Application of Sacrificial Point Anode for Prevention of SteelCorrosion in Cracked ConcreteMuhammad Akbar Caronge , Hidenori Hamada Rita Irmawaty, , Yasutaka Sagawa

Journal of Advanced Concrete Technology, volume ( ), pp.13 2015 479-488

Daisuke Yamamoto,

Steel Corrosion Induced by Chloride or Carbonation in Mortar with Bending Cracks or JointsShin-ichi Miyazato , Nobuaki OtsukiJournal of Advanced Concrete Technology, volume ( ), pp.8 2010 135-144

Test Method for Cracking Resistance of Cover Concrete due to Corrosion of ReinforcementHiroshi Shima , Songkram PiyamahantJournal of Advanced Concrete Technology, volume ( ), pp.9 2011 169-176

Durability against Steel Corrosion of HPFRCC with Bending CracksShin-ichi Miyazato , Youichi HiraishiJournal of Advanced Concrete Technology, volume ( ), pp.11 2013 135-143

Crack Formation and Chloride Induced Corrosion in Reinforced Strain Hardening Cement-BasedComposite (R/SHCC)Suvash C. Paul , Gideon P. A. G. van ZijlJournal of Advanced Concrete Technology, volume ( ), pp.12 2014 340-351

Journal of Advanced Concrete Technology Vol. 13, 479-488, October 2015 / Copyright © 2015 Japan Concrete Institute 479

Scientific paper

Application of Sacrificial Point Anode for Prevention of Steel Corrosion in Cracked Concrete Muhammad Akbar Caronge1*, Hidenori Hamada2, Rita Irmawaty3, Yasutaka Sagawa4 and Daisuke Yamamoto5

Received 22 March 2015, accepted 16 October 2015 doi:10.3151/jact.13.479

Abstract The effectiveness of a commercially available sacrificial point anode for corrosion prevention of steel in cracked concrete is presented. Reinforced concrete prisms with dimensions of 150 mm x 150 mm x 500 mm were prepared with a water to cement ratio (W/C) of 0.4 showing crack widths ranging from 0.1 to 0.4 mm obtained by pre-cracking. These specimens were exposed to three conditions: (1) laboratory air (temperature of 20±2°C and relative humidity of 60%); (2) immersed in 3% NaCl solution; and (3) dry/wet cycles of above mentioned conditions. Measurements included the free corrosion potential, polarization behavior of the sacrificial point anode, anodic-cathodic polarization curve of the reinforcement steel and visual observation. The test results show that the sacrificial point anode was effective to prevent the embedded steel from corrosion in cracked concrete. Specimens exposed to dry/wet cycles or immersed in 3% NaCl solution demonstrated a better protection than those exposed to laboratory air due to the high moisture condition. Thus, a sacrificial point anode becomes active to protect the steel bars even in cracked concrete.

1. Introduction

The presence of cracks in reinforced concrete can reduce the service life of a structure by permitting more rapid access of moisture, chloride ions and oxygen to the embedded steel bar, thus causing damage to the passive film which eventually results into corrosion initiation. From there, a series of events cause progressive dete-rioration of the concrete. The corrosion products of iron oxides and hydroxides deposited in the restricted space between concrete and steel bar will set up expansive force which eventually will lead to the cracking and spalling of the concrete cover, followed by further contamination and deterioration (Saraswathy and Won Song 2007).

In general, there are two types corrosion cells exist for steel bar in concrete namely microcell corrosion and macrocell corrosion. Microcell corrosion is defined that the anodic and cathodic reactions take place closely side by side. While for macrocell corrosion both the anodic and cathodic reactions take place some distance apart.

In the last decades many studies have been carried out to investigate the effect of crack width on the corrosion rate of steel bars. Several researchers found a clear relationship between crack width and corrosion rate (Okada and Miyagawa 1980; Ohno et al. 1986) in the case that a crack permits oxygen and chloride ions to reach the steel bars. Furthermore, Suzuki et al. (1990) reported that for specimen with a single crack, the steel bars in a cracked area were depassivated earlier than in an uncracked area which was attributed to macrocell corrosion.

Most of design codes specify limiting values for crack widths in a reinforced concrete structure from a durability point of view (Japan Society of Civil Engineers – JSCE 1986; British Standard Institution-BSI 1992; Bureau of Indian Standards - BIS 2005; American Concrete Institute - ACI 2009). However, the limitation of crack width does not guarantee the prevention of reinforcement corrosion on the long term.

