Designation: D 6938 – 08a
Standard Test Method for
In-Place Density and Water Content of Soil and SoilAggregate by Nuclear Methods (Shallow Depth) 1 This standard is issued under the fixed designation D 6938; 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 supers cript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope Scope* *
1.4.1 Procedure A describes the direct transmission method in which the gamma source rod extends through the base of the gauge into a pre-formed hole to a desired depth. The direct transmission is the preferred method. 1.4.2 Procedure B involves the use of a dedicated backscatter gauge or the source rod in the backscatter position. This places the gamma and neutron sources and the detectors in the same plane. Units its—T 1.5 SI Un —The he va valu lues es st stat ated ed in SI un unit itss ar aree to be regarded as the standard. The values in inch-pound units (ft – lb units) are provided for information only. 1.6 All observed observed and calc calculate ulated d values shall conform conform to the guide for significant digits and rounding established in Practice D 6026. 6026. 1.6.1 The procedures used to to specify how data are are collected, recorded, and calculated in this standard are regarded as the industry standard. In addition, they are representative of the significant digits that should generally be retained. The procedures dur es use used d do not con consid sider er mat materi erial al var variat iation ion,, pur purpos posee for obtaining the data, special purpose studies, or any considerations for the user’s objectives; and it is common practice to increa inc rease se or red reduce uce sig signifi nifican cantt dig digits its of rep report orted ed dat dataa 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. standard d doe doess not purport purport to add addre ress ss all of the 1.7 This standar safe sa fety ty co conc ncer erns ns,, if an anyy, as asso soci ciat ated ed wi with th its us use. e. It is th thee responsibility of the user of this standard to establish appro priate safety and health practices and determine the applicability of regulatory limitations prior to use.
1.1 This test method describes describes the procedures for measuring measuring in-place density and moisture of soil and soil-aggregate by use of nuc nuclea learr equ equipm ipment ent.. The den densit sity y of the material material may be measured meas ured by direc directt tran transmis smission, sion, backs backscatt catter er,, or backs backscatt catter/ er/ air-gap air -gap rati ratio o meth methods. ods. Measu Measureme rements nts for wate waterr (moi (moistur sture) e) content are taken at the surface in backscatter mode regardless of the mode being used for density. It is the intent of this subcommittee that this standard replace D 2922 and D 3017. 1.1.1 For limitations limitations see Section Section 5 on Interferences. 1.2 The total or wet density density of soi soill and soil-agg soil-aggreg regate ate is measur mea sured ed by the att attenu enuati ation on of gam gamma ma rad radiat iation ion whe where, re, in direct transmission, the source is placed at a known depth up to 300 mm (12 in.) and the detector (s) remains on the surface (some gauges may reverse this orientation); or in backscatter or backscatter/air-gap the source and detector(s) both remain on the surface. 1.2.1 The density of the test sample in mass per unit volume volume is calculated by comparing the detected rate of gamma radiation with previously established calibration data. 1.2.2 1.2 .2 The dry den densit sity y of the test sample sample is obtained obtained by subtr sub tract acting ing the wat water er mas masss per uni unitt vol volume ume from the test samplee wet densi sampl density ty (Sect (Section ion 11 11)). Mos Mostt gau gauges ges dis displa play y thi thiss value directly. 1.3 The gauge is calibrated calibrated to read the water mass per unit volume of soil or soil-aggregate. When divided by the density of water and then multiplied by 100, the water mass per unit volume vol ume is equ equiva ivalen lentt to the vol volume umetri tricc wat water er con conten tent. t. The water mass per unit volume is determined by the thermalizing or slowing of fast neutrons by hydrogen, a component of water. The neutron source and the thermal neutron detector are both located at the surface of the material being tested. The water content most prevalent in engineering and construction activities is known as the gravimetric water content, w, and is the ratio of the mass of the water in pore spaces to the total mass of solids, expressed as a percentage. 1.4 Two alternative alternative procedures are provided.
2. Referenced Documents 2.1 ASTM Standards: 2 D 653 Terminology Relating to Soil, Rock, and Contained Fluids D 698 Test Methods for Laboratory Compaction Characteristics of Soil Using Standard Effort (12 400 ft-lbf/ft 3(600 kN-m/m3))
1 This test method is under the jurisdiction of ASTM Committee D18 on Soil and Rock and is the dir Rock direct ect resp respons onsibi ibility lity of Sub Subcom commit mittee tee D18 D18.08 .08 on Spe Special cial and Construction Control Tests. Curren Cur rentt edit edition ion app approv roved ed Jun Junee 1, 200 2008. 8. Pub Publish lished ed Jun Junee 200 2008. 8. Ori Origin ginally ally approved in 2006. Last previous edition approved in 2008 as D 6938 – 08.
2
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*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.
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D 6938 – 08a D 1556 Test Method for Density and Unit Weight of Soil in Place by Sand-Cone Method D 1557 Test Methods for Laboratory Compaction Characterist ter istics ics of Soi Soill Usi Using ng Mod Modifie ified d Ef Effor fortt (56 (56,00 ,000 0 ftft-lbf lbf/ / ft3(2,700 kN-m/m3)) D 2167 Test Method for Density and Unit Weight of Soil in Place by the Rubber Balloon Method D 2487 Practice for Classification of Soils for Engineering Purposes (Unified Soil Classification System) D 2488 Practice for Description and Identification of Soils (Visual-Manual (Vis ual-Manual Procedure) D 2216 Test Methods for Laboratory Determination of Water (Moisture) Content of Soil and Rock by Mass D 2937 Test Test Method Method for Density Density of Soi Soill in Place by the Drive-Cylinder Method D 3740 Practice for Minimum Requirements for Agencies Engaged in Testing and/or Inspection of Soil and Rock as Used in Engineering Design and Construction D 4253 Test Methods for Maximum Index Density and Unit Weight of Soils Using a Vibratory Table D 4254 Test Methods for Minimum Index Density and Unit Weight of Soils and Calculation of Relative Density D 4643 Test Method for Determination of Water (Moisture) Content of Soil by Microwave Oven Heating D 4718 Practice for Correction of Unit Weight and Water Content for Soils Containing Oversize Particles D 4944 Test Test Met Method hod for Fie Field ld Det Determ ermina inatio tion n of Wate aterr (Moisture) Content of Soil by the Calcium Carbide Gas Pressure Tes Tester ter D 4959 Test Method for Determination of Water (Moisture) Content of Soil By Direct Heating D 6026 Practice for Using Significant Digits in Geotechnical Data D 7013 Guide for Nucle Nuclear ar Surfa Surface ce Mois Moisture ture and Densi Density ty Gauge Calibration Facility Setup
be lowered to specified depths for testing. Probes containing only a radioactive source are commonly referred to as “Source Rods.” 3.2.9 thermalization—the process of “slowing down” fast neutrons by collisions with light-weight atoms, such as hydrogen. 3.2.10 water content —the —the ratio of the mass of water contained in the pore spaces of soil or soil-aggregate, to the solid mass of particles in that material, expressed as a percentage this is is so some metim times es ref efer errred to in so some me sc scie ient ntifi ificc fie field ldss as (th gravimetric grav imetric water conte content nt to dif differ ferentiat entiatee it fro from m volum volumetric etric water cotent ). ). 3.2.11 volumetric water content —the —the volume of water as a percent of the total volume of soil or rock material. 3.2.12 test count , n —the measured output of a detector for a specific type of radiation for a given test. 3.2.13 prepared blocks —blocks prepared of soil, solid rock, concrete, and engineered materials, that have characteristics of various degrees of reproducible uniformity. 4. Signi Significanc ficancee and Use 4.1 The test method describe described d is usefu usefull as a rapid, nondestructive technique for in-place measurements of wet density and water content of soil and soil-aggregate and the determination of dry density. 4.2 The test method method is used for quality quality control and accepacceptance testing of compacted soil and soil-aggregate mixtures as used in construction and also for research and development. The nondestructive nature allows repetitive measurements at a single test location and statistical analysis of the results. 4.3 Density—The fundamental assumptions inherent in the methods are that Compton scattering is the dominant interaction and that the material is homogeneous. 4.4 Water Content —The —The fundamental assumptions inherent in the test method are that the hydrogen ions present in the soil or soil-aggregate are in the form of water as defined by the water content derived from Test Methods D 2216, 2216, and that the material is homogeneous. (See 5.2 5.2))
