ASTM D4643-17

Standard Test Method for Determination of Water Content of Soil and Rock by Microwave Oven Heating

SIGNIFICANCE AND USE
5.1 The water content of a soil is used throughout geotechnical engineering practice both in the laboratory and in the field. The use of Test Method D2216 for water content determination can be time consuming and there are occasions when a more expedient method is desirable. The use of a microwave oven is one such method.  
5.2 The principal objection to the use of the microwave oven for water-content determination has been the possibility of overheating the soil, thereby yielding a water content higher than would be determined by Test Method D2216. While not eliminating this possibility, the incremental drying procedure described in this test method will minimize its effects. Some microwave ovens have settings at less than full power, which can also be used to reduce overheating.  
5.3 The behavior of a soil, when subjected to microwave energy, is dependent on its mineralogical compositions, and as a result no one procedure is applicable for all types of soil. Therefore, the procedure recommended in this test method is meant to serve as a guide when using the microwave oven.  
5.4 This test method is best suited for minus 4.75-mm (No. 4) sieve sized material. Larger size particles can be tested; however, care must be taken because of the increased chance of particle shattering.  
5.5 The use of this method may not be appropriate when highly accurate results are required, or the test using the data is extremely sensitive to moisture variations.  
5.6 Due to the localized high temperatures that the specimen is exposed to in microwave heating, the physical characteristics of the soil may be altered. Degregation of individual particles may occur, along with vaporization or chemical transition. It is therefore recommended that samples used in this test method not be used for other tests subsequent to drying.
Note 1: The quality of the results produced by this test method is dependent on the competence of the personnel performing it and the suitability of the equi...
SCOPE
1.1 This test method outlines procedures for determining the water content of soils by incrementally drying soil in a microwave oven.  
1.2 This test method can be used as a substitute for Test Method D2216 when more rapid results are desired to expedite other phases of testing and slightly less accurate results are acceptable.  
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 significant amounts of dissolved solids (such as salt in the case of marine deposits), this test method may not yield reliable water content values due to the potential for heating above 110°C or lack of means to account for the presence of precipitated solids that were previously dissolved.  
1.5 The values stated in SI units are to be regarded as the standard. Performance of the test method utilizing another system of units shall not be considered non-conformance. The sieve designations are identified using the “standard” system in accordance with Specification E11, such as 2.0-mm and 19-mm, followed by the “alternative” system of No. 10 and 3/4-in., respectively, in parentheses.  
1.6 All observed and calculated values shall conform to the guidelines for significant digits and rounding established in Practice D6026, unless otherwise superseded by this standard.  
1.6.1 The procedures used to specify how data are collected/recorded or calculated in this standard are regarded as the industry standard. In addition, they are representative of the significant digits that generally should be retained. The procedures used do not consider material variation, purpose for obtaining the data, special purpose studies...

General Information

• Status: Published
• Publication Date: 31-Jan-2017
• ICS: 13.080.40 - Hydrological properties of soils
• Technical Committee: D18 - Soil and Rock
• Drafting Committee: D18.08 - Special and Construction Control Tests

