1、Designation: C 876 09Standard Test Method forCorrosion Potentials of Uncoated Reinforcing Steel inConcrete1This standard is issued under the fixed designation C 876; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last
2、revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method covers the estimation of the electricalcorrosion potential of uncoated reinforcing steel in field andlabor
3、atory concrete, for the purpose of determining the corro-sion activity of the reinforcing steel.1.2 This test method is limited by electrical circuitry.Concrete surface in building interiors and desert environmentslose sufficient moisture so that the concrete resistivity becomesso high that special
4、testing techniques not covered in this testmethod may be required (see 5.1.4.1). Concrete surfaces thatare coated or treated with sealers may not provide an accept-able electrical circuit. The basic configuration of the electricalcircuit is shown in Fig. 1.1.3 The values stated in inch-pound units a
5、re to be regardedas standard. The values given in parentheses are mathematicalconversions to SI units that are provided for information onlyand are not considered standard.1.4 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibilit
6、y 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 Standards:2G3 Practice for ConventionsApplicable to ElectrochemicalMeasurements in Corrosion TestingG15 Termino
7、logy Relating to Corrosion and CorrosionTestingG16 Guide forApplying Statistics toAnalysis of CorrosionData3. Terminology3.1 For definitions of terms used in this test method, refer toTerminology G15.4. Significance and Use4.1 This test method is suitable for in-service evaluation andfor use in rese
8、arch and development work.4.2 This test method is applicable to members regardless oftheir size or the depth of concrete cover over the reinforcingsteel. Concrete cover in excess of 3 in. (75 mm) can result inan averaging of adjacent reinforcement corrosion potentialsthat can result in a loss of the
9、 ability to discriminate variationin relative corrosion activity.4.3 This test method may be used at any time during the lifeof a concrete member.4.4 The results obtained by the use of this test method shallnot be considered as a means for estimating the structuralproperties of the steel or of the r
10、einforced concrete member.4.5 The potential measurements should be interpreted byengineers or technical specialists experienced in the fields ofconcrete materials and corrosion testing. It is often necessary touse other data such as chloride contents, depth of carbonation,delamination survey finding
11、s, rate of corrosion results, andenvironmental exposure conditions, in addition to corrosionpotential measurements, to formulate conclusions concerningcorrosion activity of embedded steel and its probable effect onthe service life of a structure.1This test method is under the jurisdiction of ASTM Co
12、mmittee G01 onCorrosion of Metals and is the direct responsibility of Subcommittee G01.14 onCorrosion of Metals in Construction Materials.Current edition approved April 1, 2009. Published May 2009. Originallyapproved in 1977. Last previous edition approved in 1999 as C 87691(1999),which was withdraw
13、n September 2008 and reinstated in April 2009.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.1Copyright ASTM
14、 International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.5. Apparatus5.1 The testing apparatus consists of the following:5.1.1 Reference Electrode:5.1.1.1 The reference electrode selected shall provide astable and reproducible potential for the measurement
15、of thecorrosion potential of reinforcing steel embedded in concreteover the temperature range from 32 to 120F (0 to 49C).5.1.1.2 For the purposes of this standard, corrosion poten-tials shall be based upon the half-cell reaction Cu Cu+ +2e- corresponding to the potential of the saturated copper-copp
16、er sulfate reference electrode as referenced to the hydro-gen electrode being 0.30 V at 72F (22.2C).3The copper-copper sulfate reference electrode has a temperature coefficientof approximately 0.0005 V more negative per F for thetemperature range from 32 to 120F (0 to 49C).5.1.1.3 Other reference el
17、ectrodes having similar measure-ment range, accuracy, and precision characteristics to thecopper-copper sulfate electrode may also be used. Calomelreference electrodes have been used in laboratory studies. Forconcrete submerged in seawater, using silver-silver chloridereference electrodes avoids chl
18、oride contamination problems3Hampel, C. A., The Encyclopedia of Electrochemistry, Reinhold PublishingCo., New York, 1964, p. 433.FIG. 1 Reference Electrode CircuitryFIG. 2 Sectional View of a Copper-Copper Sulfate ReferenceElectrodeC876092that may occur with copper-copper sulfate electrodes. Silver/
