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ASTM C127 is the ASTM International test method for the relative density (specific gravity) and absorption of coarse aggregate. Its one job is to give a single, comparable number for how dense the solid particles are and how much water their pores can take up, so that the number can be used in mix volume calculations.
Short answer
ASTM C127 determines the relative density (specific gravity) and the absorption of coarse aggregate. Relative density can be reported three ways: oven-dry (OD), saturated-surface-dry (SSD) or apparent. The ASTM store page for C127-24 is marked historical, and its version list shows C127-25 as the active edition (checked 2026-10-29), so confirm the edition with ASTM before citing it.
Definition and scope
The standard is developed by ASTM Committee C09 on Concrete and Concrete Aggregates, subcommittee C09.20, and is published in Volume 04.02 of the Book of ASTM Standards. According to the scope in the ASTM store listing (checked 2026-10-29):
- It covers the determination of relative density (specific gravity) and absorption of coarse aggregates.
- Relative density is a dimensionless ratio, reported on an oven-dry, saturated-surface-dry or apparent basis.
- It is not intended for lightweight aggregates that comply with Specification C332, Group I.
- SI units are regarded as the standard, and no other units are included in the text.
This page summarises scope-level information only. The full text, including the procedure, is sold by ASTM, and anyone running the test should work from a licensed copy of the current edition.
How the result is produced in practice
ASTM’s scope notes that the oven-dry value depends on drying the aggregate, while the saturated-surface-dry value and the absorption depend on soaking it for a set time. One testing laboratory’s public summary of the method (Geocomp) describes the sample as immersed in water for 24 ± 4 hours so the pores are essentially filled, with the sample then weighed in the surface-dry condition, weighed again by water displacement, and finally oven-dried and weighed. The relative densities and the absorption are calculated from those masses. Another commercial laboratory’s description (Wiss, Janney, Elstner Associates) gives the same outline: dry for the oven-dry value, soak for the saturated-surface-dry value and absorption. Because these are routine bench measurements, labs normally write their local handling into a controlled document; see standard operating procedure (SOP) for how those documents are structured.
Oven-dry, saturated-surface-dry, apparent and absorption compared
The scope and the significance statements of C127 separate four quantities that are easy to mix up. Each row below comes from the ASTM store listing (checked 2026-10-29).
| Quantity | What it describes | Condition of the aggregate |
|---|---|---|
| Relative density (OD) | Dimensionless ratio, reported on an oven-dry basis | Dried before the value is determined; used when the aggregate is dry or assumed to be dry |
| Relative density (SSD) | Dimensionless ratio, reported on a saturated-surface-dry basis | Soaked for a set time first; used when the aggregate is saturated-surface-dry |
| Apparent relative density | Refers only to the solid material of the particles, not to pore space that water can reach | Excludes the water-accessible pores |
| Absorption | An estimate of the water taken into the pores, relative to the dry condition | Assumes enough contact time to fill most of the pore capacity |
Per ASTM, the SSD value applies when the aggregate’s absorption is satisfied and the OD value when the aggregate is dry or assumed dry, so a reported “specific gravity” should always state its basis.
Where the result is used in labs and mix design
ASTM’s significance statements give these uses (store listing, checked 2026-10-29):
- Absolute-volume mix proportioning. Relative density is used to calculate the volume an aggregate occupies in mixtures proportioned on an absolute-volume basis, such as concrete and bituminous mixtures.
- Voids calculations. It is also used in the calculation of voids in aggregate under Test Method C29/C29M.
- Moisture interpretation. Absorption is the laboratory benchmark for how much water the pores can hold. ASTM notes that field moisture can differ from it, for example aggregate taken from below the water table may hold more water, and aggregate not kept moist may hold less.
C127 sits beside other aggregate and concrete tests rather than replacing them. Sieve analysis, which gives grading, is covered in ASTM C136: Sieve Analysis of Aggregates Explained, and the density of freshly mixed concrete is a different measurement, covered in ASTM C138: Fresh Concrete Density, Yield and Air Content. For how density-by-displacement is handled for a different material class, see ASTM D792: Density and Specific Gravity of Plastics by Displacement. Measuring equipment used for tests like this is covered by general calibration practice; see what is calibration.
A records checklist for reporting a C127 result
This checklist is derived only from the scope and significance statements above. It is a way to make a reported value reusable, not a substitute for the standard.
- Which basis was reported: oven-dry, saturated-surface-dry or apparent relative density.
- The absorption value, reported with the relative densities it was measured alongside.
- The edition of C127 used, by year.
- Units: SI is the standard in the text.
- Whether the aggregate is within scope; lightweight aggregate complying with C332 Group I is outside it.
- The soaking time recorded, since SSD and absorption depend on a set soak.
Common misunderstandings
Is relative density the same as bulk density?
No. ASTM’s significance statement says relative density reflects the absolute volume of the particles, while the bulk density measured under C29 includes the voids between the particles.
Is absorption the same as moisture content?
No. Absorption is a laboratory estimate of the water the pores can take up compared with the dry condition. ASTM notes that moisture in the field can differ from it, and that free surface moisture is the total moisture determined under Test Method C566 minus the absorption.
Does the apparent relative density include the pores?
No. The apparent value refers only to the solid material making up the particles and excludes water-accessible pore space.
FAQ
What does ASTM C127 measure?
It measures the relative density (specific gravity) and the absorption of coarse aggregate. Relative density is dimensionless and can be reported as oven-dry, saturated-surface-dry or apparent.
What is the current edition of ASTM C127?
On 2026-10-29 the ASTM store page for C127-24 was marked historical and its version list showed C127-25 as active. Check ASTM for the edition in force before citing it in a report.
Does C127 apply to lightweight aggregate?
Not to lightweight aggregates that comply with Specification C332, Group I; the scope excludes them.
Sources
- ASTM International, C127-24 store listing: scope, significance and use, committee and edition status, checked 2026-10-29.
- Geocomp, test summary for density, relative density (specific gravity) and absorption of coarse aggregate, checked 2026-10-29.
- Wiss, Janney, Elstner Associates, laboratory page for ASTM C127, checked 2026-10-29.