Relations

• Replaces: ASTM D4643-08 - Standard Test Method for Determination of Water (Moisture) Content of Soil by Microwave Oven Heating
• Effective Date: 01-Feb-2017
• Refers: ASTM D4753-24 - Standard Guide for Evaluating, Selecting, and Specifying Balances and Standard Masses for Use in Soil, Rock, and Construction Materials Testing
• Effective Date: 01-Feb-2024
• Refers: ASTM D3740-23 - Standard Practice for Minimum Requirements for Agencies Engaged in Testing and/or Inspection of Soil and Rock as Used in Engineering Design and Construction
• Effective Date: 01-Nov-2023
• Refers: ASTM D3740-19 - Standard Practice for Minimum Requirements for Agencies Engaged in Testing and/or Inspection of Soil and Rock as Used in Engineering Design and Construction
• Effective Date: 01-Oct-2019
• Refers: ASTM D4753-15 - Standard Guide for Evaluating, Selecting, and Specifying Balances and Standard Masses for Use in Soil, Rock, and Construction Materials Testing
• Effective Date: 01-May-2015
• Refers: ASTM D653-14 - Standard Terminology Relating to Soil, Rock, and Contained Fluids
• Effective Date: 01-Aug-2014
• Refers: ASTM E11-13 - Standard Specification for Woven Wire Test Sieve Cloth and Test Sieves
• Effective Date: 01-Oct-2013
• Refers: ASTM D3740-12a - Standard Practice for Minimum Requirements for Agencies Engaged in Testing and/or Inspection of Soil and Rock as Used in Engineering Design and Construction
• Effective Date: 01-May-2012
• Refers: ASTM D3740-12 - Standard Practice for Minimum Requirements for Agencies Engaged in Testing and/or Inspection of Soil and Rock as Used in Engineering Design and Construction
• Effective Date: 01-Mar-2012
• Refers: ASTM D653-11 - Standard Terminology Relating to Soil, Rock, and Contained Fluids
• Effective Date: 01-Sep-2011
• Refers: ASTM D3740-11 - Standard Practice for Minimum Requirements for Agencies Engaged in Testing and/or Inspection of Soil and Rock as Used in Engineering Design and Construction
• Effective Date: 01-Sep-2011
• Refers: ASTM D2216-10 - Standard Test Methods for Laboratory Determination of Water (Moisture) Content of Soil and Rock by Mass
• Effective Date: 01-Jul-2010
• Refers: ASTM D3740-10 - Standard Practice for Minimum Requirements for Agencies Engaged in Testing and/or Inspection of Soil and Rock as Used in Engineering Design and Construction
• Effective Date: 01-Mar-2010
• Refers: ASTM E11-09e1 - Standard Specification for Woven Wire Test Sieve Cloth and Test Sieves
• Effective Date: 01-May-2009
• Refers: ASTM D653-09 - Standard Terminology Relating to Soil, Rock, and Contained Fluids
• Effective Date: 01-Jan-2009

Overview

ASTM D4643-17, titled "Standard Test Method for Determination of Water Content of Soil and Rock by Microwave Oven Heating," is a geotechnical engineering standard issued by ASTM International. This standard specifies procedures for determining the water content of soil and rock using incremental drying in a microwave oven. Compared to traditional oven drying (such as ASTM D2216), microwave oven drying is a faster alternative, providing timely results needed in both laboratory and field settings when rapid water content determination is beneficial and marginally reduced accuracy is acceptable.

Understanding soil water content is essential in site investigations, construction materials testing, and geotechnical analysis. The use of microwave oven heating offers a more expedient solution for water content measurements, especially when project schedules demand quicker data turnaround.

Key Topics

• Purpose: Provides a rapid method for measuring the water (moisture) content of soil and rock samples by drying them in a microwave oven.
• Scope: Applicable to most soil types and some rock specimens, particularly those passing the 4.75-mm (No. 4) sieve.
• Limitations: Caution should be exercised with soils containing high levels of organic matter, certain clay minerals (e.g., halloysite, mica, montmorillonite, gypsum), or significant dissolved salts, since microwave drying can introduce inaccuracies for these materials.
• Incremental Drying: Emphasizes an incremental approach to minimize overheating and physical alteration of the sample, which can otherwise result in higher water content readings or particle breakdown.
• Sample Preparation: Recommends thorough mixing, proper sample sizing, and careful handling to maintain sample integrity and representativeness.
• Apparatus Requirements: Details the use of microwave ovens with adjustable power settings, microwave-safe containers, and appropriate balances in accordance with related ASTM standards.
• Safety Considerations: Addresses hazards such as hot containers, possible sample ignition, glass breakage, and the need for adequate personal protection and proper oven maintenance.

Applications

• Geotechnical Investigations: Used for expedient determination of soil moisture in site characterization, soil classification, and material specification.
• Construction Quality Control: Provides rapid feedback on water content during compaction control of earthworks or aggregate placement, supporting real-time field decisions.
• Materials Testing Labs: Enables faster throughput of soil and rock samples where a slight trade-off in absolute accuracy is permissible.
• Educational and Research Use: Serves as a practical method for comparative testing or where equipment resources are limited.

While ASTM D4643-17 offers significant time savings, it is not recommended where the highest accuracy is essential or for follow-up tests on the same sample, as the physical and chemical properties of the soil may be altered during microwave drying.