19、silver chloride/potassium chloride reference electrodes are alsoapplied to atmospherically exposed concrete. Potentials mea-sured by reference electrodes other than saturated copper-copper sulfate should be converted to the copper-copper sulfateequivalent potential. The conversion technique can be f
20、ound inPractice G3and “Reference Electrodes, Theory and Practice”by Ives and Janz.45.1.2 Electrical Junction DeviceAn electrical junctiondevice shall be used to provide a low electrical resistance liquidbridge between the surface of the concrete and the referenceelectrode. It shall consist of a spon
21、ge or several spongespre-wetted with a low electrical resistance contact solution.The sponge may be folded around and attached to the tip of thereference electrode so that it provides electrical continuitybetween the porous plug and the concrete member. Theminimum contact area of the electrochemical
22、 junction deviceshall be the area equivalent of a circle with 33 the nominaldiameter of the concrete coarse aggregate to a maximum of 16in.2(0.01 m2).5.1.3 Electrical Contact SolutionIn order to standardizethe potential drop through the concrete portion of the circuit, anelectrical contact solution
23、shall be used to wet the electricaljunction device. One such solution is composed of a mixture of95 mLof wetting agent (commercially available wetting agent)or a liquid household detergent thoroughly mixed with 5 gal(19 L) of potable water. Under working temperatures of lessthan about 50F (10C), app
24、roximately 15 % by volume ofeither isopropyl or denatured alcohol must be added to preventclouding of the electrical contact solution, since clouding mayinhibit penetration of water into the concrete to be tested.Conductive gels may be employed to reduce drift in themeasured corrosion potential that
25、 can derive from dynamicliquid junction potentials. On large horizontal reinforced con-crete, such as bridges, preliminary cleaning of the concretesurface with “street sweepers” has proven successful.5.1.4 VoltmeterThe voltmeter shall allow dc voltage read-ings, have the capacity to be battery opera
26、ted, and provideadequate input impedance and ac rejection capability for theenvironment where this test method is applied.5.1.4.1 Prior to commencing testing, a digital voltmeterwith a variable input impedance ranging from 10 to 200 MVmay be used to determine the input impedance required toobtain pr
27、ecision readings. The use of a meter with variableinput impedance avoids meter loading errors from high con-crete resistivity. An initial reading is taken in the 10 MVposition and then switching to successively higher impedanceswhile watching the meter display until the reading remainsconstant throu
28、gh two successive increases. Then decrease theimpedance on setting to reduce noise and provide the mostprecise readings. If the voltmeter does not display a constantreading through 200 MV, then the use of galvanometer withinput impedance of 1 or 2 GV should be considered. Loggingvoltmeters may also
29、be used.5.1.4.2 Electromagnetic interference or induction resultingfrom nearby ac power lines or radio frequency transmitters canproduce error. When in the proximity of such interferencesources, the readings may fluctuate. An oscilloscope can beused to define the extent of the problem and be coupled
30、 withthe dc voltmeter manufacturers specification for ac rejectioncapability to determine resolution of induced ac interferencewith successful application of this test method.5.1.5 Electrical Lead WiresThe electrical lead wire shallbe of such dimension that its electrical resistance for the lengthus
31、ed will not disturb the electrical circuit by more than 0.0001V. This has been accomplished by using no more than a total of500 linear ft (150 m) of at least AWG No. 24 wire. The wireshall be coated with a suitable insulation such as direct burialtype of insulation.5.1.6 In addition to single refere
32、nce electrodes connected toa voltmeter, multiple electrode arrays, reference electrodeswith a wheel junction device and logging voltmeters thatrecord distance and potential may also be used.6. Calibration and Standardization6.1 Care of the Reference ElectrodeFollow the manufac-turers instructions fo
33、r storage, calibration, and maintenance.Electrodes should not be allowed to dry out or becomecontaminated. The porous plug (salt bridge) shall be coveredwhen not in use for long periods to ensure that it does notbecome dried to the point that it becomes a dielectric (upondrying, pores may become occ
34、luded with crystalline fillingsolution).6.2 Calibration of the Reference ElectrodeReferenceelectrodes shall be calibrated against an approved standardtraceable to a national standard at regular intervals. If cells donot produce the reproducibility or agreement between cellsdescribed in Section 12, c
