that changes. Finer sand has more surface to coat, so it wants more paste and water. Coarser opens up the texture. It shows in strength and color, too.
Slide 3: Sample It, Split It, Dry It, Wash It
A good test starts with a good sample. Follow ASTM D75 and grab from several spots, not just the handy side of the pile.
Then cut it down with ASTM C702. Dry sand goes through a splitter. Damp sand, quarter it. Don't scoop out an exact number of grams. Split down to about what you need.
Dry it to constant mass at 110 Celsius, give or take 5. That's 230 Fahrenheit, give or take 9. C136 wants at least 300 grams of fine aggregate after dryin'.
Washed sand still carries a little fine stuff. C117 washes it over the No. 200 till the water runs clear. Dry it again. Then base every percent on the dry mass before washin'.
Slide 4: Stack 'Em and Shake 'Em
Stack 'em coarse to fine: No. 4, 8, 16, 30, 50, 100, and the pan. Coarser stuff? Add a 3/8-inch on top. Then pour in the dry sand.
Shake by machine or by hand till every grain's had its chance. Don't overload. On an 8-inch sieve finer than the No. 4, keep it under about 200 grams.
How do you know you're done? Do the C136 check. Hand sieve one sieve for a minute. If more than 1 percent of what's on it falls through, keep shakin'.
Slide 5: Weigh It, Jar It, Check It
Weigh what stayed on each sieve, and the pan. Brush the cloth gentle and handle sieves by the frame. Here's a trainin' trick: pour each one in its own jar and line 'em up.
Now you can see your gradation. Just a pinch on the No. 4. Most of it rides on the 30 and the 50. Then it tapers off on the 100 and in the pan.
[Bubba chuckles] Buckley likes the pan jar best. Reckon he's a fines man. Lid stays on, buddy.
Add 'em up. You should be within 0.3 percent of the original dry mass. More than that? Don't use it for acceptance. Find the spill and rerun it.
Slide 6: Do the Math
Percent retained: grams on the sieve over the original dry mass, before washin', times 100. The No. 30 jar has 119.4 out of 512.4 grams. That's 23.3 percent.
Cumulative's the runnin' total: 2.3, 13.6, 29.7, 53, 78.6, 92.9. Passing's 100 minus that. 7.1 got through the 100.
[On screen: the example, all in one table. See the worked example below.]
Slide 7: Fineness Modulus, and What ASTM C33 Says
Fineness modulus: add the cumulative percent retained on the No. 100, 50, 30, 16, 8, and 4, plus 3/8-inch and up if any. Divide by 100. No. 200 and pan stay out.
Add 'em up: 2.3, 13.6, 29.7, 53, 78.6, and 92.9. That's 270.1. Divide by 100: FM, 2.70.
2.70. Clicker's so excited, it jumped the gun again.
ASTM C33, the concrete aggregate spec a lot of plants lean on, wants fine aggregate FM from 2.3 to 3.1. Our 2.70 sits right in there.
Here's the one folks miss. For continuin' shipments from one source, C33 keeps FM within 0.20 of the base. Base 2.70? Stay 2.50 to 2.90.
Slide 8: Back at the Plant, Safely
How often to test? As often as your plant's QC plan says, and more when somethin' changes. Log every FM and chart it. Watch the trend, not just one point.
FM drops? Finer sand, more paste and water demand. FM climbs? Coarser, more open texture. Either way, check your mix and your color. Then call your supplier, friendly-like.
And stay safe. Dry fines can carry silica dust, so wear your respirator. Glove up at the oven and let pans cool. Carry sieves by the frame.
Slide 9: Come See Us
Want it easier? CC&T builds custom spreadsheet tools for producers. Type in your sieve weights, and a gradation and FM workbook does the math, checks the totals, and charts it.
Mandie: Hey there! Got questions? I'm Mandie. Chat with me at conradyct.com.
Check out our website up on that billboard. We'll help y'all from the stockpile to the cube. Good sand, steady numbers, happy block.
[The billboard reads: conradyct.com, info@conradyct.com]
Bubba, Buckley and Mandie are AI-generated animated characters. Created with Grok.
Why gradation and FM matter
Gradation
Gradation tells you how much of your sand lands on each sieve size, from the coarse particles down to the fines. It's the full picture of your sand.
Fineness modulus
FM boils the gradation down to one number. A bigger number means coarser sand; a smaller number means finer sand. One number is easy to log, chart, and compare from load to load.
Why the plant should care: finer sand has more surface to coat, so it wants more paste and water. Coarser sand opens up the texture. Either way, a change in the sand can show up in the strength and color of the block.
Sample, split, dry, and wash
- Get a good sample (ASTM D75). Grab from several spots, not just the handy side of the pile.
- Reduce it to test size (ASTM C702). Run dry sand through a splitter; quarter damp sand. Don't scoop out an exact number of grams. Split down to about what you need.