Related Standards

• ASTM D2216: Standard Test Methods for Laboratory Determination of Water (Moisture) Content of Soil and Rock by Mass - often used as the reference method for accuracy.
• ASTM D653: Terminology Relating to Soil, Rock, and Contained Fluids.
• ASTM E11: Specification for Woven Wire Test Sieve Cloth and Test Sieves.
• ASTM D4220: Practices for Preserving and Transporting Soil Samples.
• ASTM D3740: Practice for Minimum Requirements for Agencies Engaged in Testing and/or Inspection of Soil and Rock.
• ASTM D6026: Practice for Using Significant Digits in Geotechnical Data.

For projects where rapid soil moisture content assessment is necessary, ASTM D4643-17 is a valuable resource. By adhering to this standard, laboratories and field technicians can obtain timely water content data while balancing the need for expedience and reliability. Proper implementation, attention to sample-specific behavior, and awareness of related standards will help ensure accurate results and support successful geotechnical engineering outcomes.

Standards Content (Sample)

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.
Designation: D4643 − 17
Standard Test Method for
Determination of Water Content of Soil and Rock by
Microwave Oven Heating
This standard is issued under the fixed designation D4643; 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 (´) indicates an editorial change since the last revision or reapproval.
This standard has been approved for use by agencies of the U.S. Department of Defense.
1. Scope* dures used do not consider material variation, purpose for
obtaining the data, special purpose studies, or any consider-
1.1 Thistestmethodoutlinesproceduresfordeterminingthe
ations for the user’s objectives; and it is common practice to
water content of soils by incrementally drying soil in a
increase or reduce significant digits of reported data to be
microwave oven.
commensuratewiththeseconsiderations.Itisbeyondthescope
1.2 This test method can be used as a substitute for Test
of this standard to consider significant digits used in analysis
Method D2216 when more rapid results are desired to expedite
methods for engineering design.
other phases of testing and slightly less accurate results are
1.6.2 Significant digits are especially important if the water
acceptable.
content will be used to calculate other relationships such as
moist mass to dry mass or vice versa, wet unit weight to dry
1.3 When questions of accuracy between this test method
and Test Method D2216 arise, Test Method D2216 shall be the unit weight or vice versa, and total density to dry density or
vice versa. For example, if four significant digits are required
referee method.
in any of the above calculations, then the water content has to
1.4 This test method is applicable for most soil types. For
be recorded to the nearest 0.1 %, for water contents below
some soils, such as those containing significant amounts of
100 %. This occurs since 1 plus the water content (not in
halloysite, mica, montmorillonite, gypsum or other hydrated
percent) will have four significant digits regardless of what the
materials, highly organic soils, or soils in which the pore water
value of the water content is (below 100 %); that is, 1 plus
contains significant amounts of dissolved solids (such as salt in
0.1/100 = 1.001, a value with four significant digits. While, if
the case of marine deposits), this test method may not yield
three significant digits are acceptable, then the water content
reliable water content values due to the potential for heating
can be recorded to the nearest 1 %.
above 110°C or lack of means to account for the presence of
1.7 This standard does not purport to address all of the
precipitated solids that were previously dissolved.
safety concerns, if any, associated with its use. It is the
1.5 The values stated in SI units are to be regarded as the
responsibility of the user of this standard to establish appro-
standard. Performance of the test method utilizing another
priate safety and health practices and determine the applica-
system of units shall not be considered non-conformance. The
bility of regulatory limitations prior to use. See Section 7.
sieve designations are identified using the “standard” system in
accordance with Specification E11, such as 2.0-mm and
2. Referenced Documents
19-mm, followed by the “alternative” system of No. 10 and
2.1 ASTM Standards:
⁄4-in., respectively, in parentheses.
D653 Terminology Relating to Soil, Rock, and Contained
1.6 All observed and calculated values shall conform to the
Fluids
guidelines for significant digits and rounding established in
D2216 Test Methods for Laboratory Determination of Water
Practice D6026, unless otherwise superseded by this standard.
(Moisture) Content of Soil and Rock by Mass
1.6.1 Theproceduresusedtospecifyhowdataarecollected/
D3740 Practice for Minimum Requirements for Agencies
recorded or calculated in this standard are regarded as the
Engaged in Testing and/or Inspection of Soil and Rock as
industry standard. In addition, they are representative of the
Used in Engineering Design and Construction
