1、Designation: D 4643 00Standard Test Method forDetermination of Water (Moisture) Content of Soil by theMicrowave Oven Heating1This standard is issued under the fixed designation D 4643; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision
2、, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript 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 *1.1 This test method out
3、lines procedures for determining thewater (moisture) content of soils by incrementally drying soilin a microwave oven.1.2 This test method can be used as a substitute for TestMethod D 2216 when more rapid results are desired to expe-dite other phases of testing and slightly less accurate results are
4、acceptable.1.3 When questions of accuracy between this test methodand Test Method D 2216 arise, Test Method D 2216 shall bethe referee method.1.4 This test method is applicable for most soil types. Forsome soils, such as those containing significant amounts ofhalloysite, mica, montmorillonite, gypsu
5、m or other hydratedmaterials, highly organic soils, or soils in which the pore watercontains dissolved solids (such as salt in the case of marinedeposits), this test method may not yield reliable water contentvalues.1.5 The values stated in SI units are to be regarded as thestandard.1.6 This standar
6、d does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use. See Section 7.2. Referenced Do
7、cuments2.1 ASTM Standards:D 653 Terminology Relating to Soil, Rock, and ContainedFluids2D 2216 Test Method for Laboratory Determination of Water(Moisture) Content of Soil and Rock2D 3740 Practice for Minimum Requirements for AgenciesEngaged in the Testing and/or Inspection of Soil and Rockas Used in
8、 Engineering Design and Construction2D 4753 Specification for Evaluating, Selecting, and Speci-fying Balances and Scales for Use in Testing Soil, Rock,and Related Construction Materials23. Terminology3.1 Definitions:3.1.1 All definitions are in accordance with TerminologyD 653.3.2 Definitions of Ter
9、ms Specific to This Standard:3.2.1 microwave heatinga process by which heat is in-duced within a material due to the interaction between dipolarmolecules of the material and an alternating, high frequencyelectric field. Microwaves are electromagnetic waves with 1mm to 1 m wavelengths.3.2.2 water (mo
10、isture) contentthe ratio, expressed as apercentage, of the mass of “pore” or “free” water in a givenmass of soil to the mass of the solid particles.4. Summary of Test Method4.1 A moist soil specimen is placed in a suitable containerand its mass is determined. It is then placed in a microwaveoven, su
11、bjected to an interval of drying, and removed from theoven and its new mass is determined. This procedure isrepeated until the mass becomes nearly constant.4.2 The difference between the mass of the moist specimenand the dried specimen is used as the mass of water originallycontained in the specimen
12、. The water content is determined bydividing the mass of water by the dry mass of soil, multipliedby 100. For a given soil and sample size, the time to achieve aconstant dry mass can be noted and used as a minimum dryingtime for subsequent tests using the same size specimen of thesame soil.5. Signif
13、icance and Use5.1 The water content of a soil is used throughout geotech-nical engineering practice both in the laboratory and in thefield. The use of Test Method D 2216 for water contentdetermination can be time consuming and there are occasionswhen a more expedient method is desirable. The use of
14、amicrowave oven is one such method.5.2 The principal objection to the use of the microwaveoven for water-content determination has been the possibilityof overheating the soil, thereby yielding a water content higherthan would be determined by Test Method D 2216. While noteliminating this possibility
15、, the incremental drying procedure1This test method is under the jurisdiction of ASTM Committee D-18 on Soiland Rock and is the direct responsibility of Subcommittee D18.08 on Special andConstruction Control Tests.Current edition approved Feb. 10, 2000. Published April 2000. Originallypublished as D
16、4643 87. Last previous edition D4643 93.2Annual Book of ASTM Standards, Vol 04.08.1*A Summary of Changes section appears at the end of this standard.Copyright ASTM, 100 Barr Harbor Drive, West Conshohocken, PA 19428-2959, United States.described in this test method will minimize its effects. Somemic
17、rowave ovens have settings at less than full power, whichcan also be used to reduce overheating.5.3 The behavior of a soil, when subjected to microwaveenergy, is dependent on its mineralogical compositions, and asa result no one procedure is applicable for all types of soil.Therefore, the procedure
18、recommended in this test method ismeant to serve as a guide when using the microwave oven.5.4 This test method is best suited for minus No. 4 sizedmaterial. Larger size particles can be tested; however, caremust be taken because of the increased chance of particleshattering.5.5 The use of this metho
