ASTM D7928-21e1

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
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Designation: D7928 − 21
Standard Test Method for
Particle-Size Distribution (Gradation) of Fine-Grained Soils
Using the Sedimentation (Hydrometer) Analysis
This standard is issued under the fixed designation D7928; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
ε NOTE—Summary of Changes section was editorially added in June 2021.
1. Scope* 1.5 The sedimentation analysis is based on the concept that
larger particles will fall through a fluid faster than smaller
1.1 This test method covers the quantitative determination
particles. Stokes’ Law gives a governing equation used to
of the distribution of particle sizes of the fine-grained portion
determine the terminal velocity of a spherical particle falling
of soils. The sedimentation by hydrometer method is used to
through a stationary liquid. The terminal velocity is propor-
determine the particle-size distribution (gradation) of the
tionaltothesquareoftheparticlediameter.Therefore,particles
material that is finer than the No. 200 (75-µm) sieve and larger
are sorted by size in both time and position when settling in a
than about 0.2-µm. The test is performed on material passing
container of liquid.
theNo.10(2.0-mm)orfinersieveandtheresultsarepresented
1.5.1 Stokes’ Law has several assumptions which are: the
as the mass percent finer of this fraction versus the log of the
particles are spherical and smooth; there is no interference
particle diameter.
between the particles; there is no difference between the
1.2 This method can be used to evaluate the fine-grained
current in the middle of the container and the sides; flow is
fraction of a soil with a wide range of particle sizes by
laminar; and the particles have the same density. These
combining the sedimentation results with results from a sieve
assumptions are applied to soil particles of various shapes and
analysis using D6913 to obtain the complete gradation curve.
sizes.
The method can also be used when there are no coarse-grained
1.6 A hydrometer is used to measure the fluid density and
particles or when the gradation of the coarse-grained material
determine the quantity of particles in suspension at a specific
is not required or not needed.
time and position. The density of the soil-water suspension
NOTE 1—The significant digits recorded in this test method preclude
depends upon the concentration and specific gravity of the soil
obtaining the grain size distribution of materials that do not contain a
particlesandtheamountofdispersantadded.Eachhydrometer
significant amount of fines. For example, clean sands will not yield
measurement at an elapsed time is used to calculate the
detectable amounts of silt and clay sized particles, and therefore should
not be tested with this method. The minimum amount of fines in the percentageofparticlesfinerthanthediametergivenbyStokes’
sedimentation specimen is 15 g.
Law.Theseriesofreadingsprovidethedistributionofmaterial
mass as a function of particle size.
1.3 When combining the results of the sedimentation and
sieve tests, the procedure for obtaining the material for the
1.7 This test method does not cover procurement of the
sedimentation analysis and calculations for combining the
sample or processing of the sample prior to obtaining the
results will be provided by the more general test method, such
reduced sample in any detail. It is assumed that the sample is
as Test Methods D6913 (Note 2).
obtained using appropriate methods and is representative of
site materials or conditions. It is also assumed that the sample
NOTE 2—Subcommittee D18.03 is currently developing a new test
method “Test Method for Particle-Size Analysis of Soils Combining the has been processed such that the reduced sample accurately
Sieve and Sedimentation Techniques.”
reflects the particle-size distribution (gradation) of this finer
fraction of the material.
1.4 The terms “soil” and “material” are used interchange-
ably throughout the standard.
1.8 Material Processing—Material is tested in the moist or
as-received state unless the material is received in an air-dried
state. The moist preparation method shall be used to obtain a
sedimentation test specimen from the reduced sample. Air-
ThistestmethodisunderthejurisdictionofASTMCommitteeD18onSoiland
Rock andisthedirectresponsibilityofSubcommitteeD18.03onTexture, Plasticity
driedpreparationisonlyallowedwhenthematerialisreceived
and Density Characteristics of Soils.
in the air-dried state. The method to be used may be specified
Current edition approved May 1, 2021. Published May 2021. Originally
by the requesting authority; however, the moist preparation
approved in 2016. Last previous edition approved in 2017 as D7928–17. DOI:
10.1520/D7928-21E01 method shall be used for referee testing.
*A Summary of Changes section appears at the end of this standard
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
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D7928 − 21
1.9 This test method is not applicable for the following priate safety, health, and environmental practices and deter-
soils: mine the applicability of regulatory limitations prior to use.
1.15 This international standard was developed in accor-
1.9.1 Soils containing fibrous peat.
dance with internationally recognized principles on standard-
1.9.2 Soils containing less than approximately 5% of fine-
ization established in the Decision on Principles for the
grained material (Note 1).
Development of International Standards, Guides and Recom-
1.9.3 Soils containing extraneous matter, such as organic
mendations issued by the World Trade Organization Technical
solvents, oil, asphalt, wood fragments, or similar items (Note
Barriers to Trade (TBT) Committee.
3).
NOTE 3—If extraneous matter, such as wood, can be easily removed by
2. Referenced Documents
hand, it is permissible to do so. However, there may be cases where the
extraneous matter is being evaluated as part of the material and it should 2.1 ASTM Standards:
not be removed from the material.
