1、Designation: C876 09C876 15Standard Test Method forCorrosion Potentials of Uncoated Reinforcing Steel inConcrete1This standard is issued under the fixed designation C876; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of
2、last 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 electrical corrosion potential of uncoated reinforcing steel in field an
3、dlaboratory concrete, for the purpose of determining the corrosion activity of the reinforcing steel.1.2 This test method is limited by electrical circuitry. Concrete surface in building interiors and desert environments losesufficient moisture so that the concrete resistivity becomes so high that s
4、pecial testing techniques not covered in this test methodmay be required (see 5.1.4.1). Concrete surfaces that are coated or treated with sealers may not provide an acceptable electricalcircuit. The basic configuration of the electrical circuit is shown in Fig. 1.1.3 The values stated in inch-pound
5、units are to be regarded as standard. The values given in parentheses are mathematicalconversions to SI units that are provided for information only and are not considered standard.1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the re
6、sponsibilityof the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatorylimitations prior to use.2. Referenced Documents2.1 ASTM Standards:2E691 Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Me
7、thodG3 Practice for Conventions Applicable to Electrochemical Measurements in Corrosion TestingG15 Terminology Relating to Corrosion and Corrosion Testing (Withdrawn 2010)3G16 Guide for Applying Statistics to Analysis of Corrosion Data3. Terminology3.1 For definitions of terms used in this test meth
8、od, refer to Terminology G15.4. Significance and Use4.1 This test method is suitable for in-service evaluation and for use in research and development work.4.2 This test method is applicable to members regardless of their size or the depth of concrete cover over the reinforcing steel.Concrete cover
9、in excess of 3 in. (75 mm) can result in an averaging of adjacent reinforcement corrosion potentials that can resultin a loss of the ability to discriminate variation in relative corrosion activity.4.3 This test method may be used at any time during the life of a concrete member.4.4 The results obta
10、ined by the use of this test method shall not be considered as a means for estimating the structural propertiesof the steel or of the reinforced concrete member.4.5 The potential measurements should be interpreted by engineers or technical specialists experienced in the fields of concretematerials a
11、nd corrosion testing. It is often necessary to use other data such as chloride contents, depth of carbonation, delamination1 This test method is under the jurisdiction of ASTM Committee G01 on Corrosion of Metalsand is the direct responsibility of Subcommittee G01.14 on Corrosion ofMetals in Constru
12、ction Materials.Current edition approved April 1, 2009Nov. 1, 2015. Published May 2009April 2016. Originally approved in 1977. Last previous edition approved in 19992009 asC87691(1999)C876, which was withdrawn September 2008 and reinstated in April 2009. DOI: 10.1520/C0876-09.09. DOI: 10.1520/C0876-
13、15.2 For referencedASTM standards, visit theASTM website, www.astm.org, or contactASTM Customer Service at serviceastm.org. For Annual Book of ASTM Standardsvolume information, refer to the standards Document Summary page on the ASTM website.3 The last approved version of this historical standard is
14、 referenced on www.astm.org.This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Becauseit may not be technically possible to adequately depict all changes accurately, ASTM recommends
15、that users consult prior editions as appropriate. In all cases only the current versionof the standard as published by ASTM is to be considered the official document.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States1survey findings, rat
16、e of corrosion results, and environmental exposure conditions, in addition to corrosion potential measurements,to formulate conclusions concerning corrosion activity of embedded steel and its probable effect on the service life of a structure.5. Apparatus5.1 The testing apparatus consists of the fol
17、lowing:5.1.1 Reference Electrode:5.1.1.1 The reference electrode selected shall provide a stable and reproducible potential for the measurement of the corrosionpotential of reinforcing steel embedded in concrete over the temperature range from 32 to 120F (0 to 49C).5.1.1.2 For the purposes of this s
18、tandard, corrosion potentials shall be based upon the half-cell reaction Cu Cu+ + 2e-corresponding to the potential of the saturated copper-copper sulfate reference electrode as referenced to the hydrogen electrodebeing 0.30 V at 72F (22.2C).4 The copper-copper sulfate reference electrode has a temp
