Investigation of Corrosion Damage and Repair System in a Concrete Jetty Structure Farid Moradi-Marani1; Mohamad Shekarchi2; Ali Dousti3; and Barzin Mobasher, M.ASCE4 Abstract: This paper presents the diagnostic investigation of a reinforced concrete jetty after 15 years of service. The main cause of the deterioration was reinforcement corrosion, which initiated within few years after the completion of the jetty structure. The structure underwent major corrosion rehabilitation after 7 years of service. Despite the use of high-strength concrete in the construction of the jetty structure, inadequate cover thickness for reinforced concrete elements intensified corrosion rate and caused early age corrosion problems to reappear. Other contributing factors included high salinity of the seawater by simultaneous action of climatic factors such as exposure to high relative humidity and air temperature. After the initial repair work, a new investigative procedure was carried out to reevaluate the repaired and surrounding unrepaired areas. Results indicate that the deterioration progressed even in concrete elements that were undamaged during the first step of the investigation. No sign of steel corrosion appeared on repaired areas; but shrinkage cracking and incipient corrosion around repaired areas were indications of dimensional and electrochemical incompatibility between repair concrete and substrate. The repair strategy was reevaluated through the repair index method proposed by Andrade and Izquierdo. The results showed that the patching repair method was more suitable and feasible in comparison with other techniques. DOI: 10.1061/共ASCE兲CF.1943-5509.0000112 CE Database subject headings: Sea water; Corrosion; Cracking; Durability; Reinforced concrete; Rehabilitation; Jetties; Case studies; Marine terminals. Author keywords: Sea water corrosion; Cracking; Durability; Reinforced concrete; Reinforcement; Jetties; Repair; Concrete durability; Rehabilitation; Case reports; Corrosion; Chlorides; Marine terminals.
Introduction Concrete is the most commonly used construction material throughout the world and there is a staggering demand for its utilization. The exponential growth of infrastructure especially in the developing countries has further increased the demand for concrete materials, such that the worldwide production and use of concrete will soon surpass the 10 billion t/year mark 共Aïtcin 1998兲. Despite the fact that concrete is a reliable structural material with good durability performance, exposure to severe environments makes it vulnerable 共Guettala and Abibsi 2006兲. The main causes of degradation of concrete subjected to chemical degradation by environmental factors are lack of specifications and poor workmanship. The lack of knowledge of the deteriora1
Ph.D. Candidate, Civil Engineering Dept, Université de Sherbrooke, Sherbrooke, QC, Canada J1K 2R1. 2 Associate Professor and Director, Construction Materials Institute 共CMI兲, School of Civil Engineering, Univ. of Tehran, P.O. Box 113564563, Tehran, Iran. 3 Ph.D. Candidate, School of Civil Engineering, Univ. of Tehran, P.O. Box 11356-4563, Tehran, Iran. 4 Professor, School of Sustainable Engineering and the Built Environment, Civil, Environmental, and Sustainable Engineering Program, Ira A. Fulton Schools of Engineering, Arizona State Univ., P.O. Box 875306, Tempe, AZ 85287-5306. Note. This manuscript was submitted on August 26, 2008; approved on December 23, 2009; published online on December 29, 2009. Discussion period open until January 1, 2011; separate discussions must be submitted for individual papers. This paper is part of the Journal of Performance of Constructed Facilities, Vol. 24, No. 4, August 1, 2010. ©ASCE, ISSN 0887-3828/2010/4-294–301/$25.00.
tion mechanisms results in insufficient planning and accounting for the environmental effects. Corrosion of reinforcing bars induced by chloride ion ingress is a major cause of damage in marine environments 共Shekarchi et al. 2009; Costa and Appleton 2002; Bertolini et al. 2002兲. Reinforcement corrosion causes reduction in the service life of reinforced concrete 共RC兲 structures; therefore a regular schedule for maintenance and repair protocol is fundamentally important in controlling safe and efficient operation of a structure 共Marseguerra and Zio 2000兲. Once a detailed investigation to determine the extent and cause of degradation has been conducted, corrosion damage assessment can lead to the selection of effective repair schemes 共Al-Bahar et al. 1998兲. Regular inspections after repair work are necessary to ensure satisfactory performance of repair systems. In addition, field investigations of repaired concrete structures are necessary to develop guidelines for the adequate selection of concrete repair systems, improved repair procedures, extended durability of rehabilitated structures, and evaluation of discrepancies between laboratory results and field performance 共Cusson et al. 2006兲. This paper presents a case study where a concrete jetty structure is exposed to the severe marine environment of Persian Gulf. The structure showed an early age corrosion of reinforcing bars and prestressing tendons. The principal causes of this accelerated deterioration are highlighted and analyzed. In consideration to the properties of the substrate concrete, a patch repair system was used for extending the service life. A second condition assessment was conducted, and the performance of the repair work after 7 years in service was measured. One of the main reasons for continued assessment was because of the incompatibility between repair concrete and substrate.