3. Terminology 3.1 Definitions: See Terminology D 653 653 for general definitions. 3.2 Definitions of Terms Specific to This Standard: nuclear gauge—a de 3.2.1 nuclear devi vice ce co cont ntai aini ning ng on onee or mo more re radioactive sources used to measure certain properties of soil and soil-aggregates. density sity—s 3.2.2 wet den —sam amee as bu bulk lk de dens nsit ity y (a (ass de defin fined ed in Terminology D Terminology D 653) 653); the total mass (solids plus water) per total volume of soil or soil-aggregate. 3.2.3 dry density—same as density of dry soil or rock (as defined in Terminology D 653); 653); the mass of solid particles per the total volume of soil or soil-aggregate. 3.2.4 gamma (radiation) source—a sealed source of radioactive material that emits gamma radiation as it decays. 3.2.5 neutron (radiation) source—a sealed source of radioactive material that emits neutron radiation as it decays. Compton scat scatterin tering g—t 3.2.6 Compton —the he in inter teract action ion bet betwee ween n a gamma ray (photon) and an orbital electron where the gamma ray loses energy and rebounds in a different direction. 3.2.7 detector —a —a device to detect and measure radiation. 3.2.8 probe—a met metal al rod attache attached d to a nuc nuclea learr gau gauge ge in which a radioactive source or a detector is housed. The rod can
NOTE 1—Th 1—Thee qua quality lity of the result produced produced by this standard standard tes testt method is dependent on the competence of the personnel performing it, and the suitability of the equipme equipment nt and facilities used. Agencie Agenciess that meet the cri criter teria ia of Pra Practic cticee D 3740 are gen genera erally lly con conside sidered red cap capabl ablee of competent and objective testing/sampling/inspection, and the like. Users of this standard are cautioned that compliance with Practice D Practice D 3740 does 3740 does not in itse itself lf assu assure re rel reliab iable le res results ults.. Rel Reliab iable le res results ults depend depend on man many y factors; Practice D Practice D 3740 3740 provides a means of evaluating some of those factors.
5. Interference Interferencess 5.1 In-Place Density Interferences 5.1.1 Measu Measureme rements nts may be affected affected by the chemical chemical composition of the material being tested. 5.1.2 Measurements may be affected affected by non-homogeneous soils and surface texture (see 10.2 10.2). ). 5.1.3 Measurements in in the Backscatter Mode Mode are influenced more by the density and water content of the material in close proximity to the surface. 2
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D 6938 – 08a 5.1.4 Measurements in the Direct Direct Transmission Transmission mode are an average of the density from the bottom of the probe in the soil or soil aggregate back up to the surface of the gauge. 5.1.5 Oversize particles particles or large voids in the source-detector source-detector path may cause higher or lower density measurements. Where lack lac k of uni unifor formit mity y in the soil due to lay layeri ering, ng, agg aggreg regate ate or voids voi ds is sus suspec pected ted,, the test sit sitee sho should uld be exc excava avated ted and visually examined to determine if the test material is representative tat ive of the in-situ in-situ mat materi erial al in gen genera erall and if an ove oversi rsize ze correction is required in accordance with Practice D 4718. 4718. 5.1.6 5.1. 6 The mea measur sured ed vol volume ume is app approx roxima imatel tely y 0.00 0.0028 28 m3(0.10 ft3) for the Backscatter Mode and 0.0057 m 3(0.20 ft3) for the Direct Transmission Mode when the test depth is 150 mm (6 in.). The actual measured volume is indeterminate and varies with the apparatus and the density of the material. 5.1.7 Other radioact radioactive ive sources sources must not be withi within n 9 m (30 ft.) of equipment in operation. 5.2 In-Place Water (Moisture) Content Interferences 5.2.1 The chemical composition composition of the material material being tested can affect the measurement and adjustments may be necessary (see Section 10.6). 10.6). Hydrogen in forms other than water and carbon will cause measurements in excess of the true value. Some chemical elements such as boron, chlorine, and cadmium will cause measurements lower than the true value. 5.2.2 The water content content measured measured by this test method method is not necessarily the average water content within the volume of the sample involved in the measurement. Since this measurement is by backscatter in all cases, the value is biased by the water content of the material closest to the surface. The volume of soill and soi soi soill-agg aggreg regate ate rep repres resent ented ed in the mea measur sureme ement nt is indete ind etermi rminat natee and wil willl var vary y wit with h the water con conten tentt of the materi mat erial. al. In gen genera eral, l, the gre greate aterr the wat water er con conten tentt of the material, the smaller the volume involved in the measurement. Approximately 50 % of the typical measurement results from the water content of the upper 50 to 75 mm (2 to 3 in.). 5.2.3 Other neutron neutron sources sources must not be with within in 9 m (30 ft) of equipment in operation.
to the required smoothness, smoothness, and in the Direc Directt Tra Transmi nsmissio ssion n Method, guiding the drive pin to prepare a perpendicular hole. 6.4 Drive Pin—A pin of slightly larger diameter than the probe in the Direct Transmission Instrument used to prepare a hole in the test site for inserting the probe. 6.4.1 Drive Pin Guide—A fixture that keeps the drive pin perp pe rpen endi dicu cula larr to th thee te test st si site te.. Ge Gene nera rall lly y pa part rt of th thee si site te preparation device. 6.5 Hammer —Heavy —Heavy enough to drive the pin to the required depth without undue distortion of the hole. 6.6 Drive Pin Extractor —A —A tool that may be used to remove remove the drive pin in a vertical direction so that the pin will not distort the hole in the extraction process. 6.7 Slide Hammer , with a drive pin attached, may also be used both to prepare a hole in the material to be tested and to extract the pin without distortion to the hole. 7. Haza Hazards rds 7.1 These gauges utilize utilize radi radioact oactive ive materials materials that may be hazardous to the health of the users unless proper precautions are taken. Users of these gauges must become familiar with applicable safety procedures and government regulations. 7.2 Eff Effective ective user instructions, together with routine safety procedures and knowledge of and compliance with Regulatory Requir Req uireme ements nts,, are a man mandat datory ory par partt of the ope operat ration ion and storage of these gauges. 8. Cali Calibrati bration on 8.1 Calibrat Calibration ion of the gauge will be in acc accord ordanc ancee wit with h Annex A1 and Annex A2. A2. 8.2 For further reference reference on gauge calibrati calibration, on, see Guide D 7013, 7013, Sta Standa ndard rd Gui Guide de for Nuc Nuclea learr Sur Surfac facee Moi Moistu sture re and Density Gauge Calibration Facility Setup. 9. Standardization 9.1 Nucle Nuclear ar moisture density density gauges are subject to long long-term aging of the radioactive sources, which may change the relationship between count rates and the material density and water wat er con conten tent. t. To cor correc rectt for thi thiss agi aging ng ef effec fect, t, gau gauges ges are calibrated as a ratio of the measurement count rate to a count rate made on a reference standard or to an air-gap count (for the backscatter/air-gap ratio method). 9.2 Stand Standardi ardizati zation on of the gauge shall be performed performed at the start of each day’s use, and a record of these data should be retained for the amount of time required to ensure compliance with either subsection 9.2.2 or or 9.2.3 9.2.3,, whichever is applicable. Perform the standardization with the gauge located at least 9 m (30 ft) away from other nuclear moisture density gauges and clear of large masses of water or other items which can affect the reference count rates. 9.2.1 Tur Turn n on the gauge and allow for stab stabiliz ilizatio ation n according to the manufacturer’s recommendations. 9.2.2 Using the reference reference standard, standard, take a reading that is at least four times the duration of a normal measurement period (where a normal measurement period is typically one minute) to const constitut itutee one stand standardiz ardization ation check. Use the proc procedure edure recomm rec ommend ended ed by the gau gauge ge man manufa ufactu cturer rer to est establ ablish ish the compliance of the standard measurement to the accepted range.
