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ASTM International · Aggregate · Laboratory test
ASTM C29: Bulk Density (Unit Weight) and Voids in Aggregate
Rodded and loose unit weight of aggregate — the value mix designers need to convert between mass and volume batching and to check void content of a coarse aggregate.
| Designation | ASTM C29 |
| Setting | Laboratory |
| Service line | Construction Materials Testing |
Testing is performed to the current edition of ASTM C29 referenced by your project specification. This page is a plain-language overview, not a substitute for the published standard.
What the ASTM C29 test measures
ASTM C29 measures the bulk density, also called unit weight, of an aggregate and, from that and its specific gravity, the percentage of voids between the particles. A container of known volume is filled with aggregate either by rodding, jigging, or shoveling loose, then weighed. The result is reported in pounds per cubic foot or kilograms per cubic meter.
Unit weight is the bridge between mass and volume. Concrete mixes are designed by mass but concrete is bought by the cubic yard, and coarse aggregate content in the ACI mix design method is chosen directly from the dry-rodded unit weight.
How the ASTM C29 test works, step by step
A calibrated measure, sized to the maximum aggregate size, is filled in three lifts with each lift rodded 25 times for the rodded method, or filled from a shovel held no more than two inches above the rim for the loose method. The surface is struck level, the filled measure is weighed, and bulk density is the net mass divided by the measure volume.
Void content is calculated using the aggregate's bulk specific gravity from ASTM C127 or C128. The sample is oven dried or its moisture content corrected so the result is on a dry basis.
What the numbers mean
Normal-weight coarse aggregate typically runs 90 to 110 pcf dry rodded. Lightweight aggregate may be 40 to 70 pcf and is often specified with a maximum unit weight. Voids in a single-sized crushed stone can exceed 45 percent, while a well-graded gravel might drop below 35 percent; lower voids mean less paste to fill them, which is why gradation and unit weight are read together.
What can throw the result off
Segregation while filling the measure, rodding that hits the bottom of the measure and compacts unevenly, and testing damp aggregate without correcting for the water are the common errors. The measure itself must be calibrated by water fill at a known temperature.
Common questions about ASTM C29
Which method do I need, rodded or loose?
Mix design uses dry-rodded unit weight. Loose unit weight is used for shipping, stockpile volume, and some lightweight aggregate specifications. The report should state which was run.
Is this the same as density of concrete?
No. Fresh concrete density is ASTM C138. C29 is the aggregate alone.
How we help with ASTM C29 testing
We run C29 with C127, C128, and C136 as a source qualification package, so a mix designer receives gradation, specific gravity, absorption, and unit weight from the same sample and the same day.
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