D653Terminology Relating to Soil, Rock, and Contained
Fluids
1.9.4 Materials that contain cementitious components, such
D854Test Methods for Specific Gravity of Soil Solids by
as cement, fly ash, lime, or other stabilization admixtures.
Water Pycnometer
1.10 This test method may not produce consistent test
D1140Test Methods for Determining the Amount of Mate-
results within and between laboratories for the following soils.
rialFinerthan75-µm(No.200)SieveinSoilsbyWashing
To test these soils, this test method must be adapted and these
D2216Test Methods for Laboratory Determination ofWater
adaptations documented.
(Moisture) Content of Soil and Rock by Mass
1.10.1 Soils that flocculate during sedimentation. Such ma-
D2487Practice for Classification of Soils for Engineering
terials may need to be treated to reduce salinity or alter the pH
Purposes (Unified Soil Classification System)
of the suspension.
D2488Practice for Description and Identification of Soils
1.10.2 Friable soils in which processing changes the grada-
(Visual-Manual Procedures)
tion of the soil. Typical examples of these soils are some
D3740Practice for Minimum Requirements for Agencies
residual soils, most weathered shales, decomposed granites,
Engaged in Testing and/or Inspection of Soil and Rock as
and some weakly cemented soils.
Used in Engineering Design and Construction
1.10.3 Soils that will not readily disperse, such as glauco-
D4220/D4220MPractices for Preserving and Transporting
nitic clays or some dried plastic clays.
Soil Samples
D4318Test Methods for Liquid Limit, Plastic Limit, and
1.11 Samples that are not soils, but are made up of particles
Plasticity Index of Soils
maybetestedusingthismethod.Theapplicablesectionsabove
D4753Guide for Evaluating, Selecting, and Specifying Bal-
should be used in applying this standard.
ances and Standard Masses for Use in Soil, Rock, and
1.12 Units—The values stated in SI units are to be regarded
Construction Materials Testing
as standard. Except the sieve designations, they are identified
D6026Practice for Using Significant Digits in Geotechnical
usingthe“alternative”systeminaccordancewithPracticeE11,
Data
suchas3-in.andNo.200,insteadofthe“standard”designation
D6913Test Methods for Particle-Size Distribution (Grada-
of 75-mm and 75-µm, respectively. Reporting of test results in
tion) of Soils Using Sieve Analysis
units other than SI shall not be regarded as non-conformance
E11Specification forWovenWireTest Sieve Cloth andTest
with this test method. The use of balances or scales recording
Sieves
poundsofmass(lbm)shallnotberegardedasnonconformance
E100Specification for ASTM Hydrometers
with this standard.
E126Test Method for Inspection, Calibration, and Verifica-
tion of ASTM Hydrometers
1.13 Allobservedandcalculatedvaluesshallconformtothe
guidelines for significant digits and rounding established in E177Practice for Use of the Terms Precision and Bias in
ASTM Test Methods
Practice D6026, unless superseded by this test method.
1.13.1 The procedures used to specify how data are
3. Terminology
collected/recorded and calculated in the standard are regarded
as the industry standard. In addition, they are representative of
3.1 Definitions:
the significant digits that generally should be retained. The
3.1.1 Fordefinitionsofcommontechnicaltermsusedinthis
proceduresuseddonotconsidermaterialvariation,purposefor
standard, refer to Terminology D653.
obtaining the data, special purpose studies, or any consider-
3.2 Definitions of Terms Specific to This Standard:
ations for the user’s objectives; and it is common practice to
3.2.1 reduced sample, n—the minus ⁄8-in. (9.5-mm) sieve
increase or reduce significant digits of reported data to be
or finer material that has been separated from the sample and
commensuratewiththeseconsiderations.Itisbeyondthescope
of this test method to consider significant digits used in
analysis methods for engineering or other data.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
1.14 This standard does not purport to address all of the
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
safety concerns, if any, associated with its use. It is the
Standards volume information, refer to the standard’s Document Summary page on
responsibility of the user of this standard to establish appro- the ASTM website.
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D7928 − 21
then split to reduce the mass while still having sufficient 4.4 The sedimentation test specimen is mixed with a dis-
quantity to meet the minimum mass requirements of Table 1. persing agent and test water.The slurry is allowed to condition
and is then thoroughly mixed and placed in a cylinder with
3.2.2 sample, n—material collected without limitation on
additionaltestwater.Readingsaretakenwithahydrometerand
the total mass or size range of particles meeting the minimum
thermometer over specific time intervals.
mass requirements provided in Table 1.
4.5 The mass of particles passing specified particle diam-
3.2.3 sedimentation sample, n—the minus No. 10 (2.0-mm)
eters are calculated and recorded. The results produce a
or finer material separated from the reduced sample using the
tabulationofparticlesizeversuspercentpassingtheseparation
separationsievewhichisthenusedtoobtainthesedimentation
sieve size that can be graphically presented as a gradation
specimen and a water content specimen.
curve. The plot is typically expressed as percent passing/finer
3.2.4 sedimentation specimen, n—the material obtained
than the separation sieve size versus the log of the particle size
from the sedimentation sample having a maximum particle-
in millimeters. These results can then be combined with the
sizenogreaterthantheNo.10(2.0-mm)sievetobeusedinthe
results of a mechanical sieve analysis to obtain a complete
sedimentation test and in sufficient quantity to satisfy the
particle size distribution.
minimum mass requirements of Table 1.