6. Appar Apparatus atus 6.1 Nuclear Density / Moisture Gauge—While exact details of construction of the apparatus may vary, the system shall consist of: Gamma Sou Sourc rcee—A sea 6.1.1 Gamma sealed led sou source rce of hig high-e h-ener nergy gy gamma radiation such as cesium or radium. 6.1.2 Gamma Detector —Any —Any type of gamma detector such as a Geiger-Mueller tube(s). 6.1.3 Fast Neutron Source —A sealed mixture of a radioactive material such as americium, radium and a target material such as beryllium, or a neutron emitter such as californium252. Neutron on Detect Detector or —Any 6.1.4 Slow Neutr —Any typ typee of slo slow w neu neutro tron n detector detec tor such as boron trifluoride trifluoride or heli helium-3 um-3 proportional proportional counter. Reference Standa Standard rd —A 6.2 Reference — A bl bloc ock k of ma mate teri rial al us used ed fo forr checking instrument operation, correction of source decay, and to establish conditions for a reproducible reference count rate. 6.3 Site Preparation Device—A plate plate,, stra straight ightedge, edge, or other suitable leveling tool that may be used for planing the test site 3 Copyright by ASTM Int'l (all rights reserved); Mon Dec 22 18:14:53 EST 2008 Downloaded/printed Downloaded/printed by
D 6938 – 08a Without specific recommendations from the gauge manufacturer, use the procedure in 9.2.3 9.2.3.. 9.2.3 If the value valuess of the current standardi standardizatio zation n count countss are outside the limits set by Eq 1 and Eq 2, repeat the standardization check. If the second standardization check satisfies Eq 1 and Eq 2, the gauge is considered in satisfactory operating condition. –~ln~2 !!t
0.99~ N dc!e
T d ~1/2!
9.3.1 For this example, 9.3.1 example, a tot total al of 245 days hav havee ela elapse psed d between the date of calibration or verification (March 1) and the date of the gauge standardization (November 1). Therefore: t = 245 days Td(1/2)= 11 023 days Tm(1/2)= 157 788 days Ndc= 2800 counts Nmc= 720 counts 9.3.2 Accor According ding to Eq 1, therefore, therefore, the lower limit for the density standard count taken on November 1, denoted by N d0, is:
–~ln~2!!t #
N d 0 # 1.01~ N dc!e
T d ~ 1/2!
(1)
–~ln~2!!t T m~1/2!
(2)
and –~ln~2!!t T m~1/2! # N m0 #
0.98~ N mc!e
1.02~ N mc!e
–~ln~2!!t
0.99~ N dc !e
where: T d(1/2)
= the halfhalf-lif lifee of the isoto isotope pe that that is used used for the densit den sity y det determ ermina inatio tion n in the gau gauge. ge. For example, ampl e, for 137Cs, the radioactive radioactive isotope most common com monly ly use used d for den densit sity y det determ ermina inatio tion n in these gauges, Td(1/2), is 11 023 days, = the halfhalf-lif lifee of the isoto isotope pe that that is used used for the T m(1/2) water content determination in the gauge. For example, exam ple, for 241 Am, the radioactive isotope in Am:Be, the radioactive source most commonly used for water content determinat determination ion in these gauges, Tm(1/2), is 157 788 days, N dc = the densit density y system system stand standard ardiza izatio tion n count count acquir qu ired ed at th thee ti time me of th thee la last st ca cali libr brat atio ion n or verification, = the mois moisture ture syst system em stan standardi dardizatio zation n count count ac N mc quir qu ired ed at th thee ti time me of th thee la last st ca cali libr brat atio ion n or verification, N d0 = the the current current densit density y system system standardi standardizat zation ion count, N m0 = the current current moistur moisturee system system standardi standardizat zation ion count, t = the tim timee that that has ela elapse psed d betw between een the cur curren rentt standa sta ndardi rdizat zation ion test and the dat datee of the las lastt calibration or verification. The units selected for t, Td(1/2), and Tm(1/2) should be consistent, that is, if Td(1/2) is expressed in days, then t should also be expressed in days, ln(2) = the natur natural al logari logarithm thm of 2, 2, which which has has a value of approximately 0.69315, e = the inve inverse rse of the nat natura urall loga logarit rithm hm fun functi ction, on, which has a value of approximately 2.71828. 9.2.4 9.2 .4 If for any rea reason son the mea measur sured ed den densit sity y or moi moistu sture re becomes suspect during the day’s use, perform another standardization check. 9.3 Example—A nuclear gauge conta containing ining a 137 Cs sourc sourcee forr de fo dens nsit ity y de dete term rmin inat atio ion n (h (hal alff-li life fe = 11 02 023 3 da days ys)) an and d 241 an Am:Be source for moisture determination (half-life = 157 788 days) is calibrated on March 1 of a specific year. At the time of calibration, the density standard count was 2800 counts per minute (prescaled), and the moisture standard count was 720 counts per minute (prescaled). According to Eq 1 and Eq 2 from Section 9.2.3, 9.2.3, what is the allowed range of standard counts for November 1 of the same year?
–~ln~2!! · 245
5 0.99~2800!e
11 023
5 2772e–0.01541 5 2730 counts
9.3.3 Lik 9.3.3 Likewi ewise, se, the upp upper er lim limit it for the den densit sity y sta standa ndard rd count taken on November 1, denoted by N d0, is: 1.01~ N dc !e
–~ln~2!!t –~ln~2!! · 245 T d ~1/2! 5 1.01~ 2800!e 11 023
5 2828e–0.01541 5 2785 counts
9.3.4 The 9.3.4 Theref refore ore,, the den densit sity y sta standa ndard rd cou count nt acq acquir uired ed on November 1 should lie somewhere between 2730 and 2785 counts, or 2730 # Nd0# 2785. According to Eq 2, the lower limit for the moisture standard count taken on November 1, denoted by Nm0, is: –~ln~2!!t
0.98~ N mc!e
T m~ 1/2!
–~ln~2!! · 245
5 0.98~720!e
157 788
5 706 e–0.00108 5 705 counts
9.3.5 Likew Likewise, ise, the upper limit for the moisture moisture stan standard dard count taken on November 1, denoted by N d0, is: –~ln~2!!t
1.02~ N mc!e
T m~ 1/2!