19、d may not be appropriate whenhighly accurate results are required, or the test using the data isextremely sensitive to moisture variations.5.6 Due to the localized high temperatures that the specimenis exposed to in microwave heating, the physical characteristicsof the soil may be altered. Degregati
20、on of individual particlesmay occur, along with vaporization or chemical transition. It istherefore recommended that samples used in this test methodnot be used for other tests subsequent to drying.NOTE 1The quality of the results produced by this test method isdependent on the competence of the per
21、sonnel performing it and thesuitability of the equipment and facilities used. Agencies that meet thecriteria of Practice D 3740 are generally considered capable of competentand objective testing. Users of this test method are cautioned thatcompliance with Practice D 3740 does not in itself ensure re
22、liable results.Reliable results depend on many factors; Practice D 3740 provides ameans of evaluating some of those factors.6. Apparatus6.1 Microwave OvenA microwave oven, preferably witha vented chamber, is suitable. The required size and powerrating of the oven is dependent on its intended use. Ov
23、ens withvariable power controls and input power ratings of about 700W have been found to be adequate for this use. Variable powercontrols are important and reduce the potential for overheatingof the test specimen.NOTE 2Microwave ovens equipped with built-in scales and computercontrols have been deve
24、loped for use in drying soils. Their use iscompatible with this test method.6.2 Balances, having a capacity of 2000 g or greater andmeeting the requirements of Specification D 4753 for a balanceof 0.1 g readability.6.3 Specimen ContainersSuitable containers made of anonmetallic nonabsorbent material
25、, resistant to thermal shock,and not subject to changes in mass or shape when subjected torepeated heating, cooling, or cleaning. Porcelain evaporatingdishes and standard borosilicate glass dishes perform satisfac-torily. Other containers, such as paper cups or plates, also havebeen used satisfactor
26、ily; however, they may require pre-dryingprior to use.6.4 Container Handling ApparatusA glove or holder,suitable for removing hot containers from the oven.6.5 DesiccatorA desiccator cabinet or jar of suitable sizecontaining silica gel, anhydrous calcium phosphate, or equiva-lent. It is preferable to
27、 use a desiccant that changes color toindicate that it needs reconstitution.6.6 Heat SinkA material or liquid placed in the micro-wave to absorb energy after the moisture has been driven fromthe test specimen. The heat sink reduces the possibility ofoverheating the specimen and damage to the oven. G
28、lassbeakers filled with water and materials that have a boiling pointabove water, such as nonflammable oils, have been usedsuccessfully. Moistened bricks have also been used.6.7 Stirring ToolsSpatulas, putty knives, and glass rodsfor cutting and stirring the test specimen before and during thetest.
29、Short lengths of glass rods have been found useful forstirring and may be left in the specimen container duringtesting, reducing the possibility of specimen loss due toadhesion to the stirring tool.7. Hazards7.1 Handle hot containers with a container holder. Some soiltypes can retain considerable he
30、at, and serious burns couldresult from improper handling.7.2 Suitable eye protection is recommended due to thepossibility of particle shattering during the heating, mixing, ormass determinations.7.3 Safety precautions supplied by the manufacturer of themicrowave should be observed. Particular attent
31、ion should bepaid to keeping the door sealing gasket and door interlocksclean and in good working condition.NOTE 3The use of a microwave oven for the drying of soils may beconsidered abusive by the manufacturers and consitute voiding of war-ranties. Microwave drying of soils containing metallic mate
32、rials maycause arcing in the oven. Highly organic soils and soils containing oils andcoal may ignite and burn during microwave drying. Continued operationof the oven after the soil has reached constant weight may also causedamage or premature failure of the microwave oven.NOTE 4When first introduced
33、, microwave ovens were reported toaffect heart pacemakers, primarily because of the operating frequencies ofthe two devices. Since that time, pacemakers have been redesigned, andthe microwave oven is not regarded as the health hazard it once was.However, it may be advisable to post warnings that a m
34、icrowave is in use.7.4 Highly organic soils and soils containing oil or othercontaminates may ignite into flames during microwave drying.Means for smothering flames to prevent operator injury or ovendamage should be available during testing. Fumes given offfrom contaminated soils or wastes may be to