significant digits that generally should be retained. The proce-
D4220 Practices for Preserving and Transporting Soil
Samples
ThistestmethodisunderthejurisdictionofASTMCommitteeD18onSoiland
Rock and is the direct responsibility of Subcommittee D18.08 on Special and For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Construction Control Tests. contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
Current edition approved Feb. 1, 2017. Published February 2017. Originally Standards volume information, refer to the standard’s Document Summary page on
approved in 1987. Last previous edition approved in 2008 as D4643 – 08. the ASTM website. DOI: 10.1520/D4643-08.
*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 − 17
D4753 Guide for Evaluating, Selecting, and Specifying Bal- Therefore, the procedure recommended in this test method is
ances and Standard Masses for Use in Soil, Rock, and meant to serve as a guide when using the microwave oven.
Construction Materials Testing
5.4 This test method is best suited for minus 4.75-mm (No.
D5079 Practices for Preserving and Transporting Rock Core
4) sieve sized material. Larger size particles can be tested;
Samples (Withdrawn 2017)
however,caremustbetakenbecauseoftheincreasedchanceof
D6026 Practice for Using Significant Digits in Geotechnical
particle shattering.
Data
5.5 The use of this method may not be appropriate when
E11 Specification for Woven Wire Test Sieve Cloth and Test
highly accurate results are required, or the test using the data is
Sieves
extremely sensitive to moisture variations.
3. Terminology
5.6 Duetothelocalizedhightemperaturesthatthespecimen
3.1 Definitions:
isexposedtoinmicrowaveheating,thephysicalcharacteristics
3.1.1 For definitions of common technical terms used in this of the soil may be altered. Degregation of individual particles
standard, refer to Terminology D653. may occur, along with vaporization or chemical transition. It is
3.2 Definitions of Terms Specific to This Standard:
therefore recommended that samples used in this test method
3.2.1 microwave heating—a process by which heat is in- not be used for other tests subsequent to drying.
duced within a material due to the interaction between dipolar
NOTE 1—The quality of the results produced by this test method is
molecules of the material and an alternating, high frequency
dependent on the competence of the personnel performing it and the
electric field. Microwaves are electromagnetic waves with 1
suitability of the equipment and facilities used. Agencies that meet the
mm to 1 m wavelengths. 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 results.
4. Summary of Test Method
Reliableresultsdependonmanyfactors;PracticeD3740providesameans
4.1 A moist soil specimen is placed in a suitable container
of evaluating some of those factors.
and its mass is determined. It is then placed in a microwave
oven, subjected to an interval of drying, and removed from the
6. Apparatus
oven and its new mass is determined. This procedure is
6.1 Microwave Oven—Amicrowaveoven,preferablywitha
repeated until the mass becomes nearly constant.
vented chamber, is suitable.The required size and power rating
4.2 The difference between the mass of the moist specimen
of the oven is dependent on its intended use. Ovens with
and the dried specimen is used as the mass of water originally
variable power controls and input power ratings of about 700
contained in the specimen. The water content is determined by
W have been found to be adequate for this use. Variable power
dividing the mass of water by the dry mass of soil, multiplied
controls are important and reduce the potential for overheating
by 100. For a given soil and sample size, the time to achieve a
of the test specimen.
constant dry mass can be noted and used as a minimum drying
NOTE 2—Microwave ovens equipped with built-in scales and computer
time for subsequent tests using the same size specimen of the
controls have been developed for use in drying soils. Their use is
same soil.
compatible with this test method.
6.2 Balances—All balances must meet the requirements of
5. Significance and Use
Specification D4753 and this section. A Class GP2 balance of
5.1 The water content of a soil is used throughout geotech-
0.1 g readability is generally required. However, the balance
nical engineering practice both in the laboratory and in the
used may be controlled by the number of significant digits
field. The use of Test Method D2216 for water content
needed (see 1.6).
determination can be time consuming and there are occasions
6.3 Specimen Containers—Suitable, microwave safe con-
when a more expedient method is desirable. The use of a
tainers made of a nonmetallic nonabsorbent material, resistant
microwave oven is one such method.
to thermal shock, and not subject to changes in mass or shape
5.2 The principal objection to the use of the microwave
when subjected to repeated heating, cooling, or cleaning.
oven for water-content determination has been the possibility
Porcelain evaporating dishes and standard borosilicate glass
of overheating the soil, thereby yielding a water content higher
dishes perform satisfactorily. Other containers, such as paper