3.2.5 separation sieve, n—the No. 10 (2.0-mm) sieve or
5. Significance and Use
finer(Note4)usedtoseparatethereducedsampletoobtainthe
5.1 Particle-size distribution (gradation) is a descriptive
material for the sedimentation sample.
term referring to the proportions by dry mass of a soil
NOTE 4—The methodology for using a sieve finer than the No. 10
distributed over specified particle-size ranges. The gradation
(2.0-mm) is not defined in this standard. The methodology used to obtain
curvegeneratedusingthismethodyieldsthedistributionofsilt
arepresentativesampleusingasievefinerthantheNo.10(2.0-mm)isnot
and clay size fractions present in the soil based on size
thesameasobtainingtherepresentativesampleusingtheNo.10(2.0-mm)
sieveaspresentedinthisstandard.Additionaleffortorstepsarenecessary
definitions, not mineralogy or Atterberg limit classification.
tomakesurethematerialpassingthefinersieveadequatelyrepresentsthe
5.2 Unlessthesedimentationsampleisrepresentativeofthe
sample. Such additional effort or steps should be documented if using a
entiresample,thesedimentationresultsmustbecombinedwith
sieve finer than the No. 10 (2.0-mm) sieve to obtain the sedimentation
specimen.
a sieve analysis to obtain the complete particle size distribu-
tion.
4. Summary of Test Method
5.3 The clay size fraction is material finer than 2 µm. The
4.1 This test method is used to determine the particle-size
clay size fraction is used in combination with the Plasticity
distribution (gradation) of material finer than the No. 200
Index (Test Methods D4318) to compute the activity, which
(75-µm) sieve as a percentage of the mass used in the
provides an indication of the mineralogy of the clay fraction.
sedimentation test.
5.4 The gradation of the silt and clay size fractions is an
4.2 When the source material contains particles larger than
important factor in determining the susceptibility of fine-
3 3
the ⁄8-in. (9.5-mm) sieve, a reduced sample passing the ⁄8-in.
grained soils to frost action.
(9.5-mm)sieveshallbeobtainedusingtechniquespresentedin
Test Methods D6913 or another standard.This reduced sample 5.5 The gradation of a soil is an indicator of engineering
properties such as hydraulic conductivity, compressibility, and
shall meet the minimum mass requirements in Table 1 for the
⁄8-in. (9.5-mm) sieve. The material is processed using the shear strength. However, soil behavior for engineering and
other purposes is dependent upon many factors, such as
moist (referee) preparation method unless the material is
received in the air-dried state. effective stress, mineral type, structure, plasticity, and geologi-
cal origin, and cannot be based solely upon gradation.
4.3 The reduced sample is separated using the separation
sieve to obtain a sedimentation sample. The sedimentation 5.6 Some types of soil require special treatment in order to
sample is then split to obtain the appropriate mass for the correctly determine the particle sizes. For example, chemical
sedimentationtestspecimenandawatercontenttestspecimen. cementing agents can bond clay particles together and should
TABLE 1 Minimum Dry Mass Requirements
Maximum Particle Size of Material Minimum Dry Mass of Specimen
(smallest sieve that 99% or more passes) (g or kg)
Alternative Maximum Reporting
Sieve Particle Results
Designation Size, mm to Nearest 1 %
No. 40 0.425 50 g
No. 10 2.00 50 g
No. 4 4.75 75 g
⁄8 in. 9.50 165 g
⁄4 in. 19.0 1.3 kg
1 in. 25.4 3 kg
1 ⁄2 in. 38.1 10 kg
2 in. 50.8 25 kg
3 in. 76.2 70 kg
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D7928 − 21
be treated in an effort to remove the cementing agents when accuracy of at least 60.5°C.The thermometric device must be
possible. Hydrogen peroxide and moderate heat can digest capable of being immersed in the suspension and reference
organics.Hydrochloricacidcanremovecarbonatesbywashing solutions to a depth ranging between 25 and 80 mm. Full
and Dithionite-Citrate-Bicarbonate extraction can be used to immersion, also known as complete or total immersion
remove iron oxides. Leaching with test water can be used to thermometers,shallnotbeused.Thethermometricdeviceshall
reducesaltconcentration.Allofthesetreatments,however,add be standardized by comparison to a nationally or internation-
significant time and effort when performing the sedimentation ally traceable thermometric device and shall include at least
testandareallowablebutoutsidethescopeofthistestmethod. one temperature reading within the range of testing. The
thermometric device shall be standardized at least once every
5.7 The size limits of the sedimentation test are from about
twelve months. The same thermometric device shall be used
100 µm to about 0.1 µm. The length of time required to obtain
for all measurements.
a stable initial reading on the hydrometer controls the upper
range of results, and the test duration controls the lower range. 6.5 Timing Device—A clock, stopwatch, digital timer, or
comparable device readable to one second or better.