–~ln~2!! · 245
5 1.02~720!e
157 788
5 734 e–0.00108 5 733 counts
9.3.6 There Therefore fore,, the moisture moisture stand standard ard count acqui acquired red on November Novemb er 1 sho should uld li liee som somewh ewhere ere between between 705 and 733 counts, or 705 # Nm0# 733. 10. Proc Procedur eduree 10.1 When possible, possible, select select a test location location where the gauge will be placed at least 600 mm (24.0 in) away from any object sitting on or projecting above the surface of the test location, when the presence of this object has the potential to modify gauge response. Any time a measurement must be made at a specific location and the aforementioned clearance cannot be achieved, such as in a trench, follow the gauge manufacturer’s correction procedure(s). 10.2 Prepare the test site in the following manner : 10.2.1 Remov Removee all loose and disturbed disturbed material material and addi addi-tional material as necessary to expose the true surface of the material to be tested. 10.2.2 Prepare an area sufficient sufficient in size to accommodate the gauge by grading or scraping the area to a smooth condition so as to obtain maximum contact between the gauge and material being tested. 10.2.3 The depth of the maximum void beneath beneath the gauge shall not exceed 3 mm ( 1 ⁄ 8 in.). Use native fines or fine sand to fill the voids and smooth the surface with a rigid straight edge or other suitable tool. The depth of the filler should not exceed approximately 3 mm ( 1 ⁄ 8 in.).
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T d ~1/2!
D 6938 – 08a 10.2.4 The placeme 10.2.4 placement nt of the gauge gauge on the surface surface of the material to be tested is critical to accurate density measurements. ment s. The optimum condition condition is total contact contact betwe between en the bottom surface of the gauge and the surface of the material being tested. The total area filled should not exceed approximately 10 percent of the bottom area of the gauge. 10.3 10. 3 Tu Turn rn on and allow allow the gauge to sta stabil bilize ize (warm (warm up) according to the manufacturer’s recommendations (see Section 9.2.1). 9.2.1 ). 10.4 Procedure A - The Direct Transmission Procedure : 10.4.1 Select a test location location where the gauge gauge in test position position will wi ll be at le leas astt 15 150 0 mm (6 in in.) .) aw away ay fr from om an any y ve vert rtic ical al projection 10.4.2 Make a hole perpendicul perpendicular ar to the prepared prepared surfa surface ce usin us ing g th thee ro rod d gu guid idee an and d dr driv ivee pi pin. n. Th Thee ho hole le sh shou ould ld be a mini mi nimu mum m of 50 mm (2 in inch ches es)) de deep eper er th than an th thee de desi sire red d measurement depth and of an alignment that insertion of the probe will not cause the gauge to tilt from the plane of the prepared area. 10.4.3 10. 4.3 Mar Mark k the test are areaa to all allow ow the placeme placement nt of the gauge over the test site and to align the source rod to the hole. Follow the manufacturer’s recommendations if applicable. 10.4.4 Remove the hole-forming hole-forming device carefully carefully to prevent the distorti distortion on of the hole, damage damage to the surface surface,, or loo loose se material to fall into the hole.
backscatter/air-gap ratio mode, follow the manufacturer’s instructio stru ctions ns regar regarding ding gauge setu setup. p. Take the same number of readings read ings for the normal measurement measurement period in the air-gap position as in the standard backscatter position. Calculate the air-gap ratio by dividing the counts per minute obtained in the air-ga air -gap p pos positi ition on by the cou counts nts per mi minut nutee obt obtain ained ed in the standard stan dard position. position. Many gauges have built-in provisions provisions for automatically calculating the air-gap ratio and wet density. 10.5.5 Read the in-place in-place wet dens density ity or determine determine one by use of the calibration curve or table previously established. 10.5.6 Read the water content content or dete determin rminee one by use of the cal calibr ibrati ation on cur curve ve or pre previo viousl usly y est establ ablish ished ed tab table le (se (seee Section 10.6 Section 10.6)). 10.6 Water Content Correction and Oversize Particle Correction 10.6.1 For proper use of the gauge and accurate accurate values of both water content and dry density, both of these corrections need to be made when applicable. Prior to using the gauge-derived water content on any new material, the value should be verified by comparison to another ASTM method such as Test Methods D Methods D 2216, 2216, D 4643, 4643, D 4944, 4944, or D or D 4959. 4959. As part of a user developed procedure, occasional samples should be taken from beneath the gauge and comparison tes testin ting g don donee to con confirm firm gau gaugege-der derive ived d wat water er con conten tentt values. All gauge manufacturers have a procedure for correcting the gauge-derived water content values. 10.6.2 When oversize particles particles are present, present, the gauge can be rotated about the axis of the probe to obtain additional readings as a check. When there is any uncertainty as to the presence of these particles it is advisable to sample the material beneath the gauge to verify the presence and the relative proportion of the oversize particles. A rock correction can then be made for both water wat er con conten tentt and wet den densit sity y by the method method in Pra Practi ctice ce D 4718. 4718. 10.6.3 10. 6.3 When When sam sampli pling ng for wat water er con conten tentt cor correc rectio tion n or oversize particle correction, the sample should be taken from a zone zo ne di dire rect ctly ly un unde derr th thee ga gaug uge. e. Th Thee si size ze of th thee zo zone ne is approximately 200 mm (8 in.) in diameter and a depth equal to the depth setting of the probe when using the direct transmission sio n mod mode; e; or app approx roxima imatel tely y 75 mm (3 in. in.)) in dep depth th whe when n using the backscatter mode.
NOTE 2—Care must be taken in the preparation of the access hole in uniform cohesionless cohesionless granul granular ar soils. Measurements Measurements can be af affecte fected d by damage to the density of surrounding materials when forming the hole.
10.4.5 Place the gauge on the material material to be tested, tested, ensuring maximum surface contact as described previously in 10.2.4 10.2.4.. 10.4.6 10. 4.6 Low Lower er the pro probe be int into o the hole to the desired desired test depth. Pull the gauge gently toward the back, or detector end, so that the back side of the probe is in intimate contact with the side of the hole in the gamma measurement path. NOTE 3—As a safety measure, measure, it is recommended recommended that a probe containing radioactive sources not be extended out of its shielded position prior to placing it into the test site. When possible, align the gauge so as to allow placing the probe directly into the test hole from the shielded position.
10.4.7 Keep all other radioacti radioactive ve sources at least 9 m (30 feet) away from the gauge to avoid any effect on the measurement. 10.4.8 If the gauge is so equipped, equipped, set the depth selector selector to the same depth as the probe. 10.4.9 Secur Securee and record one or more one-minut one-minutee densi density ty and wat water er con conten tentt rea readin dings. gs. Rea Read d the inin-pla place ce wet den densit sity y directly or determine one by use of the calibration curve or table previously established. 10.4.10 10.4.1 0 Read the water content content directly or dete determin rminee the water content by use of the calibration curve or table previously established. 10.5 Procedure B -The Backscatter or Backscatter/Air-Gap Ratio Procedur Proceduree: 10.5.1 Seat the gauge gauge firmly (see Note (see Note 2) 2). 10.5.2 Keep all other radioacti radioactive ve sources at least 9m (30 ft) away from the gauge to avoid affecting the measurement. 10.5.3 Set the gauge into the Backscatte Backscatterr (BS) posi position. tion. 10.5.4 Secur Securee and reco record rd one or more set(s) of one-minute one-minute dens de nsit ity y an and d wa wate terr co cont nten entt re read adin ings gs.. Wh When en us usin ing g th thee
11. Calculation of Results Results 11.1 Determine the Wet Density 11.1.1 On most gauges read read the value directly directly in kg/m3(lbm/ 3 ft ). If the density reading is in “counts”, determine the in-place wet density by use of this reading and the previously established calibration curve or table for density. 11.1.2 11 .1.2 Recor Record d the densi density ty to the nearest nearest 1 kg/m3(0.1 lbm/ 3 ft ). 11.2 Water Content 11.2.1 11 .2.1 Use the gauge reading reading for w if the gauge converts to that value. 11.2.2 11 .2.2 If the gaug gaugee dete determin rmines es water mass per unit volume volume in kg/m3(lbm / ft3), calculate w using the formula: w 5
or, 5
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M m 3 100
rd
(3)
D 6938 – 08a w 5
M m 3 100 r 2 M m
12.1.10 12.1.1 0 Max Maxim imum um lab labora orator tory y den densit sity y val value ue in kg/ kg/m m 3 or lbm/ft 3. 12.1.11 12.1.1 1 Dry density density in kg/m3 or lbm/ft3. 12.1.12 12.1.1 2 Wet density in kg/m3 or lbm/ft3. 12.1.13 Water content in percent. 12.1.14 Percent Compaction. Compaction. 12.2 Final Report (minimum required information): 12.2.1 Tes Testt Number. Number. 12.2.2 Gauge Serial number number. 12.2.3 Location of test (for example, example, Station number number or GPS or Coordinates or other identifiable information). 12.2.4 Lift number number or elev elevation ation or depth. 12.2.5 Mois Moisture ture (Water (Water)) conte content nt as a perce percent. nt. 12.2.6 12. 2.6 Maximu Maximum m lab labora orator tory y den densit sity y val value ue in kg/ kg/m m 3 or 3 lbm/ft . 12.2.7 Dry Density Density result in kg/m3 or lbm/ft3. 12.2.8 Percent Compaction. Compaction. 12.2.9 Name of Operator(s). Operator(s).