35、xic, and the ovenshould be vented accordingly.7.5 Due to the possibility of steam explosions, or thermalstress shattering porous or brittle aggregates, a covering overthe sample container may be appropriate to prevent operatorinjury or oven damage. A cover of heavy paper toweling hasbeen found satis
36、factory for this purpose. This also preventsscattering of the test sample in the oven during the dryingcycle.7.6 Do not use metallic containers in a microwave ovenbecause arcing and oven damage may result.7.7 Observe manufacturers operating instructions wheninstalling and using the oven.7.8 The plac
37、ement of the test specimen directly on the glassliner tray provided with some ovens is strongly discouraged.The concentrated heating of the specimen may result in theglass tray shattering, possibly causing injury to the operator.8. Samples8.1 Keep the samples that are stored prior to testing inD 464
38、32noncorrodible airtight containers at a temperature betweenapproximately 3 and 30C in an area that prevents directexposure to sunlight.8.2 The water content determination should be performed assoon as practical after sampling, especially if potentiallycorrodible containers (such as steel thin-walle
39、d tubes, paintcans, and the like) or unsealed sample bags are used.9. Test Specimen9.1 For water contents being determined as part of anotherASTM test method, the specimen selection process and tech-niques specified in that test method should be followed.9.2 The manner in which the test specimen is
40、selected andits required mass is basically dependent on the purpose(application) of the test, type of material being tested, and thetype of sample (specimen from another test, bag, tube, split-barrel, and the like). In all cases, however, a representativeportion of the total sample shall be selected
41、. If a thinly layeredsoil or more than one soil type is encountered, select anaverage portion or individual portions, or both, and note whichportion(s) was tested in the report of the results.9.2.1 For bulk samples, select the test specimen from thematerial after it has been mixed thoroughly. The ma
42、ss of moistmaterial selected shall be in accordance with Table 1.9.2.2 For small (jar) samples, select a representative portionin accordance with the following procedure:9.2.2.1 For cohesionless soils, mix thoroughly the material,then select a test specimen having a mass of moist material inaccordan
43、ce with Table 1.9.2.2.2 For cohesive soils, remove about 3 mm of materialfrom the exposed periphery of the sample and slice theremaining specimen in half (to check if the material is layered),prior to selecting the test specimen. If the soil is layered, see9.2. The mass of moist material selected sh
44、ould be in accor-dance with Table 1, if coarse-grained particles are noted.Breaking or cutting of cohesive samples to approximately6-mm (14-in.) particles will speed drying and prevent crustingor the overheating of the surface while drying the interior.9.3 Using a test specimen smaller than the mini
45、mum massindicated previously requires discretion, though it may beadequate for the purpose of the test. A specimen having a massless than the previously indicated value shall be noted in thereport of the results.NOTE 5In many cases, when working with a small sample containinga relatively large coars
46、e-grained particle, it is appropriate not to includethis particle in the test specimen. If this occurs, it should be noted in thereport of the results.9.4 When results of a water (moisture) content determina-tion by the use of this test method are to be compared to theresults of another method, such
47、 as Test Method D 2216, asecond sample should be obtained during the selection of thesample for this test method. Precautions should be taken toobtain a sample of the same water (moisture) content. Thecomparison sample should be processed as quickly as possibleto avoid moisture losses.10. Conditioni
48、ng10.1 Prepare and process the specimens as quickly aspossible to minimize unrecorded moisture loss that will resultin erroneous water content determinations.10.2 Cut or break up the soil into small size aggregations toaid in obtaining more uniform drying of the specimen.10.3 If the specimens are no
49、t to be tested immediately, storethem in sealed containers to prevent loss of moisture.11. Procedure11.1 Determine the mass of a clean, dry container or dish,and record.11.2 Place the soil specimen in the container, and immedi-ately determine and record the mass.11.3 Place the soil and container in a microwave oven withthe heat sink and turn the oven on for 3 min. If experience witha particular soil type and specimen size indicates shorter orlonger initial drying times can be used without overheating, theinitial and subsequent drying times may be adjusted.NOTE 6The 3-m
