30 YEARS’ RESEARCH ON THE DURABILITY OF PORT & HARBOR STRUCTURES

N Otsuki*, Tokyo Institute of Technology, Japan

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33rd Conference on OUR WORLD IN CONCRETE & STRUCTURES: 25 – 27 August 2008, Singapore

30 YEARS’ RESEARCH ON THE DURABILITY OF PORT & HARBOR STRUCTURES

N Otsuki*, Tokyo Institute of Technology, Japan

Abstract

In this century, it is generally accepted that the durability is one of the most important research in the engineering field. In 1975, when the author got a job in Port and Harbor Research Institute, the research on durability has been gradually recognized as important in Japan. Then, the author believed that the research on durability should be his life work and has continued the work up to now. In this paper, the author’s 30 years’ researches on the durability, especially related to port & harbor structures, are summarized. The contents are as follows: 1) Outline of the deterioration of port & harbor structures in Japan 2) Developed methods for the durability researches 3) Long term exposure experimental works 4) Recent advances in the author’s research

Keywords: Durability, Port & Harbor Structure, Exposure Experimental Works

1. Introduction In Japan also in many other countries, the researchers began to be interested in the durability in

the early 1970s. The author got his first job as a researcher at Port & Harbor Research Institute, Ministry of

Transportation (Now, Port and Air Port Institute). Already at that time, the main theme of the material laboratory, in which the author was belonged, was the durability of the concrete and steel port structures.

The author had been working there 14 years and his main work was related to the investigation of existed structures and long term exposure tests. Even after 1989, in this year the author changed his job and be an associate professor of Tokyo Tech. and then become a professor in 1995, the main theme of the author has been also the durability of structures. From 2000, the author decided to reinforce his study with some theory.

In this paper, the author summarized his 30 years study on the durability of port structures. The author focused not on the details but his thinking ways. Also, the author introduced his and organizations’ failures which could not be officially published. The author is hoping this paper shall help the younger engineers to do their researches more creative and happier.

2. Outlines of the deterioration In this chapter, outline of the deterioration of the concrete structures and the steel structures

of port will be introduced. 2.1. Deterioration of the super structures of piers 2.1.1 Outline In 1984 the Port and Harbor Institute conducted a survey, with the help of branch offices of the Bureau of Port and Harbor, Japan, on the deterioration of the super structures of piers. The number of the surveyed piers was 95. The reason why the authors aimed at the super structures of piers was the deterioration of the super structures were most severely deteriorated compared to other structures like caisson type, cell type and others.

Figs.2-1~2.-4 shows some examples of severely deteriorated beams and slabs. Fig.2-5 shows a relationship between the years from construction and the level of cracks, and roughly after 15 years most of the beams and slabs were cracked. Also in Table 2-1, the causes of the crack are shown.

It is very clear that even in severe marine environment, the percentage of pure chloride attack is less than 30% and some kinds of poor construction, summarizing lack of cover and shrinkage, might be more than 50%. 2.1.2 Statistical analysis

With the collected data from 95 piers, the authors performed multiple regression analysis. The target values were the rank of deterioration (Y1: shown in Table 2-2) and the numbers of deterioration (Y2) for each pier. And the factors were years from the construction (X1), the weights of the vehicle on the pier(X2), the effect of the wind(X3), and the effect of the wave(X4). In this analysis, the mix proportions nor the kinds of cement was not considered. Because the W/C ratios depended on the construction year (shown in Fig.2-6) and all concrete was using OPC. The results of the regression analysis are shown in Table2-3. From this table, the coefficients of regression are below 0.5. There are at least 2 reasons.

One is the influence of the cover depth. The cover depth was one of the independent factors and also included in the regression analysis and their correlation coefficients were very low. The authors measured several cover depths and found the measured ones were sometimes much different from those in design. The other reason is the time dependent changes of w/c. As shown in Fig.2-6, the w/c ratio was lower in older structures.

In spite of these reasons, the deterioration can be related to ages, weight of vehicles, the frequency of strong wind and the waves. 2.1.3 Conclusions (1) The deterioration of 95 wharves in Japan was investigated. And it was confirmed that the super structures (beams and slabs) were most severely damages. (2) The major reason of the deterioration might be the poor construction including the difference of cover depth between measured and designed. (3) The major factors of deterioration can be the age, weight of the vehicles, the frequency of strong wind and waves, in spite of the poor coefficient of regression. (4) There was a tendency the w/c of the older structure was lower. 3. Developed methods for the durability research and their applications

In this chapter, several methods, which were developed by the author, are introduced. Some applications are also introduced. 3.1. Measurement of passivity and its application 3.1.1 Measurement of passivity The most theoretical method to determine the threshold value is to check the passivity. And the evaluation of passivity is also a very difficult matter and should be discussed. In this paper, however, the comprehensive evaluation method proposed by the author is introduced [1]. This method is based on the study of the potentiostatic anodic polarization curves (with 1mV/sec of the scanning speed) of mild steel bars in different solutions. The solutions were; a) saturated calcium hydroxide solution (it is considered that the passivation film around steel bars would exist in this solution), b) extracted cement paste solution (pH=12), c) 0.1% NaCl solution, d) 3.6% NaCl

solution, e) 1.8% NaCl in extracted cement paste solution, f) 3.6% NaCl in extracted cement paste solution.

