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ASTM International · Aggregate · Laboratory test
ASTM C128: Relative Density (Specific Gravity) and Absorption of Fine Aggregate
Specific gravity and absorption of sand and manufactured fines using the cone test for saturated-surface-dry condition — the companion to ASTM C127 for the fine fraction.
| Designation | ASTM C128 |
| Setting | Laboratory |
| Service line | Construction Materials Testing |
Testing is performed to the current edition of ASTM C128 referenced by your project specification. This page is a plain-language overview, not a substitute for the published standard.
What the ASTM C128 test measures
ASTM C128 is the fine aggregate counterpart to ASTM C127: relative density, or specific gravity, and absorption of sand and manufactured fines passing the No. 4 sieve. The values feed concrete and asphalt mix design in exactly the same way the coarse aggregate values do.
How the ASTM C128 test works, step by step
The sample is soaked, then dried gradually with warm air while being stirred. The saturated-surface-dry point is found with the cone test: sand is placed in a small metal cone, tamped, and the cone lifted. If the sand slumps slightly, it is SSD. If it holds the cone shape it is still too wet; if it collapsed completely it went past the point.
A known mass of SSD sand is placed in a pycnometer flask, filled with water, agitated to remove air, and weighed. The sand is then oven dried and weighed. The gravimetric procedure gives bulk dry, bulk SSD, and apparent specific gravity and absorption.
What the numbers mean
Natural sands are commonly 2.55 to 2.70 bulk SSD with absorption of 0.5 to 2 percent. Manufactured sands from crushed stone can run higher absorption because of the dust and angular shape. Absorption drives batch water corrections at the plant, and a sand whose absorption changes by half a percent shifts the water-cement ratio enough to see in strength.
What can throw the result off
The cone test is a judgment call and is the largest source of variation between technicians. Angular manufactured sands can be difficult to read because they hold the cone shape from interlock rather than moisture. Air trapped in the pycnometer and temperature effects on the water are the other common problems.
Common questions about ASTM C128
Why does absorption matter for batching?
Aggregate absorbs part of the mix water. The plant must add that water on top of the design water or the mix arrives with a lower water-cement ratio than designed, stiff and hard to place.
Can C128 be run on a blended sand?
Yes, but the result is for that blend only. Change the proportions and it must be rerun or calculated from the components.
How we help with ASTM C128 testing
Fine aggregate specific gravity and absorption are part of our standard source qualification package with gradation, minus-200, and unit weight, delivered together so a mix design can be finalized from one report.
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Call for same-day dispatch questions, or send project documents for a written proposal.