Sampling and Reducing Aggregate Samples

An aggregate test result is only as good as the sample behind it. Aggregate segregates easily, coarse particles rolling to the outside of a pile and fines collecting in the middle, so a sample scooped from the most convenient spot can differ widely from the material going into the mix. Sampling practice has two parts: getting a field sample that represents the material, and reducing it to the size each test needs without changing it (Western Alliance for Quality Transportation Construction, 2025¹).

The national practices are AASHTO R 90 (ASTM D75) for sampling and AASHTO R 76 (ASTM C702) for reducing. They were long numbered T 2 and T 248, and older articles and specifications still use those numbers.

Where to Sample

The best place to sample is where the material is moving and fully mixed, as close as practical to where it is used.

• Conveyor belt. Stop the belt and take the whole cross section from a measured length, using templates shaped to the belt and sweeping the fines into the sample. Combine several such increments taken at random times. Stopping the belt is the reason this is the reference method for gradation.
• Flowing stream from a bin, chute or belt discharge. Pass a sampling device through the entire width and depth of the stream at a uniform rate. Taking only part of the stream catches only part of the gradation.
• Roadway. For a base course placed on grade, take full-depth increments at random locations, avoiding the material immediately next to the underlying layer so that it isn't contaminated.
• Stockpiles. Stockpiles are the hardest place to get a good sample and should be used only when nothing else is available. Where needed, sample from a face cut into the pile by a loader, taking increments from the top, middle and bottom, with a board pushed in above each spot to stop material rolling down into it. Fine aggregate can be sampled with a sampling tube pushed into the pile at several places (California Department of Transportation, 2022²).

Sample Size

The field sample has to be large enough for every test that will be run on it, with some left over. The minimum grows with the nominal maximum size of the aggregate, because larger particles are fewer per kilogram and one more or one fewer changes the result. The sampling practice and each test method give minimums; the field sample is usually several times the largest single test portion (Western Alliance for Quality Transportation Construction, 2025¹).

Reducing to Test Size

A 25 kg field sample can't go on a sieve shaker in one piece, and a handful taken from the top of the bag isn't representative. R 76 gives three ways to reduce a sample:

• Method A, mechanical splitter. A riffle splitter has an even number of equal chutes that send material alternately to two pans. Pour the sample in evenly across the full width of the chutes, set one half aside, and repeat with the other half until the portion is the right size. The chutes must be wide enough for the largest particles. The splitter is the preferred method for coarse aggregate and for fine aggregate that is drier than saturated surface-dry.
• Method B, quartering. Mix the sample on a hard, clean surface or canvas, shape it into a cone, flatten it into a circle of uniform thickness, and divide it into four equal quarters. Two opposite quarters are kept and two are discarded, and the process repeats as needed.
• Method C, miniature stockpile. For damp fine aggregate only: mix the sample into a small stockpile and take increments at random places with a small scoop.

Damp fine aggregate sticks in a splitter and comes out biased, which is why quartering or the miniature stockpile is used when fine aggregate has free moisture (Western Alliance for Quality Transportation Construction, 2025¹).

Never reduce a sample to an exact target mass. Adding or removing particles to hit a number is selecting material, which defeats the purpose. Test methods give a minimum mass for a reason: reduce to a portion at least that large and test all of it.

Calculator

Sieve analysis and fineness modulus

AASHTO T 27 · AASHTO T 11 · ASTM C136 · ASTM C117

Enter the mass left on each sieve. The percentages are of the original dry mass, so what washed through the 75 µm sieve counts with the pan.

MethodA: the whole sample over one nest of sievesB: whole sample washed, then the minus 4.75 mm (No. 4) split and sievedC: coarse sieved dry, then the minus 4.75 mm (No. 4) split washed and sieved

B and C sieve a reduced split of the minus 4.75 mm, for samples with a lot of coarse and fine material. Your agency says which to use.

Original dry mass, M, g

Dry mass after washing, g (optional)

Blank when the sample was sieved without washing (T 27 alone).

Mass retained on each sieve

Sieve	Sieve opening, mm	Mass retained, g
1
2
3
4
5
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8
9
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11
12

Sieve openings in millimeters: 37.5, 25, 19, 12.5, 9.5, 4.75 (No. 4), 2.36 (No. 8), 1.18 (No. 16), 0.6 (No. 30), 0.3 (No. 50), 0.15 (No. 100), 0.075 (No. 200). Any order.

Mass in the pan, g

Specification

Specification band, percent passing

Limit	Sieve opening, mm	Minimum, %	Maximum, %
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Optional. The example row is the 5 to 30 percent passing the No. 50 (0.300 mm) sieve that most specifications allow for concrete sand (IMCP manual, chapter 4).

Fineness modulus minimum (optional)

Concrete sand: 2.3 to 3.1 (ASTM C33 and AASHTO M 6, as the IMCP manual gives them). Leave both blank for coarse aggregate.

Fineness modulus maximum (optional)

CalculateExample values: a concrete sand. Your specification sets the band.

Records and Custody

Each sample should carry a label with the material, source, location (station, belt, bin or pile), date and time, who sampled it, and what it is for. Samples for acceptance or independent assurance stay under the control of the agency or its representative from sampling to the laboratory (see Independent Assurance and Acceptance).

Related Articles

• Gradation Test
• Moisture Content
• Segregation & Temperature Differentials

Standard Test Methods

• AASHTO R 90, ASTM D75: Sampling aggregate products
• AASHTO R 76, ASTM C702: Reducing samples of aggregate to testing size

@misc{pavint-sampling-and-reducing-aggregate-samples,
  author = {{Pavement Interactive}},
  title = {Sampling and Reducing Aggregate Samples},
  year = {2026},
  publisher = {HeadLight},
  howpublished = {\url{https://pavementinteractive.org/reference-desk/testing/sampling/sampling-and-reducing-aggregate-samples/}},
  note = {Accessed [date]}
}