durability-based ranking of typical structural repairs

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Durability-Based Ranking of Typical Structural Repairsfor Corrosion-Damaged Marine Piles

D. V. Reddy, Ph.D., P.E., C.Eng., M.ASCE 1 ; Juan C. Bolivar, P.E. 2 ; and Khaled Sobhan, Ph.D. 3

Abstract: Corrosion damage is a main cause of deterioration for concrete marine structures. It has become increasingly important to rehabil-itate structures and develop repair techniques that prolong their life cycles. This investigation compares the performance of recognizedrepair techniques, in terms of corrosion resistance, structural integrity, and cost-effectiveness. Eight sets of three cylindrical piles were preparedto conduct seven types of repairs with one control set. Following initial exposure to corrosion, the specimens were repaired using the proposedtechniques and tested for durability under simulated tidal conditions, with corrosion monitoring, determination of time-to-corrosion threshold,and visual inspections. The structural integrity was determined by crack scoring and ultimate load testing, and synthesized with a cost-effectiveness evaluation to rank the repair techniques. The repairs comprising carbon wrapping, high-density polyethylene (HDPE) jacketing,and MMFX steel outperformed the others, slurry-in ltrated brous concrete (SIFCON) repair, styrene-butadiene grout with woven rovingfabric wrapping, normal concrete repair with spliced berglass reinforcing plastic (FRP) (glass) reinforcement, and the modi ed ASANOrefresh method. DOI: 10.1061/(ASCE)SC.1943-5576.0000157 . 2013 American Society of Civil Engineers.

CE Database subject headings: Corrosion; Durability; Cracking; Underwater structures; Rehabilitation.

Author keywords: Corrosion repairs; Durability; Cost-effectiveness; Crack scoring; Ranking.

Introduction and Background

Corrosion is one of the major contributors to the permanent de-terioration of existing infrastructure. According to the U.S. FederalHighway Administration, corrosion cost studies carried out in theUnited States, Europe, and Japan have shown that . . ., a cost gureof 3% to 4% of the gross national product (GNP) can be attributedto the direct and indirect costs of corrosion (Scannell et al. 1996 ).Marine concrete structuresare subjected to a very harsh surroundingenvironment, whichaffects their structural integrity. The continuous

exposure to seawater makes them vulnerable to physical damage,debonding, and strength loss caused by corrosion. While repairs of marine corrosion-damaged structures have become widespread,they provide a great cause of concern. It has been estimated that the annual expenditure involved in repairing the existing marinepiles in the United States alone amounts to about $1 billion ( Fam et al. 2003 ). In addition, the repairs of marine structuresare currentlycarried out as an intuitive process, because of the lack of signi cant analytical and experimental research that can be used to predict their effectiveness. Therefore, this investigation intends to evaluate theperformance of different repairs, in terms of cost-effectiveness,

corrosion activity, and structural integrity after long-term marineexposure.

Corrosion of steel reinforcement limitsthe service life of concreteexposed to seawater. Because of the formation of rust layers causedby corrosion, concrete piles are extremely susceptible to crackingand spalling. Although steel reinforcing bars are initially protectedby the alkaline nature of the surrounding concrete, chloride ionsfrom seawater can slowly in ltrate through the concrete cover andinto the reinforcement. All chloride-contaminated concrete must beremoved and replaced with low-shrinkage, low-modulus, high-

creep, high-tensile-strength patch material having the same ther-mal expansion and oxygen permeability ( Emmons and Vaysburd1997). Such repairs can barely be carried out under wet conditionsand are unrealistic for piles corroding in tidal waters ( Mullins et al.2005). Surface treatments have been tested by Sagues ( 1994) toevaluate whether thecorrosionprocess canbe reducedor eliminated.This process was tested on exposed marine piles above the water line. The two types of surface treatments used included an alkylalkoxy silane and an alkyl alkoxy siloxene. The Allen Creek Bridge,located in tidal waters inClearwater, Florida, hasrecently undergonerepairs on its prestressed piles ( Emmons and Vaysburd 1997 ).Carbon and glass ber-reinforced polymer materials were wrappedunderwater to repair damaged concrete. The underwater wrap con-sisted of a water-cured polyurethane resin system that can be used

