技報 第 16 号（2018 年）

Development of Titanium Wire Sensor for Corrosion Monitoringin the Concrete Structures

Headquarter

Technical Division, Rahmita Sari RAFDINALHeadquarter

Technical Division, Toshiyuki AOYAMAHeadquarter

Technical Division, Naotoshi FUKAGAWA

Abstract： This study was carried out to propose the titanium wire sensor with
3mm diameter as the new model of embeddable reference electrode to use incorrosion monitoring of concrete structures. The performance of titanium wiresensor exposed to variant temperature and linear polarization which comparedto silver-silver chloride electrode (SSE) as a verification electrode in feasibility
study conducted first. Then wire sensor embedded into the concrete structures
and testing by half-cell potential method was carried out to observe the reliabilityof wire sensor with various type of lengths (0.1 m, 1 m, and 2 m). The result
indicates that wire sensor exhibits stability in ambient temperature and reliable
to monitor the change of rebar potential in concrete as same as like the SSE
electrode. Moreover, the potential measured by embeddable wire sensors applied
to observe corrosion potential of rebar in the concrete and the average value of thenatural potential of rebar measured by SSE in the same section of wire sensor
position indicated similar trend. Also, wire sensor has features being able tomeasure rebar potential in concrete in wide range by changing the wire sensor
length.

Keywords：Titanium wire sensor, reference electrode, natural potential of rebar,
corrosion monitoring

1.

Introduction
Reinforced concrete may undergo physical deterioration (frost, cracking, fire, etc.), chemicaldegradation (acid attack, sea water attack, alkali-aggregate reaction, etc.) and steel corrosion.
Reinforcement steel corrosion is viewed as a major problem in the maintenance of the structural
integrity of concrete structures.
Half-cell potential (HCP) method is used worldwide as one of the non-destructive tests to detect andinspect the corrosion of reinforcing steel in concrete by measure the natural potential of rebar. In thismethod, the presence of corrosion on the rebar is judged by difference of the value of the potential
between the reference electrode and the rebar by using the digital multimeter. In the HCP method, thenatural potential of rebar is measured only in the vicinity where the movable reference electrode applies
on the surface of the concrete. This electrode is not efficient to use to investigate the deterioration ofconcrete structures with a large area. Also, reference electrodes are expensive, and the potential
readings are very influenced by the wet or dry conditions of the surface layer of the concrete.

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技報 第 16 号（2018 年）

On the other hand, a new generation of electrode called embeddable reference electrodes that arebeneficial in corrosion monitoring of concrete structures for long-term monitoring and inexpensive, andcould be connected to the internet based wireless system. It is difficult to count influence by the moisture
content of concrete.

Therefore, in this research, attempts have been made on the corrosion monitoring of reinforcing
steel in concrete structures by employing a small size embeddable titanium wire sensor with theflexible application. Stability of wire sensor exposed to variant temperature, linear polarization test,
and the natural potential of rebar in reinforced concrete (RC) beam measured by wire sensor
against SSE as verification electrode was reported.

2.

Feasibility Study of Titanium Wire Sensor

2.1 Experimental Outline
The wire sensor consists of titanium
probe activated with iridium-enriched
mixed metal oxide and 3 mm in diameter
was used as sensor electrodes in thisstudy. Photo-1 shows the schematic of theembeddable titanium wire sensor (WS)for concrete structures.
Electrical contact is through the body

Photo-1 Titanium wire sensor fabricated by P.S. Mitsubishi

length of wire sensor. Fifteen wire sensors were used to observe during this feasibility study. Sealant wasdesigned to keep long-term durability of WS and lead wire connection. The fifteen wire sensors with 100mm length exposed to under the variant of temperatures, i.e., 0 ºC, 31 ºC, 48 ºC, and 66 ºC.
2.2 Response Test of Wire Sensor ElectrodeAll the electrochemical tests wereperformed using voltmeter andpotentiostat devices.
The potential of WS electrode wasmeasured

underdifferenttemperatures (0 ºC, 31 ºC, 48 ºC, and66 ºC) to investigate the influence ofenvironmental temperature on theelectrode potential. Furthermore, thetemperature coefficients of these WS
was measured and compared with(a) Type 1(b) Type 2

Figure-1 Potential measurement method for wire sensor

reference electrodes such as CSE, Pband Mn/MnO2. Stability test and effect of temperature test for WS is illustrated in Figure-1(a).
The linear polarization condition corresponded to a potential sweep rate of 1 mV/s and potential
ranges of +200 to -1500 mV from the open circuit potential. Linear polarization measurement of WS
compared to SSE. The overview of this test is depicted in Figure-1(b). Here, “A” means Anode and “C”
means cathode.