(4)
where: = wat water er con conten tentt w rd = dry den densit sity y in kg/ kg/m m3 or (lbm/ft3), r = wet den densit sity y in kg/ kg/m m3 or (lbm/ft3), and M m = water mass per per unit unit volume volume in kg/m kg/m3 or (lbm/ft3) 11.2.3 11. 2.3 If the water content content reading was in “cou “counts,” nts,” deterdetermine the water mass per unit volume by use of this reading and previously established calibration curve or table. Then convert to gravimetric water content as per 11.2.2 11.2.2.. 11.2.4 11. 2.4 Recor Record d water content to the near nearest est 0.1 %. 11.3 Determine the Dry Density of the soil by one of the following methods: 11.3.1 11. 3.1 If the water content content is obta obtained ined by nuclear methods, methods, use the gauge readings directly for dry density in kg/m 3(lbm/ ft3). The value can also be calculated from: rd 5 r 2 M m
(5)
11. 1.3.2 3.2 If th thee wa wate terr co cont nten entt is to be de dete term rmin ined ed fr from om a sample samp le of so soil il ta take ken n as pr pres escr crib ibed ed in ( 10.6.3 10.6.3), ), fo foll llow ow th thee procedure proce duress and perf perform orm the calculations calculations of the chosen Test Method (D (D 2216, 2216, D 4643, 4643, D 4944, 4944, or or D D 4959) 4959). 11.3.3 11. 3.3 Wi With th a water content content value from 11.3.2 from 11.3.2 calculate calculate the dry density from: rd 5
100 3 r 100 1 w
13. Prec Precisio ision n and Bias 13.1 Precision: Wet Density—Cri 13.1.1 Wet —Criteri teriaa for judgi judging ng the accep acceptabil tability ity of wet den densit sity y tes testt res result ultss obt obtain ained ed by thi thiss tes testt met method hod are given in Table Table 1. The figure in column three represents the standard deviations that have been found to be appropriate for the materials tested in column one. The figures given in column four are the limits that should not be exceeded by the difference betwee bet ween n the res result ultss of two pro proper perly ly con conduc ducted ted tes tests. ts. The figures given are based upon an interlaboratory study in which five test sites containing soils, with wet densities as shown in column two were tested by eight different nuclear gauges and operators. The wet density of each test site was measured three times by each device. 13.1.2 Water Content —Criteria —Criteria for judging the acceptability of the water content results obtained by this test method are given give n in Table Table 2. The value value in co colu lumn mn two is in th thee un unit itss actually reported by the nuclear gauge. The figures in column three represent the standard deviations that have been found to be app approp ropri riate ate for the mat materi erials als tes tested ted in col column umn one one.. The figures given in column four are the limits that should not be exceeded by the difference between the results of two properly conducted condu cted tests. The figures given are based upon an interlaboratory study in which five test sites containing soils, with water content as shown in column two were tested by eight different nuclear gauges and operators. The water content of each test site was measured three times by each device. 13.2 Bias: 13.2.1 There are no acce accepted pted reference reference values values for these test methods, therefore, bias cannot be determined
(6)
11.3.4 Report 11.3.4 Report the dry den densit sity y to the nearest nearest 1 kg/ kg/m m 3(0.1 3 lbm/ft ). 11.4 Determine the Percent Compaction: 11.4.1 11. 4.1 It may be desi desired red to express the in-place in-place dry densi density ty as a percentage of a laboratory density such as Test Methods D 698, 698, D 1557, 1557, D 4253, 4253, or or D D 4254. 4254. This relationship can be calculated by dividing the in-place dry density by the laboratory maximum dry density and multiplying by 100. Procedures for calculating relative density are provided in Test Method D 4254 which which req requir uires es tha thatt Test Met Method hod D 4253 also also be perfor per formed med.. Cor Correc rectio tions ns for ove oversi rsize ze mat materi erial, al, if req requir uired, ed, should be performed in accordance with Practice D 4718. 4718. 12. Report: Test Test Data Sheet(s)/Form(s)/Final Report(s) 12.1 The Field Data Records shall include, as a minimum, the following: 12.1.1 Te Test st Number or Test Identification. Identification. 12.1.2 Location of test test (for example, example, Station number number or GPS or Coordinates or other identifiable information). 12.1.3 Visu Visual al description of material tested. tested. 12.1.4 Lift number number or elevation elevation or depth depth.. 12.1.5 Name of the operator(s). operator(s). 12.1.6 Make Make,, model and serial number of the test gauge. 12.1.7 Test mode, Meth Method od A (dir (direct ect transmission transmission and test depth), or Method B (backscatter, backscatter/air-gap), 12.1.8 Stand Standardiz ardization ation and adjustment adjustment data for the date of the tests. 12.1.9 12. 1.9 Any cor correc rectio tions ns ma made de in the rep report orted ed val values ues and reasons for these corrections (that is, over-sized particles, water content).
14. Keyw Keywords ords 14.1 Compaction test; acceptance acceptance testing; construction construction control; quality control; field density; in-place density; wet density; sit y; wat water er con conten tent; t; dry den densit sity; y; nuc nuclea learr met method hods, s, nuc nuclea learr gauge 6
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D 6938 – 08a TABLE TAB LE 1 Results of Statistical Analysis (Wet Density)A Precision and Soil Average TypeB kg/m3 or (lbm/ft 3)
Single Operator Precision: Direct Transmissi Transmission: on: CL 1837 (114.7) SP 1937 (120.9) ML 2084 (130.1) Backscatter: ML 1996 (124.6) Multi-laboratory Multi-labora tory Precision: Direct Transmissi Transmission: on: CL 1837 (114.7) SP 1937 (120.9) ML 2084 (130.1) Backscatter: ML 1996 (124.6)
Standard Deviation kg/m3 or (lbm/ft 3)
Acceptable RangeC of Two Results kg/m3 or (lbm/ft 3)
5.4 (0.3) 4.3 (0.3) 7.4 (0.5)
15.1 (0.9) 11.8 (0.7) 20.5 (1.3)
19.4 (1.2)
54.3 (3.4)
10.6 (0.7) 10.9 (0.7) 12.3 (0.8)
29.8 (1.9) 30.6 (1.9) 34.4 (2.1)
38.1 (2.4)
106.8 (6.7)
A
The data used to establish this precision statement is contained in a Research Report available from ASTM Headquarters. Request RR: D18-1004. B For definitions of soil types see Practices D 2487 and 2487 and D 2488. 2488. C Two separate readings at a singular site with constant gauge orientation and settings.