with woven glass fabric, unidirectional glass fabric, woven carbonfabric, and unidirectional carbon fabric. This system eliminated theneed for cofferdam construction that is required for dewatering of a site, which may adversely cause restrictions to the cross sectionof the water body. The process of wrapping the piles in berglassreinforcing plastic (FRP) sleeves is one of the most popular waysto x the damaged piles once they fail. According to Darby(1999), FRP composites contain carbon or glass bers that possessa high tensile strength in a vinylester or epoxy matrix. In thismethod, the problem area is replaced and the pile is wrapped in theFRP sleeve to prolong the amount of time until the piles becomeexposed. Whiting et al. ( 2000) simulated marine conditions to test

1 Professor and Director, Centerfor MarineStructures and Geotechnique,Civil, Environmental and Geomatics Engineering, Florida Atlantic Univ.,

Boca Raton, FL 33431. E-mail: [email protected] Project Engineer/Project Manager, Corzo Castella Carballo ThompsonSalman, P.A. (C3TS), 21301 Powerline Rd., Suite 311, Boca Raton, FL33433. E-mail: [email protected]

3 Associate Professor, Civil,Environmentaland Geomatics Engineering,Florida Atlantic Univ. Boca Raton, FL 33431 (corresponding author).E-mail: [email protected]

Note. This manuscript was submitted on January 30, 2012; approved onNovember 16, 2012; published online on November 20, 2012. Discussionperiod open until April 1, 2014; separate discussions must be submittedfor individual papers. This paper is part of the Practice Periodical onStructural Design and Construction , Vol. 18, No. 4, November 1, 2013.ASCE, ISSN 1084-0680/2013/4-225 237/$25.00.

PRACTICE PERIODICAL ON STRUCTURAL DESIGN AND CONSTRUCTION ASCE / NOVEMBER 2013 / 225

Pract. Period. Struct. Des. Constr. 2013.18:225-237.
http://dx.doi.org/10.1061/(ASCE)SC.1943-5576.0000157mailto:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]://dx.doi.org/10.1061/(ASCE)SC.1943-5576.0000157


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conventional repairs such as patches, sealers, and coatings. Their study included a survey of 12 prestressed bridges with evidence of deterioration because of corrosion, as well as an extensive laboratoryexamination of the repairs. The tests included visual examinations,cover surveys, delamination surveys, half-cell potential measure-ments, corrosion rate (linear polarization) measurements, chloridesampling, and petrographic analysis.

The method of choice for repairing one of the longest bridges,the Lake Pontchartrain Causeway located in New Orleans, con-sisted of using an all-polymer encapsulation process as reported

by Trader (1997 ) of the MADCON Corporation. Engineers chosethe all-polymer or advanced encapsulation process (A-P-E) over other repair processes such as epoxy paste, crack injection, andseveral wrap methods. The basic features included using trans-lucent FRP jackets and pumping aggregate- lled polymer grout into the jackets from the bottom up. While the engineers of theLake Pontchartrain Causeway claimed to have positive resultsusing a jacket, Sohanghpurwala and Scannell ( 1994) obtainedunsuccessful results when providing jacketing for protectionagainst corrosion. Their reasons include (1) capillary actionallowing water fromthe submerged section of the pile to rise up thepile; and (2) high levels of chloride ions remaining in the unre-paired areas.