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3.

Wire Sensor Embedded in RC Beam (150x2100x150 mm)

3.1. Outline of Specimen
The dimension of the specimen is 150 x 150 x 2100 mm as shownin Figure-1. The main rebar and stirrup use D13 as reinforcing

Table 1.Mix concrete proportions

steel with longitudinal and transversal distance arrangement of 75

W/C
(%)

Wmm and 200 mm, respectively. Wire sensors applied to the concrete

40170

Ckg/m3S1S2G1425

298991447

with various lengths of wire sensor; 5pcs @ 0.125 m, 1pcs @ 1 m,
and 1 pcs @ 2 m embedded longitudinally in the concrete near the main rebar. Water-cement ratio of40 % used in this RC beam as shown in Table 1.
ポテンショスタット
SSE 2m区 間 の 測 定 値
SSE 1m区 間 の 測 定 値

15020 110 20

プラスチック棒

S120 110 20
150

50

2,000

150

50

9@200=1,800

150

2,100

ワイ ヤセン サ ー ①

リード線

2,000
リード線
圧着端子

圧着端子

ワイ ヤセン サ ー ②
1,000500
WR1

ワイ ヤセン サ ー ⑤188125WR2250

125500

WR3250125WR4250125

WR5250125

188

Figure-2 Outline of RC beam specimen
3.2. Test Method
When the potential of rebar reading shifts from positive to more negative value, it means the rebar inconcrete corrodes. In this experiment, to partially change the potential in the axial direction of thespecimen, the potential of the red bar in the vicinity of the central part of the specimen (S1) was forciblychanged to -300 mV and -500 mV using the Potentiostat device. The potential of rebar in the axial
direction of the specimen measured with a commercially available reference electrode (referred to asSSE) from the concrete surface as shown in Figure-2. The measurement of SSE was carried out atintervals of 100 mm from the concrete surface. Furthermore, the potential of rebar measured withembedded WS electrodes with 0.125 m, 1 m and 2 m lengths of sensors against to SSE.

4.

Test Results

4.1. Effect of Temperature
Temperature is one of the external factors which affect the potential of a reference electrode (RE).
Potential of RE changes with temperature for the reason that both electrochemical reactions andchemical solubility. In electrical resistance, a temperature coefficient describes the relative change of aphysical property that associated with a given change in temperature. It is necessary to know thetemperature coefficient (TC) to minimize errors in potential reading and to know the electrical resistanceof RE. Equation (1) estimates the TC as following:
E = E025 + (t – 25) dE/dt(1)Here, E is potential of RE at t (mV), E025 is potential of RE at t = 25 ºC (mV), t is temperature (ºC) anddE/dt is temperature coefficient (mV/°C).
Figure-3(a) illustrates the effect of temperatures (i.e., 10 ºC, 31 ºC, 48 ºC, and 66 ºC) on the potential of
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WS against SSE electrode. From this test, it was observed that potential of WS steadily decreased withthe raised of temperature.
Furthermore, the bar charts in Figure-3(b) exhibit the temperature coefficient for several referenceelectrodes namely Titanium Wire Sensor (WS), Copper Sulphate Electrode (CSE), Plumbum Electrode(Pb) and Manganese Dioxide Electrode (Mn/MnO2). Accordingly to this figure, the TC of CSE and Pb
have the positive temperature coefficient which means the higher coefficient, the greater increase inelectrical resistance for a given temperature increase. Meanwhile, WS, SSE, and Mn/MnO2 have thenegative temperature coefficient which means the lower the coefficient, the greater decrease in electricalresistance for a given temperature increase. It means even though WS reference electrode shows
stability at ambient temperature, but it had a decrease in electrical resistance when the temperature
raised.