TABLE TAB LE 2 Results of Statistical Analysis Analysis of % Water ContentA Precision and Soil TypeB
Average %
Standard Deviation %
Acceptable Range of Two Results C
0.38 0.45 0.32
0.9 1.2 0.9
0.50 0.73 0.52
1.4 2.0 1.5
Single Operator Precision: CL 11.8 SP 18.3 ML 17.7 Multi-laboratory Multi-laborat ory Precision: CL 11.8 SP 18.3 ML 17.7
A The data used to establish this precision statement is contained in a Research Report available from ASTM Headquarters. Request RR: D18-1004. B For definitions of soil types see Practices D 2487 and 2487 and D 2488. 2488. C Two separate readings at a singular site with constant gauge orientation and settings.
ANNEXES (Mandatory Information) A1. WET DENSITY CALIBRATION CALIBRATION & VERIFICATION
A1.1 Calibration: Gauges shall be calibrated initially and after aft er any rep repair airss tha thatt can affect affect the gau gauge ge geo geomet metry ry or the existi exi sting ng cal calibr ibrati ation. on. To be wit within hin spe specifi cified ed tol tolera erance ncess by procedure proce duress desc described ribed in A1.2, A1.2, calibrat calibration ion curv curves, es, tabl tables, es, or equiva equ ivalen lentt coe coefffici icient entss sha shall ll be ver verifie ified, d, at per period iodss not to exceed 12 months. At any time these tolerances cannot be met, the gau gauge ge sha shall ll be cal calibr ibrate ated d to est establ ablish ish new cal calibr ibrati ation on curves, tables, or equivalent coefficients. If the owner does not establish a verification procedure, the gauge shall be calibrated at a period not to exceed 12 months.
block density. The method used for calibration shall be capable of generating a general curve covering the entire density range of the materials to be tested in the field. The density of the bloc bl ock( k(s) s) sh shal alll be de dete term rmin ined ed in su such ch a ma mann nner er th that at th thee estimated standard deviation of the measurement results shall not exceed 0.2 % of the measured block density. A1.1.2 Reestablish or verify the density density of the block(s) used to calibrate or verify calibrations at a period not to exceed 5 year ye ars. s. Th Thee de dens nsit ity y va valu lues es of th thee es esta tabl blis ishe hed d bl bloc ock( k(s) s) of materi mat erials als tha thatt hav havee the pot potent ential ial for cha change ngess ove overr tim timee in density dens ity or mois moisture ture content, content, such as soil, concrete, concrete, or soli solid d rock, shall be reestablished or verified at periods not exceeding 12 months.
A1.1.1 Gauge Calibratio Calibration n Respo Response nse shall be with within in 6 16 3 3 kg/m (6 1.0 lbm/ft ) on the block(s) on which the gauge was calibrated. This calibration may be done by the manufacturer, the user, or an independent vendor. Nuclear gauge response is influenced by the chemical composition of measured materials. This response must be taken into account in establishing the
NOTE A1.1—Changes in background conditions or locations of blocks used for gau used gauge ge cal calibra ibration tionss or ver verific ificatio ation n of cal calibra ibration tionss can imp impact act measurements on those blocks. Care must be taken to ensure uniform
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D 6938 – 08a A1.2 Verification: The method used for verification should be capable of confirming the accuracy of the general calibration curve representing the density range of the materials to be tested in the field. The verification process and the resulting tolerances obtained over the depths at which the gauge will be used, use d, sha shall ll be for formal mally ly rec record orded ed and doc docume umente nted. d. If thi thiss verification process indicates a variance beyond the specified tolerances, the gauge shall be calibrated
conditions when performing gauge calibrations or verifying gauge calibrations.
A1.1.3 Suf Suffficie icient nt data shall be taken on each densi density ty block to ensure a gauge count precision of at least one-half the gauge count cou nt pre precis cision ion req requir uired ed for fiel field d use ass assumi uming ng fiel field d use measurement of one minute duration and four-minute duration used for cali calibrati bration, on, or an equiv equivalent alent relationshi relationship. p. The data may be pre presen sented ted in the form of a gra graph, ph, table, table, equ equati ation on coeffficie coef icients, nts, or stor stored ed in the gauge gauge,, to allow converting converting the count rate data to density. A1.1.4 The method and test procedures procedures used in establishing the calibration count rate data shall be the same as those used for obtaining the field count rate data. A1.1.5 A1. 1.5 The mat materi erial al typ type, e, act actual ual den densit sity y, or est establ ablish ished ed density of each calibration block used to establish or verify the gauge calibration shall be stated as part of the calibration data for each measurement depth. If the actual or established block density varies with measurement depth, then the density data for each mea measur sureme ement nt dep depth th sha shall ll be sta stated ted as par partt of the calibration. A1.1.6 The calibration blocks should be suffic sufficient ient in size so that the count rate will not change if the block is enlarged in any dimension.
A1.2.1 Gauge verification verification response shall be with within in 632 3 3 kg/m (62.0 lbm/ft ) on block(s) of established density at each calibration depth. A1.2.2 Using the proc procedure edure described described in eithe eitherr A3.1.1 or A3.1.2,, ensure a gauge count precision of at least one-half the A3.1.2 gauge count precision required for field use, assuming field use measurement of one-minute duration and four-minute duration are used for calibration, or an equivalent relationship. A1.2.3 The gauge calibration calibration may be verified on calibration calibration block( blo ck(s) s) whi which ch wer weree use used d for calibrat calibration ion of the gau gauge, ge, or prepared blocks. A1.2.4 Prepa Prepared red block(s) block(s) of soil, soli solid d rock, concrete, concrete, and engineere engi neered d block block(s) (s) that have chara character cteristi istics cs of repro reproducib ducible le uniformity may be used, but care must be taken to establish density values and to minimize changes in density and water content over time. A1.2.5 Densi Density ty values of prep prepared ared block(s) block(s) shall be dete deterrmined in such a manner that the estimated standard deviation of the mea measur sureme ement nt res result ultss sha shall ll not exc exceed eed 0.5 % of the measured block density value. A1.2.6 Reestablish Reestablish or veri verify fy densi density ty value valuess for prep prepared ared block(s) of soil, solid rock, or concrete that have the potential of changes over time in density or moisture content at periods not exceeding 12 months. A1.2.7 The method used to esta establis blish h or veri verify fy the bloc block(s) k(s) density values shall be stated as part of the verification data. A1.2. A1 .2.8 8 All ga gaug uges es sh shal alll be ve veri rifie fied d or ca cali libr brat ated ed at a minimum frequency of 12 months.
NOTE A1.2—Minimum surface dimensions of approximately 610 mm by 430 mm (24 3 17 inches), have proven satisfactory. For the backscatter method a minimum depth of 230 mm (9 inches) is adequate; while for the direct transmission method the depth should be at least 50 mm (2 inches) deeper than the deepest rod penetration penetration depth. A large largerr surface area should be considered for the backscatter/air-gap method. For blocks with widths or lengths smaller than the sizes specified, follow the block manufacturer’s recommendations for proper installation and use. The most successful blocks that have been established for calibration have been made of magnesium, aluminum, aluminum/magnesium, granite, and limestone. These blocks have been used in combina combination tion with each other,, with historical curve inform other information, ation, and with other prepa prepared red block(s) to produce accurate and reliable calibration.
