ASTM_D_6938-2017.pdf

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for theDevelopment of International Standards,Guides and Recommendations isued by the World Trade Organization Technical Barriers to Trade(TBT)Committee.Designation:D6938-17INTERNATIONALStandard Test Methods forIn-Place Density and Water Content of Soil and Soil-Aggregate by Nuclear Methods(Shallow Depth)This standard is issued under the fixed designation D6938;the number immediately following the designation indicates the year oforiginal adoption or,in the case of revision,the year of last revision.A number in parentheses indicates the year of last reapproval.Asuperscript epsilon(8)indicates an editorial change since the last revision or reapproval.1.Scope*The neutron source and the thermal neutron detector are both1.1 This test method describes the procedures for measuringlocated at the surface of the material being tested.The waterin-place density and moisture of soil and soil-aggregate by usecontent most prevalent in engineering and construction activi-of nuclear equipment(hereafter referred to as gauge).Theties is known as the gravimetric water content,w,and is thedensity of the material may be measured by directratio of the mass of the water in pore spaces to the total masstransmission,backscatter,or backscatter/air-gap ratio methods.of solids,expressed as a percentage.Measurements for water(moisture)content are taken at the1.4 Two alternative procedures are provided.surface in backscatter mode regardless of the mode being used1.4.1 Procedure A describes the direct transmission methodfor density.in which the probe extends through the base of the gauge into1.1.1 For limitations see Section 5 on Interferences.a pre-formed hole to a desired depth.The direct transmission is1.2 The total or wet density of soil and soil-aggregate isthe preferred method.measured by the attenuation of gamma radiation where,in1.4.2 Procedure B involves the use of a dedicated backscat-direct transmission,the source is placed at a known depth up toter gauge or the probe in the backscatter position.This places300 mm(12 in.)and the detector(s)remains on the surfacethe gamma and neutron sources and the detectors in the same(some gauges may reverse this orientation);or in backscatter orplane.backscatter/air-gap the source and detector(s)both remain on1.4.3 Mark the test area to allow the placement of the gaugethe surface.over the test site and to align the probe to the hole.1.2.1 The density of the test sample in mass per unit volume1.5 SI Units-The values stated in SI units are to beis calculated by comparing the detected rate of gamma radia-regarded as the standard.The values in inch-pound units(ft-tion with previously established calibration data.Ib units)are provided for information only.1.2.2 The dry density of the test sample is obtained by1.6 All observed and calculated values shall conform to thesubtracting the water mass per unit volume from the testguide for significant digits and rounding established in Practicesample wet density(Section 11).Most gauges display thisD6026.value directly.1.6.1 The procedures used to specify how data are collected,1.3 The gauge is calibrated to read the water mass per unitrecorded,and calculated in this standard are regarded as thevolume of soil or soil-aggregate.When divided by the densityindustry standard.In addition,they are representative of theof water and then multiplied by 100,the water mass per unitsignificant digits that should generally be retained.The proce-volume is equivalent to the volumetric water content.Thedures used do not consider material variation,purpose forwater mass per unit volume is determined by the thermalizingobtaining the data,special purpose studies,or any consider-or slowing of fast neutrons by hydrogen,a component of water.ations for the users objectives;and it is common practice toincrease or reduce significant digits of reported data to be This test method is under the jurisdiction of ASTM Committee D18 on Soil andcommensurate with these considerations.It is beyond the scopeRock and is the direct responsibility of Subcommittee D18.08 on Special andof this standard to consider significant digits used in analysisConstruction Control Tests.methods for engineering design.Current edition approved March 1,2017.Published March 2017.Originallyapproved in 2006.Last previous edition approved in 2015 as D6938-15.DOI:1.7 This standard does not purport to address all of the10.1520/D6938-17.safety concerns,if any,associated with its use.It is the*A Summary of Changes section appears at the end of this standardCopyright ASTM Intemational,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United StatesCopyright ASTM IntemationalProvided by IHS under license with ASTMreproduction or networking permitted without license from IHSNot for Resale.04/11/2017 23:40:15 MDTD6938-17responsibility of the user of this standard to establish appro-3.2.1 nuclear gauge-a device containing one or morepriate safety and health practices and determine the applica-radioactive sources used to measure certain properties of soilbility of regulatory limitations prior to useand soil-aggregates3.2.2 gamma(radiation)source-a