A passivation film is generally considered to exist in solutions a) and b), whereas for solutions c) through f), it is unlikely to exist. The anodic polarizations curves of steel bars in each solution are shown in Fig 3-1.

Based on Fig 3-1, the passivity of a steel bar in concrete could be graded as shown in Fig. 3-2. The details of the passivity grades are as follows; Grade 0 :( no passivity exists): potentials between 0.2 and 0.6V (vs.SCE), current density is over 100µA/cm2 at least one time. Grade 1 :( certain degree of passivity exists): potential between 0.2 and 0.6V, current density is between 10 to 100µA/cm2. Grade 2 :( certain degree of passivity exists): potential between 0.2 and 0.6V, current density is over 10µA/cm2 at least once but not qualified to Grades 0 and 1. Grade 3 :( certain degree of passivity exists): potential between 0.2 and 0.6V, current density is between 1 to 10µA/cm2. Grade 4 :( certain degree of passivity exists): potential between 0.2 and 0.6V, current density is over 1µA/cm2 at least once but not qualified to Grades 0-3. Grade 5 :( excellent passivity exists): potential between 0.2 and 0.6V, current density is less than 1µA/cm2. 3.1.2 Application

This method was used to determine threshold values of chloride concentration in concrete (mortar) for the initiation of corrosion. 3.2 Measurement of the solution on the surface of steel bars 3.2.1 Measurement of the solution on the surface of steel bars

Mortar specimens, 50x100 mm cylinders, each embedded with a 50 mm long round bar, were prepared as shown in Fig.3-3. The chemical composition of the steel bar and the mix proportions of mortar are shown in Tables 3-1 and 3-2 respectively. The cement type used is OPC. After 28 days’ curing in water, the specimens were immersed in NaCl solution (20,000 ppm), and after the specified immersion period, the chloride concentration at the surface solution of the round steel bar was measured as shown in Fig. 3-4. 3.2.2 An application-Relation between the passivity grade and the chloride concentration around the steel bar

Fig.3-5 shows the relationship between chloride concentration around steel bar and the depth of color change measured by the silver nitrate spray method. In this case the cover depth of the steel bar is 20.5mm. Also in our previous study [1], the region of color change shown by the silver nitrate spray method was confirmed to have a (free chloride)/ (cement) ratio (weight basis) of more than 0.15%. Table 3-3 shows the relationship between the depth of color change region and the passivity grade.

Figure 3-5 shows that in the region where (free chloride/ cement) is less than 0.15%, the chloride concentration around steel bar is less than 10,000ppm, and from Table 3-3 there exists a passivity with a possibility of 100%. Also if the chloride concentration is over 10,000ppm, the possibility of having passivity is almost 0 %.

So the author is confident that if the chloride concentration around the steel bar was measured, the possibility of having passivity can be evaluated with a good possibility in the case of using ordinary portland cement. 3.3 Micro strength test and diffusion test Concrete is a heterogeneous system, which is formed by mixing cement, water, aggregate (sand and gravel) and some admixtures. Each region in concrete has its own distinct properties and strength behavior. The study of each region in concrete is highly important for deeper understanding the complex structure of concrete. To accomplish this, new test methods called minute compression, minute tension, minute flexure and minute diffusion methods were developed. 3.3.1 Minute compression, tension and flexure test

From concrete or mortar specimens, 3mmx3mmx3mm size specimens are taken by cutting and grinding. And these specimens are compressed and measured their compressive strength.

Also the size of specimens for minute tensile test is 15mmx4mmx1mm and the size for minute flexure test is 12mmx5mmx0.5mm. 3.3.2 Minute diffusion test -Cl

- diffusivity of minute region in concrete-

In order to evaluate the temperature effect on Cl- diffusivity of minute region in concrete, the minute

diffusion test was conducted under three levels of fixed exposure temperatures (20ºC, 30ºC or 40ºC). The details of the experiment are shown as follows;

The preparation technique for the test piece is shown in Fig. 3-5. The test piece was then placed inside an acrylic cylinder cell. A thin rubber sheet was used as a water proof membrane. One side of the cell was filled with NaCl solution (3.0 wt %) and the other side was filled with saturated Ca (OH) 2 solution. To measure the time-dependent changes of chloride ion concentrations in the Ca (OH) 2 solution side, the sample solution was checked everyday. The concentration of chloride ions was then measured using ion chromatography. The concentration changes of chloride ions at the saturated Ca (OH)2 solution side are schematically shown in Fig.3-6. In this figure, the slope where the concentration change became constant is called the penetration speed. The flux can be calculated from the penetration speed, because the penetration speed and the flux have the following relationships

