ASTM C876-91(1999)
(Test Method)Standard Test Method for Half-Cell Potentials of Uncoated Reinforcing Steel in Concrete (Withdrawn 2008)
Standard Test Method for Half-Cell Potentials of Uncoated Reinforcing Steel in Concrete (Withdrawn 2008)
SCOPE
1.1 This test method covers the estimation of the electrical half-cell potential of uncoated reinforcing steel in field and laboratory concrete, for the purpose of determining the corrosion activity of the reinforcing steel.
1.2 This test method is limited by electrical circuitry. A concrete surface that has dried to the extent that it is a dielectric and surfaces that are coated with a dielectric material will not provide an acceptable electrical circuit. The basic configuration of the electrical circuit is shown in Fig. 1.
1.3 The values stated in inch-pound units are to be regarded as the standard.
1.4 This standard does not purport to address the safety problems associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
WITHDRAWN RATIONALE
This test method covers the estimation of the electrical half-cell potential of uncoated reinforcing steel in field and laboratory concrete, for the purpose of determining the corrosion activity of the reinforcing steel.
Formerly under the jurisdiction of Committee G01 on Corrosion of Metals, this test method was withdrawn in August 2008 in accordance with section 10.5.3.1 of the Regulations Governing ASTM Technical Committees, which requires that standards shall be updated by the end of the eighth year since the last approval date.
General Information
Relations
Standards Content (Sample)
NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information
Designation:C876–91 (Reapproved 1999)
Standard Test Method for
Half-Cell Potentials of Uncoated Reinforcing Steel in
Concrete
This standard is issued under the fixed designation C876; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
1. Scope 3.5 The potential measurements should be interpreted by
engineers or technical specialists experienced in the fields of
1.1 This test method covers the estimation of the electrical
concretematerialsandcorrosiontesting.Itisoftennecessaryto
half-cell potential of uncoated reinforcing steel in field and
use other data such as chloride contents, depth of carbonation,
laboratory concrete, for the purpose of determining the corro-
delamination survey findings, rate of corrosion results, and
sion activity of the reinforcing steel.
environmental exposure conditions, in addition to half-cell
1.2 This test method is limited by electrical circuitry. A
potential measurements, to formulate conclusions concerning
concretesurfacethathasdriedtotheextentthatitisadielectric
corrosion activity of embedded steel and its probable effect on
and surfaces that are coated with a dielectric material will not
the service life of a structure.
provideanacceptableelectricalcircuit.Thebasicconfiguration
of the electrical circuit is shown in Fig. 1.
4. Apparatus
1.3 Thevaluesstatedininch-poundunitsaretoberegarded
4.1 The testing apparatus consists of the following:
as the standard.
4.1.1 Half Cell:
1.4 This standard does not purport to address the safety-
4.1.1.1 Acopper-copper sulfate half cell (Note 1) is shown
concerns, if any, associated with its use. It is the responsibility
in Fig. 2. It consists of a rigid tube or container composed of
of the user of this standard to establish appropriate safety and
a dielectric material that is nonreactive with copper or copper
health practices and determine the applicability of regulatory
sulfate, a porous wooden or plastic plug that remains wet by
limitations prior to use.
capillary action, and a copper rod that is immersed within the
2. Referenced Documents tubeinasaturatedsolutionofcoppersulfate.Thesolutionshall
be prepared with reagent grade copper sulfate crystals dis-
2.1 ASTM Standards:
solved in distilled or deionized water. The solution may be
G3 PracticeforConventionsApplicabletoElectrochemical
2 considered saturated when an excess of crystals (undissolved)
Measurements in Corrosion Testing
lies at the bottom of the solution.
3. Significance and Use 4.1.1.2 The rigid tube or container shall have an inside
diameter of not less than 1 in. (25 mm); the diameter of the
3.1 Thistestmethodissuitableforin-serviceevaluationand
porous plug shall not be less than ⁄2 in. (13 mm); the diameter
for use in research and development work.
oftheimmersedcopperrodshallnotbelessthan ⁄4in.(6mm),
3.2 This test method is applicable to members regardless of
and the length shall not be less than 2 in. (50 mm).
their size or the depth of concrete cover over the reinforcing
4.1.1.3 Present criteria based upon the half-cell reaction of
steel.
++
Cu→ Cu +2e indicate that the potential of the saturated
3.3 Thistestmethodmaybeusedatanytimeduringthelife
copper-copper sulfate half cell as referenced to the hydrogen
of a concrete member.
electrode is−0.316 V at 72°F (22.2°C). The cell has a
3.4 The results obtained by the use of this test method shall
temperature coefficient of about 0.0005 V more negative per°
not be considered as a means for estimating the structural
F for the temperature range from 32 to 120°F (0 to 49°C).
properties of the steel or of the reinforced concrete member.