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Table 1. Mix Design for Concrete Elements of the Jetty Structure -U nlo ad ing P
ier
84.67m - Connector
1600m - Channel Bridge
1
2
3 4
5
6
7
8
9 10
60 Pump Station
64
308 m
Coast
68
Fig. 1. General layout of the RC jetty structure
Components
Weight 共kg/ m3兲
Cement Total water Free water W/C Gravel 共15 mm兲 Sand
440 150 91 0.34 720 1,161
Superplastisizer Total weight
8.8 2,471
Jetty Structure The jetty is located in the northern coast of Persian Gulf, north of Strait of Hormoz, near the port of Bandar-Abbas. The structural layout is shown in Fig. 1 and consists of two main parts which are the Unloading Pier and Channel Bridge. It was constructed at the beginning of the 1990s as a loading dock for minerals such as iron ore. Fig. 2 shows a cross section of structural system in the Channel Bridge. The unloading pier is made from cast-in-place RC cross girders along with steel-concrete composite deck, and the channel bridge consists of a 64 span bridge with the length of 1,600 m which connects the Unloading Pier and the coast. Every span is composed of three prestressed box girders and two steel cross girder-pile systems. The concrete mixture used met the criteria specified for durable concrete in the Gulf region as listed in Table 1. The only deviation from the code was the use of ASTM Type I portland cement which according to ACI 318-05 关American Concrete Institute 共ACI兲 Committee 2005a兴 and ACI 350-01 共ACI Committee 2005b兲 is not recommended under moderate seawater sulfate exposure. The concrete elements were designed for nominal compressive strength of 40 MPa. In situ strength of concrete was tested on some concrete elements using a nondestructive Schmidt hammer. The measured strength ranged from 48.5⫾ 6.5 to 65.0⫾ 5.0 MPa, reflecting good compressive strength. According to ACI 350-01 共ACI Committee 2005b兲, corrosion protection of RC exposed to seawater required a minimum compressive strength of 34.5 MPa 共or 5,000 psi兲. This structure is located in a region classified as hot and wet according to the climatic classifications of Fookes et al. 共1986兲. The average day time temperature varies from 18° C in January to 34° C in July, while day time temperature reaches as high as 50° C in summertime. The average daily relative humidity ranges
Prestressed Box Girders Prestressed Box Girders
Steel P ile-Girder System
Steel Pile-Girder System
Fig. 2. Cross section of load-carrying system of the bridge channel
Description ASTM type I — — — Moisture= 2.10%—Absorption= 1.52% 共SSD兲 Moisture= 6.90%—Absorption= 2.18% 共SSD兲 Sika R-4 —
from 60% in October to 70% in February with the maximum 共since 1957兲 recorded relative humidity of 98% 共“Climatic statistics” 2008兲.