A

VQJ cell.∆=

(5)

J : Flux of Ion (mol/cm2/sec)

Q∆ : Penetration Speed (mol/l/sec)

cellV : Solution Volume of Saturated Ca (OH)2 Solution Side (cm

3)

A : Cross sectional Area of Test Piece (cm2)

The diffusion coefficient was calculated using the Fick’s First law of diffusion. When the concentration gradient of Chloride ion was determined, the flux of chloride ion was estimated. Finally, the diffusion coefficient of the chloride Ion was calculated from the following equation.

x

C

JD

cl

cl

cl

∂∂

=

(6) 3.4 Measurement of macro cell corrosion current The steel corrosion in concrete is generally divided into two patterns as macro-cell corrosion and micro-cell corrosion and the total corrosion is the sum of the two kinds of corrosion. Macro-cell corrosion occurs when anode and cathode are separated by more than several centimeters. This macro-cell corrosion likely occurs when different parts of the steel are subjected to different environments. The anodic and the cathodic region may be visibly divided due to difference of Cl

- concentration, O2 concentration and local de-passivation due to materials segregation,, the cracks

or the construction defects such as cold-joint and so on. For example, the parts with relatively high Cl-

or the relatively low pH might be anodes. When the anode parts and cathode parts are separated the steel corrosion is locally very severe. On the other hand, micro-cell corrosion occurs when anode and cathodes are uniformly distributed and uniform corrosion is produced. Compared to macro-cell corrosion, the rate of micro-cell corrosion is small.

In macro-cell corrosion, the anode and cathode are separated while in case of micro-cell corrosion the anode and cathode are uniformly distributed. In order to measure the macro-cell corrosion and micro-cell corrosion, the divided steel bar method was proposed [3]. The measurement for macro-cell corrosion rate is as follows;

The macro-cell current density in the steel was measured using an ammeter device. Fig.3-8 shows the diagram of the measurement method. As an example, the macro-cell current density flowing in the middle bar (Fig.3-8) can be calculated by substituting in the following equation the readings obtained from the device and dividing it with the surface area of the steel.

i

iiiimacro S

III

1,,1- -+

=

where: Imacro : macrocell corrosion current density (A/cm2), Si : surface area of steel element i (cm

2), Ii-1,

i : current flowing from component i-1 to steel element i (A), Ii,i+1 : current flowing from steel element i to steel element i+1 (A)

For sign convention purposes, the anodic current density is denoted as positive (+) and the cathodic current density as negative (-). In order to obtain the micro-cell current density, the polarization resistance in the steel element is measured using AC impedance with Frequency Response Analyzes (FRA) (Fig.3-9). The supplied voltage was 50 mV with amplitude ranging from 0.05 Hz to 5000 Hz. The polarization resistance reading obtained from the device is substituted in the following equation.

ipi

microSR

KI

×=

where: Imicro : microcell corrosion current density (A/cm

2), K : constant (= 0.0209V), Rpi : polarization

resistance (Ω), Si : surface area of component i (cm2).

The total current density is obtained by the sum of the microcell and macrocell corrosion current

density. And the total corrosion rate per year is calculated using the conversion factor (100µA/cm2

current density = 1.16 mm/year corrosion rate per year) 4. Long term exposure tests The author has been planned and experimented many series of long term (more than 10 years) exposure tests. In this chapter, some of them are introduced. 4.1 Influence of kinds of cement In this series, the exposure condition was tidal, exposure duration was 10 years and cover depth was 2, 4 and 7cm. The kinds of cement were ordinary portland cement (N0 and N2), high early strength cement (H0 and H2), moderate heat cement (M0), blast furnace slag cement (type-B) (B0 and B2) and aluminum cement (A0). The SO3 contents of N0, H0, M0, B0 and B0 cement were due to JIS at that time (1970) and the SO3 contents of N2, H2 and B2 were 2% higher (vs. cement weight) than the JIS standard and now the contents is within the late JIS partly because of this exposure tests. (1) Materials, mix proportions and fabrication The maximum size of aggregate was 25mm, unit cement content was 290kg/m3, W/C ratio was about 53%. For mixing water, tap water and sea water were used. Cylindrical specimens (D150mm x H300mm) were fabricated in each of which 3 180mm steel bars were embedded (2cm, 4cm and 7cm cover depth).

