1、Designation: G51 95 (Reapproved 2012)Standard Test Method forMeasuring pH of Soil for Use in Corrosion Testing1This standard is issued under the fixed designation G51; the number immediately following the designation indicates the year of originaladoption or, in the case of revision, the year of las
2、t revision. A number in parentheses indicates the year of last reapproval. A superscriptepsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method covers a procedure for determining thepH of a soil in corrosion testing. The principle use of the testis
3、 to supplement soil resistivity measurements and therebyidentify conditions under which the corrosion of metals in soilmay be accentuated (see G5778(1984).1.2 The values stated in SI units are to be regarded asstandard. No other units of measurement are included in thisstandard.1.3 This standard doe
4、s not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Stan
5、dards:2E177 Practice for Use of the Terms Precision and Bias inASTM Test MethodsE691 Practice for Conducting an Interlaboratory Study toDetermine the Precision of a Test MethodG57 Test Method for Field Measurement of Soil ResistivityUsing the Wenner Four-Electrode Method3. Significance and Use3.1 In
6、formation on pH of soil is used as an aid in evaluatingthe corrosivity of a soil environment. Some metals are moresensitive to the pH of their environment than others, andinformation on the stability of a metal as a function of pH andpotential is available in the literature.34. Apparatus4.1 pH Meter
7、sA portable, battery-powered pH meter isnecessary for field measurements. Most instruments can alsofunction as a high-impedance voltmeter. An LCD display ispreferred for its readability in a bright, outdoor environment.4.2 Calomel and Glass Electrodes:4.2.1 Use a saturated calomel reference electrod
8、e or itsequivalent in the pH determination. A few crystals of solidpotassium chloride should always be present within the cham-ber surrounding the calomel to assure that the solution issaturated under the conditions of use. The design of theelectrode must permit the formation of a fresh liquid junct
9、ionbetween the solution of potassium chloride and the buffer ortest soil for each test and allow traces of soil to be readilyremoved by washing.4.2.2 A glass electrode of rugged construction is required.The performance of the glass electrode is satisfactory if itfurnishes the correct pH value (60.1
10、pH unit) for standardbuffered solutions.4.2.3 A combination electrode consisting of a saturatedcalomel reference electrode and a glass electrode (4.2.1 and4.2.2) combined as a single electrode is acceptable. However,the requirements outlined above are equally applicable to theelectrodes used in this
11、 combination unit.4.3 Subsurface ProbeWhen pH measurements below thesurface of the soil are required, it is necessary to use a probe ofsuitable length which will allow measurements to be made atthe depth of interest. This probe consists of a glass electrode ora combination electrode in a rubber hous
12、ing at the end of aplastic tube. One type of probe is illustrated in Fig. 1.4.4 Soil ThermometerSome pH electrodes have tempera-ture compensation built in as part of the pH electrode, but mostdo not (see manufacturers specifications). A thermometer ofrugged construction is required for soil use, and
13、 a stainlesssteel sheathed thermometer is preferred. Metal sheathed ther-mometers come in different lengths, and a length appropriatefor the depth of interest should be chosen.1This test method is under the jurisdiction of ASTM Committee G01 onCorrosion of Metals and is the direct responsibility of
14、Subcommittee G01.10 onCorrosion in Soils.Current edition approved May 1, 2012. Published June 2012. Originallyapproved in 1977. Last previous edition approved in 2005 as G5195(2005). DOI:10.1520/G0051-95R12.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer
15、 Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.3Pourbaix, M., Atlas of Electrochemical Equilibria in Aqueous Solutions,Pergamon Press, 1966.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box
16、C700, West Conshohocken, PA 19428-2959, United States.5. Reagents and Materials5.1 During the calibration procedure for the pH meter,standard buffered solutions of known pH are necessary. Thesesolutions, or tablets to make up these solutions, can bepurchased from chemical supply companies or pH equi
17、pmentmanufacturers.6. Sampling6.1 By the nature of the measurement, pH is determined fora small volume of soil at each reading, and it is important thatat least three measurements at different locations be made anda simple average calculated. The regions of interest, surface,subsurface, or both, whe
18、re applicable, must be sampled.7. Calibration and Standardization7.1 Test for LinearityPrior to field use, or periodicallywhen used extensively in the field, test the apparatus forlinearity of response. This procedure is as follows:7.1.1 Turn on the instrument, allow to warm up thoroughly,and bring
19、to electrical balance in accordance with the manu-facturers instructions. Before use, clean and rinse the glass andcalomel electrodes in distilled water.47.1.2 At least two standard buffered pH solutions that spanthe soil pH to be measured are required. From practicalexperience standard solutions of
20、 pH 4, 7, and 8 are recom-mended. For the test, the temperature of these solutions shallnot differ from each other by more than 5C. A laboratorythermometer can be used for these measurements.7.1.3 Adjust the temperature compensating dial on the pHmeter to the standard solution temperature.7.1.4 Imme
21、rse the electrodes in a small volume of the firstknown standard solution. Now adjust the pH meter to read thisknown pH.7.1.5 Remove the electrodes from the first standard solution,and rinse in distilled water. Immerse the electrodes in thesecond known standard solution and read the pH value. Judgeth
22、e system to be operating satisfactorily if the reading obtainedfor the second standard agrees within 60.1 unit of the assignedpH.7.2 Calibration of pH MeterCalibrate the pH meter im-mediately before use. If a series of measurements are to bemade, repeat the calibration procedure at intervals of abou
23、t 30min. Perform the pH meter calibration as follows:7.2.1 Use a standard pH solution in the range of the pH ofthe soil to be tested, if such information is known beforehand.Otherwise, begin with a standard solution having a pH of 7.Stabilize the temperature of the solution so that it matches thetem