5.8 The shape and density of the grains are important to the
results. Stokes’ Law is assumed to be valid for spherical 6.6 Balance—Balancesshallconformtotherequirementsof
particles even though fine silt- and clay-sized particles are Specification D4753.
more likely to be plate-shaped and have greater mineral 6.6.1 To determine the mass of the specimen, the balance
densities than larger particles. shall have readability without estimation of 0.01 g. The
capacity of this balance will need to exceed the mass of the
5.9 High plasticity clays develop structured water layers on
3 container plus soil used to contain the soil suspension after the
their surfaces. According to Zhang and Lu this near surface
completionofthesedimentationtest.Ingeneral,abalancewith
water can be as dense as 1.4 g/L. This high-density structured
a minimum capacity of 1,800 g is sufficient.
water causes an error in this test method and shifts the particle
size distribution curve upwards. Correction for the structured 6.7 Drying Oven—Vented, thermostatically controlled oven
waterisbeyondthescopeofthisstandardbutvaluesofpercent capable of maintaining a uniform temperature of 110 6 5°C
passing above 100% are possible and should not be excluded throughout the drying chamber. These requirements typically
from the report. require the use of a forced-draft oven.
NOTE 5—The quality of the result produced by this standard is
6.8 Plate—Aclean, nonporous, smooth, solid surface that is
dependent on the competence of the personnel performing it, and the
large enough to pile and split about 500 g of material. The
suitability of the equipment and facilities used. Agencies that meet the
surface shall not be made of any type of paper product.
criteria of Practice D3740 are generally considered capable of competent
and objective testing/sampling/inspection/etc. Users of this standard are
6.9 Specimen-Mixing Container—Aglass beaker or equiva-
cautioned that compliance with Practice D3740 does not in itself assure
lentinertcontainerwithenoughcapacitytoholdthespecimen,
reliable results. Reliable results depend on many factors; Practice D3740
provides a means of evaluating some of those factors. the test water, and dispersant. A container of about 250 mL is
sufficient.
6. Apparatus
6.10 Temperature Maintaining Device—Unless otherwise
6.1 Hydrometer—ASTM hydrometer type 151H or 152H.
specified by the requesting agency, the standard test tempera-
These hydrometers shall be in general conformance with the
ture shall be in the range of 22 6 5°C. In addition, the
requirements in Specification E100 with the exception of
temperature of the soil suspension shall not vary more than
dimensional specifications as indicated in Annex A1.
62°C. Normally, this temperature maintenance is accom-
6.2 Sedimentation Cylinder—At least two glass cylinders plished by performing the test in a room with a relatively
having a height of about 457 mm, an inside diameter between
constant temperature. If such a room is not available, the
55and64mm,andacapacityof1,000mL.Thecylindersshall cylinders shall be placed in an automatically temperature
haveanindicationmarkat1,000 65mL.Onecylinderisused
controlled insulated chamber or water bath that maintains a
for the soil suspension and the other one can be used as the temperature within the tolerance specified above.
control cylinder or the wash cylinder. The control cylinder
6.11 Soil Suspension Oven-Drying Container
shallhavethesameamountofdispersantasthesoilsuspension
(Optional)—A container having smooth walls and capable of
cylinder. See Annex A1.
holding approximately 1.5-L of the soil suspension. This
6.3 Separation Sieve—No. 10 (2-mm) or finer sieve used to container shall have a tight fitting lid or fit into a desiccator, to
separate the reduced sample. This sieve is subjected to rough
prevent moisture gain during cooling of the oven-dried speci-
operation and shall not be used for quantitative grain size men.Thisisonlyrequiredwhenthereisinsufficientmaterialto
analysis.
obtain the initial water content from a companion specimen.
6.4 Thermometric Device—A thermometric device capable 6.12 Dispersion Apparatus—Use one of the following de-
of measuring the temperature range within which the test is
vicestodispersethespecimen;howeverforrefereetesting,the
being performed readable to 0.5°C or better and having an
stirring apparatus shall be used.
6.12.1 Stirring Apparatus (Referee)—A mechanically oper-
ated stirring device in which a suitably mounted electric motor
Zhang, C and Lu, N. “What is the Range of Soil Water Density? Critical
turns a vertical shaft at a minimum speed of 10,000 rpm
Reviews with a Unified Model,” Reviews of Geophysics, Vol 56, No. 3, July 2019,
pp. 532–562. without load. The shaft shall be equipped with a replaceable
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D7928 − 21
stirring paddle made of metal, as shown in Fig. 1. The shaft inserted on top of and in the center of the larger disk. This
shall be of such length that the stirring paddle will operate device shall be used for referee testing.
between 19.0 mm and 37.5 mm above the bottom of the
6.14 Agitation of the Soil Slurry—Any of the following
dispersion cup.
items may be used to break up the soil aggregations as
6.12.1.1 Dispersion Cup—A special dispersion cup con-
described in 11.1:
forming to either of the designs shown in Fig. 2 shall be
6.14.1 Erlenmeyer Flask—A glass flask having a capacity
provided to hold the sample while it is being dispersed. The
between 250 mL and 500 mL.