The specimens were cast in molds and de-molded 24 hours later and immersed in tap water for 7 days after casting. Then they were immersed in tidal condition. (2) Measured items

The chloride contents, surface observation of steel bars, potentials of steel bars and the compressive strength were measured. (3) Test results - Observation of steel bars The steel bars with N, H and M mixed with tap water, 4 were corroded out of 27, and 12 out of 36 were corroded in case of sea water. In B, 1 out of 9 was corroded in case of tap water and 2 out of 18 were corroded in case of sea water. In A, 2 out of 6 were corroded in case of tap water and 9 out of 9 in case of sea water. Rearranging the data (excluding the results of A), in case of 2 cm 10 out of 30 , and in case of 4cm 3 out of 30 and in case of 7cm 6 out of 30 were corroded. - Potentials The time dependent changes of potentials of steel bars in concrete with different kinds of cement are shown in Fig.4.1. The tendency with the kinds of cement can be distinguished to 3 groups. With portland cements (N, H, M), the potentials are gradually towards base or negative, while the chloride contents might be increasing. Also, with aluminum cement, the potentials are towards base or negative, but the potentials are much noble compared to those of portland cement. While in the case of blast furnace cement, the potentials are towards noble in spite of the chloride contents might be increasing. The reason is still not clear.

The author would like to say the interpretation of the potentials is very difficult especially when the kinds of cement are different. -Chloride contents The measured chloride contents after 10 years exposure are shown in Table4.1. The contents are large compared to the contents from sea water as mixing water and 0.3 or 0.6kg/m3 which are limits in mixing. Also, the contents are larger with portland cements. (4) Discussions and conclusions From Table4.2, with tap water as mixing water, the corrosion are less using high early strength, moderate heat and blast furnace cement. Also, the chloride contents are less using blast furnace cement and aluminum cement. Also, it can be seen that when the concrete cover is large, then the corrosion of steel bars is less. Especially, in the case of 7cm and with tap water, no corrosion was observed.

So, from this series, the author concludes the corrosion protection ability of concrete using blast furnace cement is better than those of using portland cements and also the influence of cover depth is large. 4.2 Pre-stressed concrete piles

In this series, pre-stressed concrete piles (PC piles) were exposured in marine environments for 10 years. The exposure condition was tidal. In this section, outline of the study is shown. (1) Fabrication of PC piles

The outlines of the piles are shown in Fig.4.2. The upper side one is RC piles for comparison. And, there were 8 cases of piles. Namely, “1: RC piles with steam curing and cover depth was 12.0mm and tap water as mixing water, 2:RC piles same as 1 except cover depth was 26.5mm, 3:PC piles with steam curing and cover depth was 12.0mm and tap water as mixing water, 4:PC piles same as 3 except cover depth was 26.5mm, 5:PC piles with auto-clave curing after steam curing and cover depth was 12.0mm and tap water as mixing water, 6: PC piles same as 5 except cover depth was 26.5mm, 7: PC piles same as 5 except using sea water as mixing water, 8:PC piles same as 7 except cover depth was 26.5mm”

For each case 2 piles were fabricated and one had no crack and another had cracks before exposure. Then all the piles were exposed in tidal zone most severe condition for chloride attack. (2) Measurement

After 10 years’ exposure, a) appearance observation, b) compressive strength tests, c) chloride contents, c) flexural loading tests for piles, and observation of the steel bars and PC wires were performed. (3) Results -The color had changed to just a little brownish and a small amount of corn barnacles were attached. Also no visible cracks were newly developed. -The compressive strength were 570kgf/cm2 from 428kgf/cm2 at 28days in the case of 1 and 2, 542kgf/cm2 from 530kgf/cm2 at 28days in the case of 3 and 4, 778kgf/cm2 from 841kgf/cm2 at 28days in the case of 5 and 6, 731kgf/cm2 from 847kgf/cm2 at 28days in the case of 7 and 8. -The average chloride contents of the control specimens were about 9.0kg/m3 in the case of 1 and 2, 8.0 kg/m3 in the case of 3 and 4, 7.0 kg/m3 in the case of 5 and 6, 7.8 kg/m3 in the case of 7 and 8. -Flexural loading moments of the piles were shown in Table4.3. And the effective prestress at 28days and after 10 years’ exposure are shown in Table4.4. There might be some inconsistency, but there was no decrease after 10 years’ exposure. -The corroded area percentages of steel bars and PC wires are shown in Table4.5. With the cover depth of 12mm (cases 1,3,5 and 7), the corroded area % is much larger than that of 26.5mm (cases 2,4,6 and 8). Also, PC piles cover depth 26.5mm and with no cracks and mixed with tap water (cases 4 and 6) the corroded areas were 0.63% and 2.67% and almost negligible. (5) Summary

After 10 years’ exposure, there were some corrosion in every case, however, in the cases with cover depth 26.5mm, no initial cracks and mixed with tap water, the corrosion was almost negligible. And also no decreases of effective prestress were measured. So, if there were enough cover and no initial cracks, the PC piles can be judged more durable than RC piles. 4.3 Joints – Reinforced Concrete –

In this series, cylindrical specimens (15cm diameter and 30cm height) with several kinds of joint had been exposed in tidal zone, submerged zone and sea shore (about 15m from a breakwater). The purpose of this section is to examine the influences of the joints on the carbonation and chloride attack of the concrete and reinforcing bars.

