This test method covers the estimation of the electrical
corrosion potential of uncoated reinforcing steel in field and
laboratory concrete, for the purpose of determining the corrosion
activity of the reinforcing steel.
2. apparatus required
Fig. 1: Reference Electrode Circuitry of Corrosion Monitoring System
Fig. 2: Copper Sulphate Reference Electrode
The reference electrode selected shall provide a stable and reproducible potential for the measurement of the
corrosion potential of reinforcing steel embedded in concrete
over the temperature range from 32 to 120°F (0 to 49°C).
ASTM C876-15 “Standard Test Method for Corrosion Potentials of Uncoated Reinforcing Steel in Concrete”.
4.1 Spacing Between Measurements
While there is no
pre-defined minimum spacing between measurements on the
surface of the concrete member, it is of little value to take two
measurements from virtually the same point. Conversely,
measurements taken with very wide spacing may neither detect
corrosion activity that is present nor result in the appropriate
accumulation of data for evaluation. The spacing shall therefore
be consistent with the member being investigated and the
intended end use of the measurements.
4.2 Electrical Connection to the Steel
The type of connection used will depend on whether a
temporary or permanent connection is required. Make a direct
electrical connection to the reinforcing steel by means of a
compression-type ground clamp, by brazing or welding a
protruding rod, or by using a self tapping screw in a hole
drilled in the bar. To ensure a low electrical resistance
connection, scrape the bar or brush the wire before connecting
to the reinforcing steel to ensure a bright metal to bright metal
contact. In certain cases, this technique may require removal of
some concrete to expose the reinforcing steel. Electrically
connect the reinforcing steel to the positive terminal of the
voltmeter. Special care should be exercised with prestressing
steels to avoid serious injury and only mechanical connections
should be made. Where welding is employed to make connections
to conventional reinforcing steel, preheating will be
necessary to avoid forming a brittle area in the rebar adjacent
to the weld and such welding should be performed by certified
Attachment must be made directly to the reinforcing
steel except in cases where it can be documented that an
exposed steel member is directly 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 steel can be established by measuring
the resistance between widely separated steel components
on the deck. Where duplicate test measurements are continued
over a long period of time, identical connection points should
be used each time for a given measurement.
Care should be taken that the whole area of reinforcing
mat being measured is electrically continuous by checking
electrical continuity between diagonally opposite ends of the
4.3 Electrical Connection to the Reference Electrode
Electrically connect one end of the lead wire to the reference
electrode and the other end of this same lead wire to the
negative (ground) terminal of the voltmeter.
4.4 Pre-Wetting of the Concrete Surface
Saturate sponges with the Electrical Contact solution
and place on the concrete surface at locations described in 4.1.
Leave the sponges in place for the period of time till the measured value of the corrosion potential does not
change or fluctuate with time. Do not remove the
sponges from the concrete surface until after the reference
electrode potential reading is made. In making the corrosion
potential measurements, place the electrical junction device
firmly on top of the pre-wetting sponges for the duration of the measurement.
5. Recording Corrosion Potential Values
Record the electrical corrosion potentials to the nearest
0.01 V. Report all corrosion potential values in volts and
correct for temperature if the reference electrode temperature is outside the range of
72 ± 10°F (22.2 ± 5.5°C) as per para 188.8.131.52 of ASTM C876-15.
The corrosion categories are broken down from A to G. Category A being the higher possibility of corrosion.
||High Chance of Corrosion
||No Chance of Corrosion
Table 1 : Categorisation of chance of Corrosion