Corrosion may actually be accelerated within these repairs

because the concrete is never allowed todry out and thereis alwaysa strong presence of oxygen. One example of jackets havinga detrimental effect was found in the pilings at the Bryant PattonBridges in Florida. The Florida DOT (FDOT) found that over 50%of the piles that had been repaired previously using berglass jackets were now de cient. This caused the FDOT to start a newrehabilitation project to improve the conditions of all the pre-viously jacketed piles. High-density polyethylene (HDPE)has alsobeen used recently in some studies as an admixture in the concretemix. It has been shown that a concrete mix containing HDPEdisplayed a higher compressive strength than concrete mixeswithout HDPE particles ( Naik et al. 1996 ). HDPE pipes were wrappedaround the piles to provide surface protection and prevent seawater intrusion into the specimens.

A study performed in Australia at Monash University showedthe effectiveness of a composite wrap around the aging concretebeam, compared with the normal setup ( Hanna and Jones 1997 ).Tests wereperformed on damaged and undamaged concrete beamsto evaluate the ef ciency of the wrapping. The conclusion was that the composite wrapping is an ef cient method to repair agingstructures.

Materials and Methods

Fabrication of Test Specimens

This project utilized 24 specimens, 1,067 mm (42 in.) long and152 mm (6 in.) in diameter, reinforced with 9.5-mm (3/8-in.) steelreinforcementbarsand3.2-mm (1/8-in.) stirrups placed with152-mm (6-in.) spacing. The proposed specimens were divided into groups of threepiles, withsevensets of test piles andone control set. The controlspecimens were not subjected to corrosion or tidal exposure, to allow

the comparison of repaired piles and new piles.

Accelerated Corrosion Damage with Induced Current

All test specimens, with the exception of the MMFX TechnologiesCorp.-reinforced piles, were subjected to accelerated corrosionduring 20 days, using a direct anodic currentof 140 mA and elevatedchloride content. The current required to corrode the reinforcement was determined by previous calculations developed by Reddy andAhn(1995). Themiddle third segments of the specimens (tidalzone)were enclosed in a plexiglass jacket and exposed to seawater. Theanodic current was supplied by a direct current supplier, whichpassed through the electrolyte fromthe specimen, to a noncorroding303stainlesssteel sheet,whichacted as thecounterelectrode(Fig. 1).

Specimen Repairs After corrosion developed, the exposed specimens were repaired(Fig. 2). The corrosion products of the original piles were removedwith theuseof severaltechniquessuch as saw-cutting, sand blasting,and chipping. The specimens were then repaired following thetechniques outlined here:

1. Repair with slurry-in ltrated ber concrete (SIFCON) andspliced FRP (glass) reinforcement (Fig. 3). ThemixcomprisedType I and Type II portland cements, sand, y ash, water,Florida Pearock aggregate, and polyole n bers. The propor-tions were as follows: 1:2 water to binder and 1:1.25:1.25(binder:sand:aggregate). The polyole n bers were 5.85% byvolume in the SIFCON mixture.

2. Styrene-butadiene latex polymer grouting followed by wovenroving fabric wrapping (Fig. 4). Prepacked aggregate andcement were used in the mixture, along with sand, water,and lime. The proportions were as follows: 1:2.65 water tobinder and 1:1.25 binder to sand, with the binder including theaggregate. The lime content was 10% by volume of aggregate.After the mixture was cured, surface treatments consisting of

Fig. 1. Schematic for accelerated corrosion

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contributing 6.5% to the binder (cementitious mixture). Theremaining proportions were as follows: 1:1.22:1.09 (binder:sand:aggregate). Polyole n bers were added at 1.5% by total

volume, and the superplasticizer at 2% by weight of cement.The repaired region was wrapped with one semicylindricalpiece of corrugatedHDPE pipe sealedwith polyurethane resin.

6. Modi ed ASANO refresh method (Fig. 8). This mixtureconsists of using binder with prepacked aggregate, andstyrene-butadiene latex mortar. Water, sand, and lime werealso included in the mixture. The water to binder ratio was1:2.27, andthe binder to sand ratio was 1:1.25 (including theaggregate). The styrene-butadiene latex mortar was mixedat 10% by weight of binder. Lime was added at only 5%by volume of the binder. Surface coatings were used for salt-damage prevention, consisting of organic paint andvinylester.