(1) Kinds of joints and fabrication of the specimens The author selected 7 kinds of joints shown below considering the factors as of the effect of

laitance, which was a thin layer formed on the surface of the joints, and of resins. Namely, A: without any treatment B: place 5mm layer of mortar on the joint with no treatment for the laitance C: brushing off the laitance (no adhesive material) D: brushing off the laitance and place 5mm layer of mortar E: coating the surface of the joint with epoxy resin with no treatment for the laitance F: brushing off the laitance and coating the surface of the joint G: brushing off the laitance and coating with latex mortar

Cylindrical specimens (15mm diameter and 30mm height) were used, and 3 bars whose cover depths were 2, 4 and 7cm each were embedded in each specimen.

The new concrete was placed about 24 hours after the old concrete was placed and the joint was formed 15cm from the bottom of the specimen.

The mix proportion of concrete was determined as the cement was high early strength cement, the slump was 12cm, W/C was 49.4% and the maximum size of the aggregate was 25mm. The 28 days strength of concrete was about 40MPa. As steel bars, SR24 daimater9mm bars were used and the mill scales were entirely removed before placing concrete.

The specimens were cured under the standard condition for 28 days and then cured in a room. After the curing, the specimens were exposed under tidal zone, submerged zone and sea shore condition. The outlines of these 3 conditions are shown as below; Tidal condition: the ebb and flow condition was simulated in an artificial pool. Submerged condition: the specimens were always in sea water in this condition. Sea shore condition: sea breezes were always blowing and sometimes splash came in this condition. In Fig.4-3, the tidal and submerged conditions and the specimens are shown. (2) Test methods

In this series, the authors tested the carbonation of the concrete, the chloride penetration depths (approximately 0.15% vs. concrete weight) and the corrosion of the embedded steel bars after the observation of the appearance of the specimens. (3) Results

In Fig.4-4, the chloride penetration depths in tidal zone after 1.5 and 25 years are shown. From this figure, after 25 years exposure, the chloride ion penetrated into the center of the specimens, however, there were some differences at 1.5 years. From this figure, in the cases of no joint surface treatment (A,B,C) the coefficients were larger compared to the cases with joint surface treatment (D,E,F,G) except F with epoxy resin. Of course the smallest one is in the case of no joint (H).

In Fig.4-5, the corrosion rates of steel bars after 25 years exposure are shown. The same tendency as Fig.4-4 can be seen. Also, the effect of cover depth is clarified.

In Fig.4-6, corrosion patterns of steel bars in the case of chloride attack were shown after the 1.5, 10 and 25 years exposure are shown. Up to 10 years, the joint treatment matters and the most corrosion were observed near the joint and upper half of the steel bars, however, after 25 years exposure the corrosion can be observed all part of the bars.

In Fig.4-7, the carbonation depths after 1.5, 5, 10 and 25 years exposure in sea shore condition are shown. From this figure same as Fig.4-4, the carbonation proceeded in the center of the specimen except in the case of no joint (H). Also, in Fig.4-8, the carbonation rate coefficients from accelerated test results are shown. From these 2 figures, in the cases of no joint surface treatment (A,B,C), the depths and coefficients were larger compared to the cases with joint surface treatment (D,E,G) except F with epoxy resin.

In Fig.4-9, the corrosion rates of steel bars are shown, same as in the case of carbonation depth, except with epoxy resin, the no laitance joint cases had much smaller rates than the no treated ones.

In Fig.4-10, corrosion patterns of steel bars are shown, different from the cases of chloride attack, the corrosion was observed only in the vicinity of the joints. Mainly because the carbonation had not reached the depth of the steel bars except in the vicinity of joints. (4) Conclusions

The joint surface treatment to clean the laitance is very effective from the view point of durability. -The chloride attack in tidal condition is so severe that after 25 years exposure the steel bars were all corroded despite better joint treatments. So, it is recommended to avoid joint in tidal zone (in submerged condition, there were only slight corrosion). -The carbonation is also severe and all the steel bars in the vicinity of joint were corroded, however, in the cases with no laitance, the corroded areas were limited and the corrosion rates were also small. -The more effective treatment methods on the joints should be developed.

5. Another interesting factors and findings – present works-

There are a lot of interesting factors related to durability and the author is still working and trying to find out useful conclusions. The followings are the items which are now investigated and the author shows some findings and prospects. (1)ITZ -There are many interfacial transition zones (ITZ) in RC members. One is between mortar (or paste) and steel bars and the other are between aggregates and paste[4]. -If the ITZ is perfect between mortar and steel bars, it means no space around steel bars, the corrosion process is very difficult to proceed and the deterioration by chloride attack is very little. -The influence of ITZ between aggregates and paste is larger for the transportation of substances in concrete, it means if ITZ is better the durability is much better. The influence of ITZ on strength is about 20-30% at maximum. (2)Temperature -If the other conditions are same, many reactions are faster when the temperature increases, and the rate may be explained by Arrhenius law with the activation energies. However, usually the oxygen concentrations are smaller when temperature rises, so sometimes temperature rises and the process is slow down. -In the case of RC members in splash zone, the oxygen supply is enough and the corrosion rate is clearly explained by Arrhenius law up to 40 degree centigrade[5]. -In the case of steel plates in submerged zone, the oxygen supply might be the critical condition and the corrosion rate decreases with temperature rise. (3) The other topics

