ASTM D4643-00
(Test Method)Standard Test Method for Determination of Water (Moisture) Content of Soil by the Microwave Oven Method
Standard Test Method for Determination of Water (Moisture) Content of Soil by the Microwave Oven Method
SCOPE
1.1 This test method outlines procedures for determining the water (moisture) content of soils by incrementally drying soil in a microwave oven.
1.2 This test method is not intended as a replacement for Test Method D2216; but, rather as a supplement when more rapid results are required or desired to expedite other phases of testing. Test Method D2216 is to be used as the method to compare for accuracy checks and correction.
1.3 When questions of accuracy between this test method and Test Method D2216 arise, Test Method D2216 shall be the referee method.
1.4 This test method is applicable for most soil types. For some soils, such as those containing significant amounts of halloysite, mica, montmorillonite, gypsum or other hydrated materials, highly organic soils, or soils in which the pore water contains dissolved solids (such as salt in the case of marine deposits), this test method may not yield reliable water content values.
1.5 The values stated in SI units are to be regarded as the standard.
1.6 This standard does not purport to address all of the safety problems, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use. See Section 7. Note 1-Notwithstanding statements of precision and bias contained in this standard, the precision of this test method is dependent on the competence of the personnel performing it and the suitability of the equipment and facilities used. Agencies that meet the criteria of Practice D3740 are generally considered capable of competent and objective testing. Users of this test method are cautioned that compliance with Practice D3740 does not in itself ensure reliable testing. Reliable testing depends on many factors; Practice D3740 provides a means of evaluating some of those factors.
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Designation:D4643–00
Standard Test Method for
Determination of Water (Moisture) Content of Soil by the
Microwave Oven Heating
This standard is issued under the fixed designation D 4643; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
This standard has been approved for use by agencies of the Department of Defense.
1. Scope * as Used in Engineering Design and Construction
D 4753 Specification for Evaluating, Selecting, and Speci-
1.1 Thistestmethodoutlinesproceduresfordeterminingthe
fying Balances and Scales for Use in Testing Soil, Rock,
water (moisture) content of soils by incrementally drying soil
and Related Construction Materials
in a microwave oven.
1.2 This test method can be used as a substitute for Test
3. Terminology
Method D 2216 when more rapid results are desired to expe-
3.1 Definitions:
dite other phases of testing and slightly less accurate results are
3.1.1 All definitions are in accordance with Terminology
acceptable.
D 653.
1.3 When questions of accuracy between this test method
3.2 Definitions of Terms Specific to This Standard:
and Test Method D 2216 arise, Test Method D 2216 shall be
3.2.1 microwave heating—a process by which heat is in-
the referee method.
duced within a material due to the interaction between dipolar
1.4 This test method is applicable for most soil types. For
molecules of the material and an alternating, high frequency
some soils, such as those containing significant amounts of
electric field. Microwaves are electromagnetic waves with 1
halloysite, mica, montmorillonite, gypsum or other hydrated
mm to 1 m wavelengths.
materials, highly organic soils, or soils in which the pore water
3.2.2 water (moisture) content—the ratio, expressed as a
contains dissolved solids (such as salt in the case of marine
percentage, of the mass of “pore” or “free” water in a given
deposits), this test method may not yield reliable water content
mass of soil to the mass of the solid particles.
values.
1.5 The values stated in SI units are to be regarded as the
4. Summary of Test Method
standard.
4.1 A moist soil specimen is placed in a suitable container
1.6 This standard does not purport to address all of the
and its mass is determined. It is then placed in a microwave
safety concerns, if any, associated with its use. It is the
oven, subjected to an interval of drying, and removed from the
responsibility of the user of this standard to establish appro-
oven and its new mass is determined. This procedure is
priate safety and health practices and determine the applica-
repeated until the mass becomes nearly constant.
bility of regulatory limitations prior to use. See Section 7.
4.2 The difference between the mass of the moist specimen
and the dried specimen is used as the mass of water originally
2. Referenced Documents
contained in the specimen. The water content is determined by
2.1 ASTM Standards:
dividing the mass of water by the dry mass of soil, multiplied
D 653 Terminology Relating to Soil, Rock, and Contained
by 100. For a given soil and sample size, the time to achieve a
Fluids
constant dry mass can be noted and used as a minimum drying
D 2216 TestMethodforLaboratoryDeterminationofWater
time for subsequent tests using the same size specimen of the
(Moisture) Content of Soil and Rock
same soil.