than would be determined by Test Method D2216. While not
cups or plates, also have been used satisfactorily; however,
eliminating this possibility, the incremental drying procedure
they may require pre-drying prior to use.
described in this test method will minimize its effects. Some
microwave ovens have settings at less than full power, which 6.4 Container Handling Apparatus—A glove or holder,
suitable for removing hot containers from the oven.
can also be used to reduce overheating.
5.3 The behavior of a soil, when subjected to microwave 6.5 Desiccator (optional)—A desiccator cabinet or jar of
energy, is dependent on its mineralogical compositions, and as
suitable size containing silica gel, anhydrous calcium
a result no one procedure is applicable for all types of soil. phosphate, or equivalent. It is preferable to use a desiccant that
changes color to indicate that it needs reconstitution.
6.6 Heat Sink—Amaterialorliquidplacedinthemicrowave
The last approved version of this historical standard is referenced on
www.astm.org. to absorb energy after the moisture has been driven from the
D4643 − 17
test specimen. The heat sink reduces the possibility of over- 8. Samples
heating the specimen and damage to the oven. Glass beakers
8.1 Soil samples shall be preserved and transported in
filled with water and materials that have a boiling point above
accordance with Practice D4220 Section 8, Groups B, C, or D.
water, such as nonflammable oils, have been used successfully.
Rock samples shall be preserved and transported in accordance
Moistened bricks have also been used.
with Practice D5079 Section 7.5.2, Special Care Rock. Keep
the samples that are stored prior to testing in noncorrodible
6.7 Stirring Tools—Spatulas, putty knives, and glass rods
airtight containers at a temperature between approximately 3
for cutting, breaking up, and stirring the test specimen before
and 30°C and in an area that prevents direct contact with
andduringthetest.Shortlengthsofglassrodshavebeenfound
sunlight. Disturbed samples in jars or other containers shall be
useful for stirring and may be left in the specimen container
stored in such a way to minimize moisture condensation on the
during testing, reducing the possibility of specimen loss due to
insides of the containers.
adhesion to the stirring tool.
8.2 Thewatercontentdeterminationshouldbeperformedas
7. Hazards
soon as practical after sampling, especially if potentially
corrodible containers (such as steel thin-walled tubes, paint
7.1 Handlehotcontainerswithacontainerholder.Somesoil
cans, and the like) or unsealed sample bags are used.
types can retain considerable heat, and serious burns could
result from improper handling.
9. Test Specimen
7.2 Suitable eye protection is recommended due to the
9.1 For water contents being determined as part of another
possibility of particle shattering during the heating, mixing, or
ASTM test method, the specimen selection process, specimen
mass determinations.
mass requirement, and techniques specified in that test method
shallbefollowed.Ifnominimumspecimenmassisprovidedin
7.3 Safety precautions supplied by the manufacturer of the
that method then the values given in Table 1 below shall apply.
microwave should be observed. Particular attention should be
paid to keeping the door sealing gasket and door interlocks
9.2 For those samples consisting entirely of rock or gravel-
clean and in good working condition.
sized aggregate, the minimum specimen mass shall be 500 g.
Representative portions of the sample may be broken into
NOTE 3—The use of a microwave oven for the drying of soils may be
smaller particles.
considered abusive by the manufacturers and constitute voiding of
warranties. Microwave drying of soils containing metallic materials may
9.3 Using a test specimen smaller than the minimum mass
causearcingintheoven.Highlyorganicsoilsandsoilscontainingoilsand
indicated previously requires discretion, though it may be
coal may ignite and burn during microwave drying. Continued operation
adequate for the purpose of the test.Aspecimen having a mass
of the oven after the soil has reached constant weight may also cause
damage or premature failure of the microwave oven.
less than the previously indicated value shall be noted in the
NOTE 4—When first introduced, microwave ovens were reported to
report of the results.
affect heart pacemakers, primarily because of the operating frequencies of
9.4 In many cases, when working with a small sample
the two devices. Since that time, pacemakers have been redesigned, and
the microwave oven is not regarded as the health hazard it once was. containing a relatively large coarse-grained particle, it is
However, it may be advisable to post warnings that a microwave is in use.
appropriate not to include this particle in the test specimen. If
this occurs, it should be noted in the report of the results.
7.4 Highly organic soils and soils containing oil or other
contaminates may ignite into flames during microwave drying.
9.5 When the test specimen is a portion of a larger amount
Meansforsmotheringflamestopreventoperatorinjuryoroven
of material,
...