In addition to (1) and (2), the author and colleagues are working about “chloride threshold values”, “influence of waves”, “poor aggregates”, “electro-deposition methods”, “calcium leaching”, “use of by-products” and including “corrosion of marine steel structures”. 4. Concluding remarks

In this paper, the author summarized his 30 years research especially on the long-term durability of RC structures in marine environments. In the 21

st century, “maintenance” is one of the major

concerns from the view point of society and economy as well as engineering. So, it is the author’s great pleasure if this paper can help to the readers to be interested in this field.

Also, the author would like to appreciate Prof. C T Tam, Prof. Gary K Ong, Prof. Shoji Ikeda and Er.John S Y Tan for offering this special opportunity. REFERENCES [1] Nobuaki Otsuki, Shigeyoshi Nagataki, Kenji Nakashita, “Evaluation of AgNO3 Solution spray Method for Measurement of Chloride Penetration into Hardened Cementitious Matrix Materials”, American Concrete Institute Materials Journal, November-December 1992, pp.587-592 [2] Nobuaki Otsuki, Wanchai Yodsudjai, Takahiro Nisida, Hiroyuki Yamane, “New Test Methods for Measuring Strength and Chloride Ion Diffusion Coefficient of Minute Regions in Concrete”, American Concrete Institute Materials Journal, March-April 2004, pp.146-153 [3] Tarek Uddin Mohammad, Nobuaki Otsuki, Hidenori Hamada, ”Corrosion of Steel Bars in Cracked Concrete under Marine Environment”, American Society for Civil Engineers, Journal of Materials in Civil Engineering, September/December 2003, pp.460-469 [4] Nobuaki Otsuki, Shin-ichi Miyazato, Wanchai Yodsudjai, “Influence of Recycled Aggregate on Interfacial Transition Zone, Strength, Chloride Penetration and Carbonation of Concrete”, American Society for Civil Engineers, Journal of Materials in Civil Engineering, September/December 2003, pp.443-451 [5] N.Otsuki, T.Nishida, M.A.Baccay, “INFLUENCE OF TEMPERATURE ON DETERIORATION PROCESS OF REINFORCED CONCRETE DUE TO CHLORIDE ATTACK OR CARBONATION”, 10

th

Interntional conference of Inspection, Appraisal,, Repair & Maintenance of Structures, October 2006, pp.41-54

Table 2-1 Numbers of structures with causes of deterioration

No Damaged Structures

Damaged Structures

With Corroded Steel Bars Deterioration of concrete itself (Shrinkage and others)

Damaged by external force (collision of timbers and others)

Chloride Attack Lack of Cover depth

Beams 22 (23.2%) 27 (28.4%) 8 (8.4%) 41 (43.2%) 31 (32.6%)

Slabs 45 (47.4%) 6 (6.3%) 16 (16.8%) 32 (33.7%) 4 (4.2%)

Notes: the total number of the structures was 95. Some structures had more than one causes of deterioration. So, the sum was over 95. In ( ), it shows the percentage out of 95. Table 2-2 Rank of deterioration for regression analysis

Rank of deterioration Judgment by observation (Pier)

0 1 2 3 4 5

-No deterioration -Several cracks by collision or other external force, or several exposed steel bars by lack of concrete cover. -Only several cracks (perpendicular to the main bars) are observed or only several rusts are observed in 1 span of the pier. -More than several cracks or more than several rusts are observed in 1 span of the pier. -Vertical as well as perpendicular cracks (crack network) and corrosion of steel bars are also observed. - Large area or many parts of the concrete are delaminated.

Table 2-3 The results of regression analysis (normalized)

Dependent variables (Y)

Linear regression Coefficient of regression

Rank of deterioration Y = 0.581X1 + 0.317X2 - 0.173X3 - 0.090X4 0.376

Amount of cracks per unit length of the facility

Y = 0.113X1 + 0.494X2 + 0.264X3 + 0.139X4 0.437

Amount of deterioration per unit length of the facility

Y = 0.142X1 + 0.494X2 + 0.260X3 + 0.091X4 0.411

where

X1: the age, X2: the weight of vehicles (by weight), X3: the frequency of strong wind ( more than 10m/s), X4: the influence of waves

Fig 2-1 A deteriorated beam of a pier in splash zone

Fig.2-2 A deteriorated beam of a pier in splash zone (Concrete cover was delaminated partly because of lack of cover.)