A2. WATER CONTENT CALIBRA CALIBRATION TION and VERIFICA VERIFICATION TION
A2.1 Calibration: Gauges shall be calibrated initially and after any rep after repair airss tha thatt can affect affect the gau gauge ge geo geomet metry ry or the existing exist ing cali calibrat bration. ion. Calib Calibrati ration on curve curves, s, tabl tables, es, or equiv equivalen alentt coefffici coe icient entss sha shall ll be ver verifie ified d at per period iods, s, not exc exceed eeding ing 12 months, to be within specified tolerances by procedures described in A2.2 A2.2.. At any time these tolerances cannot be met, the gauge shall be calibrated to establish new calibration curves, tables, or equivalent coefficients. If the owner does not establish a verification procedure, the gauge shall be calibrated at a period not to exceed 12 months.
factory curve information, or historical data. Due to the effect of che chemi mical cal com compos positi ition, on, the cal calibr ibrati ation on sup suppli plied ed by the manufa man ufactu cturer rer wit with h the gau gauge ge wil willl not be app applic licabl ablee to all materials. It shall be accurate for silica and water; therefore, the calibr cal ibrati ation on mus mustt be ver verifie ified d and adj adjust usted, ed, if nec necess essary ary,, in accordance with section A2.2 A2.1.2 Reest Reestabli ablish sh or veri verify fy the assi assigned gned water content of blocks used to calibrate or verify calibrations at periods which shall be recommended by the block manufacturer. The water content values of blocks prepared of materials that have the potential of changes over time in density or moisture content, such as soil, concrete, or solid rock, shall be reestablished or verified at periods not exceeding 12 months. A2.1.3 All calibration blocks should be suffi sufficient cient in size so that the count rate will not change if the block is enlarged in any dimension.
A2.1.1 Gauge A2.1.1 Gauge Cal Calibr ibrati ation on Res Respon ponse se sha shall ll be wit within hin 16 3 3 kg/m (1 lbm/ lbm/ft ft ) on th thee bl bloc ock( k(s) s) on wh whic ich h th thee ga gaug ugee wa wass calibrated. This calibration may be done by the gauge manufacturer, the user, or an independent vendor. The block(s) used for calibration should be capable of generating a general curve covering the entire water content range of the materials to be tested teste d in the field field.. The calibration calibration curve can be esta establis blished hed using counts and water contents of standard blocks, previous
NOTE A2.1—Dimensions of approximately 610 mm long by 460 mm wide by 200 mm deep (approximately 24 by 18 by 8 inches) have proven
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D 6938 – 08a D 2937. 2937. The water content of the material at each of the test sites shall be determined using Test Method D 2216. 2216. Use the mean value of the replicate readings as the calibration point value for each test site.
satisfacto satisfa ctory ry.. For blocks with width or len length gth sma smaller ller than the siz sizes es specified, follow block manufacturer’s recommendations for proper installation and use.
A2.1.4 Prepa Prepare re a homog homogeneo eneous us block of hydro hydrogenou genouss materials having an equivalent water mass per unit volume value determined by comparison (using a nuclear instrument) with a saturated satur ated silica sand standard prepared prepared in accor accordance dance with A2.1.3.. Metallic blocks used for wet density calibration such as A2.1.3 magnesium or aluminum are a convenient zero water mass per unit volume block. A block of alternating sheets of aluminum or magnesium and polyethylene is convenient for a high water mass per unit volume block. A2.1.5 A2. 1.5 Pre Prepar paree con contai tainer nerss of com compac pacted ted ma mater terial ial wit with h a water content determined by oven dry (Test Method D 2216) 2216) and a wet density calculated from the mass of the material and the inside dimensions of the container. The water mass per unit volume may be calculated as follows: M m 5
r 3 w 100 1 w
A2.2 Verification: The method used used for verification verification should be capable of confirming the accuracy of the general calibration curve representing the water content of the materials to be tested tes ted in the fiel field. d. The ver verific ificati ation on pro proces cesss and res result ultant ant tolera tol erance ncess obt obtain ained ed sha shall ll be for formal mally ly rec record orded ed and doc docuumented. If the verification process indicates a variance beyond the spe specifi cified ed tol tolera erance nces, s, new cal calibr ibrati ation on cur curves ves,, tab tables les,, or equivalent coefficients shall be established. A2.2.1 Verif erify y an exis existing ting cali calibrat bration ion by taki taking ng suf suffi ficien cientt number of counts on one or more blocks of established water content to ensure the accuracy of the existing calibration within 616 kg/m3 or (61 lbm/ft3). The water content block(s) should be prepared in accordance with section A2.1.4 and A2.1.5 A2.2.2 Suff Sufficient icient data shall be taken to ensure a gauge count precision of at least one half the gauge count precision required for field use assuming field use measurement of one minute duration and four minute duration used for calibration, or an equivalent relationship. A2.2.3 Calibrati Calibration on bloc block(s) k(s) used to esta establish blish calibration calibration parameters and prepared blocks can be used to verify calibration. A2.2.4 Prepared block(s) that have characteristics characteristics of reproducibl duc iblee uni unifor formit mity y can be use used, d, but care mus mustt be tak taken en to minimize changes in density and water content over time. A2.2.5 The established established water content of the bloc block(s) k(s) used for verifica verificatio tion n of the gau gauge ge shall be sta stated ted as par partt of the verification data. A2.2. A2 .2.6 6 All ga gaug uges es sh shal alll be ve veri rifie fied d or ca cali libr brat ated ed at a minimum frequency of 12 months.
(A2.1)
Where: M m = water mass per unit unit volum volume, e, kg/m kg/m 3 or lbm/ft3, w = water conte content, nt, perc percent ent of dry mass mass,, and and r = wet (tot (total) al) dens density ity,, kg/m3 or lbm/ft 3. A2.1.6 Wher Wheree neit neither her of the previous calibrati calibration on stan standards dards are available, the gauge may be calibrated by using a minimum of three selected test sites in an area of a compaction project where whe re mat materi erial al has bee been n pla placed ced at sev severa erall dif differ ferent ent wat water er conten con tents. ts. The tes testt sit sites es sha shall ll rep repres resent ent the ran range ge of wat water er contents over which the calibration is to be used. At least three replicate nuclear measurements shall be made at each test site. The density at each site shall be verified by measurements with calibrated calib rated equipment equipment in acco accordanc rdancee with the proce procedure duress described scrib ed in this standard, standard, Test Meth Methods ods D 1556, 1556, D 2167, 2167, or
A3. GAUG GAUGE E PRECISION PRECISION
A3.1 Gauge precis precision ion is defined defined as the change change in density density or water mass per unit volume that occurs corresponding to a one standard deviation change in the count due to the random decay of the radioactive source. The density of the material and time period of the count must be stated.
of the signals (detected gamma rays or detected neutrons) in counts per minute (cpm), as follows: P 5 s / S S
(A3.1)
where: P = preci precision sion s = stand standard ard deviati deviation, on, cpm S = slope slope,, cpm/k cpm/kg/m g/m3 or cpm/lbm/ft 3
Calculate using the methods in either A3.1.1 A3.1.1 or or A3.1.2 A3.1.2.. For wet density , use a material having a density of 2000 6 80 kg/m3(125.0 6 5.0 lbm/ lbm/ft ft3). Typi Typica call va valu lues es of P ar aree < 10 kg/m3(0.6 lbm/ft 3) in backscatter or backscatter/air-gap; and < 5 kg/m3(0.3 lbm/ft 3) for direct transmission measured at a 15 cm (6 in) depth. Use a water mass per unit volume value of 160 6 10 kg/m3(10.0 6 0.6 lbm/ lbm/ft ft3) for determining determining slope and count rates. The value of P is typically less than 4.8 kg/m 3(0.3 lbm/ft3). A3.1.1 Gauge Precision - Slope Method Determine the gauge precision of the system, P, from the slope of the calibration curve, S , and the standard deviation, s ,
NOTE A3.1 A3.1—Di —Displa splayed yed gau gauge ge cou counts nts may be sca scaled led.. Con Contac tactt the manufacturerr to obtain the appropr manufacture appropriate iate pre-scale factor.