Several protection techniques have been developed including the use of corrosion inhibitors (Nmai et al. 1982; Collepardi et al. 1990). However, the results showed that the addition of corrosion inhibitor did not perform well to prevent macrocell corrosion in cracked concrete. Another way of achieving corrosion prevention is the use of cathodic protection to cracked reinforced concrete by means of sacrificial point anodes. On the other hand, the use of cathodic protection for new con-structions is relatively expensive. However, prevention of further corrosion of deteriorated reinforced concrete structure can be competitively achieved through cathodic protection (Fratesi et al. 1992).

Recently, sacrificial point anodes have become com-mercially available. The anode material is zinc-based metal embedded in porous mortar containing a lithium

1Doctoral Student, Graduate School of Engineering,Kyushu University, Fukuoka, Japan. Corresponding author, E-mail: caronge_eng@yahoo.co.id 2Professor, Department of Civil Engineering, Kyushu University, Fukuoka, Japan. 3Associate Professor, Department of Civil Engineering, Hasanuddin University, Makassar, Indonesia. 4Associate Professor, Department of Civil Engineering, Kyushu University, Fukuoka, Japan. 5Technical Officer, Department of Civil Engineering, Kyushu University, Fukuoka, Japan.

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monohydrate solution to maintain the zinc in an active corrosion state. The type and sizes of this sacrificial point anode are variable, depending on the manufacturing and distributing company. The anode used in this study is commercially available with a diameter of 60 mm and a thickness of 30 mm as shown in Fig. 1. In addition, these anodes are already on the market for more than 10 years.

The objective of this research is to investigate the possibility of using commercially available sacrificial point anodes for prevention of steel corrosion in cracked concrete. In addition, some factors affecting the effec-tiveness of the point anode were evaluated.

2. Experimental procedure

2.1 Materials and mix proportion Ordinary Portland Cement (OPC), crushed river stone and washed sea sand were used and the physical proper-ties of these materials are presented in Table 1. For all specimens a concrete mix with water to cement ratio (W/C) of 0.4 was used, which is the maximum limit of W/C for reinforced concrete exposed to a chloride en-vironment according to ACI 318-08 (2008). Both air-entraining agent and water-reducing admixture were used based on the cement mass to obtain a slump and air content in the range of 10±2.5 cm and 4.5±1%, respec-tively. The mix proportion of the concrete used is presented in Table 2. 2.2 Preparation of specimens Prismatic specimens with dimensions of 150 mm x 150 mm x 500 mm were casted. Each specimen contained 2

plain steel bars of 13 mm diameter i.e. one plain steel bar (PS) and a plain steel bar with sacrificial point anode (PSCP). Both placed at a cover depth of 30 mm. Before placing concrete in the molds, sacrificial point anodes were installed on the steel bar (PSCP) and the maximum acceptable electrical resistance of 0.3 Ω was checked by using a resistance meter. The manufacturing company has defined the maximum effective distance of anode is 300 mm (DENKA Galvashield XP 2011). In this ex-periment, the distance between the point anode and the crack location was 100 mm in order to provide a suffi-cient protection as shown in Fig. 2. Thereupon, the con-crete was placed and demolded after 24 hours. The specimens were cured under sealed conditions in a wet towel for 28 days in a room at a constant temperature of 20±2°C. As noted, the point anode and steel bar (PSCP) were fixed already before casting and could not be dis-connected during exposure. Details of the specimen design are shown in Fig. 3. In addition, the compressive

Table 2 Mix proportion of concrete.

W/C Water (kg/m3)

Cement (kg/m3)

Sand (kg/m3)

Gravel (kg/m3)

AEWR (kg/m3)

AE (mL/m3)

Air content (%)

Slump (cm)

0.4 161 403 680 1108 1.25 1163 4.0 7.5

Fig. 1 Sacrificial point anode.

Fig. 2 Setting up of the sacrificial anode for PSCP.

Table 1 Physical properties of materials.