Causes of Degradation The first sign of distress in the RC elements was reported within a few years after the construction in 1997. Detailed investigations showed evidence of rust staining, minor cracking to spalling, and delamination of concrete cover mainly due to chloride-induced steel corrosion. In regions exposed to seawater splash and spray, severe distress was observed in both prestressing tendons and reinforcing bars of the box girders 关Figs. 3共a and b兲兴. Damaged areas were mostly localized to the bearing zones. Stress concentration at the location of prestressed steel anchorage points and box girder-bearing was mainly responsible for intensified microcracks at these regions. These microcracks were a direct pathway for the ingress of chloride and other aggressive ions into concrete. Due to high evaporation rates, chloride ions from spray or splash of seawater have a concentration of 21.6 g/L 共Table 2兲 and present a significant source of marine salts in the atmosphere 共Novokshchenov 1995兲. Concrete cover is the main protective mechanism against weather and other aggressive effects, and the time to corrosion initiation for conventional carbon steel is most sensitive to its cover depth 共Zhang and Lounis 2006兲. Iranian codes have thus limited the minimum specified concrete cover for structures in contact with seawater from 55 to 90 mm, depending on the type and exposure conditions of concrete elements 共Building and Housing Research Center 2005兲. The specified depth of concrete cover for prestressed box girders and cross girders was 40 mm, which was inadequate to meet service-life criteria in the Persian Gulf region. The thickness of concrete cover in several locations was surveyed. Examination of deteriorated elements indicated that the depth of concrete cover in some box girders was as low as 20 mm with an average value of 43 mm for noncorroded and 29 mm for corroded reinforcing bars. This error in construction detailing may have intensified reinforcement corrosion in many locations. The chloride threshold for active corrosion of the reinforcing steel is not a unique value as it depends on several factors 共Alonso et al. 2000兲. Two categories of damage defined by the boundary of undetectable visual corrosion 共no corrosion products visible to the naked eye兲 and slight corrosion 共loss of steel area up to 5%兲 were considered in correlating the damage with chloride threshold values. The BS8110 standard 共British Standard Institu-
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Chloride Content, (% by weight of Concrete)
0.25 corroded uncorroded
0.2 0.15 0.1
Threshold Value
0.05 0
20 40 60 Depth of Concrete Cover, mm
(a)
Fig. 4. Estimation of chloride threshold value
well above the estimated threshold value of 0.070%. These profiles correlated quite well with the degree of steel corrosion as the major cause of deterioration of this structure. A negligible depth of carbonation was observed which led to the exclusion of carbonation as a contributing factor to the corrosion process. It is known that high humidity and salt crystallization on the surface of concrete elements in marine structures usually prevent CO2 diffusion as a protection against carbonation 共Castro et al. 2000a,b; Al-Khaiat and Haque 1997兲.
Repair Strategy
Fig. 3. 共a兲 Severe corrosion of reinforcing bars in a prestressed box girders; 共b兲 outset of steel corrosion in a prestressed box girder
tion 1997兲 recommends 0.40% chloride content by weight of cement as the threshold value which according to cement content and total weight of ingredients in Table 1, is converted into 0.070% by weight of concrete. This chloride level was also supported by other investigations conducted in the Gulf region 共Pargar et al. 2007兲, and was used as a threshold value for the depassivation of the reinforcing steel as shown in Fig. 4. According to Fig. 5, chloride profiles from damaged surfaces indicated chloride contents at the level of corroded steel reinforcement ranging from 0.094 to 0.193% by weight of concrete which was
Table 2. Chemical Analyses of the Gulf and Potable Water of BandarAbbas Components 共g/L兲 −
Cl SO42− Na+ K+ Ca2+ Mg2+ pH
Gulf water Sample 1
Sample 2
Sample 3
Potable water
21.30 3.09 12.13 0.41 0.80 1.34 7.96
21.55 3.54 11.49 0.40 0.75 1.34 8.12
21.16 2.96 11.87 0.41 0.80 1.49 8.03
0.16 0.04 0.04 Negligible 0.003 0.002 8.05
A patch repair method was selected to repair deteriorated elements. Table 3 shows the mix design of the repair material. The repair methodology consists of the total removal of all layers of deteriorated and contaminated concrete. Corrosion products were removed from the reinforcement bars by sand blasting and the reinforcement was exposed at least 2 cm beyond the cover. The corroded rebar was replaced with a new one and all reinforcements were painted by zinc-rich coating in the form of an anodic coat for corrosion protection. A high-quality concrete mixture that was compatible with substrate concrete was used. The surface coating system comprised of a single component, penetrating Chloride Content, (% by weight of Concrete)
(b)
0.4 Designated Concrete Cover
0.3
Span 1 Span 3 Span 10 Span 30
0.2
0.1
0
Threshold Value
0
20 40 60 80 Depth of Concrete Cover, mm
100
Fig. 5. Chloride profiles from concrete surface on damaged concrete elements during the initial investigation in 1997. Vertical line at 40 mm shows designed cover thickness; no field measured cover.