7. Regular concrete and MMFX steel specimens. For this

repair, MMFX steel was used instead of normal reinforcingsteel. The concrete mixture included sand, 9.5 mm (3/8 in.)Florida Pearock aggregate, cement, and water. The propor-tions were as follows: 1:1.8 water to binder and 1:2.25:2.63(binder:sand:aggregate).

Durability Testing

Specimen SetupTo monitor the corrosion of the specimens, standard silver-silver chloride (Ag =AgCl) reference electrodes were used, as shown

in Fig. 9. In addition, titanium wire was used as a counter-electrode.

Setup of Tidal Cycle SimulationThe piles were subjected to simulated tidal conditions in seawater tanks, by alternatively raising and lowering the water level, so that the repaired section experienced dry and wet cycles, similar to

those occurring in the tidal and splash zones on marine structures.This cyclical change in environment exposure favors the corro-sion rate in concrete piles because of increased chloride content at the surface. When wetting and drying occurs, the evaporationof water leads to the enrichment of chloride ions ( Bertolini et al.2004 ).

Corrosion Monitoring and EvaluationConcurrent with the continuous exposure to tidal cycles, the speci-mens were monitored for corrosion damage (see Fig. 10). With theuse of a Gamry G 750 series potentiostat and the Gamry InstrumentsFramework and Gamry Echem Analyst software programs, dailyreadings of corrosion potentials and corrosion rates were carried out throughout the total 280 tidal cycles.

Corrosion normally occurs at a rate determined by equili-brium between the opposing electrochemical reactions, becausethe current in the metal exactly balances the ionic current through the concrete ( Whitten and Gailey 1981 ). When thesetwo reactions are in equilibrium, the ow of electrons from eachreaction is balanced, and no net electron ow occurs, as shownby the schematic Tafel plot in Fig. 11 (Gamry Instruments2007 ), relating the rate of the electrochemical reactions to theoverpotential.

Analysis of Structural Integrity

Crack Survey and Scoring

After tidal exposure, once the specimens were fully dry, everycrack in each specimen was counted and measured for total lengthand maximum width (Fig. 12).

Ultimate LoadsAfter the assessment of cracking was nished, the specimens wereevaluated in terms of their structural integrity. The piles were subjected to a static, ultimate testing, in which the ultimate loads wereestimated with a simple beam with centerpoint load test, with a clear span of 1,016 mm (40 in.). The load wasapplied at a constantrate of 18.14 kg/s (25 lb =s), until failure of the beam occurred.

Fig. 5. Silica fume concrete patching and carbon ber wrapping

Fig. 6. Regular concrete patching and glass FRP splicing




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Experimental Evaluation of Repairs

Seven major evaluations are presented:

Visual InspectionVisual inspections took place ve times throughout the research, at 0, 70, 140, 210, and 280 tidal cycles, and the methodology followedthe criteria setforth by O Neil (1980). After all the inspections werecompleted,a summation of all the individual scores foreachpile wasmade, and a nal average score for each group was calculated(Fig. 13). Because the system assigns the lowest scores to the least damaged piles, those groups that presented the lowest average scoreat the end of the 280 tidal cycles were the ones that deteriorated theleast after the seawater exposure. While Groups 1 and 6 presenteda fairly rapid and progressive damage, Groups 2 and 4 showeda slower pace in deterioration, Groups 3 and 7 developed very late

signs of deterioration, and Group 5 showed barely any signs of worsening after prolonged marine exposure.