D 3740 Practice for Minimum Requirements for Agencies
Engaged in the Testing and/or Inspection of Soil and Rock
5. Significance and Use
5.1 The water content of a soil is used throughout geotech-
This test method is under the jurisdiction of ASTM Committee D-18 on Soil nical engineering practice both in the laboratory and in the
and Rock and is the direct responsibility of Subcommittee D18.08 on Special and
field. The use of Test Method D 2216 for water content
Construction Control Tests.
determination can be time consuming and there are occasions
Current edition approved Feb. 10, 2000. Published April 2000. Originally
published as D4643 – 87. Last previous edition D4643 – 93.
Annual Book of ASTM Standards, Vol 04.08.
*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.
D4643
when a more expedient method is desirable. The use of a 6.4 Container Handling Apparatus—A glove or holder,
microwave oven is one such method. suitable for removing hot containers from the oven.
5.2 The principal objection to the use of the microwave
6.5 Desiccator—A desiccator cabinet or jar of suitable size
oven for water-content determination has been the possibility
containing silica gel, anhydrous calcium phosphate, or equiva-
of overheating the soil, thereby yielding a water content higher
lent. It is preferable to use a desiccant that changes color to
than would be determined by Test Method D 2216. While not
indicate that it needs reconstitution.
eliminating this possibility, the incremental drying procedure
6.6 Heat Sink—A material or liquid placed in the micro-
described in this test method will minimize its effects. Some
wave to absorb energy after the moisture has been driven from
microwave ovens have settings at less than full power, which
the test specimen. The heat sink reduces the possibility of
can also be used to reduce overheating.
overheating the specimen and damage to the oven. Glass
5.3 The behavior of a soil, when subjected to microwave
beakersfilledwithwaterandmaterialsthathaveaboilingpoint
energy, is dependent on its mineralogical compositions, and as
above water, such as nonflammable oils, have been used
a result no one procedure is applicable for all types of soil.
successfully. Moistened bricks have also been used.
Therefore, the procedure recommended in this test method is
6.7 Stirring Tools—Spatulas, putty knives, and glass rods
meant to serve as a guide when using the microwave oven.
for cutting and stirring the test specimen before and during the
5.4 This test method is best suited for minus No. 4 sized
test. Short lengths of glass rods have been found useful for
material. Larger size particles can be tested; however, care
stirring and may be left in the specimen container during
must be taken because of the increased chance of particle
testing, reducing the possibility of specimen loss due to
shattering.
adhesion to the stirring tool.
5.5 The use of this method may not be appropriate when
highly accurate results are required, or the test using the data is
7. Hazards
extremely sensitive to moisture variations.
7.1 Handlehotcontainerswithacontainerholder.Somesoil
5.6 Duetothelocalizedhightemperaturesthatthespecimen
types can retain considerable heat, and serious burns could
isexposedtoinmicrowaveheating,thephysicalcharacteristics
result from improper handling.
of the soil may be altered. Degregation of individual particles
7.2 Suitable eye protection is recommended due to the
may occur, along with vaporization or chemical transition. It is
possibility of particle shattering during the heating, mixing, or
therefore recommended that samples used in this test method
mass determinations.
not be used for other tests subsequent to drying.
7.3 Safety precautions supplied by the manufacturer of the
NOTE 1—The quality of the results produced by this test method is
microwave should be observed. Particular attention should be
dependent on the competence of the personnel performing it and the
paid to keeping the door sealing gasket and door interlocks
suitability of the equipment and facilities used. Agencies that meet the
clean and in good working condition.
criteria of Practice D 3740 are generally considered capable of competent
and objective testing. Users of this test method are cautioned that
NOTE 3—The use of a microwave oven for the drying of soils may be
compliance with Practice D 3740 does not in itself ensure reliable results.
considered abusive by the manufacturers and consitute voiding of war-
Reliable results depend on many factors; Practice D 3740 provides a
ranties. Microwave drying of soils containing metallic materials may
means of evaluating some of those factors.
causearcingintheoven.Highlyorganicsoilsandsoilscontainingoilsand
coal may ignite and burn during microwave drying. Continued operation
6. Apparatus
of the oven after the soil has reached constant weight may also cause
6.1 Microwave Oven—A microwave oven, preferably with
damage or premature failure of the microwave oven.
a vented chamber, is suitable. The required size and power
NOTE 4—When first introduced, microwave ovens were reported to
rating of the oven is dependent on its intended use. Ovens with
affect heart pacemakers, primarily because of the operating frequencies of
variable power controls and input power ratings of about 700 the two devices. Since that time, pacemakers have been redesigned, and
the microwave oven is not regarded as the health hazard it once was.
W have been found to be adequate for this use. Variable power
However, it may be advisable to post warnings that a microwave is in use.
controls are important and reduce the potential for overheating
of the test specimen.