sealed source of radio-2.Referenced Documentsactive material that emits gamma radiation as it decays.2.1 ASTM Standards:23.2.3 neutron(radiation)source-a sealed source of radio-D653 Terminology Relating to Soil,Rock,and Containedactive material that emits neutron radiation as it decaysFluidsD698 Test Methods for Laboratory Compaction Character-3.2.4 Compton scattering-the interaction between aistics of Soil Using Standard Effort(12,400 ft-lbf/ft(600gamma ray(photon)and an orbital electron where the gammakN-m/m)ray loses energy and rebounds in a different direction.D1556 Test Method for Density and Unit Weight of Soil in3.2.5 detector-a device to detect and measure radiation.Place by Sand-Cone Method3.2.6 gravimetric water content-same as water content(asD1557 Test Methods for Laboratory Compaction Character-defined in Terminology D653),a nomenclature used in someistics of Soil Using Modified Effort(56,000 ft-Ibf/ftscientific fields to differentiate it from volumetric water con-(2.700kN-m/m)tent.D2167 Test Method for Density and Unit Weight of Soil inPlace by the Rubber Balloon Method3.2.7 thermalization-the process of slowing downfastD2487 Practice for Classification of Soils for Engineeringneutrons by collisions with light-weight atoms,such as hydro-Purposes(Unified Soil Classification System)genD2488 Practice for Description and Identification of Soils3.2.8 volumetric water content-the volume of water as a(Visual-Manual Procedure)percent of the total volume of soil or rock material.D2216 Test Methods for Laboratory Determination of Water3.2.9 test count.n-the measured output of a detector for a(Moisture)Content of Soil and Rock by Massspecific type of radiation for a given test.D2937 Test Method for Density of Soil in Place by theDrive-Cylinder Method3.2.10 prepared blocks-blocks prepared of soil,solid rock.D3740 Practice for Minimum Requirements for Agenciesconcrete,and engineered materials,that have characteristics ofEngaged in Testing and/or Inspection of Soil and Rock asvarious degrees of reproducible uniformity.Used in Engineering Design and ConstructionD4253 Test Methods for Maximum Index Density and Unit4.Significance and UseWeight of Soils Using a Vibratory Table4.1 The test method described is useful as a rapid,nonde-D4254 Test Methods for Minimum Index Density and Unitstructive technique for in-place measurements of wet densityWeight of Soils and Calculation of Relative Densityand water content of soil and soil-aggregate and the determi-D4643 Test Method for Determination of Water Content ofnation of dry density.Soil and Rock by Microwave Oven Heating4.2 The test method is used for quality control and accep-D4718 Practice for Correction of Unit Weight and Watertance testing of compacted soil and soil-aggregate mixtures asContent for Soils Containing Oversize Particlesused in construction and also for research and development.D4944 Test Method for Field Determination of Water(Mois-The nondestructive nature allows repetitive measurements at ature)Content of Soil by the Calcium Carbide Gas Pressuresingle test location and statistical analysis of the results.TesterD4959 Test Method for Determination of Water Content of4.3 Density-The fundamental assumptions inherent in theSoil By Direct Heatingmethods are that Compton scattering is the dominant interacD6026 Practice for Using Significant Digits in Geotechnicaltion and that the material is homogeneous.Data4.4 Water Content-The fundamental assumptions inherentD7013 Guide for Nuclear Surface Moisture and Densityin the test method are that the hydrogen ions present in the soilGauge Calibration Facility Setupor soil-aggregate are in the form of water as defined by theD7759 Guide for Nuclear Surface Moisture and Densitywater content derived from Test Methods D2216.and that theGauge Calibrationmaterial is homogeneous.(See 5.2)3.TerminologyNorE 1-The quality of the result produced by this standard test methodis dependent on the competence of the personnel performing it,and the3.1 Definitions-See Terminology D653 for general defini-suitability of the equipment and facilities used.Agencies that meet thetions.criteria of Practice D3740 are generally considered capable of competentand objective testing/sampling/inspection.and the like.Users of this3.2 Definitions of Terms Specific to This Standard:standard are cautioned that compliance with Practice D3740 does not initself ensure reliable results.Reliable results depend on many factors;Practice D3740 provides a means of evaluating some of those factors.2 For referenced ASTM standards,visit the ASTM website,www.astm.org.orcontact ASTM Customer Service at serviceastm.org.For Annual Book of ASTM5.InterferencesStandards volume information.refer to the standards Document Summary page onthe AASTM website5.1 In-Place Density Interterences2No reproduction or networking permited without lcense from IHSNot for Resale 04/11/2017 23-40:15 MDTD6938-179.Standardizationthe time that has elapsed between the current9.1 Nuclear moisture density gauges are subject to long-standardization test and the date of the last calibra-term aging of the radioactive sources,which may change thetion or verification.The units selected for t,Trelationship