Corrosion Potential AnalysisCorrosion potential measurements were taken for all specimens,with the use of an Ag =AgCI reference electrode and a state-of-the-art potentiostat with specialized software. This technology wasnecessary to analyze the very small daily variations in corrosion.The ASTM C876 criterion for copper-copper sulfate referenceelectrodes (Elsener and Bhni 1990 ) states that a value morenegative than 2 350 mV implies a possibility greater than 90% that corrosion has developed. Fig. 14 shows the average minimum corrosion potential ( E corr) per group after 280 cycles of tidalexposure. All repairs exceeded the limiting corrosion thresholdvalue and were grouped in three categories: Groups 3, 5, and 7 were

Fig. 7. High-performance ber-reinforced concrete patching with a HDPE jacket

Fig. 8. Modi ed ASANO refresh method




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located between 2 300and 2 500 mV, equivalent to 187, 164, and205%, respectively, of the limiting corrosion threshold; Groups 2and 6 were located between 2 500and 2 700 mV, equivalent to 276and 246% of the threshold value; and Groups 1 and 4 had E corr values below 2 700 mV, equivalent to 355 and 392% of thethreshold value.

The corrosion potential values presented give a clear indicationthat Groups1 and4 developeda more criticalcorrosionstate than therest of the repairs. The average minimum E corr values for Group 4

were more than twice negative than those of Groups 3 and 5, whilealso being more negative thanthe values of Groups1, 2, 6,and 7, by10, 42, 60, and 91%, respectively. Group 5 was the repair with theleast amount of corrosion development, with a corrosion rate of 2 377 mV, only about 64% more negative than the corrosionthreshold value, followed by Group 3, with a corrosion potentialvalue 87% more negative than the corrosion threshold value.

Time to CorrosionThe total cycles that each specimen took to surpass the corrosionthreshold were determined, and the average per group was calcu-lated to compare the corrosion retardation abilities of the repairs.

Fig. 15 shows a summary of the average number of cycles tocorrosion for eachgroup.This illustrates the signi cant difference inthe rate of corrosion development between the different groups. Themost criticalsituation wasevidencedby Group 4,which took only 11tidal cycles to surpass the corrosion threshold under simulatedmarine conditions. This is an indication that it may not be an ad-equate long-term solution for corrosion retardation. The next levelshows Groups 1 and 2, which took 36 and39 cycles, respectively, toreach the corrosion threshold. While these groups took over threetimes longer than Group 4 to develop a high probability of corrosion,theyare still a questionable alternative for long-termrepairs. Group 6surpassed the corrosion threshold at 69 tidal cycles. This is ap-proximately six times longer than Group 4, and about twice as longas Groups 1 and 2. Nevertheless, Group 6 was outperformed byGroups 3 and 5 by approximately 1.5 times, and by Group 7 1.65times, which on average took the longest to reach the corrosionthreshold value. The difference between the fastest and the slowest groups to reach this limiting value (Groups4 and7, respectively) was10.4 times the number of cycles that is, 11 and 114 tidal cycles,respectively.

Maximum Corrosion RatesConcurrent with the measurement of corrosion potential values,durability testing also included monitoring of corrosion rates for all specimens. Tafel plots and linear polarization techniques weredeveloped with state-of-the-art instrumentation to estimate the corro-sion rates during exposure in seawater tanks. Although the experi-

mentation required in estimating corrosion potentials and corrosionrates is intrinsically related, half-cell potentials cannot be correlateddirectly with the corrosion rate of the rebars (Bertolini et al. 2004 ).For this reason, the potentiostat equipment was used in conjunctionwith specialized corrosion analysis software ( Gamry Instruments2007) to perform all calculations and iterations necessary to nd theinstantaneous and average corrosion rates after a series of current and potential measurements.

The objective of the corrosion rates estimation was to predict theevolution of structural degradation of the specimens as a long-term average value of the loss in cross section of the reinforcement (Bertolini et al. 2004 ). Clear (1989) developed a model to nd the

Fig. 9. Schematic for connection of electrodes with the specimens

Fig. 10. Corrosion monitoring setup (photo by authors)




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relationship between corrosion rates and the remaining service lifeof a structure. Table 1 shows the criteria developed by him.