Material Description Cement Ordinary Portland Cement (OPC), Density = 3.16 g/cm3, SSA = 3390 cm2/g Sand Washed sea sand, SSD density = 2.58 g/cm3, F.M = 2.77, Chloride content <0.04% by weight. Gravel Crushed stone, SSD density = 2.85 g/cm3, MSA = 20 mm AEWR agent Polycarboxylate ether based AE agent Alkylcarboxylic

SSD: Saturated Surface Dry; F.M: Fineness Modulus; MSA: Maximum Size of Aggregates; SSA: Specific Surface Area; AEWR: Water Reducer; AE: Air Entraining agent.

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strength of concrete was determined on ∅100x200 mm concrete cylinders after 28 days of curing in water.

At 28 days moisture curing, a single crack was created on the specimen under one point flexural loading (Fig. 4a). Each specimen was provided with one set of dis-placement transducer (±2 mm) fixed at the bottom side of the specimen in order to check the crack width. Crack width was varied with loading and unloading stage so that the maximum crack widths after unloading were measured for the work (Fig. 4b).

After cracking, both ends of each specimen were sealed with epoxy resin. Thereafter, all specimens were either exposed to constant laboratory air (T: 20±2°C, RH: 60%), immersed in 3% NaCl solution or dry/wet cycles. Overall, twelve prismatic test specimens were prepared (4 specimens for each exposure). Specimens exposed to laboratory air are identified by A (A1 to A4); specimens immersed in 3% NaCl solution by B (B1 to B4) and specimens exposed to dry/wet cycles by C (C1 to C4). Details of exposure condition of the specimen are de-scribed in Table 3. For the 4 specimens exposed in the 3% NaCl solution (B1 to B4), only 40 mm from the bottom surface was immersed (Fig. 5).

2.3 Method of investigation The average compressive strength at 28 days amounted to 46.6 MPa. Potential values of steel bars were meas-ured during exposure for all specimens (A, B and C). Meanwhile, depolarization tests, polarization behavior, anodic-cathodic polarization curve and visual observa-tion were carried out for the 3 specimens (A4, B4 and

C4) showing crack with larger than 0.40 mm in each exposure condition at the end of test periods (around 530 days). These tests were performed during 24 hours upon disconnecting the sacrificial point anode from steel bar (PSCP). (1) Potential value and concrete resistance measurements Both half-cell potential of the PS bar and the “On-potential” (the potential under steady state condition, in which the IR drops are eliminated) of PSCP were monitored periodically by using a digital voltmeter (Yo-

(a) (b)

Fig.4 (a) Bending loading for cracking; (b) Crack width measurement.

150

150 PSCP

PS30

Single cracklocation

Sacrificialpoint anode

90 60 100

250 250

PSCP

500

Concrete W/B = 40%

Measurement point of the potential value (15 mm from the crack)

150

Casting direction

Fig. 3 Detail of specimen design (unit: mm).

Table 3 List of test specimen. Specimen

series Maximum crack

width (mm) Exposure Condition

A1 0.15 A2 0.22 A3 0.38 A4 0.45

Laboratory air at temperature (T): 20±2°C, relative humidity

(RH): 60%

B1 0.14 B2 0.17 B3 0.30 B4 0.45

Immersed in 3% NaCl solution

C1 0.18 C2 0.25 C3 0.37 C4 0.45

Dry/wet cycles (2 days in 3% NaCl solution & 5 days dry)

Notation: A, B, C: Exposure condition. 1, 2, 3 & 4: Target crack width 0.1 mm, 0.2 mm, 0.3 mmand 0.4 mm, respectively.

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kogawa) and the silver/silver chloride reference elec-trode (Ag/AgCl). The potential value is converted to the copper/copper sulfate reference electrode (CSE). The corrosion potential value of each steel bar was taken at 15 mm from the crack location (see Fig. 3). For specimens exposed to alternate wetting and drying (C1 to C4), the potential value of PS and PSCP were measured at the end of wet cycle after air dried for one hour. Exposure was continued until around 530 days.

The interpretation of potential readings of PS was carried out according to ASTM C876-09 (2009) as de-scribed in Table 4. Meanwhile, for PSCP it is said that the protective potential of steel bar is lower than -750 mV vs. CSE (Rincon et al. 2008).