7.4 Highly organic soils and soils containing oil or other
contaminates may ignite into flames during microwave drying.
NOTE 2—Microwave ovens equipped with built-in scales and computer
Meansforsmotheringflamestopreventoperatorinjuryoroven
controls have been developed for use in drying soils. Their use is
compatible with this test method. damage should be available during testing. Fumes given off
from contaminated soils or wastes may be toxic, and the oven
6.2 Balances, having a capacity of 2000 g or greater and
should be vented accordingly.
meetingtherequirementsofSpecificationD 4753forabalance
7.5 Due to the possibility of steam explosions, or thermal
of 0.1 g readability.
stress shattering porous or brittle aggregates, a covering over
6.3 Specimen Containers—Suitable containers made of a
the sample container may be appropriate to prevent operator
nonmetallic nonabsorbent material, resistant to thermal shock,
injury or oven damage. A cover of heavy paper toweling has
and not subject to changes in mass or shape when subjected to
been found satisfactory for this purpose. This also prevents
repeated heating, cooling, or cleaning. Porcelain evaporating
scattering of the test sample in the oven during the drying
dishes and standard borosilicate glass dishes perform satisfac-
cycle.
torily. Other containers, such as paper cups or plates, also have
been used satisfactorily; however, they may require pre-drying 7.6 Do not use metallic containers in a microwave oven
prior to use. because arcing and oven damage may result.
D4643
NOTE 5—In many cases, when working with a small sample containing
7.7 Observe manufacturer’s operating instructions when
a relatively large coarse-grained particle, it is appropriate not to include
installing and using the oven.
this particle in the test specimen. If this occurs, it should be noted in the
7.8 The placement of the test specimen directly on the glass
report of the results.
liner tray provided with some ovens is strongly discouraged.
9.4 When results of a water (moisture) content determina-
The concentrated heating of the specimen may result in the
tion by the use of this test method are to be compared to the
glass tray shattering, possibly causing injury to the operator.
results of another method, such as Test Method D 2216, a
8. Samples
second sample should be obtained during the selection of the
8.1 Keep the samples that are stored prior to testing in sample for this test method. Precautions should be taken to
noncorrodible airtight containers at a temperature between
obtain a sample of the same water (moisture) content. The
approximately 3 and 30°C in an area that prevents direct comparison sample should be processed as quickly as possible
exposure to sunlight. to avoid moisture losses.
8.2 Thewatercontentdeterminationshouldbeperformedas
soon as practical after sampling, especially if potentially
10. Conditioning
corrodible containers (such as steel thin-walled tubes, paint
10.1 Prepare and process the specimens as quickly as
cans, and the like) or unsealed sample bags are used.
possible to minimize unrecorded moisture loss that will result
in erroneous water content determinations.
9. Test Specimen
10.2 Cut or break up the soil into small size aggregations to
9.1 For water contents being determined as part of another
aid in obtaining more uniform drying of the specimen.
ASTM test method, the specimen selection process and tech-
10.3 If the specimens are not to be tested immediately, store
niques specified in that test method should be followed.
them in sealed containers to prevent loss of moisture.
9.2 The manner in which the test specimen is selected and
its required mass is basically dependent on the purpose
11. Procedure
(application) of the test, type of material being tested, and the
11.1 Determine the mass of a clean, dry container or dish,
type of sample (specimen from another test, bag, tube, split-
and record.
barrel, and the like). In all cases, however, a representative
11.2 Place the soil specimen in the container, and immedi-
portion of the total sample shall be selected. If a thinly layered
ately determine and record the mass.
soil or more than one soil type is encountered, select an
11.3 Place the soil and container in a microwave oven with
average portion or individual portions, or both, and note which
the heat sink and turn the oven on for 3 min. If experience with
portion(s) was tested in the report of the results.
a particular soil type and specimen size indicates shorter or
9.2.1 For bulk samples, select the test specimen from the
longer initial drying times can be used without overheating, the
material after it has been mixed thoroughly. The mass of moist
initial and subsequent drying times may be adjusted.
material selected shall be in accordance with Table 1.
9.2.2 For small (jar) samples, select a representative portion
NOTE 6—The 3-min initial setting is for a minimum sample mass of
in accordance with the following procedure: 100 g, as indicated in Table 1. Smaller samples are not recommended
when using the microwave oven because drying may be too rapid for
9.2.2.1 For cohesionless soils, mix thoroughly the material,
proper control. When very large samples are needed to represent soil
then select a test specimen having a mass of moist material in
containing large gravel particles, the sample may need to be split into
accordance wi
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