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Components Cement Silica-fume Total water Free water W/C Gravel 共15 mm兲 Sand Superplastisizer Additive Total weight
Weight 共kg/ m3兲
Description
380 35 187 158 0.380 670 1,123 6 1.80–2.25 2375
ASTM type II — — — — Absorption= 1.52% 共SSD兲 Absorption= 2.10% 共SSD兲 Melcrit Expansive material–Conbax —
silane/siloxane primer for inhibiting passage of water and water borne contaminants followed by a single component pigmented coating. The dry film thickness of the coating was at a minimum of 150 m in order to act as an obstacle against the penetration of aggressive ions. In order to increase the depth of concrete cover up to 80 mm, framing was provided with spacers to increase the cover thickness beyond the initial concrete cover. This repair method was according to the classification of Raupach 共2006兲, aimed at restoring passivity and creating chemical conditions in which the reinforcement surface was returned to, or maintained at a passive condition while controlling anodic areas. To control the corrosion process in the prestressing tendons, the corroded elements were classified into two main groups of moderate and severe corrosion. The structure was analyzed for moderate corrosion. Results indicated that the reduction in loadcarrying capacity was not below the service load levels. Thus, the tendons were cleaned by abrasive blasting, coated with a rustpreventive paint, and then covered by repair concrete according to Table 3. Fig. 3共b兲 shows severe corrosion in some prestressing tendons. These types of corroded tendons were replaced. The damaged sections were cut away 关Fig. 3共b兲兴 and a new piece of strand was spliced onto the ends of the original strand using couplers. The new tendons were reloaded. After the treatment of the tendons, a new repair concrete cover was applied as shown in Table 3.
Chloride Content, (% by weight of Concrete)
Table 3. Mix Design for Repair Concrete
0.25 Span 16 in 2000 Span 16 in 2007
0.2 0.15
Designated Concrete Cover
0.1
Threshold Value
0.05 0
0
20 40 60 80 Depth of Concrete Cover, mm
100
Fig. 6. Example of variation in chloride profile from concrete surface in the duration of 7 years. Vertical line at 40 mm shows designed cover thickness; no field measured cover.
Postrepair Investigation The second part of the study was the condition assessment of the jetty structure which was conducted 7 years after the repair was in place. Steel corrosion had progressed in RC elements ranging from negligible to very severe conditions in both reinforcing bars and prestressing tendons. Corrosion levels were confirmed by the mass loss of the reinforcing steel and chloride content near the corroded areas. Mass loss of sections of the bars in several anodic zones at the prestressed box girder and the cross girders was used for obtaining average corrosion rates. Average steel cross section loss ranged from 12.4 to 54.8%, representing a significant corrosion state 共Table 4兲. Variations in chloride concentration were also studied during the 7-year postrepair evaluation and results are presented in Fig. 6. While no signs of damage were observed during the initial postrepair period, the chloride concentration increased at the level of reinforcement after 7 years in which active corrosion set off and cracks propagated in concrete cover. According Fig. 6, the chloride concentration at the depth corresponding to the concrete cover of 40 mm, increased from 0.035% in 2000 to 0.091% by weight of concrete in 2007, well above the 0.070% estimated threshold value. Assuming a liner regression as a func-
Table 4. Loss of Steel Cross Section due to Reinforcement Corrosion
Locations Channel Bridge
Unloading pier
Original diameter of bar d 共mm兲
Mass of corroded bar ms 共kg/m兲
Average reduction in bar diameter ⌬d 共m兲
Cross-sectional area loss 共%兲
8 8 8 8 10 10 16 16 16 16 16
0.247 0.312 0.346 0.277 0.316 0.279 1.029 0.869 1.258 1.130 1.338
1,674 891 513 1,301 2,845 3,277 3,089 4,135 1,724 2,470 1,278
37.5 21.0 12.4 29.9 48.8 54.8 34.9 45.0 20.4 28.5 15.3
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Substrate Concrete
Repaired Area
Repaired Area
Substrate Concrete
Fig. 7. Potential measurement mapping 共millivolt兲 on repaired areas and substrate concrete by Ag/AgCl electrode—potential gradients show the incipient anodes. 共Discontinued line shows boundary of repaired area and substrate concrete.兲
tion of time, the chloride concentration at 40 mm reached the threshold value within 4 years after the repair. In addition to the growth of corrosion damage in various parts of the structure, repaired surfaces did not perform as well as expected and cracks with various sizes in the repaired areas as well as progressive corrosion in the boundary of substrate concrete and repaired areas were observed. Compatibility of the repair material with the existing substrate is an important aspect of the repair methodology. Stress is induced by processes such as volume change, stiffness mismatch, thermal coefficients of expansion mismatch, electrochemical effects, etc. Emmons et al. 共1993兲 defined compatibility as a balance of physical, chemical, and electrochemical properties and also dimensional changes between a repair material and the substrate concrete. Accordingly, repair materials should withstand induced stresses without distress and deterioration over the designated period of time. Early age cracking of repaired areas due to shrinkage or early age corrosion due to imbalance electrochemical conditions between repaired and substrate concrete 共electrochemical incompatibility兲 are the two main types of incompatibility 共Vaysburd and Emmons 2000兲. The measured potentials by half-cell test method indicate active corrosion in some elements and incipient corrosion around repaired areas 共Fig. 7兲. To locate ongoing corrosion, potential gradients between active and passive areas were used 共Elsener 2001兲. These gradients indicate electrochemical incompatibility between repair concrete and substrate in the early ages. Fig. 7