In addition, the concrete resistances of the specimen (A, B and C) were recorded by using a handy type po-larization resistance measuring system after 530 days exposure. (2) Depolarization tests The difference between 24 hours off potential and instant-off potential is defined as the depolarization value. When cathodic protection is applied to steel in concrete, it is commonly considered as “effective” if the 24 hours depolarization value is more than 100 mV based on JSCE Concrete Library 107 (2011). In this study, 300 mV ca-thodic polarization value (On-potential – 24 hours off potential), was used to demonstrate the effectiveness of the sacrificial point anode. (4) Polarization behavior Polarization behavior of the sacrificial point anode was measured after depolarization tests. The anodic polari-zation curve of the sacrificial point anode and the ca-thodic polarization curve of the steel bar were obtained by the so-called contact method. The contact method is a measuring method using a double layer counter electrode contacted on the surface of the specimen. A Potentiostat

HA-151A (Hokuto Denko) and a function generator HB-III (Hokuto Denko) were used to control potential and current, respectively. (5) Anodic and cathodic polarization curve of steel The anodic polarization curve is related to the passivity condition of steel bars (Table 5). When the current den-sity becomes larger, the grade of passivity film of steel bars becomes worse (Otsuki 1985). The cathodic polarization curve is related to diffusion of oxygen (O2). When the current density becomes larger, the level of O2 diffusion becomes larger. For this, a similar testing equipment as for the polarization behavior test was used. The potential of the steel bar (Ecorr) was shifted to +700 mV for anodic polarization curve and -700 mV for cathodic polarization curve from the natural potential with a scan speed of 1 mV/sec. The current at each po-tential sweep was recorded. This test was performed on both PS and PSCP bar. (6) Visual observation and corroded area The corroded area of all steel bars was traced over in a transparent paper and then corroded area of steel bar was quantified by using ImageJ software. Also, corrosion of the steel bar and leaching products of the sacrificial point anode in the cracked area was observed. 3. Results and discussion

3.1 Half-cell potential of plain steel bar (PS) The half-cell potential of PS under different exposure conditions is shown in Fig. 6. It was observed that the potential value of PS in laboratory air was about -250 mV for all crack widths until 50 days as presented in Fig. 6a. However, the half-cell potential value became more positive around -150 mV from 50 to 150 days exposure. It is found that the relationship between potential value and crack width at the early age is existed and changed by time because the steel bars remain in a passive con-dition. After 150 days exposure, it was observed that the potential of PS shifts to negative values between -200 mV to -270 mV for all crack widths and categorized following ASTM C876-09 criteria as an uncertain prob-ability of corrosion. Visual examination after breaking

Table 4 Corrosion probability. Half-cell potential (mV;CSE) Corrosion probability

-200 < E 90% no corrosion -350 < E < -200 Uncertainty

E > -350 90% corrosion

Single crack

Sacrificialpoint anode

Plastic container Plain

steel bar

3% NaCl solution 40 m

m

Fig. 5 Immersion in 3% NaCl solution.

M. A. Caronge, H. Hamada, R. Irmawaty, Y. Sagawa and D. Yamamoto / Journal of Advanced Concrete Technology Vol. 13, 479-488, 2015 483

the specimen (A4) revealed that a slight corrosion was observed on the steel surface near the crack location.

Figure 6b shows the half-cell potential of PS im-mersed in 3% NaCl solution. It is found that the potential value becomes more positive to -100 mV for crack width of 0.30 mm (B3) up to 300 days exposure. Nevertheless, it is obvious that the potential of PS falls to -350 mV after 530 days exposure. This is caused by the amount of oxygen and chloride ions are sufficient to accelerate the corrosion of steel bar. On the other hand, for specimen having a crack width of 0.45 mm (B4), it is evidenced that, after 50 days exposure the potential value of PS falls to -450 mV and categorized the 90% probability of corrosion. It indicates that crack width affect the corro-sion rate.

The half-cell potential value of PS under dry/wet cy-cles is shown in Fig. 6c. It shows that crack width less than 0.20 mm reached the potential value around -250 mV at early age and relationship between crack width and potential value changed to more positive value with time. However, after 350 days the potential values shifts to -450 mV and categorized of 90% of corrosion prob-ability. It implies that the chloride ions and oxygen can reach the surface of steel bars after certain period. While for specimen whose crack width is larger than 0.20 mm, it is observed that the potential value shifts to the 90% of corrosion probability at 90, 100 and 320 days for crack

width of 0.45 mm (C4), 0.37 mm (C3) and 0.25 mm (C2), respectively. This is attributed to the effect of crack which permitted easy access of chloride ions and oxygen to the steel bars and accelerated the onset of corrosion. The results indicate that the relationship between crack width and corrosion rate is existed due to the environ-mental condition.