(a)(b)
Figure-3 Potential of wire sensor exposed to variant temperatures (a) and temperature coefficient (b)4.2. Linear Polarization
The graphs in Figure-4 show the potential ofrebar during linear polarization measurement
measured by WS and SSE. The potential of therebar was varied from + 200 mV to -1500 mV (vs.
SSE). The data measured by the WS electrodeexhibits the same trend as the SSE electrode evenwith 57 mV in difference. It indicates that WS isreliable to monitor the change of rebar potential inconcrete as same as SSE electrode.

Figure-4 Potential of rebar vs WS & SSE

4.3. Potential of Rebar Measured by Wire Sensor Electrodes
Figure-5 shows the potential distribution of rebar measured by 0.125 m, 1 m and 2 m lengths of wire
sensor, and SSE electrodes in the RC beam. Wire sensor 0.125 m was able to detect the anode potential
given in S1 position as same as SSE value. The small wire sensor was able to detect the local position if
the position of embedded close to the corrosion point. The potential readings by wire sensor 0.125 m
shown the same as SSE result in the same section position of measurement. Meanwhile, the potential of4/6

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rebar measured by 2m wire sensor indicates the same as the average potential of 0.125m wire sensors in
the 2m position of embedded.

(a)

(b)

Figure-5 Potential of rebar with potential shift -300 mV (a) and -500 mV (b) at S1 position,
respectively

(b)

(a)

Figure-6 Potential of rebar with potential shift -300 mV (a) and -500 mV (b) at S1 position,
respectively
Also, from the graphs in Figure-6, it is experimentally confirmed that potential of rebar measured by 1m and 2 m wire sensor has identical value with the average potential in 1m and 2m interval measured
by SSE. From Figure-5 and Figure-6 above, it's concluded that potential of rebar measured by 1 m and 2
m wire sensor will equal with the average value of SSE in the same section of measurement.
Also, from this results, it can be seen that wire sensor has features being able to measure rebar
potential in a wide measurement area in concrete by changing the wire sensor length. It means titanium
wire sensor is reliable to utilize as a reference electrode as same as like SSE electrode and user-friendly
to use in the wide measurement area.

5.

Conclusions

Based on the experimental results, the following findings are derived:
1)

Wire sensor reference electrode shows stability performance at ambient temperature, but it had adecrease in electrical resistance when the temperature raised.
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2)During linear polarization test to rebar, potential reading by wire sensor electrode indicates thesame trend as the SSE electrode. It means that wire sensor is reliable to monitor the change of rebar
potential in concrete.

3)

Wire sensor 0.125 m was able to detect the local corrosion in concrete if the position of embedded
close to the corrosion point.

4)

Potential of rebar measured by 1 m and 2 m wire sensor has similar value with the averagepotential in 1m and 2m interval measured by SSE. It means wire sensor has features being able tomeasure rebar potential in concrete in wide range by changing the wire sensor length.

References
1)

Ansuini, F. J., Dimond, J. R., “Long-Term Field Tests of Reference Electrodes for Concrete – Ten
Years Results”, Corrosion, NACE, Paper No. 01296, 2001.

2)

Japan Society of Civil Engineers., “Recommendation for Design and Construction ofElectrochemical Corrosion Control Method”, Concrete Library 1087, Nov., 2001.

3)

Maruthapandian, V., Saraswathy, V., Muralidharan, S., “Development of Solid State
Embeddable Reference Electrode for Corrosion Monitoring of Steel in Reinforced ConcreteStructures”, Cement and Concrete Composites, Vol. 74, pp. 100-108, No., 2016.

4)

Muralidharan, S., et. all., “A Promising Potential Embeddable Sensor for Corrosion Monitoring
Application in Concrete Structurs”, Measurement, Vol. 40, pp. 600-606, 2007.

5)

Muralidharan, S., et. all., “Evaluation of Embeddable Potential Sensor for Corrosion
Monitoring in Concrete Structures”, Electrochimica Acta, Vol. 53, pp. 7248-7254, 2008.

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