The experimental corrosion rate results for all groups are com-pared in Fig. 16. The comparison of the experimental results withClear s (1989) criteria demonstrates considerable development of corrosion for most repairs. Group 5 presented the least rate of corrosion, being the only repair located within the second zone of Clear s (1989) model (corrosion damage possible within 10 15years). Nevertheless, its averagecorrosion rate neared the maximum

value for the category, separated by only 0 :02 mil=year. The thirdzone was occupied by Groups 3, 5, and 7, which classi ed in theregion with corrosion damage expected within 2 10 years. Thegroups in this zone canalreadybe considered as groups with signs of active corrosion development. Groups 1, 2, 4, and 6 were all locatedwithinthe criticalzone in Clear s (1989) model.These arethe groupsthat can expect corrosion development within 2 years or less. Theaverage corrosion rate values for these groups exceeded the mini-mum bracket value by a substantial difference, with their averagecorrosion rates being 1.7 to 8.2 times higher than the minimum,which is a serious indication of high corrosion development.

The estimation of these values required the measurement of themaximum corrosion rates per specimen after durability testing.These maximum values were combined for each group, and aver-aged to provide a comparable number per repair. Fig. 16 shows howeach repair is categorized within Clear s (1989) model and dem-onstrates the substantial corrosion rate differences between thedifferent groups. Groups 1, 2, and 4 show a substantial structuraldegradation and an aggressive growth of corrosion. The corrosionrate for Group 4 (the highest among all groups) is about 83 timeshigher than that of Group 5 (the lowest among all groups).

Cracking EvaluationFollowing the completion of the corrosion monitoring phase,microstructural analysis was performed for all specimens with the

use of crack scoring criteria. A modi ed version of the methodemployed by Thornton ( 1984) was developed to score and rank therepairs. The scoring criteria used is based on the principle that the specimens with the highest area of cracking will be more vul-nerable to developing corrosion. The rst step to obtain the totalscore wasthe estimation of the total number of cracksper repair. Thecracks in each specimen were marked and counted, and their totalnumber was recorded. The totals for each specimen were thencombined to estimate the average number of cracks per group(Fig. 17). Following the estimation of the average number of cracks,the length of each individual crack was measured, and the averagelengths of cracks were calculated for each specimen (Fig. 18). The

Fig. 11. Standard Tafel plot for corrosion potential measurements

Fig. 12. Cracked specimen after seawater exposure (photo by authors)




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Fig. 13. Average total visual inspection scores per specimen group

Fig. 14. Average minimum corrosion potential

Fig. 15. Average number of tidal cycles to reach the corrosion threshold value




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maximum crack widths were also measured for each crack, and theaverage per specimen was calculated (Fig. 19). After the number of cracks, the average crack lengths, and their maximum widths werecalculated, the total crack score per specimen, C s , was determined asfollows:

C s P number of cracks average crack length

average maximum crack width (1)

Table 1. Criteria for Correlation between Corrosion Rates and ServiceLife (Data from Clear 1989)

ZoneCorrosion rate

m m =year mil=year Corrosion condition (year)

Zone 1 , 6 , 0:24 No damage expectedZone 2 6 30 (0.24 1.18) Damage possible in 10 15Zone 3 30 300 (1.18 11.81) Damage expected in 2 10Zone 4 . 300 . 11:81 Damage expected in , 2

Fig. 16. Average maximum corrosion rates per group (1 mil 5 25.4 m m)

Fig. 17. Average number of cracks per group




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The total cracked areas for the specimens comprising each repair,were added together to obtain the total crack score per group. The

groups with the lowest scores were those that developed the least cracking after the durability testing

Crack score per group P C S (2)