Fig.2-3 A deteriorated slab of a pier in splash zone (the cover was delaminated)

Fig.2-4 One of the most deteriorated beam in tidal zone

0

5

10

15

20

25

30

35

40

45

0-5 6-10 11-15 16-20 21-25 26-30

years

Nu

mb

er

of

Str

uct

ure

s(n

um

be

rs)

rank3:structures with manycracks(more than several cracksin a block)

rank2:structures with a fewcracks(a few cracks ina block)

rank1:no crucked structure

Fig 2.5 The ages and the number of cracked structures

Fig 2-6 Relationship between the elapsed years and water-cement ratio

0.6

0.0

-1.2

-0.6Po

ten

tia

l v

sS

.C.E

(V)

Current Density(nA/cm2)10 102 103 105104

a Saturated Ca(OH)2 solution

b Extracted cement

c 0.1 % NaCl solution

d 3.6% NaCl solution

e 1.8% NaCl in extracted

cement solution

f 3.6 % NaCl in extracted

cement solutiona

f

b

d

e

c

Gra

de

5

Gra

de

4

Gra

de

3

Gra

de

2

Gra

de

1

Gra

de

0

1.0

0.6

0

-0.5

-1.01 10010

Ele

ctr

od

e P

ote

nti

al

(V v

sS

.C.E

)

Current Density (μA/cm2)

Table 3-1 Chemical composition of steel bars Chemical composition, percent

C Si Mn P S

0.013 0.012 0.049 0.0026 0.0021

Table 3-2 Mix proportions of mortar W/C Water, kg Cement, kg Fine, kg

0.4 292 731 1179

0.5 288 575 1317

0.6 281 468 1404

Reinforcement

Mortar

(unit in mm)

50

9

10

0

50

Reinforcement

Mortar

(unit in mm)

50

9

10

0

50

Fig 3-1 Polarization curves of steel bars in various solutions

Fig. 3-3 Mortar specimen with steel bar

Fig 3-2 Passivity grades

Pincette

Sample container

Taking out the reinforcing bar

Electronic balance

Weighing

Distilled water

Washing with

distilled water

Measuring the Cl- concentration

in wash liquor

Reweighing after drying for

24 hr in a desiccators after

the weighing

(measurement of adherent)

Pincette

Sample container

Taking out the reinforcing bar

Electronic balance

Weighing

Distilled water

Washing with

distilled water

Measuring the Cl- concentration

in wash liquor

Reweighing after drying for

24 hr in a desiccators after

the weighing

(measurement of adherent)

Cl- around Steel (ppm)

Cl-

De

pth

(m

m)

0

10

20

10000 40000

Cl- around Steel (ppm)

Cl-

De

pth

(m

m)

0

10

20

10000 40000

Fig.3-4 Outline of the measurement of chloride concentration around steel bar

Fig.3-5 Relationship between chloride concentration around steel bar and discolored distance

Table 3-3. Relation between the passivity grade and color changed depth (grade 0 means no passivity) Cl- depth, mm Grade, percent

0 1 2 3 4 5

0-10 0 7.6 19.1 1.2 9.4 0

10-15 0 2.9 11.1 0 0 0

10-20.5 0 1.8 12.3 0.6 1.2 0

20.5-25 17.0 5.8 9.9 1.2 0 0

Tidal

A few cm

a c

anode cathode cathode

a c

a c

a c

a c

a c

a c

Steel bar

Macrocell corrosion

Microcell corrosion

Fig.3-7 Concept of micro-cell and macro-cell

50mm

15mm

4mm

4mm

15m

m

15mm

MortarMatrix

15m

m

Electron Wax

Glass Plate

4mm

Concrete Specimen

AdhereAdhereAdhereAdhere

200 mm

100mm

15mm

5mm

5mm

5mm

4 mm

5mm

CutCutCutCut

0.5mm

Exposed Test Piece

Epoxy Resin Matrix

35mm

5mm

5mm

4mm

Unified with Unified with Unified with Unified with Epoxy ResinEpoxy ResinEpoxy ResinEpoxy Resin

PolishPolishPolishPolish

12

3

4

5

CutCutCutCutCutCutCutCut

Detach from Detach from Detach from Detach from Glass PlateGlass PlateGlass PlateGlass Plate

6

7

50mm

15mm

4mm

4mm

15m

m

15mm

MortarMatrix

15m

m

Electron Wax

Glass Plate

4mm

Concrete Specimen

AdhereAdhereAdhereAdhere

200 mm

100mm

15mm

5mm

5mm

5mm

4 mm

5mm

CutCutCutCut

0.5mm

Exposed Test Piece

Epoxy Resin Matrix

35mm

5mm

5mm

4mm

Unified with Unified with Unified with Unified with Epoxy ResinEpoxy ResinEpoxy ResinEpoxy Resin

PolishPolishPolishPolish

12

3

4

5

CutCutCutCutCutCutCutCut

Detach from Detach from Detach from Detach from Glass PlateGlass PlateGlass PlateGlass Plate

6

7

Fig.3-5 Preparation for the test piece for minute diffusion test

C (m ol/l)

Ｔ(sec)

ΔＣ

Δｔ

ΔＱ =ΔＣ /Δｔ

Cl- 濃

度

時間

ΔＣ

Δｔ

ΔＱ =ΔＣ /Δｔ

Cl- 濃

度

時間

Cl-Concentration

Tim e

C (m ol/l)