3.2 On-potential of plain steel bar with sacrifi-cial point anode (PSCP) Figure 7a shows the on-potential value of PSCP exposed in the laboratory air. It is observed that potential value of PSCP reached to about -550 mV at the initial stage, and moved to noble value around -300 mV after 530 days exposure. This may be due to the high resistivity of concrete, which decreases the current flow of the sacri-ficial point anode to the steel bar. Although the protective potential of steel bar changes to noble value with time, the potential of steel bars are in a stable condition. It means that the steel bar is protected. This result is con-firmed by visual observation of the steel bar at the end of test periods.

The on-potential of PSCP immersed in 3% NaCl so-lution is presented in Fig. 7b. It is found that the potential value of PSCP is around -800 mV to -1000 mV, which satisfies the protective potential (lower than -750 mV vs. CSE) for all crack width at 530 days exposure. It is due to

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0.15 mm (A1)0.22 mm (A2)0.38 mm (A3)0.45 mm (A4)

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(a) Laboratory air (b) Immersed in 3% NaCl solution

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00 50 100 150 200 250 300 350 400 450 500 550

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0.18 mm (C1)0.25 mm (C2)0.37 mm (C3)0.45 mm (C4)

(c) Dry/wet cycles

Fig. 6 Half-cell potential of PS at cracked area: (a) laboratory air; (b) immersed in 3% NaCl solution; (c) dry/wet cycles.

M. A. Caronge, H. Hamada, R. Irmawaty, Y. Sagawa and D. Yamamoto / Journal of Advanced Concrete Technology Vol. 13, 479-488, 2015 484

the presence of water in concrete pores, thereby reducing the resistivity of concrete.

From Fig. 7c, it can be observed that for crack width of 0.18 mm (C1), PSCP under dry/wet cycles showed the on-potential about -650 mV. Meanwhile, specimens whose crack width of 0.25 mm (C2), 0.37 mm (C3) and 0.45 mm (C4) are presented similar protective potential of steel bar around -750 mV. From these results, it can be concluded that the sacrificial point anode is more effective in the high moisture condition even in the larger crack width of 0.45 mm.

Concrete resistance of all specimens after exposure for 530 days is presented in Fig. 8. It is clearly seen in view of the fact that a higher moisture content, a lower con-crete resistance would result.

3.3 Depolarization tests Specimens demonstrating crack widths larger than 0.40 mm were investigated 24 hours after removing the point anode from the steel bar. Depolarization values of PSCP are presented in Table 6. The result shows that the depolarization value of the specimen exposed in the laboratory air is smallest. While for specimens exposed in dry/wet cycles and immersed in 3% NaCl solution, depolarization values of 687 mV and 532 mV were achieved, respectively.

The rest potential of steel bars and sacrificial point

anode of specimens having crack width larger than 0.40 mm (A4, B4 and C4) are shown in Fig. 9. It is found that PS shows a rest potential more negative than -350 mV, while PSCP shows a value between -220 mV to -340 mV under dry/wet cycles and immersed in 3% NaCl solution. This indicates that sacrificial point anode could be effective to prevent steel corrosion in the presence of crack. In addition, it was also observed that the rest potential of sacrificial point anode under dry/wet cycles and immersed in 3% NaCl solution is about -1000 mV vs. CSE, which is similar to natural potential value of Zn alloys (Dugarte and Sagues 2014). It means that the protective criteria have changed due to the environmental condition.

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00 50 100 150 200 250 300 350 400 450 500 550

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0.15 mm (A1)0.22 mm (A2)0.38 mm (A3)0.45 mm (A4)

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00 50 100 150 200 250 300 350 400 450 500 550

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0.14 mm (B1)0.17 mm (B2)0.30 mm (B3)0.45 mm (B4)

(a) Laboratory air (b) Immersion in 3% NaCl solution

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00 50 100 150 200 250 300 350 400 450 500 550

On-

pote

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l (m

V;C

SE)

Exposured time (days)

0.09 mm (C1)0.18 mm (C2)0.29 mm (C3)0.34 mm (C4)

(c) Dry/wet cycles

Fig. 7 On-potential of PSCP at cracked area: (a) laboratory air; (b) immersed in 3% NaCl solution; (c) dry/wet cycles.