A3.1.2 Gauge Precision – Repetitive Method Determ Det ermine ine the sta standa ndard rd dev deviat iation ion of a mi minim nimum um of 20 repetitive repetiti ve readi readings ngs of one minute each, witho without ut movin moving g the gauge between readings. Calculate the standard deviation of the resulting readings. This is the gauge precision.
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D 6938 – 08a A4. FIELD MOISTURE MOISTURE CONTE CONTENT NT ADJUSTMENTS ADJUSTMENTS
A4.1 The calibration calibration should be checked prior to performing tests on mate material rialss that are dist distinctl inctly y dif differe ferent nt from material material types previously used in obtaining or adjusting the calibration. Sample materials may be selected by either A2.1.5 A2.1.5 or or A2.1.6 A2.1.6.. 6 The amount of water shall be within 2 % of the water content establishe estab lished d as opti optimum mum for compa compaction ction for these materials. materials. Determine the water content w. A microwave oven or direct heat he ater er ma may y be ut util iliz ized ed fo forr dr dryi ying ng ma mate teri rial alss th that at ar aree no nott sensitive to combustion of organic material, in addition to the method listed in A2.1.6 A2.1.6.. A minimum of three comparisons is recommended and the mean of the observed differences used as the correction factor.
A4.3 Tes Testt site(s) or the compacted material shall shall be selected selected in accordance with the procedures in A2.1.6 A2.1.6.. A4.4 The method method and test procedure proceduress used in obtaining obtaining the count rate to establish the error must be the same as those used for measuring the water content of the material to be tested. A4.5 A4 .5 Th Thee me mean an va valu luee of th thee di difffe fere renc ncee be betw twee een n th thee moisture content of the test samples as determined in A2.1.5 A2.1.5 or or A2.1.6 and A2.1.6 and the values measured with the gauge shall be used as a correction to measurements made in the field. Many gauges utilizing a microprocessor have provision to input a correction factor that is established by the relative values of water content as a percentage of dry density, thus eliminating the need to determine the difference in mass units of water.
A4.2 Conta Container( iner(s) s) of compacted compacted material material taken from from the test site shall be prepared in accordance with A2.1.5 A2.1.5..
SUMMARY OF CHANGES Committee Commit tee D18 has ide identi ntified fied the loc locati ation on of sel select ected ed cha change ngess to thi thiss sta standa ndard rd sin since ce the las lastt iss issue ue (D 6938 – 08) that may impact the use of this standard. (Approved June 1, 2008.) (1) The ph phra rase se “w “wat ater er co cont nten ent” t” is re repl plac aced ed in th thee th thre reee locations in A2.1.4 A2.1.4 with “water mass per unit volume.” This change is implemented because moisture calibration standards create cre ated d in the man manner ner des descri cribed bed in thi thiss sec secti tion on hav havee the their ir moisture values assigned as water mass per unit volume, not water content. (2) The two commas commas in the first sentence sentence of A2.1.4 have A2.1.4 have been removed. remo ved. The place placement ment of these commas left the sente sentence nce open to the interpretation that the water mass per unit volume
value assigned to the moisture calibration standards described in this section must be equivalent to the water mass per unit volume value of saturated silica sand. The actual intent of this sent se nten ence ce wa wass th that at th thee wa wate terr ma mass ss pe perr un unit it vo volu lume me va valu luee assign ass igned ed to the moi moistu sture re cal calibr ibrati ation on sta standa ndard rd be bas based ed on empirical measurements on that standard using an instrument thatt was cal tha calibr ibrate ated d wit with h sat satura urated ted sil silica ica sand as one of its calibration points.
Committee Commit tee D18 has ide identi ntified fied the loc locati ation on of sel select ected ed cha change ngess to thi thiss sta standa ndard rd sin since ce the las lastt iss issue ue (D 6938 – 07b) that may impact the use of this standard. (Approved February 1, 2008.) (1) The words “a horizonta horizontal” l” in the first sentence sentence of 10.2.2 are 10.2.2 are replac rep laced ed by the word “an “an.” .” Thi Thiss cha change nge is imp implem lement ented ed to remove language that would seem to indicate that the gauge
will only operate properly if its base is parallel with the plane of the horizon.
Committee Commit tee D18 has ide identi ntified fied the loc locati ation on of sel select ected ed cha change ngess to thi thiss sta standa ndard rd sin since ce the las lastt iss issue ue (D 6938 – 07) that may impact the use of this standard. (Approved Sept. 1, 2007.) (1) In Sec Secti tion on 9 9,, the form of the equation used to evaluate the standardi stand ardizati zation on count countss was made more math mathemat ematical ically ly com-
plex. In order to provide the user with guidance in solving this equation, and example problem was added as Section 9.3 9.3..
Commit Com mittee tee D18 has ide identi ntified fied the loc locati ation on of sel select ected ed cha change ngess to thi thiss sta standa ndard rd sin since ce the las lastt iss issue ue (D 6938 – 07) that may impact the use of this standard. (Approved July 1, 2007.) (1) “In“In-place place density” density” was replaced with “W “Wet et Density,” Density,” and “Dry Density” was added. Wet Density and Dry Density are terms defined in Terminology D Terminology D 653 and 653 and commonly known. Of course cou rse,, del deleti eting ng one defi definit nition ion and add adding ing two cau causes ses all definitions from 3.2.3 on to be incremented by one. Defining a “Source Rod” as a rod that can contain either a source or a
detector detect or lef leftt the doo doorr ope open n to the out outlan landis dish h pos possib sibil ility ity of defining a rod that contained no source and only a detector as a source rod. Consequently, “Source Rod” was replace with “probe”. Since the industry is familiar and comfortable with the term “source rod” for a probe that contains a source, the third sentence in the definition of probe in 3.2.7 was added. 10
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D 6938 – 08a (2) In Secti Section on 5.1.4 5.1.4,, it is recommended that the word “ground” be replaced with “soil or soil-aggregate” to be more technically specific about the measurement medium. (3) Con Concer cern n has bee been n rai raised sed abo about ut the dis disti tinct nction ion bet betwee ween n “verti “ve rtical cal mas mass” s” and “ve “verti rtical cal pro projec jectio tion” n” in Sec Sectio tion n 10.1. 10.1. Because of this concern, the two terms have been omitted, and the following rewrite of Section 10.1 10.1 has has been recommended. (4) The gravimetric water content content of soil and soil-aggregate soil-aggregate is defined in Section 1.3 1.3,, where “w” is also designated to denote the grav gravimet imetric ric water conte content. nt. It is there therefore fore redundant redundant and unnecessary to add “(%) of dry weight of soil” in 11.2.1 and “in percent of dry weight” in 11.2.2 after 11.2.2 after the variable w. It is therefore recommended that these two phrases be omitted. (5) In Se Sect ctio ion n A2.1 and and A2.2 A2.2,, the phrase “The method used
for ver verific ificati ation on sho should uld be cap capabl ablee of ver verify ifying ing the gen genera erall calibration curve” is used in the first sentence. Saying that the method met hod of ver verific ificati ation on sho should uld be cap capabl ablee of ver verify ifying ing is a circular statement that is not really saying anything specific. The purpose purpose of ver verific ificati ation on is to che check ck the accuracy accuracy of the calibration curve and evaluate whether or not it lies within the allowed tolerance. This purpose is stated specifically in A1.2.1 and A2.2.1 and A2.2.1,, so so A2.1 A2.1 and and A2.2 A2.2 should be consistent with this purpose. It is therefore recommended that A2.1 and and A2.2 A2.2 be re-written as follows. (6 ) In Secti Section on A1.2.1 A1.2.1,, 32 kg/m3 is actually 2.0 lbm/ft 3, not 2.9 lbm/ft 3. It is ther therefor eforee recom recommende mended d that this corr correcti ection on be made.
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