shows that the potential difference between the patch repair and substrate was around ⫺50 mV for undamaged areas, while for incipient anodes or susceptible areas it was at least ⫺100 mV. In situ the half-cell method depends mainly on the moisture level, which may end in erroneous results 共Ann and Song 2007兲. Results may not necessarily be associated with a high or low probability of steel corrosion. Potential values for concrete elements in splash and atmospheric zones with normal moisture level are most likely close to real corrosion conditions. Half-cell potential mapping in Fig. 7 shows a range of potential values from +200 to ⫺400 mV, with a clear delineation of anodic and cathodic areas. Boundary areas between repaired surfaces and substrate concrete are susceptible to corrosion with more negative and imbalanced potential, whereas cathodic areas show positive and balanced potential. In addition to half-cell potential maps which confirm activation of incipient corrosion in the boundary areas, the chloride profile of substrate concrete in boundary areas shows high concentrations at levels of the reinforcement. Fig. 8 shows variations in the chloride content of repair area, substrate concrete, and boundary area in a repaired section similar to what is presented in Fig. 7. The formation of parallel cracks at 40- to 60-cm spacing was observed which was attributed to dimensional incompatibility between the old and repair materials. Crack widths varied from hairline sized to nearly 1 mm depending on their location and order of formation. It is possible that use of a mortar mixture with
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Chloride Content, (% by weight of Concrete)
silica-fume in the repair material could have intensified shrinkage cracking. The early age and long-term deformation properties of repair concrete and mortar have been studied considering the effect of the maximum size of aggregate and using silica-fume 共Momayez et al. 2005; Brown et al. 2007兲. While the use of silica fume enhances the transport properties of the repair material, it may adversely cause mismatch of shrinkage, stiffness, and strength.
0.5 Repaired area Substrate Concrete Boundary Area
0.4 0.3
Designated Concrete Cover
0.2
Threshold Value
0.1 0
0
20 40 60 80 Depth of Concrete Cover, mm
Reevaluation of Repair Strategy 100
Fig. 8. Chloride concentration profile as a function of the concrete cover in the repair area, substrate concrete, and boundary area
Table 5. Proposed Ranking of Importance 共in Percent兲 Importance 共%兲
Requirement Safety economy Serviceability Environmental impact Durability Economy
10 10 10 35 35
Due to the incompatibility of the repair system with the base material, the repair strategy was reevaluated using the repair index method 共RIM兲 共Andrade and Izquierdo 2005兲. This is an objective approach for selecting a repair system and is based on a predominantly economical and feasible criterion for selection of repair approach. Alternatively, one would have to use empirical knowledge regarding the application, efficiency, and success/ failure of repair methods dominate the field. The patch repair and cathodic protection as two common options were compared by RIM method. This method is based on defining a set of safety, serviceability, environmental impact, durability, and economy requirements. Table 5 describes the proposed ranking for the set of requirements with durability and economy among the areas of highest importance in this type of structure. The structure was classified by levels of importance into its components and was ranked according to a range of 1–4 weight criteria proposed by Andrade
Table 6. Requirements of the Repaired Structure Classified by Levels of Importance Requirement
Repair performance index
Safety
a. Structural consequences of failure b. Failure type c. Execution control d. Feasibility of postrepair monitoring e. Safety of workers f. Safety of users Average
Serviceability functionality
Cathodic protection
Patching
Very severe Ductile Guarantee Sensors Moderate Moderate
1 3 4 4 3 3 3.0
Very severe Ductile Guarantee Visual Moderate High
1 3 4 2 3 4 2.8
a. Disturbance b. Fitness for use Average
High Very low
1 1 1.0
Moderate High
3 4 3.5
Environmental impacts
a. Emission pollutants b. Sustainability Average
Negligible Low
4 2 3.0
Low Low
2 2 2.0
Durability
a. Service life 共year兲 b. Number of types of attack c. Exposure classa Average
⬎50 Two types Splash
4 3 1 2.0
⬍15 One type Splash
1 4 1 2.5
⬎200 ⬍20 7–15 ⬎70 Low
1 1 2 1 3 1.6
100–200 ⬍20 1–7 ⬍30 High
2 1 3 4 1 2.2
a. Direct cost/ m2 共dollar兲 b. Extension of damage 共%兲 c. Period of disturbance 共days兲 d. Maintenance coast 共dollar兲 e. Preparation of substance Average a This repair performance index was defined by the writers.