between count rates and the material density andand Tm should be consistent,that is,if Ta iswater content.To correct for this aging effect,gauges areexpressed in days,then t should also be expressedcalibrated as a ratio of the measurement count rate to a countin days,rate made on a reference standard or to an air-gap count(for theIn(2)=the natural logarithm of 2.which has a value ofbackscatter/air-gap ratio method).approximately 0.69315.the inverse of the natural logarithm function,which9.2 Standardization of the gauge shall be performed at thestart of each days use,and a record of these data should behas a value of approximately 2.71828.retained for the amount of time required to ensure compliance9.2.4 If for any reason the measured density or moisturewith either subsection 9.2.2 or 9.2.3,whichever is applicable.becomes suspect during the days use,perform another stan-Perform the standardization with the gauge located at least 9 mdardization check.(30 ft)away from other nuclear moisture density gauges and9.3 Example-A nuclear gauge containing a 37Cs sourceclear of large masses of water or other items which can affectfor density determination(half-life=11 023 days)andthe reference count rates.an24Am:Be source for moisture determination(half-life=1579.2.1 Turn on the gauge and allow for stabilization accord-788 days)is calibrated on March I of a specific year.At theing to the manufacturers recommendations.time of calibration,the density standard count was 2800 counts9.2.2 Using the reference standard,take a reading that is atper minute(prescaled),and the moisture standard count wasleast four times the duration of a normal measurement period720 counts per minute(prescaled).According to Eq 1 and Eq(where a normal measurement period is typically one minute)2 from Section 9.2.3.what is the allowed range of standardto constitute one standardization check.Use the procedurecounts for November I of the same year?recommended by the gauge manufacturer to establish the9.3.1 For this example,a total of 245 days have elapsedcompliance of the standard measurement to the accepted range.between the date of calibration or verification(March 1)andWithout specific recommendationsfromthe gaugethe date of the gauge standardization(November 1).Therefore:manufacturer,use the procedure in 9.2.3.t=245 days9.2.3 If the values of the current standardization counts areTa2)=11 023 daysoutside the limits set by Eq I and Eg 2,repeat the standard-Tm12=157788daysization check.If the second standardization check satisfies EqNae=2800 countsI and Eq 2,the gauge is considered in satisfactory operatingNme=720 countscondition.9.3.2 According to Eq 1,therefore,the lower limit for the0.99NeNo1.01(N)e(1)density standard count taken on November 1,denoted by Nao.andis:0.98(N)e器No1.02N)e(2)0.99N4e=0.9(2800e=2772e-a41=2730comswhere:9.3.3 Likewise,the upper limit for the density standardthe half-life of the isotope that is used for thecount taken on November 1.denoted by Nao.is:density determination in the gauge.For example,for137Cs,the radioactive isotope most commonly1.01(N小e=1.01(280)e7=2828ea14=2785 comtsused for density determination in these gauges.9.3.4 Therefore,the density standard count acquired onTis 11 023 days,November 1 should lie somewhere between 2730 and 2785Tmn)the half-life of the isotope that is used for the watercounts.or 2730 Nao 2785.According to Eq 2,the lowercontent determination in the gauge.For example.limit for the moisture standard count taken on November 1,for24Am,the radioactive isotope in Am:Be,thedenoted by Nmo,is:radioactive source most commonly used for watercontent determination in these gauges,Tm is0.98N)e7=0.98(720e高器=706e0aoa=705 counts157788days,9.3.5 Likewise,the upper limit for the moisture standardNthe density system standardization count acquiredcount taken on November 1,denoted by Nao.is:at the time of the last calibration or verification.N methe moisture system standardization count acquired1.02(Nm)e7=1.02(720)e7=734eaw1w=733consat the time of the last calibration or verification.9.3.6 Therefore,the moisture standard count acquired onthe current density system standardization count,November 1 should lie somewhere between 705 and 733the current moisture system standardization count,counts,or705Nmo733.No reproduction or networking permitted without license from IHSNot for R0sae,041120172340:15M0TD6938-1710.Procedureso that the back side of the probe is in intimate contact with the10.1 When possible,select a test location where the gaugeside of the hole in the gamma measurement path.will be placed at least 600 mm(24.0 in)away from any objectNoTE 3-As a safety measure,it is recommended that a probesitting on or projecting above the surface of the test location,containing radioactive sources not be extended out of its shielded positionwhen the presence of this object has the potential to modifyprior to placing it into the test site.When possible,align the gauge so asgauge response.Any time a measurement must be made at ato allow placing the probe directly into the test hole from the shieldedspecific location and the aforementioned clearance cannot beposition.achieved,such as in a trench,follow the gauge