19、erature coefficient of approximately0.0005 V more negative per F for the temperature range from 32 to 120F (0 to 49C).5.1.1.3 Other reference electrodes having similar measurement range, accuracy, and precision characteristics to the copper-copper sulfate electrode may also be used. Calomel referenc
20、e electrodes have been used in laboratory studies. For concretesubmerged in seawater, using silver-silver chloride reference electrodes avoids chloride contamination problems that may occurwith copper-copper sulfate electrodes. Silver/silver chloride/potassium chloride reference electrodes are also
21、applied toatmospherically exposed concrete. Potentials measured by reference electrodes other than saturated copper-copper sulfate shouldbe converted to the copper-copper sulfate equivalent potential. The conversion technique can be found in Practice G3 and“Reference Electrodes, Theory and Practice”
22、 by Ives and Janz.54 Hampel, C. A., The Encyclopedia of Electrochemistry, Reinhold Publishing Co., New York, 1964, p. 433.5 Ives, D. J. G., and Janz, G. J., Reference Electrodes Theory and Practice, Academy Press, NY, 1961.FIG. 1 Reference Electrode CircuitryC876 1525.1.2 Electrical Junction DeviceA
23、n electrical junction device shall be used to provide a low electrical resistance liquid bridgebetween the surface of the concrete and the reference electrode. It shall consist of a sponge or several sponges pre-wetted with alow electrical resistance contact solution. The sponge may be folded around
24、 and attached to the tip of the reference electrode sothat it provides electrical continuity between the porous plug and the concrete member. The minimum contact area of theelectrochemical junction device shall be the area equivalent of a circle with 3 the nominal diameter of the concrete coarseaggr
25、egate to a maximum of 16 in.2 (0.01 m2).5.1.3 Electrical Contact SolutionIn order to standardize the potential drop through the concrete portion of the circuit, anelectrical contact solution shall be used to wet the electrical junction device. One such solution is composed of a mixture of 95mL of we
26、tting agent (commercially available wetting agent) or a liquid household detergent thoroughly mixed with 5 gal (19 L)of potable water. Under working temperatures of less than about 50F (10C), approximately 15 % by volume of either isopropylor denatured alcohol must be added to prevent clouding of th
27、e electrical contact solution, since clouding may inhibit penetrationof water into the concrete to be tested. Conductive gels may be employed to reduce drift in the measured corrosion potential thatcan derive from dynamic liquid junction potentials. On large horizontal reinforced concrete, such as b
28、ridges, preliminary cleaningof the concrete surface with “street sweepers” has proven successful.5.1.4 VoltmeterThe voltmeter shall allow dc voltage readings, have the capacity to be battery operated, and provide adequateinput impedance and ac rejection capability for the environment where this test
29、 method is applied.5.1.4.1 Prior to commencing testing, a digital voltmeter with a variable input impedance ranging from 10 to 200 MM maybe used to determine the input impedance required to obtain precision readings. The use of a meter with variable input impedanceavoids meter loading errors from hi
30、gh concrete resistivity.An initial reading is taken in the 10 MMposition and then switchingto successively higher impedances while watching the meter display until the reading remains constant through two successiveincreases. Then decrease the impedance on setting to reduce noise and provide the mos
31、t precise readings. If the voltmeter does notdisplay a constant reading through 200 M,M, then the use of galvanometer with input impedance of 1 or 2 GG should beconsidered. Logging voltmeters may also be used.5.1.4.2 Electromagnetic interference or induction resulting from nearby ac power lines or r
32、adio frequency transmitters canproduce error. When in the proximity of such interference sources, the readings may fluctuate. An oscilloscope can be used todefine the extent of the problem and be coupled with the dc voltmeter manufacturers specification for ac rejection capability todetermine resolu
33、tion of induced ac interference with successful application of this test method.5.1.5 Electrical Lead WiresThe electrical lead wire shall be of such dimension that its electrical resistance for the length usedwill not disturb the electrical circuit by more than 0.0001 V. This has been accomplished b
34、y using no more than a total of 500 linearft (150 m) of at leastAWG No. 24 wire. The wire shall be coated with a suitable insulation such as direct burial type of insulation.5.1.6 In addition to single reference electrodes connected to a voltmeter, multiple electrode arrays, reference electrodes wit