24、perature of the soil to within 10C.7.2.2 Immerse the electrodes in the known standard solutionand calibrate the meter in accordance with the manufacturersinstructions.8. Procedure8.1 Soil Preparation for pH Determination:8.1.1 Ideally the pH measurement should be made in thefield with the glass elec
25、trode contacting the soil at the specificdepth of interest. If the surface soil pH is desired, then the soilcan be broken up if compacted so as to accept the electrodes.If a subsurface pH is desired, then a boring or an excavationmust be done so that the electrode can be placed in the soil atthe des
26、ired depth. The subsurface probe (Fig. 1) is ideal for usewith a boring tool such as hand auger. After boring through thesoil to the depth of interest, carefully lower the probe into thecavity without further preparation of the soil.8.1.2 Soil samples can be brought to the surface with aboring tool
27、or a post-hole digger, and the measurement made inthe field on the soil thus obtained. This technique is lessdesirable than the probe method described in this section.8.1.3 The least desirable pH measurement of soil is thatwhich is based on a soil sample transported to a laboratory forevaluation. Ho
28、wever, if this must be done, then make the pHmeasurement as quickly as possible after the soil is taken fromthe field. Place the sample in a clean, airtight, glass containeror plastic bag so that the soil is not in contact with any metal.If the pH measurement is not made within 24 h from the timethe
29、 soil sample is taken, then it is recommended that the soilsample be packed in dry ice to retard any change in pH due tochemical or biological reactions. Make the pH measurement onthe soil at room temperature and as received.8.1.3.1 The addition of water to the soil is not recommendedfor any case be
30、cause some soils are so poorly buffered thatadded moisture will change their pH. However, if a soil is4Before use, condition new glass electrodes and those that have been stored dryin accordance with the manufacturers recommendations.FIG. 1 Subsurface ProbeG51 95 (2012)2extremely dry with a resistiv
31、ity exceeding 106V-cm, a condi-tion not normally encountered, then the pH measurementcannot and should not be made. This situation will manifestitself with a random drifting of the pH meter reading.8.1.3.2 If the soil is frozen, it must be thawed prior tomaking the measurement. Frozen soil manifests
32、 itself byrandom drifting of the pH meter reading and is verified by thesoil temperature measurement.8.2 Determination of pH of Soil:8.2.1 Complete the meter calibration procedure (7.2). Thestandard solution temperature must match the temperature ofthe soil within 10C. Soil temperature can be determ
33、ined byinserting a metal sheathed thermometer into the soil to thedepth of interest.8.2.2 Clean the electrode surface by washing with distilledwater.8.2.3 Press the contact area of the glass electrode orcombination electrode, as the case may be, against undisturbedsoil at the location of interest. T
34、his step is important, since poorsoil contact or electrode movement can affect stability of themeasurement.8.2.4 The reference electrode should be placed in contactwith the soil near the glass electrode (this step is not requiredwhen using a combination-type electrode). An electrode sepa-ration of a
35、bout 30 cm is suggested for surface measurements.For subsurface readings, the reference electrode may be placedon the surface about 30 cm from the bore hole entry.8.2.5 With the electrode(s) in place, set the meter to readpH, allowing 1 or 2 min for equilibrium to be established, thentake the meter
36、reading.8.2.6 After approximately 1 min, repeat the meter reading.In general, the values will agree within 0.2 pH units. If therange of values is as large as 0.4, then repeat 8.2.3.Iftheproblem persists, check your equipment to verify that it isoperating properly, and check your measurement techniqu
37、e asdescribed in Procedure, Section 8, in this test method. Where asoil is extremely dry, it may not be possible to make a pHmeasurement as stated in 8.1.3.1. Where the soil is frozen, itmust be thawed as indicated in 8.1.3.2. Repeat Calibration ofpH Meter (7.2) if equipment malfunction is suspected
38、, whichmay cause erratic pH readings. Finally, if erratic readingspersist, it may be necessary to repeat the measurement at a newlocation in the vicinity of interest.9. Precision and Bias9.1 Interlaboratory Test ProgramAn interlaboratoryround robin was run during the May 1993 ASTM G1 meetinginAtlant
39、a, GA, in which the pH of two soils, randomly selectedfrom the grounds of the hotel, was measured with equipmentbrought to the meeting by each of the nine participants. Exceptfor the use of only two materials, Practice E691 was followedfor the design and analysis of the data. Details of the designan
40、d analysis of the data are given in the research report.59.2 Test ResultThe precision information given below inunits of pH is for the comparision of two test results, each ofwhich is an average of three determinations.9.3 Precision:Material A Material BAverage Test Value 4.53 4.2095 % repeatability
41、 limit (within lab) 0.27 0.1695 % reproducibility limit (between labs) 0.52 0.22The above terms (repeatability limit and reproducibilitylimit) are used as specified in Practice E177. The respectivestandard deviation among test results may be obtained bydividing the above limit values by 2.8.9.4 Bias
42、The procedure in this test method for measuringpH of soil has no bias because the value of pH is defined onlyin terms of this test method.10. Keywords10.1 corrosion of metals in soil; field measurement of pH;measurement of pH; pH of soil; soil pH for corrosion testing;test method for soil pH; underg
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46、he ASTM Committee on Standards, at the address shown below.This standard is copyrighted by ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959,United States. Individual reprints (single or multiple copies) of this standard may be obtained by contacting ASTM at th
47、e aboveaddress or at 610-832-9585 (phone), 610-832-9555 (fax), or serviceastm.org (e-mail); or through the ASTM website(www.astm.org). Permission rights to photocopy the standard may also be secured from the ASTM website (www.astm.org/COPYRIGHT/).5Supporting data have been filed at ASTM International Headquarters and maybe obtained by requesting Research Report RR:G01-1011.G51 95 (2012)3
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