Table 6 The 24 hours off potential and depolarization value of PSCP at the end of test.

Exposure condition

On-potential (mV;CSE)

24 hours off potential

(mV;CSE)

Depolarization(mV)

Laboratory air (A4) -347 -208 139

Immersed in 3% NaCl (B4) -930 -243 687

Dry/wet cycles (C4) -874 -342 532

M. A. Caronge, H. Hamada, R. Irmawaty, Y. Sagawa and D. Yamamoto / Journal of Advanced Concrete Technology Vol. 13, 479-488, 2015 485

3.4 Polarization behavior of the sacrificial point anode The polarization behavior of the sacrificial point anode at the end of tests for crack width larger than 0.40 mm (A4, B4 and C4) is shown in Fig. 10. It is clear that specimens exposed to dry/wet cycles and immersed in 3% NaCl solution are provided with a large current density of about 3 μA/cm2 and 4 μA/cm2, respectively. On the other hand, the specimens exposed to laboratory air provided a smaller current density of 0.3 μA/cm2. This difference may be caused by the moisture content inside concrete. High moisture content makes the sacrificial point anode more active to provide larger current protection.

As reported by previous studies (Bertolini et al. 1993; Pedeferri 1996), a current density of 0.2 μA/cm2 is con-sidered sufficient for cathodic prevention of corrosion initiation. From the test results, it can be deduced that after 530 days the current densities of all sacrificial point anodes are still over the range of cathodic prevention for all exposure conditions.

3.5 Anodic-cathodic polarization curve of steel bar Figure 11 shows the anodic-cathodic polarization curve of specimens for crack width larger than 0.40 mm (A4, B4 and C4) at 530 days exposure. Based on the grade of

the passivity film of steel bar proposed by Otsuki (1985), the passivity of steel bars was Grade 4 (good condition) for both PSCP and PS in laboratory air. For specimens immersed in 3% NaCl solution, it is observed that PS is categorized into Grade 3 (poor condition), and PSCP in Grade 4 (good condition). On the other hand, conditions of PSCP and PS under dry/wet cycles categorized into Grade 4 (good condition) and Grade 3 (poor condition), respectively. This indicates that the passivity of PS becomes worse for both in dry/wet cycles and immersed in 3% NaCl solution. This was confirmed by visual ob-servation of steel bars after removal from concrete specimens. Compared to the anodic polarization behav-ior, the difference in cathodic behavior is small in all exposure conditions. It can be concluded that the envi-ronmental condition greatly affects the passivity grade of steel bar. 3.6 Visual observation Only specimens exposed in dry/wet cycles and immersed in 3% NaCl solution having crack width larger than 0.40 mm (B4 & C4) rust products from PS were observed along the crack of the specimen (Fig. 12). It indicates that the passivity film of steel bar is damaged and corrosion was already initiated. While for PSCP exposed

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PSCP (A4) PS (A4)PSCP (B4) PS (B4)PSCP (C4) PS (C4)

Fig. 11 Anodic-cathodic polarization curve for specimen (A4), (B4), and (C4) at 530 days.

0

1

2

3

4

Con

cret

e res

ista

nce (

kΩ)

A1 A2 A3 A4 B1 B2 B3 B4 C1 C2 C3 C4

Laboratory Air

Immersed in 3% NaCl solution

Dry/wet cycles

Fig. 8 Concrete resistance of all specimens after expo-sure for 530 days. -1200

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01 2 3

Res

t pot

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l (m

V;C

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PSCPPSPoint anodes

Laboratory airImmersed in 3%

NaCl solution Dry/wet cycles

Fig. 9 The rest potential of steel bars and sacrificial point anodes for specimen (A4), (B4), and (C4).

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Fig. 10 Anodic polarization behavior of the sacrificial point anode and cathodic polarization curve of steel bar.

M. A. Caronge, H. Hamada, R. Irmawaty, Y. Sagawa and D. Yamamoto / Journal of Advanced Concrete Technology Vol. 13, 479-488, 2015 486

to dry/wet cycles, the leaching products from the inside anode were found at the bottom surface of the specimen along the crack, which may decrease the performance of sacrificial point anode for long-term exposure (Rincon et al. 2008). Also, it was confirmed by visual observation of

PSCP in dry/wet cycles that a little pitting corrosion existed on the steel surface.

