ASTM D7928-21e1 PDF

Full title and description

Standard Test Method for Particle‑Size Distribution (Gradation) of Fine‑Grained Soils Using the Sedimentation (Hydrometer) Analysis — ASTM designation D7928-21 (with editorial change). This test method specifies the hydrometer/sedimentation procedure for determining the particle‑size distribution of the fine‑grained fraction of soils (material finer than No. 200 (75 µm) and larger than the submicron range) and describes specimen preparation, apparatus, measurement and calculation, and reporting requirements.

Abstract

ASTM D7928-21 defines a laboratory hydrometer (sedimentation) procedure to quantify the mass percent finer versus particle diameter for fine‑grained soils. The method covers preparation (moist or air‑dried as applicable), dispersion, hydrometer and meniscus corrections, calculation using Stokes’ law assumptions, and combination with sieve results (where needed) to produce a complete gradation curve. Limits, typical interferences (flocculation, structured water, cemented particles, organics), and typical reporting conventions are included.

General information

• Status: Current edition approved May 1, 2021 (D7928‑21 with an editorial change). Some secondary aggregators list the record as historical/withdrawn and a revision/work item has been registered — consult ASTM for the definitive live status.
• Publication date: 01 May 2021 (edition D7928‑21; editorial change indicated in the published designation).
• Publisher: ASTM International (Committee D18, Subcommittee D18.03).
• ICS / categories: Physical properties of soils / geotechnical testing (commonly catalogued under ICS 13.080.20).
• Edition / version: D7928‑21 (published 2021) with editorial change noted in the published text (commonly rendered as D7928‑21´1 / “e1” where indicated).
• Number of pages: 26 pages (published PDF).

Scope

This test method covers the quantitative determination of the particle‑size distribution of the fine‑grained portion of soils by sedimentation (hydrometer) analysis. It is intended for material passing the No. 10 (2.0 mm) or finer sieve, reporting the fraction finer than No. 200 (75 µm) down to the method’s lower practical limit (submicron range described in the standard). The procedure is intended to be combined with a sieve analysis (for coarser fractions) when a full gradation curve is required. The standard also lists soils and conditions for which the method is not applicable or requires adaptation (for example, fibrous peat, materials with very low fines content, or cemented/stabilized materials).

Key topics and requirements

• Hydrometer/sedimentation measurement and timing, including meniscus correction and hydrometer calibration.
• Specimen preparation: moist preparation preferred for referee testing; air‑dried only when received that way; minimum fines mass requirements for reliable results.
• Use of dispersants and treatment options for organics, carbonates, and iron oxides when appropriate (noting added effort and possible out‑of‑scope treatments).
• Calculation of particle diameter based on Stokes’ law and reporting percent finer versus log(diameter); recognition of Stokes’ law assumptions and their limitations for plate‑shaped or structured‑water conditions.
• Limits and interferences: practical size range, soils that flocculate or will not readily disperse, and soils requiring documented adaptations to the method.
• Instructions for combining hydrometer results with sieve analysis (for a complete gradation) and guidance on significant digits and rounding (reference to related ASTM practices).

These requirements and topics are described in detail in the standard text.

Typical use and users

Used by geotechnical and soils testing laboratories, civil and environmental engineering firms, highway and transportation agencies, materials testing labs, and research organizations to quantify silt and clay‑sized fractions for classification, design, and assessment of engineering properties (e.g., permeability, compressibility, frost susceptibility). The method is also used when a combined sieve‑sedimentation gradation is required for specifications or filter design.

Related standards

Commonly referenced and related ASTM standards and practices include: Test Methods for sieve analysis (D6913), Plasticity Index determination (D4318), laboratory practice and competence guidance (Practice D3740), and numeric/significant‑digit guidance (Practice D6026). D7928 was developed under Committee D18 (Soil and Rock).

Keywords

hydrometer, sedimentation analysis, particle‑size distribution, gradation, fines, silt, clay, Stokes’ law, soil classification, dispersant, meniscus correction, D7928.

FAQ

Q: What is this standard?

A: ASTM D7928‑21 is a laboratory test method that defines how to perform sedimentation (hydrometer) analysis to determine the particle‑size distribution of the fine‑grained fraction of soils.

Q: What does it cover?

A: It covers specimen preparation (moist or air‑dried as appropriate), dispersion and chemical treatments where applicable, hydrometer readings and corrections, calculations based on Stokes’ law, reporting conventions, and guidance on combining sedimentation results with sieve analyses to produce complete gradation curves. It also lists soils and conditions that are not suitable or require adaptation.

Q: Who typically uses it?

A: Geotechnical testing labs, civil engineers, transportation agencies, consultants, researchers, and quality control/assurance personnel involved in soil classification, filter design, and material specification are the primary users.

Q: Is it current or superseded?

A: The edition D7928‑21 was approved 01 May 2021 and published as the current edition at that time; the published text indicates an editorial change in the designation. There is an active ASTM work item and balloting history to revise the method (indicating ongoing committee activity), and some third‑party aggregators list the record as historical/withdrawn — therefore users should confirm the live status directly with ASTM prior to specification or laboratory accreditation decisions.

Q: Is it part of a series?

A: It complements other gradation and soil‑characterization standards (notably D6913 for sieve analysis and older methods such as D422 which have been superseded in practice by the D6913/D7928 suite). It is maintained under ASTM Committee D18 (Subcommittee D18.03).

Q: What are the key keywords?

A: hydrometer, sedimentation, particle‑size distribution, gradation, fines, silt, clay, Stokes’ law, dispersant, meniscus correction, D7928.