cupshallcontaintwosetsofthreelongbafflerodsandtwosets
of three short baffle rods rigidly mounted to the interior sides
6.14.2 Dispersion Shaker—Aplatform,wristactionorsimi-
of the cup. This cup is used with the stirring apparatus. lar type shaker having a gyratory, orbital, reciprocating, or
6.12.2 Air Jet Dispersion Device (Optional)—Atubetypeor
similar motion to assist in the dispersion process by continu-
other comparable device that uses compressed air to disperse
ously agitating the soaking soil.
the slurry (Note 6). The device requires an air source capable
6.14.3 Ultrasonic Water Bath—The ultrasonic water bath
of providing up to 0.0024 m /s of air to operate the device,
must be large enough to hold a beaker or flask containing the
such that pressures between about 70 and 170 kPa can be
soil slurry to be agitated for use in the sedimentation test. The
achieved. The device shall be fitted with a pressure gauge on
water level in the bath should be equal to or higher than the
the line between the device and the air source. Water may
water level in the specimen container.
condense in the lines when not in use and this water must be
removed. There are two ways to remove the water: use of a 6.15 Desiccator (Optional)—A desiccant containing device
water trap or purging the lines before use. If a water trap is ofsuitablesizeusedtopreventmoisturegainduringcoolingof
used, it shall be installed on the air line in such a manner to the oven-dried specimen.
prevent condensed water from entering the slurry. This device
6.16 Mortar and Rubber-Covered Pestle (Optional)—
shall not be used in referee testing.
Apparatus suitable for breaking up aggregations of air-dried
NOTE 6—Use of this device or others, causes differing amounts of
soil particles without breaking individual particles.
dispersion and should be used with caution. Information on how to
appropriately use this device should be obtained from the manufacturer.
6.17 Miscellaneous Items—Items such as a wash/rinse
3 3
0.0024 m /s is equivalent to 5 ft /min. The device typically needs at least
bottle (squirt bottle), rubber scraper, spatula, and stirring rod
3 3
0.0009 m /s (2 ft /min) to operate and therefore, some small air compres-
may be useful.
sors are not capable of supplying sufficient air to operate the device.
6.13 Agitator (Optional/Referee)—A hand-held device to
7. Reagents and Materials
mix the soil suspension in the sedimentation cylinder prior to
7.1 Sodium Hexametaphosphate (NaPO ) —Also referred
testing,asshowninFig.3.Theagitatormustnothaveanytype
3 6
to as sodium metaphosphate is the dispersion agent (defloccu-
of metal, such as a screw head, protruding from the bottom of
the disk. To aid in strengthening the connection between the lant) required to prevent the fine particles in suspension from
rod and the disk, a smaller disk (about 25 mm or less) having coalescing or flocculating (Note 7). Consult the Safety Data
similar thickness and material as the larger disk, may be Sheet (SDS) for specific information regarding this chemical.
Dimensions are provided to give a sense of scale and will vary depending on manufacturer specifications.
FIG. 1 Typical Detail of Stirring Paddles
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D7928 − 21
Dimensions are provided to give a sense of scale and will vary depending on manufacturer specifications.
FIG. 2 Typical Geometry of the Dispersion Cup
Dimensions are provided to give a sense of scale and will vary depending on manufacturer specifications.
FIG. 3 Detail of Agitator
7.2 Isopropyl Alcohol—Also referred to as isopropanol al- 7.3 Test Water—Distilled or demineralized water is the only
cohol or rubbing alcohol is used as a foam inhibitor. Commer- permissible test fluid. The use of tap water is not permitted.
cially available in concentrations ranging from 70% to 99%.
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D7928 − 21
NOTE 7—Fine-grained soils requiring the use of a dispersant are those
aggregations without destroying the individual particles.Addi-
that do not readily slake in water, such as some highly plastic clays and
tional guidance for splitting material to obtain a representative
most tropical soils. Typically, 5 grams per test of dispersant is used to
specimen using a splitter, quartering, or moist stockpile sam-
prevent flocculation and is added directly to the soil, such that the
pling is given in Test Methods D6913, Annex A2.
concentration will equal 5 g/L in the final soil suspension volume. The
chemical formula for the dispersant shown above is approximate.
NOTE 8—Air drying causes irreversible changes to some clay particles
that cause permanent flocculation and decreases the fine fraction.