- Dry to constant mass. 110 ± 5 °C (230 ± 9 °F). ASTM C136 calls for at least 300 grams of fine aggregate after drying.
- Wash it (ASTM C117). Even washed sand carries a little fine material. Wash it over the No. 200 sieve until the water runs clear, then dry it again.
- Keep the original dry mass. Base every percentage on the dry mass before washing.
Stack and shake
- Stack coarse to fine: No. 4, 8, 16, 30, 50, 100, and the pan. If the sand has coarser material, add a 3/8-inch sieve on top. Then pour in the dry sand.
- Shake by machine or by hand until every particle has had its chance to pass.
- Don't overload a sieve. On an 8-inch sieve finer than the No. 4, keep it under about 200 grams.
- Check that you're done (ASTM C136). Hand sieve one sieve for one minute. If more than 1 percent of what's on it passes, keep shaking.
Weigh and check
- Weigh what stayed on each sieve, and the pan. Brush the sieve cloth gently and handle sieves by the frame.
- A training trick: pour each sieve's material into its own jar and line the jars up, coarse to fine. You can see the gradation at a glance.
- Do the mass check. Add up all the sieve masses and the pan. The total should be within 0.3 percent of the original dry mass. If it's off by more than that, don't use the result for acceptance. Find the spill and rerun it.
Do the math: a worked example
- Percent retained = grams on the sieve ÷ original dry mass (before washing) × 100
- Cumulative percent retained = the running total, coarse to fine
- Percent passing = 100 − cumulative percent retained
These are the example numbers from the video, for a washed concrete sand with an original dry mass of 512.4 g (505.9 g after washing). They show how the math works; they aren't real test data.
| Sieve | Mass retained (g) | % retained | Cumulative % retained | % passing |
|---|---|---|---|---|
| 3/8 in. 9.5 mm | 0.0 | 0.0 | 0.0 | 100.0 |
| No. 4 4.75 mm | 11.8 | 2.3 | 2.3 | 97.7 |
| No. 8 2.36 mm | 57.9 | 11.3 | 13.6 | 86.4 |
| No. 16 1.18 mm | 82.6 | 16.1 | 29.7 | 70.3 |
| No. 30 600 µm | 119.4 | 23.3 | 53.0 | 47.0 |
| No. 50 300 µm | 131.2 | 25.6 | 78.6 | 21.4 |
| No. 100 150 µm | 73.2 | 14.3 | 92.9 | 7.1 |
| Pan dry sieving | 29.2 | 5.7 | – | – |
Check it: the No. 30 sieve held 119.4 g out of 512.4 g, so 119.4 ÷ 512.4 × 100 = 23.3 percent retained. Cumulative through the No. 100 is 92.9, so 7.1 percent passed the No. 100. The sieves and pan add up to 505.3 g, 0.6 g short of the 505.9 g placed on the sieves. That's 0.12 percent of the original dry mass, inside the 0.3 percent limit.
Fineness modulus and ASTM C33
- Fineness modulus = the sum of the cumulative percent retained on the No. 100, 50, 30, 16, 8, and 4 sieves (plus 3/8 inch and larger, if any) ÷ 100. The No. 200 and the pan stay out.
- In the example: 2.3 + 13.6 + 29.7 + 53.0 + 78.6 + 92.9 = 270.1. Divide by 100, and FM = 2.70.
- ASTM C33 range: C33, the concrete aggregate specification many plants lean on, calls for fine aggregate FM from 2.3 to 3.1. The example's 2.70 sits right in there.
- The one folks miss: for continuing shipments from one source, C33 keeps FM within 0.20 of the base fineness modulus for that source. With a base of 2.70, stay between 2.50 and 2.90.
Skip the hand math: our free fineness modulus (FM) calculator turns your sieve masses into % retained, % passing, FM, a mass check, and the C33 range check, right in your browser.
Back at the plant, safely
Test and track
- Test as often as your plant's QC plan says, and more often when something changes.
- Log every FM and chart it. Watch the trend, not just one point.
- FM drops? The sand is finer, with more paste and water demand.
- FM climbs? The sand is coarser, with a more open texture.
- Either way, check your mix and your color, then talk with your supplier.
Stay safe
- Dry fines can carry silica dust, so wear your respirator.
- Wear gloves at the oven and let pans cool before handling.
- Carry sieves by the frame.
Want sand testing to be easier?
We build custom spreadsheet tools for producers. Type in your sieve weights, and a gradation and FM workbook does the math, checks the totals, and charts the trend. We can help from the stockpile to the cube.
Talk to us about sand testingThis page is general information based on hands-on experience. The example numbers are for illustration only. Follow the current edition of each ASTM standard and your project specifications. ASTM is a trademark of ASTM International; we're not affiliated with or endorsed by ASTM. Every plant and every source is different.