This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: D4643 − 08 D4643 − 17
Standard Test Method for
Determination of Water (Moisture) Content of Soil and Rock
by Microwave Oven Heating
This standard is issued under the fixed designation D4643; 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 (´) indicates an editorial change since the last revision or reapproval.
This standard has been approved for use by agencies of the U.S. Department of Defense.
1. 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 can be used as a substitute for Test Method D2216 when more rapid results are desired to expedite other
phases of testing and slightly less accurate results are acceptable.
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
significant amounts of dissolved solids (such as salt in the case of marine deposits), this test method may not yield reliable water
content values.values due to the potential for heating above 110°C or lack of means to account for the presence of precipitated
solids that were previously dissolved.
1.5 The values stated in SI units are to be regarded as the standard. No other units Performance of the test method utilizing
another system of units shall not be considered non-conformance. The sieve designations are identified using the “standard” system
in accordance with Specification E11of measurement are included, such as 2.0-mm and 19-mm, followed by the “alternative”
system of No. 10 and ⁄4in this test method. -in., respectively, in parentheses.
1.6 Refer to All observed and calculated values shall conform to the guidelines for significant digits and rounding established
in Practice D6026 for guidance concerning the use of significant figures. This is especially important if the water content will be
used to calculate other relationships such as moist mass to dry mass or vice versa, wet unit weight to dry unit weight or vice versa,
and total density to dry density or vice versa. For example, if four significant digits are required in any of the above calculations,
then the water content has to be recorded to the nearest 0.1 %. This occurs since 1 plus the water content (not in percent) will have
four significant digits regardless of what the value of the water content is; that is, 1 plus 0.1/100 = 1.001, a value with four
significant digits. While, if three significant digits are acceptable, then the water content can be recorded to the nearest 1 %., unless
otherwise superseded by this standard.
1.6.1 The procedures used to specify how data are collected/recorded or calculated in this standard are regarded as the industry
standard. In addition, they are representative of the significant digits that generally should be retained. The procedures used do not
consider material variation, purpose for obtaining the data, special purpose studies, or any considerations for the user’s objectives;
and it is common practice to increase or reduce significant digits of reported data to be commensurate with these considerations.
It is beyond the scope of this standard to consider significant digits used in analysis methods for engineering design.
1.6.2 Significant digits are especially important if the water content will be used to calculate other relationships such as moist
mass to dry mass or vice versa, wet unit weight to dry unit weight or vice versa, and total density to dry density or vice versa.
For example, if four significant digits are required in any of the above calculations, then the water content has to be recorded to
the nearest 0.1 %, for water contents below 100 %. This occurs since 1 plus the water content (not in percent) will have four
significant digits regardless of what the value of the water content is (below 100 %); that is, 1 plus 0.1/100 = 1.001, a value with
four significant digits. While, if three significant digits are acceptable, then the water content can be recorded to the nearest 1 %.
This test method is under the jurisdiction of ASTM Committee D18 on Soil and Rock and is the direct responsibility of Subcommittee D18.08 on Special and Construction
Control Tests.
Current edition approved Jan. 1, 2008Feb. 1, 2017. Published February 2008February 2017. Originally approved in 1987. Last previous edition approved in 20002008
as D4643 – 00.D4643 – 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 − 17
1.7 This standard does not purport to address all of the safety concerns, 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.
2. Referenced Documents
2.1 ASTM Standards:
D653 Terminology Relating to Soil, Rock, and Contained Fluids
D2216 Test Methods for Laboratory Determination of Water (Moisture) Content of Soil and Rock by Mass
D3740 Practice for Minimum Requirements for Agencies Engaged in Testing and/or Inspection of Soil and Rock as Used in
Engineering Design and Construction
D4220 Practices for Preserving and Transporting Soil Samples
D4753 Guide for Evaluating, Selecting, and Specifying Balances and Standard Masses for Use in Soil, Rock, and Construction
Materials Testing
D5079 Practices for Preserving and Transporting Rock Core Samples (Withdrawn 2017)
D6026 Practice for Using Significant Digits in Geotechnical Data
E11 Specification for Woven Wire Test Sieve Cloth and Test Sieves
3. Terminology
3.1 Definitions:
3.1.1 All definitions are in accordance with For definitions of common technical terms used in this standard, refer to