8. Sampling
9.2 Moist Preparation (Referee)—This preparation method
8.1 General—This test method does not address, in any
shall be used for materials not received in the air-dried state.
detail, procurement of the sample. It is assumed the sample is
This method is especially important for any soil whose
obtainedusingappropriatemethodsandisrepresentativeofthe
propertiesarealteredduetodryingsuchas,mostorganicsoils,
material under evaluation. However, the testing agency shall
many highly plastic fine-grained soils, tropical soils and soils
preserve all samples in accordance with Practice D4220/
containing halloysite. The material is thoroughly mixed to
D4220M, Group B, except if the as-received sample does not
obtain a uniform reduced sample. Intact fine-grained samples
meet those requirements. In which case, the water content of
should be chopped/reduced into small pieces, less than ap-
the material does not have to be maintained.
proximately 10 mm, and mixed to make uniform. There is no
8.2 Where data from this test are to be used for correlation
need to process the fine-grained materials through a sieve.
withotherlaboratoryorfieldtestdata,usethesamematerialas
9.3 Air-Dried Preparation—This preparation method shall
used for these tests where possible and as much is practical.
onlybeusedifthesampleisreceivedinthedriedcondition.In
8.3 Thesamplecanbefromavarietyofsourcesandcontain
order to obtain a uniform reduced sample, the sample is
a wide range of particle sizes. Typically, samples for particle-
blended at room temperature.
size analysis are obtained from the following sources: large
9.4 Ifthereducedsamplecontainsparticleswhicharelarger
bags or buckets, small bags, jar samples, tube samples, or
thantheNo.10(2.0-mm)sieve,thematerialshallbeseparated
specimens from other tests, such as consolidation, hydraulic
using a No. 10 (2.0-mm) or finer sieve. Process the entire
conductivity or strength tests. In some cases, such as compac-
reduced sample over the No. 10 (2.0-mm) or finer sieve using
tion testing, prior testing may have caused a reduction in
arubberscraperand,ifneeded,testwatertoaidinworkingthe
particle sizes; therefore, it may be required to obtain a sample
material through the sieve. Check that the material retained on
of the original material, the degraded sample, or both. Test
the sieve does not contain aggregations of finer particles.Any
Methods D6913, Section 9, gives additional information re-
aggregations should be broken and passed through the sieve. It
garding sampling from the different sources.
is not necessary that the separation be totally complete but the
8.3.1 Preserve the sample at its original moisture condition
materialpassingthesieveshallberepresentativeofthepassing
unless excluded above, and at no time shall the sample be
fraction.Thematerialpassingtheseparationsieveistermedthe
allowed to undergo undesirable temperature changes such as
sedimentation sample and shall meet the minimum mass
freezing or heating.
requirement of Table 1. Record the separation sieve size that is
8.4 Whenthesamplecontainsparticleslargerthanthe ⁄8-in.
used to separate the sample.
(9.5-mm) sieve, it shall be processed to obtain the reduced
9.5 Estimate the maximum amount of moist mass that can
sample. If particle-size separation is necessary, process the
beusedforthesedimentationtestusingthefollowingequation
sample to meet this requirement using the separation proce-
(Note 9):
dures provided in Test Methods D6913.
8.4.1 The reduced sample shall have a maximum particle 100 w
cest
M 5 H 3 3 1 1 (1)
S D S S DD
mest c
%est 100
size that passes through the ⁄8-in. (9.5-mm) or smaller sieve.
8.4.2 The mass of the reduced sample shall meet or exceed
where:
the mass requirements given in Table 1.
M = estimated maximum moist mass, nearest 1 g,
mest
H = hydrometercapacity,g(either45for151Hor55for
9. Preparation of the Test Specimen
c
152H),
9.1 Specimen Procurement—This standard presents two
%est = estimated percentage of material passing the No.
preparation methods to obtain the sedimentation specimen
200 (75-µm) sieve, nearest 1%, and
from the reduced sample: moist and air-dried. In these prepa-
w = estimated water content, nearest 1%.
cest
ration methods, moist and air-dried refers to the condition of
NOTE 9—The mass of the sedimentation test specimen should be
the material or sample as it is being reduced to an appropriate
selected based on the amount of material that will be in suspension at the
particle size and mass. The test shall not be performed on
time of the first reading. Using the maximum capacity of the hydrometer
provides the highest resolution but is not a requirement. Exceeding the
oven-dried material. The moist preparation method shall be
capacity will make it impossible to obtain the initial readings. The
used for referee testing and for samples not received in the
capacityofthe152Hhydrometerisabout55gofdrysoilandthecapacity
air-dried state. The air-dried method shall only be used on
ofthe151Hisabout45g.Thewetmassshouldbeadjustedtoaccountfor
materials received in the air-dried state (Note 8). Since some
fine-grained, air-dried soils aggregate, a mortar and rubber
covered pestle is used to break up aggregations. Care must be
Sridharan,A., Jose, B.T., andAbraham, B.M., Technical Note on “Determina-
taken to avoid disintegration or reduction of individual par-
tion of Clay Size Fraction of Marine Clays,” Geotechnical Testing Journal,
ticles. Use only enough force as necessary to break up the GTJODJ, Vol. 14, No. 1, March 1991, pp. 103-107.
´1
D7928 − 21
the water content and the fraction of particles smaller than the No. 200 first 5 to 8 minutes of the test can be difficult. During that time it is
(75-µm) sieve. For example, if the water content is estimated at 20%, acceptable to read the hydrometer to the nearest ⁄2 division.
using a 151H hydrometer, and an estimated percent passing the No. 200
10.1.2 To insert the hydrometer correctly do the following:
(75-µm) sieve of 95%, the estimated moist mass is 57 g.