NOTE 1—Whilethistestmethodspecifiesonlyonetypeofhalfcell,that
is, the copper-copper sulfate half cell, others having similar measurement
This test method is under the jurisdiction of ASTM Committee G01 on
range, accuracy, and precision characteristics may also be used. In
Corrosion of Metals and is the direct responsibility of Subcommittee G01.11 on
addition to copper-copper sulfate cells, calomel cells have been used in
Electrochemical Measurements in Corrosion Testing.
laboratory studies. Potentials measured by other than copper-copper
Current edition approved March 11, 1991. Published May 1991. Originally
sulfate half cells should be converted to the copper-copper sulfate
published as C876–77. Last previous edition C876–87.
Annual Book of ASTM Standards, Vol 03.02.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
C876–91 (1999)
FIG. 1 Copper-Copper Sulfate Half Cell Circuitry
G3 and it is also described in most physical chemistry or half-cell
technology text books.
4.1.2 Electrical Junction Device—An electrical junction
deviceshallbeusedtoprovidealowelectricalresistanceliquid
bridge between the surface of the concrete and the half cell. It
shall consist of a sponge or several sponges pre-wetted with a
low electrical resistance contact solution. The sponge may be
folded around and attached to the tip of the half cell so that it
provides electrical continuity between the porous plug and the
concrete member.
4.1.3 Electrical Contact Solution—In order to standardize
thepotentialdropthroughtheconcreteportionofthecircuit,an
electrical contact solution shall be used to wet the electrical
junctiondevice.Onesuchsolutioniscomposedofamixtureof
95mLofwettingagent(commerciallyavailablewettingagent)
or a liquid household detergent thoroughly mixed with 5 gal
(19 L) of potable water. Under working temperatures of less
than about 50°F (10°C), approximately 15% by volume of
either isopropyl or denatured alcohol must be added to prevent
clouding of the electrical contact solution, since clouding may
FIG. 2 Sectional View of a Copper-Copper Sulfate Half Cell
inhibit penetration of water into the concrete to be tested.
4.1.4 Voltmeter—The voltmeter shall have the capacity of
equivalent potential. The conversion technique can be found in Practice beingbatteryoperatedandhave 63%end-of-scaleaccuracyat
C876–91 (1999)
thevoltagerangesinuse.Theinputimpedanceshallbenoless steel can be established by measuring the resistance between
than 10 MV when operated at a full scale of 100 mV. The widely separated steel components on the deck. Where dupli-
divisions on the scale used shall be such that a potential cate test measurements are continued over a long period of
difference of 0.02 V or less can be read without interpolation. time, identical connection points should be used each time for
4.1.5 Electrical Lead Wires—The electrical lead wire shall a given measurement.
beofsuchdimensionthatitselectricalresistanceforthelength 6.3 Electrical Connection to the Half Cell—Electrically
used will not disturb the electrical circuit by more than 0.0001
connect one end of the lead wire to the half cell and the other
V.Thishasbeenaccomplishedbyusingnomorethanatotalof end of this same lead wire to the negative (ground) terminal of
500 linear ft (150 m) of at least AWG No. 24 wire. The wire
the voltmeter.
shall be suitably coated with direct burial type of insulation.
6.4 Pre-Wetting of the Concrete Surface:
6.4.1 Under certain conditions, the concrete surface or an
5. Calibration and Standardization
overlaying material, or both, must be pre-wetted by either of
5.1 CareoftheHalfCell—Theporousplugshallbecovered
the two methods described in 6.4.3 or 6.4.4 with the solution
when not in use for long periods to ensure that it does not
described in 4.1.3 to decrease the electrical resistance of the
become dried to the point that it becomes a dielectric (upon
circuit.
drying, pores may become occluded with crystalline copper
6.4.2 A test to determine the need for pre-wetting may be
sulfate). If cells do not produce the reproducibility or agree-
made as follows:
ment between cells described in Section 11, cleaning the
6.4.2.1 Placethehalfcellontheconcretesurfaceanddonot
copper rod in the half cell may rectify the problem. The rod
move.
may be cleaned by wiping it with a dilute solution of
6.4.2.2 Observe the voltmeter for one of the following
hydrochloricacid.Thecoppersulfatesolutionshallberenewed
conditions:
either monthly or before each use, whichever is the longer
(a) The measured value of the half-cell potential does not
period.Atnotimeshallsteelwooloranyothercontaminantbe
change or fluctuate with time.
used to clean the copper rod or half-cell tube.
(b) The measured value of the half-cell potential changes or
fluctuates with time.
6. Procedure
6.4.2.3 Ifcondition(a)isobserved,pre-wettingtheconcrete
6.1 Spacing Between Measurements—While there is no
surfaceisnotnecessary.However,ifcondition(b)isobserved,
pre-defined minimum spacing between measurements on the
pre-wetting is required for an amount of time such that the
surface of the concrete member, it is of little value to take two
voltage reading is stable (60.02 V) when observed for at least
measurements from virtually the same point. Conversely,
5 min. If pre-wetting cannot obtain condition ( a), either the
measurementstakenwithverywidespacingmayneitherdetect
electrical resistance of the circuit is too great to obtain valid
corrosion activity that is present nor result in the appropriate
half-cell potential measurements of the steel, or stray current
accumulation of data for evaluation. The spacing shall there-
fromanearbydirectcurrenttractionsystemorotherfluctuating
fore be consistent with the member being investigated and the
direct-current,suchasarcwelding,isaffectingthereadings.In
intended end use of the measurements (Note 2).
either case, the half-cell method should not be used.