Economy
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and Izquierdo 共2005兲. Table 6 shows the component ranking of the reinforcement corrosion repair. Ranking for the set of requirements 共Table 5兲 can be varied depending on the priority criteria used by the owner, contractor, or the maintenance staff considering particular conditions, budgetary, and management constrains. The partial values assigned in Table 6 for this jetty structure are described as the following: 1. Safety a. Structural consequences of failure: The consequences of the structural failure are very important 共Rank 1兲. b. Type of failure: A ductile failure for both repair methods was used 共Rank 3兲. c. Execution control: Quality control for both repair methods is important 共Rank 4兲. d. Feasibility of postrepair monitoring: Cathodic protection is monitored with sensors 共Rank 4兲 while patching is monitored with visual observation 共Rank 2兲. e. Safety of workers: Both cathodic protection and patching present similar safety risks during concrete removal or cleaning of the bars 共Rank 3兲. f. Safety of users: Cathodic protection needs instrumentation and monitoring of a permanent electrical current 共Rank 3兲 but patching has little or no risk for users after being applied 共Rank 4兲. 2. Serviceability a. Disturbance: For cathodic protection, the structure is modified by the permanent application of electrical instruments 共Rank 1兲. The disturbance of the removal of damaged concrete is comparatively small for patching 共Rank 3兲. b. Fitness for use: Cathodic protection is not suitable for repairing small areas within a larger structure 共Rank 1兲, but patching is technically suitable for the problem studied 共rank 4兲. 3. Environmental impact a. Emission of pollutants to the environment: Cathodic protection releases no pollutants to the environment 共Rank 4兲. For patching, usually some organic or polymeric based materials are used 共Rank 2兲. b. Sustainability: Both cathodic protection and patching use a relatively high amount of materials and energy 共Rank 2兲. 4. Durability a. Service life: Cathodic protection is expected to perform longer than 50 years without needing replacement 共Rank 4兲. Given the prior experiences with patching materials in similar conditions in Iran, patching usually performs less than 15 years 共Rank 1兲. b. Number of attack types: Corrosion and alkali-silica reaction 共Golam Ali 1993兲 usually affects cathodic protection 共Rank 3兲 but corrosion most likely impacts the performance of patching 共Rank 4兲. c. Exposure class: Damaged concrete elements are in the splash zone. A classification of Rank 1 was assigned for this repair performance. 5. Economy : The economical factors depend very much on the local and regional conditions and the initial and long-term costs of systems used. It is however expected that the cathodic protection will be costlier than the patch technique both for initial and long-term costs. The RI was computed for the two repair methods by multiplying the average values for each requirement from Table 6 by the importance factor from Table 5, and presented as:
• Cathodic protection RI = 共3 ⫻ 0.10兲 + 共1 ⫻ 0.10兲 + 共3 ⫻ 0.10兲 + 共2 ⫻ 0.35兲 + 共1.6 ⫻ 0.35兲 = 1.96
共1兲
• Patching RI = 共2.8 ⫻ 0.10兲 + 共2 ⫻ 0.10兲 + 共2.5 ⫻ 0.10兲 + 共3.5 ⫻ 0.35兲 + 共2.2 ⫻ 0.35兲 = 2.73
共2兲
These values indicate that patching, with higher RI, is the most feasible and economical repair method for this structure as compared to the cathodic protection. To decrease the opportunity for incipient corrosion, it was recommended that the repair size should not be restricted to visible cracking, spalling, and delaminated areas. The adjacent areas were checked by the hammer test and chloride profiles. If the results showed any sign of deterioration or a critical amount of chlorides, the deteriorated or contaminated concrete were removed by the patch repair work. To control dimensional incompatibility, it was recommended that silica-fume be eliminated from mix design and replaced with slag blended cements and fibers to increase the concrete ductility. Moreover, a higher volume of coarse aggregate was recommended to reduce opportunity of restrained shrinkage cracking in repair system. Recent studies at Construction Materials Institute 共CMI兲 共2007兲 showed that application of blended cement, with 25% slag, as well as polypropylene fibers of at least 1.0% weight of cementitious materials, significantly decreased the early age and long-term deformations of concrete in comparison with mix design in Table 3.