First, make sure the stem is dry. Then, gently hold it by the
9.6 If the sedimentation sample contains sufficient material,
stem with one or both hands and slowly lower it to the depth
then split or quarter the sedimentation sample into at least two
slightly below the point at which it just floats.The hydrometer
portions: one for the water content determination and one for
should then rise slightly and become stable. This insertion
the sedimentation test. The water content specimen shall
process should take between 5 to 15 seconds.
contain 50 610 g of material. The sedimentation specimen
10.2 Temperature-Density Correction—During a test, the
should be less than the limit computed in 9.5.
suspension fluid density changes, therefore calculations for the
9.7 If the sedimentation sample has limited material, do not
quantity of particles in suspension must account for fluid
obtain a water content specimen. Obtain the dry mass, M,of
d
densitychangesduetotemperature,presenceofdispersant,and
thesedimentationspecimenattheendofthesedimentationtest
the meniscus rise. The temperature-density correction is shift-
asdiscussedin11.12andcalculatedin12.1.2.Reducethemass
ing the hydrometer scale, which is factory set for distilled
to be less than the limit computed in 9.5.
waterat20°C.Therearetwowaystodeterminethiscorrection:
NOTE10—Ifthereisenoughmaterialaftersplitting/quarteringtoobtain
take companion measurements in a control cylinder filled with
the necessary masses for both the sedimentation and water content
thereferencesolutionduringthetestingorgenerateareusable,
specimens, the sedimentation sample is considered to have sufficient
calibration relationship. Both options require the use of a
material. If there is not enough material to obtain both the necessary
referencesolutioncomposedoftestwaterandthesameamount
masses of the specimens, the sedimentation sample is considered to have
limited material.
of dispersant used in the sedimentation test cylinder. The
meniscus correction is automatically accounted for in the
9.8 Record the mass of the moist soil, M , used for the
m
temperature-densitycorrectionforbothoptionsbyconsistently
sedimentation test to the nearest 0.01 g.
reading the hydrometer at the top of the meniscus as described
9.9 Place the sedimentation specimen in the specimen-
in 10.3.
mixingcontainerandrecordtheidentificationofthespecimen-
10.2.1 Reference Solution—The reference solution shall be
mixing container.
prepared with the same amount of dispersant as the soil
9.10 If sufficient material is available, immediately use the
suspension. Fill a control cylinder to the 1,000 mL mark with
other specimen for determination of the water content in
amixtureoftestwaterandthesameamountofdispersantused
accordance with Test Methods D2216, and record the water
in the soil suspension cylinder. The test water and dispersant
content, w , to the nearest 0.1%.
c
shall be well mixed such that no visible crystals can be seen,
and the reference solution shall be agitated to make sure the
10. Verification/Preparation of Apparatus
dispersantisadequatelymixedthroughoutthecontrolcylinder.
10.1 Hydrometer—Check and record the dimensions of the
10.2.1.1 Companion Measurements—Use a control cylinder
151H or 152H hydrometers as presented in Annex A1 in
filled with the reference solution in conjunction with the soil
accordance with the interval listed in theAnnex. The hydrom-
suspension cylinder to obtain the correction. Position the
eter shall be free of cracks and chips, which can compromise
control cylinder in the same temperature controlled location as
the integrity of the hydrometer. The body and stem of a
the test cylinders so that all cylinders are at or near the same
hydrometer seldom change over time, unless they have been
temperature. For each hydrometer and temperature reading
subjected to corrosive materials or have been damaged, that is,
taken in the soil suspension cylinder, take a corresponding
chippedorcracked.Theyonlyneedtobecheckedbeforeinitial
hydrometer and temperature reading in the control cylinder.
use or after damage has been suspected or seen. Since it is
However, it is permissible for one control cylinder reading to
possibleforthepaperscaleinsidethehydrometerstemtoslide
be used in conjunction with readings in the soil suspension for
down, the hydrometer reading in the test water, shall be
up to 30 minute intervals. Record the elapsed time and the
checkedanddocumentedaccordingtotheintervalpresentedin
hydrometerandtemperaturereadingsofthecontrolcylinderon
Annex A1 to make sure the scale has remained in its proper
the data sheet(s) only when measured (Note 12).
place.Ifthescalehasmoved,thehydrometershallbereplaced.
10.1.1 Hydrometer Readings—Hydrometer readings are
NOTE 12—Readings taken in one control cylinder may be used for
multiple test cylinders. Therefore, if the hydrometer and temperature
taken to the nearest ⁄4 division (Note 11). Reading the
readings in the control cylinder are only taken once during the first 30
hydrometer can be difficult. A properly placed hydrometer
minutes of the test, only that reading is recorded on each of the data
should neither bob nor rotate appreciably when released in the
sheet(s)towhichitapplies.Thesemeasuredreadingsarenottobewritten
soilsuspension.Itisimportantforthestemtobedryandclean
infortheothertimesduringthefirst30minuteswhenameasurementwas
when inserting it into the soil suspension. If the stem is wet
not actually determined.