NOTE 2—A spacing of 4 ft (1.2 m) has been found satisfactory for
6.4.3 Method A for Pre-Wetting Concrete Surfaces—Use
evaluation of bridge decks. Generally, larger spacings increase the
Method A for those conditions where a minimal amount of
probability that localized corrosion areas will not be detected. Measure-
pre-wetting is required to obtain condition (a) as described in
ments may be taken in either a grid or a random pattern. Spacing between
6.4.2.2. Accomplish this by spraying or otherwise wetting
measurements should generally be reduced where adjacent readings
either the entire concrete surface or only the points of mea-
exhibit algebraic reading differences exceeding 150 mV (areas of high
corrosion activity). Minimum spacing generally should provide at least a surement as described in 6.1 with the solution described in
100-mV difference between readings.
4.1.3.Nofreesurfacewatershouldremainbetweengridpoints
when potential measurements are initiated.
6.2 Electrical Connection to the Steel:
6.4.4 Method B for Pre-Wetting Concrete Surfaces—In this
6.2.1 Make a direct electrical connection to the reinforcing
method, saturate sponges with the solution described in 4.1.3
steel by means of a compression-type ground clamp, or by
and place on the concrete surface at locations described in 6.1.
brazing or welding a protruding rod.To ensure a low electrical
Leave the sponges in place for the period of time necessary to
resistance connection, scrape the bar or brush the wire before
obtain condition (a) described in 6.4.2.2. Do not remove the
connecting to the reinforcing steel. In certain cases, this
sponges from the concrete surface until after the half-cell
technique may require removal of some concrete to expose the
potential reading is made. In making the half-cell potential
reinforcing steel. Electrically connect the reinforcing steel to
measurements,placetheelectricaljunctiondevicedescribedin
the positive terminal of the voltmeter.
4.1.2 firmly on top of the pre-wetting sponges for the duration
6.2.2 Attachment must be made directly to the reinforcing
of the measurement.
steel except in cases where it can be documented that an
6.5 Underwater, Horizontal, and Vertical Measurements:
exposed steel member is directly attached to the reinforcing
steel. Certain members, such as expansion dams, date plates, 6.5.1 Potential measurements detect corrosion activity, but
lift works, and parapet rails may not be attached directly to the not necessarily the location of corrosion activity. The precise
reinforcing steel and, therefore, may yield invalid readings. location of corrosion activity requires knowledge of the elec-
Electrical continuity of steel components with the reinforcing trical resistance of the material between the half cell and the
C876–91 (1999)
corroding steel. While underwater measurements are possible, 8.1.2 Cumulative Frequency Distribution— To determine
results regarding the location of corrosion must be interpreted the distribution of the measured half-cell potentials for the
verycarefully.Oftenitisnotpossibletopreciselylocatepoints concretemember,makeaplotofthedataonnormalprobability
of underwater corrosion activity in salt water environments paper in the following manner:
because potential readings along the member appear uniform. 8.1.2.1 Arrange and consecutively number all half-cell po-
However, the magnitude of readings does serve to indicate tentials by ranking from least negative potential to greatest
whether or not active corrosion is occurring. Take care during negative potential.
allunderwatermeasurementsthatthehalfcelldoesnotbecome 8.1.2.2 Determine the plotting position of each numbered
contaminated and that no part other than the porous tip of the half-cell potential in accordance with the following equation:
copper-copper sulfate electrode half cell comes in contact with
r
f 5 3100 (1)
water. x
(n 11
6.5.2 Perform horizontal and vertically upward measure-
where:
ments exactly as vertically downward measurements. How-
f = plotting position of total observations for the ob-
x
ever, additionally ensure that the copper-copper sulfate solu-
served value,%,
tion in the half cell makes simultaneous electrical contact with
r = rank of individual half-cell potential, and
the porous plug and the copper rod at all times.
(n = total number of observations.
8.1.2.3 Label the ordinate of the probability paper “Half-
7. Recording Half-Cell Potential Values
Cell Potential (Volts, CSE),” where CSE is the designation for
7.1 Record the electrical half-cell potentials to the nearest
copper-copper sulfate electrode. Label the abscissa of the
0.01V.Reportallhalf-cellpotentialvaluesinvoltsandcorrect
probability paper “Cumulative Frequency (%).” Draw two
fortemperatureifthehalf-celltemperatureisoutsidetherange
horizontal parallel lines intersecting the−0.20 and−0.3
...
Questions, Comments and Discussion
Ask us and Technical Secretary will try to provide an answer. You can facilitate discussion about the standard in here.