From the visual observation of steel bars (A4, C4 and C4) as shown in Fig. 13, it is found that corrosion oc-curred only in the cracked area of specimens for PS ex-posed to dry/wet cycles and immersed in 3% NaCl solu-tion. Also, the passivity film of steel bars was broken due to the increase of black colored corrosion product. Meanwhile, it was observed that PSCP shows a better condition than PS for both exposure to dry/wet cycles and immersed in 3% NaCl solution. This indicates that a sacrificial point anode can prevent the occurrence of corrosion in a cracked area although the chloride ions and oxygen are available on the steel surface through the crack.

The condition of the sacrificial point anodes after removal from the concrete specimen are shown in Fig. 14. Small amounts of corrosion product for PSCP under

(a) (b)

Fig. 12 Corrosion and leaching products at the cracked area: (a) dry/wet cycles; (b) immersed in 3% NaCl solution.

(a)Laboratory air (b) Immersed in 3% NaCl solution

(c) Dry/wet cycles

Fig. 14 Condition of the sacrificial point anode after re-moving from concrete specimens: (a) laboratory air (A4); (b) immersed in 3% NaCl solution (B4); (c) dry/wet cycles(C4).

(a) Laboratory air

(b)Immersed in 3% NaCl solution

(c) Dry/wet cycles Fig. 13 Corrosion appearances of steel bars: (a) labora-tory air (A4); (b) immersed in 3% NaCl solution (B4); (c) dry/wet cycles (C4).

M. A. Caronge, H. Hamada, R. Irmawaty, Y. Sagawa and D. Yamamoto / Journal of Advanced Concrete Technology Vol. 13, 479-488, 2015 487

dry/wet cycles were found. This is probably from ex-pansive oxide or hydroxide of zinc as a corrosion product of sacrificial point anode (Dugarte and Sagues 2014).

The corroded area of steel bars for specimens having crack width larger than 0.40 mm (A4, B4 and C4) is shown in Fig. 15. The result shows that the specimens exposed in the laboratory air had a corroded area of 0.45 cm2 and 0.65 cm2 for PSCP and PS, respectively. This was significantly lower than the corroded area for the specimens exposed to dry/wet cycles and immersed in 3% NaCl solution. The specimens immersed in 3% NaCl solution showed an average corroded area of 1.16 cm2 and 6.79 cm2 for PSCP and PS, respectively whereas specimens exposed to dry/wet cycles, PSCP had 2.07 cm2 of corroded area and 10.04 cm2 for PS. Compared to PSCP, it is found that PS shows a 5 times larger corroded area than PSCP for both exposure to dry/wet cycles and immersion in 3% NaCl solution.

4. Conclusions

This investigation describes the effectiveness of sacrifi-cial point anodes as corrosion prevention of steel in cracked concrete. From the test results the following conclusions are drawn: (1) Crack width significantly affects the corrosion of

steel bars in concrete even though immersed in 3% NaCl solution, even with little oxygen supply.

(2) Sacrificial point anode demonstrates a better pro-tection under dry/wet cycles and immersed in 3% NaCl solution than for exposure to laboratory air due to the presence of water in the concrete pores, which increases the humidity of concrete.

(3) The corrosion area of steel bars without sacrificial point anode (PS) is 5 times larger than that of steel bars with sacrificial point anode (PSCP) for both exposure to dry/wet cycles and immersion in 3% NaCl solution.

(4) The visual observation reveals that the sacrificial point anode can prevent microcell corrosion in the

cracked concrete. However, it was observed that PSCP in dry/wet cycles a slight corrosion existed on the steel surface. This implies that the effectiveness of the sacrificial anode is limited by distance.

(5) A leaching product from the point anode was ob-served. This substance may decrease the perform-ance of sacrificial point anode in long-term expo-sure.

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0

0.45 1.16

2.07

0.65

6.79

10.04

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8

10

12

1 2 3

Cor

rosi

on a

rea

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PSCPPS

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Dry/wet cycles

Laboratory air

Fig. 15 Total corroded area of the steel bars for specimen (A4), (B4), and (C4).

M. A. Caronge, H. Hamada, R. Irmawaty, Y. Sagawa and D. Yamamoto / Journal of Advanced Concrete Technology Vol. 13, 479-488, 2015 488

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