manufacturers10.4.7 Keep all other radioactive sources at least 9 m(30correction procedure(s).feet)away from the gauge to avoid any effect on the measure-ment.10.2 Prepare the test site in the following manner:10.4.8 If the gauge is so equipped,set the depth selector to10.2.1 Remove all loose and disturbed material and addi-the same depth as the probe.tional material as necessary to expose the true surface of thematerial to be tested.10.4.9 Secure and record one or more one-minute densityand water content readings.Read the in-place wet density10.2.2 Prepare an area sufficient in size to accommodate thegauge by grading or scraping the area to a smooth condition sodirectly or determine one by use of the calibration curve ortable previously established.as to obtain maximum contact between the gauge and materialbeing tested.10.4.10 Read the water content directly or determine the10.2.3 The depth of the maximum void beneath the gaugewater content by use of the calibration curve or table previ-shall not exceed 3 mm(s in.).Use either native material thatously established.does not contain gravel or fine sand to fill the voids,and then10.5 Procedure B-The Backscatter or Backscatter/Air-Gapsmooth the surface with the site preparation device or otherRatio Procedure:suitable tool.The depth of the filler should not exceed10.5.1 Seat the gauge firmly(see Note 2).approximately 3 mm(s in.).10.5.2 Keep all other radioactive sources at least 9 m(30 ft)10.2.4 The placement of the gauge on the surface of theaway from the gauge to avoid affecting the measurement.material to be tested is critical to accurate density measure-10.5.3 Set the gauge into the Backscatter(BS)position.ments.The optimum condition is total contact between the10.5.4 Secure and record one or more set(s)of one-minutebottom surface of the gauge and the surface of the materialdensity and water content readings.When using thebeing tested.The total area filled should not exceed approxi-backscatter/air-gap ratio mode,follow the manufacturers in-mately 10 percent of the bottom area of the gauge.structions regarding gauge setup.Take the same number of10.3 Turn on and allow the gauge to stabilize(warm up)readings for the normal measurement period in the air-gapaccording to the manufacturers recommendations(see Sectionposition as in the standard backscatter position.Calculate the9.2.1).air-gap ratio by dividing the counts per minute obtained in the10.4 Procedure A-The Direct Transmission Procedure:air-gap position by the counts per minute obtained in thestandard position.Many gauges have built-in provisions for10.4.1 Select a test location where the gauge in test positionautomatically calculating the air-gap ratio and wet density.will be at least 150 mm(6 in.)away from any vertical10.5.5 Read the in-place wet density or determine one byprojection.use of the calibration curve or table previously established.10.4.2 Make a hole perpendicular to the prepared surface10.5.6 Read the water content or determine one by use ofusing either(a)the drive pin guide,the guide pin extractor,athe calibration curve or previously established table(seehammer,and drive pin,or(b)a slide hammer.The hole shouldSection 10.6).be a minimum of 50 mm(2 in.)deeper than the desiredmeasurement depth and of an alignment that insertion of theNoTE 4-Gauge measurements acquired using either Procedure A orprobe will not cause the gauge to tilt from the plane of theProcedure B yield both density and water content values for the materialprepared area.under test.It is good practice to record gauge density and water countscorresponding to the density and water values at the time of measurement10.4.3 Mark the test area to allow the placement of thein the event that data recording errors or improper probe depth errors aregauge over the test site and to align the probe to the hole.of concem.Follow the manufacturers recommendations if applicable.10.6 Water Content Correction and Oversize Particle Cor-10.4.4 Remove the hole-forming device carefully to preventrectionthe distortion of the hole,damage to the surface,or loosematerial to fall into the hole.10.6.1 For proper use of the gauge and accurate values ofboth water content and dry density,both of these correctionsNoTE 2-Care must be taken in the preparation of the access hole inneed to be made when applicable.uniform cohesionless granular soils.Measurements can be affected byPrior to using the gauge-derived water content on any newdamage to the density of surrounding materials when forming the hole.material,the value should be verified by comparison to another10.4.5 Place the gauge on the material to be tested,ensuringASTM method such as Test Methods D2216,D4643,D4944,maximum surface contact as described previously in 10.2.4.or D4959.As part of a user developed procedure,occasional10.4.6 Lower the probe into the hole to the desired testsamples should be taken from beneath the gauge and compari-depth.Pull the gauge gently toward the back,or detector end,son testing done to confirm gauge-derived water contentCopyright ASTM Intemational5Provided by IHS under license with ASTMreproduction or networking permitted without license from IHSNot for Resale.04/11/2017 23:40:15 MDT