Terminology D653.
3.2 Definitions of Terms Specific to This Standard:
3.2.1 microwave heating—a process by which heat is induced within a material due to the interaction between dipolar molecules
of the material and an alternating, high frequency electric field. Microwaves are electromagnetic waves with 1 mm to 1 m
wavelengths.
3.2.2 water (moisture) content—the ratio, expressed as a percentage, of the mass of “pore” or “free” water in a given mass of
soil to the mass of the solid particles.
4. Summary of Test Method
4.1 A moist soil specimen is placed in a suitable container and its mass is determined. It is then placed in a microwave oven,
subjected to an interval of drying, and removed from the oven and its new mass is determined. This procedure is repeated until
the mass becomes nearly constant.
4.2 The difference between the mass of the moist specimen and the dried specimen is used as the mass of water originally
contained in the specimen. The water content is determined by dividing the mass of water by the dry mass of soil, multiplied by
100. For a given soil and sample size, the time to achieve a constant dry mass can be noted and used as a minimum drying time
for subsequent tests using the same size specimen of the same soil.
5. Significance and Use
5.1 The water content of a soil is used throughout geotechnical engineering practice both in the laboratory and in the field. The
use of Test Method D2216 for water content determination can be time consuming and there are occasions when a more expedient
method is desirable. The use of a microwave oven is one such method.
5.2 The principal objection to the use of the microwave oven for water-content determination has been the possibility of
overheating the soil, thereby yielding a water content higher than would be determined by Test Method D2216. While not
eliminating this possibility, the incremental drying procedure described in this test method will minimize its effects. Some
microwave ovens have settings at less than full power, which can also be used to reduce overheating.
5.3 The behavior of a soil, when subjected to microwave energy, is dependent on its mineralogical compositions, and as a result
no one procedure is applicable for all types of soil. Therefore, the procedure recommended in this test method is meant to serve
as a guide when using the microwave oven.
5.4 This test method is best suited for minus No. 4 4.75-mm (No. 4) sieve sized material. Larger size particles can be tested;
however, care must be taken because of the increased chance of particle shattering.
5.5 The use of this method may not be appropriate when highly accurate results are required, or the test using the data is
extremely sensitive to moisture variations.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website. DOI: 10.1520/D4643-08.
The last approved version of this historical standard is referenced on www.astm.org.
D4643 − 17
5.6 Due to the localized high temperatures that the specimen is exposed to in microwave heating, the physical characteristics
of the soil may be altered. Degregation of individual particles may occur, along with vaporization or chemical transition. It is
therefore recommended that samples used in this test method not be used for other tests subsequent to drying.
NOTE 1—The quality of the results produced by 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 results. Reliable results depend on many
factors; Practice D3740 provides a means of evaluating some of those factors.
6. Apparatus
6.1 Microwave Oven—A microwave oven, preferably with a vented chamber, is suitable. The required size and power rating of
the oven is dependent on its intended use. Ovens with variable power controls and input power ratings of about 700 W have been
found to be adequate for this use. Variable power controls are important and reduce the potential for overheating of the test
specimen.
NOTE 2—Microwave ovens equipped with built-in scales and computer controls have been developed for use in drying soils. Their use is compatible
with this test method.
6.2 Balances, Balances—having a capacity of 2000 g or greater and meeting All balances must meet the requirements of
Specification D4753 for a and this section. A Class GP2 balance of 0.1 g readability.readability is generally required. However,
the balance used may be controlled by the number of significant digits needed (see 1.6).
6.3 Specimen Containers—Suitable Suitable, microwave safe containers made of a nonmetallic nonabsorbent material, resistant
to thermal shock, and not subject to changes in mass or shape when subjected to repeated heating, cooling, or cleaning. Porcelain
evaporating dishes and standard borosilicate glass dishes perform satisfactorily. Other containers, such as paper cups or plates, also
have been used satisfactorily; however, they may require pre-drying prior to use.
6.4 Container Handling Apparatus—A glove or holder, suitable for removing hot containers from the oven.
6.5 Desiccator—Desiccator (optional)—A desiccator cabinet or jar of suitable size containing silica gel, anhydrous calcium
phosphate, or equivalent. It is preferable to use a desiccant that changes color to indicate that it needs reconstitution.
6.6 Heat Sink—A material or liquid placed in the microwave to absorb energy after the moisture has been driven from the test
