1、Designation: D 4643 08Standard Test Method forDetermination of Water (Moisture) Content of Soil byMicrowave 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, th
2、e 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 outlines
3、 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 areaccep
4、table.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, gypsum or
5、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. No other units of me
6、asurement are included in thistest method.1.6 Refer to Practice D 6026 for guidance concerning theuse of significant figures. This is especially important if thewater content will be used to calculate other relationships suchas moist mass to dry mass or vice versa, wet unit weight to dryunit weight
7、or vice versa, and total density to dry density orvice versa. For example, if four significant digits are requiredin any of the above calculations, then the water content has tobe recorded to the nearest 0.1 %. This occurs since 1 plus thewater content (not in percent) will have four significant dig
8、itsregardless of what the value of the water content is; that is, 1plus 0.1/100 = 1.001, a value with four significant digits.While, if three significant digits are acceptable, then the watercontent can be recorded to the nearest 1 %.1.7 This standard does not purport to address all of thesafety con
9、cerns, 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 Documents2.1 ASTM Standards:2D 653 Terminology Relat
10、ing to Soil, Rock, and ContainedFluidsD 2216 Test Methods for Laboratory Determination of Wa-ter (Moisture) Content of Soil and Rock by MassD 3740 Practice for Minimum Requirements for AgenciesEngaged in the Testing and/or Inspection of Soil and Rockas Used in Engineering Design and ConstructionD 47
11、53 Guide for Evaluating, Selecting, and SpecifyingBalances and Standard Masses for Use in Soil, Rock, andConstruction Materials TestingD 6026 Practice for Using Significant Digits in Geotechni-cal Data3. Terminology3.1 Definitions:3.1.1 All definitions are in accordance with TerminologyD 653.3.2 Def
12、initions of Terms 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.
13、3.2.2 water (moisture) 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 mi
14、crowaveoven, subjected to an interval of drying, and removed from the1This test method is under the jurisdiction ofASTM Committee D18 on Soil andRock and is the direct responsibility of Subcommittee D18.08 on Special andConstruction Control Tests.Current edition approved Jan. 1, 2008. Published Febr
15、uary 2008. Originallyapproved in 1987. Last previous edition approved in 2000 as D 4643 00.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Su
16、mmary page onthe ASTM website.1*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.oven and its new mass is determined. This procedure isrepeated until the mass becomes nea
17、rly 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. 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
18、 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. Significance and Use5.1 The water content of a soil is used throughout geotech-nical engineering practice both in the laboratory and in thefield. The
19、 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 amicrowave oven is one such method.5.2 The principal objection to the use of the microwaveoven for water-content determination has been the pos
20、sibilityof overheating the soil, thereby yielding a water content higherthan would be determined by Test Method D 2216. While noteliminating this possibility, the incremental drying proceduredescribed in this test method will minimize its effects. Somemicrowave ovens have settings at less than full
21、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 recommended in this test method ismeant to se
22、rve 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 method may not be appropriate whenhighly accurate
23、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. Degregation of individual particlesmay occur, along wi
24、th 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 personnel performing it and thesuitability of th
25、e 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 reliable results.Reliable results depend on man
26、y 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. Ovens withvariable power controls and input pow
27、er 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 developed for use in drying soils. Their use isco
28、mpatible 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, resistant to thermal shock,and not subject
29、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 satisfactorily; however, they may require pre-dryingprio
30、r 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 use a desiccant that changes color toindicat
31、e 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. Glassbeakers filled with water and materials t
32、hat 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. Short lengths of glass rods have been found u
33、seful 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 heat, and serious burns couldresult from improp
34、er 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 attention should bepaid to keeping the door sealing
35、 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 constitute voiding ofwarranties. Microwave drying of soils containing metallic materials maycause arcing in the oven. Highly orga
36、nic 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, microwave ovens were reported toaffect heart
37、 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.D4643082However, it may be advisable to post warnings that a microwave is in use.7.4 Highly organic
38、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 toxic, and the ovenshould be vented acco
39、rdingly.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 satisfactory for this purpose. This also pr
40、eventsscattering 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 placement of the test specimen directly on
41、 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 innon-corrodible airtight containers at a tem
42、perature 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-walled tubes, paintcans, and the like) or unseale
43、d sample bags are used.9. Test Specimen9.1 For water contents being determined as part of anotherASTM test method, the specimen selection process, specimenmass requirement, and techniques specified in that test methodshall be followed. If no minimum specimen mass is provided inthat method then the v
44、alues given in Table 1 below shall apply.9.2 The manner in which the test specimen is 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)
45、. In all cases, however, a representativeportion of the total sample shall be selected. 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
46、, select the test specimen from thematerial after it has been mixed thoroughly. The mass 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 thorough
47、ly the material,and then select a test specimen having a mass of moist materialin accordance 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
48、 the test specimen. If the soil is layered, see9.2. The mass of moist material selected should be in accor-dance with Table 1, if coarse-grained particles are noted.Breaking or cutting of cohesive samples to approximately6-mm particles will speed drying and prevent crusting or theoverheating of the
49、surface while drying the interior.9.3 Using a test specimen smaller than the minimum 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 coarse-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) conte