Ｔ(sec)

ΔＣ

Δｔ

ΔＱ =ΔＣ /Δｔ

Cl- 濃

度

時間

ΔＣ

Δｔ

ΔＱ =ΔＣ /Δｔ

Cl- 濃

度

時間

Cl-Concentration

Tim e Fig.3-6 Slope of concentration vs time

i-1 i i+1

A

Ii-1,i

A

Ii,i+1

Ammeter

Concrete Divided Steel BarEpoxy Resin

i-1 i i+1

A

Ii-1,i

A

Ii,i+1

Ammeter

Concrete Divided Steel BarEpoxy Resin

i-1i-1 i i+1

A

Ii-1,i

A

Ii,i+1

Ammeter

Concrete Divided Steel BarEpoxy Resin

i-1i-1 i i+1

A

Ii-1,i

A

Ii,i+1

Ammeter

Concrete Divided Steel BarEpoxy Resin

ii

Concrete Divided Steel BarEpoxy Resin

RE

WE

CE

iii

Concrete Divided Steel BarEpoxy Resin

RE

WE

CE

Fig.3-8 Measurement of macro-cell current

Fig.3-9 Measurement set-up of the microcell current density test using corrosion monitor

Fig.4.1 Time dependent changes of potentials of steel bars with different cements

na

tura

l e

lec

tro

de

po

ten

tia

l (m

V)

(%)

2 1.73 1.65 1.324 1.55 1.7 1.377 1.33 1.3 1.072 1.63 2.7 2.464 1.4 1.75 1.517 1 1.5 1.262 1.08 1.5 1.274 0.8 0.98 0.757 0.4 0.98 0.752 0.364 0.167 0.08

①-②Cem ent

O rdinary PortlandC em ent (O PC )

High-early-strengeh PortlandC em ent (HPC )Blast-furnaceSlag C em ent

(BFC )

Alum ina C em ent(ALC )

0.23

0.24

0.23

0.23

C oncreteC over (cm )

M ixing w ithTap W ater

M ixing w ithSea W ater

Am ount of chlorinein Sea W ater ②

Table 4.1 Chloride contents after 10 years’ exposure

Table 4.2 Influence of cover depth after 10 years’ exposure

2 4 7Tap W ater 3/4 1/4 0/4Sea W ater 0/6 2/6 3/6Tap W ater 0/2 0/2 0/2Sea W ater 3/3 0/3 0/3Tap W ater 0/3 0/3 0/3Sea W ater 3/4 0/4 2/4Tap W ater 1/3 0/3 0/3Sea W ater 1/6 0/6 1/6Tap W ater 4/12(33.3%) 1/12(8.3%) 0/12(0%)Sea W ater 7/19(36.8%) 2/19(10.5%) 6/10(31.6%)

Blast-furnace SlagC em ent (BFC )

M ixing W ater

Average

C oncrete C over (cm )C em ent

O rdinary PortlandC em ent (O PC )

High-early-strengehPortland C em entM oderate HeatPortland C em ent

(kgf/cm 2)C ase Before Exposure 10years Exposure3 66.2 (96.2)4 74.1 70.25 76.7 80.66 79.3 84.57 57.2 78.08 57.6 78.0

Table 4-3 Flexural loading moments

C lacks Non-C lacks1 2.70 2.702 2.36 3.453 5.70 5.704 6.12 5.695 5.70 5.706 5.70 5.717 5.70 5.708 5.70 5.70

Flexural Strength (×105 kgf・cm )C ase

Table 4-4 Changes of effective prestress

Table 4-5 Corroded Area % of steel bars and PC wiers

(%)C ase C racks Non-C racks Average1 33.42 19.312 7.16 6.233 5.38 34.574 3.08 0.635 3.93 12.586 4.75 2.677 21.81 5.398 7.83 5.43

16.66

Average of 6 specim ens

10.12

5.98

10.92

Fig.4-3 Specimens in tidal and submerged conditions

Fig.4-4 Chloride ion penetration depths in tidal zone after 1.5 and 25 years exposure

Fig.4-5 The corrosion rates after 25 years exposure in tidal zone

Fig.4-6 Corrosion patters of steel bars in the case of chloride attack in tidal condition

Tidal

Submerged

laitance

1.5 y 25 y

Fig.4-7 Carbonation depth after exposure in sea shore condition

Fig.4-8 Carbonation rate coefficients after 1.5 years exposure

Fig.4-9 The corrosion rate of steel bars after 1.5 and 25 years exposure (mm/y)

Fig.4-10 Corrosion patterns of steel bars in the case of carbonation in sea shore condition

1.5 years

5 years

10 years

25years.

※ No data

1.5 y

25 y

1.5 5

10 25

1.5 5

10 25

1.5

5

10 25

1.5

25

1.5

25

1.5

25

1.5

5

25

1.5 10

25