specimen. The heat sink reduces the possibility of overheating the specimen and damage to the oven. Glass beakers filled with
water and materials that have a boiling point above water, such as nonflammable oils, have been used successfully. Moistened
bricks have also been used.
6.7 Stirring Tools—Spatulas, putty knives, and glass rods for cutting cutting, breaking up, and stirring the test specimen before
and during the test. Short lengths of glass rods have been found useful for stirring and may be left in the specimen container during
testing, reducing the possibility of specimen loss due to adhesion to the stirring tool.
7. Hazards
7.1 Handle hot containers with a container holder. Some soil types can retain considerable heat, and serious burns could result
from improper handling.
7.2 Suitable eye protection is recommended due to the possibility of particle shattering during the heating, mixing, or mass
determinations.
7.3 Safety precautions supplied by the manufacturer of the microwave should be observed. Particular attention should be paid
to keeping the door sealing gasket and door interlocks clean and in good working condition.
NOTE 3—The use of a microwave oven for the drying of soils may be considered abusive by the manufacturers and constitute voiding of warranties.
Microwave drying of soils containing metallic materials may cause arcing in the oven. Highly organic soils and soils containing oils and coal may ignite
and burn during microwave drying. Continued operation of the oven after the soil has reached constant weight may also cause damage or premature failure
of the microwave oven.
NOTE 4—When first introduced, microwave ovens were reported to affect heart pacemakers, primarily because of the operating frequencies of the two
devices. Since that time, pacemakers have been redesigned, and the microwave oven is not regarded as the health hazard it once was. However, it may
be advisable to post warnings that a microwave is in use.
7.4 Highly organic soils and soils containing oil or other contaminates may ignite into flames during microwave drying. Means
for smothering flames to prevent operator injury or oven damage should be available during testing. Fumes given off from
contaminated soils or wastes may be toxic, and the oven should be vented accordingly.
7.5 Due to the possibility of steam explosions, or thermal stress shattering porous or brittle aggregates, a covering over the
sample container may be appropriate to prevent operator injury or oven damage. A cover of heavy paper toweling has been found
satisfactory for this purpose. This also prevents scattering of the test sample in the oven during the drying cycle.
7.6 Do not use metallic containers in a microwave oven because arcing and oven damage may result.
7.7 Observe manufacturer’s operating instructions when installing and using the oven.
D4643 − 17
7.8 The placement of the test specimen directly on the glass liner tray provided with some ovens is strongly discouraged. The
concentrated heating of the specimen may result in the glass tray shattering, possibly causing injury to the operator.
8. Samples
8.1 Soil samples shall be preserved and transported in accordance with Practice D4220 Section 8, Groups B, C, or D. Rock
samples shall be preserved and transported in accordance with Practice D5079 Section 7.5.2, Special Care Rock. Keep the samples
that are stored prior to testing in non-corrodiblenoncorrodible airtight containers at a temperature between approximately 3 and
30°C and in an area that prevents direct exposure to sunlight.contact with sunlight. Disturbed samples in jars or other containers
shall be stored in such a way to minimize moisture condensation on the insides of the containers.
8.2 The water content determination should be performed as soon as practical after sampling, especially if potentially corrodible
containers (such as steel thin-walled tubes, paint cans, and the like) or unsealed sample bags are used.
9. Test Specimen
9.1 For water contents being determined as part of another ASTM test method, the specimen selection process, specimen mass
requirement, and techniques specified in that test method shall be followed. If no minimum specimen mass is provided in that
method then the values given in Table 1 below shall apply.
9.2 The manner in which the test specimen is selected and its required mass is basically dependent on the purpose (application)
of the test, type of material being tested, and the type of sample (specimen from another test, bag, tube, split-barrel, and the like).
In all cases, however, a representative portion of the total sample shall be selected. If a thinly layered soil or more than one soil
type is encountered, select an average portion or individual portions, or both, and note which portion(s) was tested in the report
of the results.For those samples consisting entirely of rock or gravel-sized aggregate, the minimum specimen mass shall be 500
g. Representative portions of the sample may be broken into smaller particles.
9.2.1 For bulk samples, select the test specimen from the material after it has been mixed thoroughly. The mass of moist material
selected shall be in accordance with Table 1.
9.2.2 For small (jar) samples, select a representative portion in accordance with the following procedure:
9.2.2.1 For cohesionless soils, mix thoroughly the material, an
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