above the reading point it will add mass to the hydrometer
10.2.2 Calibration Relationship—This option generates a
causing the reading to be too low. If the stem is not clean,
general calibration relationship between the hydrometer read-
variations in the meniscus rise will result. In this application,
ing of a control cylinder filled with the reference solution and
the hydrometers are always read at the top of the meniscus for
the temperature, which eliminates the need for companion
the reason stated in 10.3.
measurements during the test. A temperature-based general
NOTE 11—Reading the hydrometer to the nearest ⁄4 division during the calibration relationship is required and established for each
´1
D7928 − 21
1606 setting the scale to read mass of solids in solution for a particle
hydrometer.Asedimentation cylinder is filled to the 1,000 mL
specific gravity of 2.65.
mark with test water with the same amount of dispersant used
in the soil suspension. Be sure the solution is thoroughly 10.3 Meniscus Correction—Hydrometersaredesignedtobe
mixed, and the temperature is allowed to equilibrate. Then read at the fluid surface, however, the fluid is wetting to the
glass such that the soil suspension will rise up the hydrometer
insert the hydrometer as described in 10.1.2. Take the reading
at the top of the meniscus and record this reading and the stem making a reading at the fluid surface impossible at times.
It is common practice to read the hydrometer at the top of the
temperature of the solution. Rinse the hydrometer well with
test water between readings and dry it prior to taking the next meniscusanditmustbetakenthereevenwhenitispossibleto
see through the soil suspension. The meniscus rise has a small
reading. Increase/Decrease the temperature of the cylinder,
impactontheeffectivedepthdeterminationsincethereadingis
allow it to come to temperature equilibrium and repeat the
taken slightly above the surface of the suspension. This rise
measurement process. Take at least five different hydrometer
causes a change to the third significant digit in the computed
and temperature readings within the range of temperatures
particle size. The meniscus correction is performed before
expected during the sedimentation test. Calculate the constant
initial use of the hydrometer and after damage has been
A or B as discussed below.
suspected or noticed.
10.2.2.1 The 151H hydrometer measures the specific grav-
10.3.1 The meniscus correction, C , as shown in Fig. 4,is
m
ity of the fluid relative to distilled water at 20°C. The
determined by inserting the hydrometer with a clean and dry
calibrationmeasurementsareusedtocomputetheconstantAin
stem and without bobbing into the test water with the proper
the following equation. The standard deviation of the five
amount of dispersant. The reading at the top of the meniscus
computed “A” values shall be less than 0.0005. The average
and the reading where the plane of water surface intersects the
value of A is used when computing the temperature-density
stem are recorded. The difference between these two readings
correction.
(topofmeniscusminusplaneofwatersurface)isthemeniscus
26 26 2
A 5 R 1 7.784 3 10 3 T 1 4.959 3 10 3 T (2)
~ ! ~ !
n 151,n n n
correction, C . Therefore, the meniscus correction is a nega-
m
tivevalueandhasunitsofthehydrometerscale.Inaccordance
where:
with Test Method E126, the plane of water surface reading
A = average specific gravity shift (151H hydrometer),
shall be obtained using the following guidance. Observe a
nearest 0.0001,
pointslightlybelowtheplaneofthewatersurfaceandraisethe
R = 151H specific gravity hydrometer at reading, n,in
151,n
line of vision until this surface, seen as an ellipse, becomes a
reference solution, readable to 0.00025 or better,
straight line. The point where this line cuts the hydrometer
T = temperature at reading, n, readable to 0.5°C or
scale is the hydrometer reading. Holding a white card behind
better, and
the cylinder just below the water level will improve the
n = subscript indicating the reading number during
visibility of the surface. The hydrometer readings shall be
calibration.
recorded to the nearest ⁄4 division.
10.2.2.2 The 152H hydrometer measures the mass of par-
10.4 Effective Depth—The effective depth, also referred to
ticles (specific gravity of 2.65) in a suspension of distilled
as “true depth,” is used in the calculation of the particle fall
waterat20°C.Thetemperature-densitycorrectionprovidesthe
distance for each reading. The effective depth is defined as the
offset mass reading for the hydrometer for a specific tempera-
distance from the center of (volume) buoyancy of the hydrom-
ture and dispersant concentration. The calibration measure-
eter to the surface of the soil suspension. The equation to
ments are used to compute the constant B in the following
calculate the effective depth when the hydrometer is inserted
equation (Note 13). The standard deviation of the five com-
and removed between readings requires certain dimensional
puted “B” values shall be less than 0.5 g/L. The average value
measurements in order to do the calculation. Refer to Fig. 5.
of B is used when computing the temperature-density correc-
10.4.1 Determine and record the volume of the hydrometer
tion.
bulb, V , to the nearest 1 cm using the procedure given in
hb
22 23 2
B 5 R 1 1.248 3 10 3 T 1 7.950 3 10 3 T (3)
~ ! ~ !
n 152,n n n
where:
B = average mass reading shift (152H hydrometer),
nearest 0.1,
R = massinreferencesolutionhydrometeratreading, n,
152,n
readable to 0.25 g/L or better,
T = temperature at reading, n, readable to
...