35、h awheel junction device and logging voltmeters that record distance and potential may also be used.FIG. 2 Sectional View of a Copper-Copper Sulfate Reference ElectrodeC876 1536. Calibration and Standardization6.1 Care of the Reference ElectrodeFollow the manufacturers instructions for storage, cali
36、bration, and maintenance.Electrodes should not be allowed to dry out or become contaminated. The porous plug (salt bridge) shall be covered when not inuse for long periods to ensure that it does not become dried to the point that it becomes a dielectric (upon drying, pores may becomeoccluded with cr
37、ystalline filling solution).6.2 Calibration of the Reference ElectrodeReference electrodes shall be calibrated against an approved standard traceable toa national standard at regular intervals. If cells do not produce the reproducibility or agreement between cells described in Section12, cleaning ma
38、y rectify the problem. If reproducible and stable readings are not achieved the reference electrode should bereplaced.6.3 Calibration of the VoltmeterThe voltmeter shall be calibrated against an approved standard traceable to a national standardat regular intervals.7. Procedure7.1 Spacing Between Me
39、asurementsWhile there is no pre-defined minimum spacing between measurements on the surface ofthe concrete member, it is of little value to take two measurements from virtually the same point. Conversely, measurements takenwith very wide spacing may neither detect corrosion activity that is present
40、nor result in the appropriate accumulation of data forevaluation. The spacing shall therefore be consistent with the member being investigated and the intended end use of themeasurements (Note 1).NOTE 1A spacing of 4 ft (1.2 m) has been found satisfactory for rapid evaluation of structures with larg
41、e horizontal surfaces like bridge decks.Generally, larger spacings increase the probability that localized corrosion areas will not be detected. Measurements may be taken in either a grid or arandom pattern. Spacing between measurements should generally be reduced where adjacent readings exhibit rea
42、ding differences exceeding 50 mV (areasof high corrosion activity). Cracks, cold joints, and areas with dynamic structural activity can produce areas of localized corrosion activity where thecorrosion potential can change several hundred millivolts in less than 1 ft (300 mm) and care must be given t
43、hat relatively large spacing between readingsdoes not miss areas of localized corrosion activity. For small, lightly reinforced members, it may be advantageous to map the reinforcement locationswith a cover meter and place the reference electrode over the bars on a suitable grid.7.2 Electrical Conne
44、ction to the Steel:7.2.1 The type of connection used will depend on whether a temporary or permanent connection is required. Make a directelectrical connection to the reinforcing steel by means of a compression-type ground clamp, by brazing or welding a protrudingrod, or by using a self tapping scre
45、w in a hole drilled in the bar. To ensure a low electrical resistance connection, scrape the baror brush the wire before connecting to the reinforcing steel to ensure a bright metal to bright metal contact. In certain cases, thistechnique may require removal of some concrete to expose the reinforcin
46、g steel. Electrically connect the reinforcing steel to thepositive terminal of the voltmeter. Special care should be exercised with prestressing steels to avoid serious injury and onlymechanical connections should be made. Where welding is employed to make connections to conventional reinforcing ste
47、el,preheating will be necessary to avoid forming a brittle area in the rebar adjacent to the weld and such welding should be performedby certified welders.7.2.2 Attachment must be made directly to the reinforcing steel except in cases where it can be documented that an exposedsteel member is directl
48、y attached to the reinforcing steel. Certain members, such as expansion dams, date plates, lift works,scuppers, drains, and parapet rails may not be attached directly to the reinforcing steel and, therefore, may yield invalid readings.Electrical continuity of steel components with the reinforcing st
49、eel can be established by measuring the resistance between widelyseparated steel components on the deck. Where duplicate test measurements are continued over a long period of time, identicalconnection points should be used each time for a given measurement.7.2.3 Care should be taken that the whole area of reinforcing mat being measured is electrically continuous by checkingelectrical continuity between diagonally opposite ends of the area surveyed.7.3 Electrical Connection to the Reference ElectrodeElectrically connect one end of the lead wire to
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