Summary and Conclusions This jetty structure is an example of insufficient planning and weak construction from the technical and construction point of view. While the structural design is well within guidelines of the accepted and conventional RC structures, the lack of understanding of the durable aspects for concrete structures in the Persian Gulf region, e.g., inadequate concrete cover thickness and concrete transport properties, has led to severe corrosion behavior. Investigations showed that severe corrosion of reinforcing bars and prestressing tendons is the main reason of early age deterioration. Initial inspection confirmed no signs of other deterioration mechanisms, e.g., alkali-silica reaction, in this structure. Dimensional and electrochemical incompatibility between repair and substrate concrete led to further corrosion in repaired areas. Incipient anodes near to boundary zone of repair and original areas were the sign of electrochemical incompatibility and transversal cracks were the sign of dimensional incompatibility. These cracks were noticeable within a distance of 40–60 cm. The use of high percentage of silica-fume and a high volume of fine aggregate in repair concrete may have contributed to the cracking potential. Due to these incompatibilities, RIM was used to differentiate between the two methods. A detailed analysis of the data, according to Tables 5 and 6, by this method confirmed that it was not necessary to replace patch repair with others but it required some modifications to decrease dimensional incompatibility and to postpone electrochemical incompatibility in the form of incipient anodes.
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Acknowledgments The writers would like to acknowledge “Persian Mining and Metal Industries Special Zones 共P.G.S.E.Z兲” Company for financial support and “Construction Materials Institute 共CMI兲” at the University of Tehran for technical support.
References Aïtcin, P. C. 共1998兲. “High-performance concrete.” Modern concrete technology series, E & FN Spon, London. Al-Bahar, S., Attiogbe, E. M., and Kamal, H. 共1998兲. “Investigation of corrosion damage in reinforced concrete structure in Kuwait.” ACI Mater. J., 95共3兲, 226–231. Al-Khaiat, H., and Haque, M. N. 共1997兲. “Carbonation of some coastal concrete structures in Kuwait.” ACI Mater. J., 94共6兲, 602–607. Alonso, C., Andrade, C., Castellote, M., and Castro, P. 共2000兲. “Chloride threshold values to depassivate reinforcing bars embedded in a standardized OPC mortar.” Cem. Concr. Res., 30共7兲, 1047–1055. American Concrete Institute 共ACI兲 Committee. 共2005a兲. “Building code requirements for structural concrete 共ACI 318-05兲 and commentary 共318R-05兲.” ACI 318, Farmington Hills, Mich. American Concrete Institute 共ACI兲 Committee. 共2005b兲. “Code requirements for environmental engineering concrete structures 共ACI 35001兲 and commentary 共ACI 350R-01兲.” ACI 350, Farmington Hills, Mich. Andrade, C., and Izquierdo, D. 共2005兲. “Benchmarking through an algorithm of repair methods of reinforcement corrosion: The repair index method.” Cem. Concr. Compos., 27共6兲, 727–733. Ann, K. Y., and Song, H. 共2007兲. “Chloride threshold level for corrosion of steel in concrete.” Corros. Sci., 49共11兲, 4113–4133. Bertolini, L., Gastaldi, M., Pedeferri, M., and Redaelli, E. 共2002兲. “Prevention of steel corrosion in concrete exposed to seawater with submerged sacrificial anodes.” Corros. Sci., 44共7兲, 1497–1513. British Standard Institution. 共1997兲. “Structural use of concrete—Code of practice for design and construction.” BS 8110-1, London. Brown, M. D., Smith, C. A., Sellers, J. G., Folliard, K. J., and Breen, J. E. 