35、leaning may rectify the problem. Ifreproducible and stable readings are not achieved the referenceelectrode should be replaced.6.3 Calibration of the VoltmeterThe voltmeter shall becalibrated against an approved standard traceable to a nationalstandard at regular intervals.7. Procedure7.1 Spacing Be
36、tween MeasurementsWhile there is nopre-defined minimum spacing between measurements on thesurface of the concrete member, it is of little value to take twomeasurements from virtually the same point. Conversely,measurements taken with very wide spacing may neither detectcorrosion activity that is pre
37、sent nor result in the appropriateaccumulation of data for evaluation. The spacing shall there-fore be consistent with the member being investigated and theintended end use of the measurements (Note 1).NOTE 1Aspacing of 4 ft (1.2 m) has been found satisfactory for rapidevaluation of structures with
38、large horizontal surfaces like bridge decks.Generally, larger spacings increase the probability that localized corrosionareas will not be detected. Measurements may be taken in either a grid ora random pattern. Spacing between measurements should generally bereduced where adjacent readings exhibit r
39、eading differences exceeding 50mV (areas of high corrosion activity). Cracks, cold joints, and areas withdynamic structural activity can produce areas of localized corrosionactivity where the corrosion potential can change several hundred milli-volts in less than 1 ft (300 mm) and care must be given
40、 that relatively large4Ives, D. J. G., and Janz, G. J., Reference Electrodes Theory and Practice,Academy Press, NY, 1961.C876093spacing between readings does not miss areas of localized corrosionactivity. For small, lightly reinforced members, it may be advantageous tomap the reinforcement locations
41、 with a cover meter and place thereference electrode over the bars on a suitable grid.7.2 Electrical Connection to the Steel:7.2.1 The type of connection used will depend on whether atemporary or permanent connection is required. Make a directelectrical connection to the reinforcing steel by means o
42、f acompression-type ground clamp, by brazing or welding aprotruding rod, or by using a self tapping screw in a holedrilled in the bar. To ensure a low electrical resistanceconnection, scrape the bar or brush the wire before connectingto the reinforcing steel to ensure a bright metal to bright metalc
43、ontact. In certain cases, this technique may require removal ofsome concrete to expose the reinforcing steel. Electricallyconnect the reinforcing steel to the positive terminal of thevoltmeter. Special care should be exercised with prestressingsteels to avoid serious injury and only mechanical conne
44、ctionsshould be made. Where welding is employed to make connec-tions to conventional reinforcing steel, preheating will benecessary to avoid forming a brittle area in the rebar adjacentto the weld and such welding should be performed by certifiedwelders.7.2.2 Attachment must be made directly to the
45、reinforcingsteel except in cases where it can be documented that anexposed steel member is directly attached to the reinforcingsteel. Certain members, such as expansion dams, date plates,lift works, scuppers, drains, and parapet rails may not beattached directly to the reinforcing steel and, therefo
46、re, mayyield invalid readings. Electrical continuity of steel compo-nents with the reinforcing steel can be established by measur-ing the resistance between widely separated steel componentson the deck. Where duplicate test measurements are continuedover a long period of time, identical connection p
47、oints shouldbe used each time for a given measurement.7.2.3 Care should be taken that the whole area of reinforcingmat being measured is electrically continuous by checkingelectrical continuity between diagonally opposite ends of thearea surveyed.7.3 Electrical Connection to the Reference ElectrodeE
48、lectrically connect one end of the lead wire to the referenceelectrode and the other end of this same lead wire to thenegative (ground) terminal of the voltmeter.7.4 Pre-Wetting of the Concrete Surface:7.4.1 Under most conditions, the concrete surface or anoverlaying material, or both, must be pre-w
49、etted by either ofthe two methods described in 7.4.3 or 7.4.4 with the solutiondescribed in 5.1.3 to decrease the electrical resistance of thecircuit.7.4.2 A test to determine the need for pre-wetting shall bemade as follows:7.4.2.1 Place the reference electrode on the concrete surfaceand do not move.7.4.2.2 Observe the voltmeter for one of the followingconditions:(1) The measured value of the corrosion potential does notchange or fluctuate with time.(2) The measured value of the corrosion potential changesor fluctuates with time.7.4.2.3 If condition (1) is ob
