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ASTM C29/C29M is the standard test method for bulk density (“unit weight”) and voids in aggregate. It weighs aggregate that fills a calibrated measure, either loose or compacted, and from that mass reports a bulk density and, if wanted, the percentage of space between the particles. The edition in force is C29/C29M-23 (October 2023); the AASHTO equivalent is T 19M / T 19.
Short answer
C29 answers one practical question: how much mass of a given aggregate fits in a known volume, and how much of that volume is air between the particles. It applies to fine, coarse or mixed aggregates up to a nominal maximum size of 125 mm (5 in.). The result depends on how the aggregate was placed in the measure, so a C29 number is only meaningful together with the consolidation condition used to get it.
What C29 covers and the 125 mm limit
The scope, as the standard states it, is the determination of bulk density of aggregate in either a loose or a compacted condition, and the calculation of voids between aggregate particles on the same basis. It is written for fine aggregate, coarse aggregate and blends of the two, and applies to material not exceeding 125 mm (5 in.) in nominal maximum size (source: AENOR listing of ASTM C29/C29M-23, checked 2026-10-29).
Bulk density here is not the density of the rock itself. It includes the air spaces between particles, which is why the same quarry product gives a lower value loose than compacted. That gap is what the voids figure captures.
Loose, rodded and jigged: what the measure tells you
The method recognises three consolidation conditions: loose (placed by shoveling), compacted by rodding, and compacted by jigging. The NICET performance examination checklist for the 17a edition (checked 2026-10-29) describes jigging for particles of 37.5 to 150 mm and shoveling for particles up to 150 mm, with the tamping rod listed as apparatus for the rodding condition. The method itself is scoped to aggregate of 125 mm nominal maximum size or less, so particle size and nominal maximum size are not the same thing; the standard text settles which procedure applies to which material.
Because a bulk density is a property of the aggregate and its placement together, report the condition with the number. A loose value and a rodded value for the same sand are both correct and are not interchangeable.
Lab-planning checklist: what to settle before testing
- Nominal maximum size above 125 mm: outside the scope of the method.
- Larger particles (37.5 to 150 mm): the checklist describes jigging for this range.
- Loose condition: shoveling, with the aggregate discharged from a height not over 50 mm above the top of the measure and care taken to avoid segregation.
- Compacted value: rodding with the tamping rod, or jigging for large particles; always record which one was used.
These are planning cues, not the procedure. The step-by-step method, including layer counts and rod strokes, is in the standard itself.
Equipment a lab needs to run C29
The NICET checklist for the 17a edition lists the apparatus below. Confirm each item against the current C29/C29M-23 text before setting up a bench.
- Balance: capacity of at least 2 kg, sensitive to 0.5 g or better.
- Measure: a rigid container whose top rim is smooth, watertight and plane to 0.25 mm (0.01 in.) by feeler gauge, with a height between 80 and 150 percent of its diameter.
- Measure size by aggregate size: 2.8 L (1/10 ft³) for 12.5 mm nominal maximum, 9.3 L (1/3 ft³) for 25 mm, 14 L (1/2 ft³) for 37.5 mm, and 28 L (1 ft³) for 75 mm.
- Tamping rod: round, straight steel, about 600 mm (24 in.) long and 16 mm in diameter, with a hemispherical tip.
- Calibration kit: plate glass, grease and a thermometer readable to 0.5 °C in the 10 to 32 °C range, used to calibrate the measure volume.
- Oven: samples are dried to essentially constant mass or at 110 ± 5 °C.
The measure is recalibrated at least annually, or whenever its accuracy is in question. For the general logic of calibration intervals, see calibration intervals and what calibration is; for the balance side, analytical balances explains sensitivity and readability.
The sample itself is obtained under ASTM C702 and should be roughly 125 to 200 percent of the quantity needed to fill the measure.
C29 vs C136 vs C138
Aggregate and concrete testing standards are easy to confuse because several of them produce a number in kg/m³ or a mass percentage. This table sets the three CASRAI covers side by side.
| Standard | What it determines | Material tested |
|---|---|---|
| ASTM C29/C29M | Bulk density (unit weight) and voids, loose or compacted | Dried fine, coarse or mixed aggregate in a calibrated measure |
| ASTM C136 | Sieve analysis, the particle-size distribution | Aggregates |
| ASTM C138/C138M | Density (unit weight), yield and gravimetric air content | Freshly mixed concrete |
The practical consequence: C29 tells you about the aggregate before it is in the mix, C138 about the concrete after mixing, and C136 about how the particle sizes are spread. A bulk density from C29 cannot stand in for either of the others.
Where it matters for labs and supply decisions
The equipment list above is what turns this standard into a purchasing and calibration question for a testing lab: measures in the sizes matching the aggregate you test, a balance of adequate readability, a tamping rod and a drying oven. Because the measure is a volumetric reference, its calibration record belongs in the lab’s quality documents alongside balance and oven records (see calibration certificates).
Common misunderstandings
“Bulk density is the density of the stone.”
No. It includes the spaces between particles. The same material gives different bulk densities loose, rodded and jigged.
“The number describes the aggregate as delivered.”
The sample is dried to essentially constant mass or at 110 ± 5 °C before testing, so the result describes dry material. Aggregate in a stockpile or truck usually carries moisture, so a field mass-to-volume conversion needs that difference in mind.
“Inch-pound and SI values can be freely swapped.”
The measure capacities are listed in both systems (for example 28 L and 1 ft³), and the checklist reports results to the nearest 10 kg/m³ (1 lb/ft³). Keep units consistent within a report and state which system the figures use.
FAQ
What is unit weight in ASTM C29?
“Unit weight” is the traditional name for bulk density: the mass of aggregate per unit volume of the measure, including the voids between particles. The standard’s title uses both terms.
Is there an AASHTO equivalent to ASTM C29?
Yes. The NICET checklist for C29 names AASHTO T 19M / T 19 as the equivalent method.
Which edition of ASTM C29 is current?
C29/C29M-23, dated 1 October 2023, is in force. Earlier editions such as C29/C29M-17a are superseded.
How is the result reported?
Bulk density to the nearest 10 kg/m³ (1 lb/ft³), and void content, if determined, to the nearest 1 percent. Net mass is the gross mass minus the measure; density is net mass multiplied by the measure’s calibration factor, or net mass divided by the measure volume.
Sources
- AENOR, ASTM C29/C29M-23 Standard Test Method for Bulk Density (“Unit Weight”) and Voids in Aggregate, edition 2023-10-01, http://tienda.aenor.com/p/norma-astm-c29-c29m-23-116303, checked 2026-10-29.
- NICET, Performance Examination Checklist for ASTM C29/C29M-17a [AASHTO T 19M / T 19-14], https://www.NICET.org/nicetorg/assets/File/public/Performance_Examination_Checklists/Aggregate/ASTM_C29-C29M-17a.pdf, checked 2026-10-29. This describes the 17a edition; check apparatus details against the current edition.
- Related guides on this site: ASTM C136, ASTM C138.