共2007兲. “Use of alternative materials to reduce shrinkage cracking in bridge decks.” ACI Mater. J., 104共6兲, 629–637. Building and Housing Research Center. 共2005兲. “National code of practice for concrete durability in the Persian Gulf and Omman Sea 共in Farsi兲.” BHRC-PN-S428, Ministry of Housing and Urban Development, Tehran, Iran. Castro, P., Moreno, E. I., and Genescá, J. 共2000a兲. “Influence of marine micro-climate on carbonation of reinforced concrete buildings.” Cem. Concr. Res., 30共10兲, 1565–1571. Castro, P., Sanjuán, M. A., and Genescá, J. 共2000b兲. “Carbonation of concretes in the Mexican Gulf.” Build. Environment, 35共2兲, 145–149. “Climatic statistics.” 共2008兲. I. R. of Iran Meteorological Organization
(Monthly and Annual), 具http://www.irimo.ir/english/statistics/index. asp典 共Feb. 2008兲. Construction Materials Institute 共CMI兲. 共2007兲. “Diagnostic assessment of corrosion damage of Charlie 1&2 Jetty Structure in Bandar Abbas Port with aim of designing a repair method 共in Farsi兲.” CMI8708304, Univ. of Tehran, Iran. Costa, A., and Appleton, J. 共2002兲. “Case studies of concrete deterioration in a marine environment in Portugal.” Cem. Concr. Compos., 24共1兲, 169–179. Cusson, D., Qian, S., and Hoogeveen, T. 共2006兲. “Field performance of concrete repair systems on highway bridge.” ACI Mater. J., 103共5兲, 366–373. Elsener, B. 共2001兲. “Half-cell potential mapping to assess repair work on RC structures.” Constr. Build. Mater., 15共2–3兲, 133–139. Emmons, E. H., Vaysburd, A. M., and McDonald, J. E. 共1993兲. “A rational approach to durable concrete repairs.” Concr Inrern, 15共9兲, 40– 45. Fookes, P. G., Simm, J. D., and Barr, J. M. 共1986兲. “Marine concrete performance in different climatic environments.” Proc., Int. Conf. on Concrete in the Marine Environment, The Concrete Society, London. Golam Ali, M. 共1993兲. “Cathodic protection current accelerates the alkalisilica reaction.” ACI Mater. J., 90共3兲, 247–252. Guettala, A., and Abibsi, A. 共2006兲. “Corrosion degradation and repair of a concrete bridge.” Mater. Struct., 39共4兲, 471–478. Marseguerra, M., and Zio, E. 共2000兲. “Optimizing maintenance and repair policies via a combination of genetic algorithms and Monte Carlo simulation.” Reliab. Eng. Syst. Saf., 68共1兲, 69–83. Momayez, A., Ehsani, M. R., Rajaie, H., and Ramezanianpour, A. 共2005兲. “Cylindrical specimen for measuring shrinkage in repaired concrete members.” Constr. Build. Mater., 19共2兲, 107–116. Novokshchenov, V. 共1995兲. “Deterioration of reinforced concrete in the marine industrial environment of the Gulf-A case study.” Mater. Struct., 28共7兲, 392–400. Pargar, F., Layssi, H., and Shekarchi, M. 共2007兲. “Investigation of chloride threshold value in an old concrete structure.” Proc., 5th Int. Conf. on Concrete under Severe Conditions: Environment and Loading (CONSEC’07) Tours, Laboratoire central des ponts et chaussées 共LCPC兲, France. Raupach, M. 共2006兲. “Patch repairs on reinforced concrete structures— Model investigations on the required size and practical consequences.” Cem. Concr. Compos., 28共8兲, 679–684. Shekarchi, M., Moradi-Marani, F., and Pargar, F. 共2009兲. “Corrosion damage of a reinforced concrete jetty structure in the Persian Gulf: A case study.” Struct. Infrastruct. Eng., in press. Vaysburd, A. M., and Emmons, P. H. 共2000兲. “How to make today’s repairs durable for tomorrow—Corrosion protection in concrete repair.” Constr. Build. Mater., 14共4兲, 189–197. Zhang, J., and Lounis, Z. 共2006兲. “Sensitivity analysis of simplified diffusion-based corrosion initiation model of concrete structures exposed to chlorides.” Cem. Concr. Res., 36共7兲, 1312–1323.
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