The results of the crack scoring shown in Table 2 indicate that Groups 3, 5, and 7 showed little vulnerability to the development of cracking, with scarce presence of cracks and a cumulative score of 0.3, 0.55, and 0.0, respectively. This performance is consistent withtheir performance in the categories previously analyzed, becausethese three groups reached the least negative corrosion potentialvalues throughout thedurability testing, requiredthe longest number

of tidal cycles to surpass the corrosion threshold value, and had thelowest corrosion rates, with thehighestservice life expectancybased

on Clear

s (1989) criteria. Groups 2 and 4 presented a more sig-ni cant susceptibility to cracking development, with a more con-sistent presence of cracks in each specimen, and slightly longer or wider cracks than those of the previous groups. These groups werealso intermediate performers throughout the visual inspection as-sessment. A different situation occurred with Groups 1 and 6, witha crackingscore about5 to17 timeshigherthan the rest ofthe repairs.These groups were also the lowest ranked in the visual inspectionassessment, and were both located in the worst category of servicelife based on Clear s (1989) criteria. Therefore, there is a correlationbetween the visual assessment of the specimens and the crackingand durability conditions of the piles.

Fig. 18. Average crack length per group (1 in. 5 25.4 mm)

Fig. 19. Average crack width per group (1 in. 5 25.4 mm)




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Evaluation of Ultimate LoadsThe experimental evaluation of ultimate loads was based on theapplication of a center point load for each of the specimens untilfailure.The ultimate loads were recorded for eachspecimen, and theaverage value calculated for each group. The results shown next summarize the nal values per repairs. An important comparisoncan be derived from these results. Out of the seven experimentalgroups, only four reached, or exceeded, the ultimate load bearingcapacity of the original piles. Group 3 resisted the highest loading,with an average ultimate load of 44% more than those of the control

specimens. This was followed by Group 7, which presented an av-erage ultimate load 29% higher than the control group; Group 5,with an average ultimate load 20% higher than the control group;and Group 1, with an average ultimate load 14% higher than that of the control group. Contrarily, Groups 2, 4, and 6 were unable toattain the original ultimate load capacity of the piles, with averageultimate loads 9, 17, and 76% lower than that of the control group.Fig. 20 shows the ultimate load comparison of all groups studied.

Cost-Effectiveness AnalysisThe last qualifying factor for the full assessment of the investi-gation involved the preparation of a cost analysis, to establish the

feasibility of application of each repair, based on performance andservice life prediction. Because of the small quantities of materialsnormally required for patch repairs and the variability in the cost of materials over time, basing the cost-effectiveness of the repairs on a cost and quantity estimate would undermine the reliability of therecommendations. Moreover, the variability in cost from one repair method to the next will generally be small, because the mobilization,equipment, and workmanship cost would be very similar for all theproposed repairs. For this reason, the discussion of the cost-effectiveness of the repair methods must be primarily focused on

the performance and service life bene ts of each repair. A repair that extends the service life of the structure by several years will provideimportant cost savings in future repairs or replacement over a longperiod of time. With this in mind, the cost analysis for this in-vestigation was directed following Clear s (1989) criteria. Thesecriteria intend to predictthe service life of the structuresbased onthecorrosion rates previously estimated.

The analysis of service life expectancy based on the corrosionrates shown in Table 3 indicates that Group 5 is the most cost-effective alternative, with possible corrosion damage anticipatedwithin 10 to 15 years. Immediately following are Groups 3, and 7,with corrosion damage expected within 2 to 10 years. The rest of thegroups are expected to develop corrosion damage in less than 2years, based on their corrosion rates. However, the corrosion rate

estimated for Group 6 is about 3 times smaller than that of Group 2,and approximately 4.7 times smaller than that of Groups 1 and 4.Because the corrosion rate is a measurement of the structuraldegradation of the specimens, it is safe to assume that the life ex-pectancy of Group 6 will be higher than that anticipated for Groups 1, 2, and 4. Therefore, the repair method for Group 6 isconsidered more cost-effective than those groups. Table 3 shows theaverage corrosion rates per group and their corresponding cost-effectiveness rank.

Table 2. Final Crack Scoring

Group Crack score mm 2

(in:2) Rank

1 3,277 (5.08) 62 677 (1.05) 53 194 (0.30) 24 477 (0.74) 45 355 (0.55) 36 3,555 (5.20) 77 0 (0) 1

Fig. 20. Average ultimate load per group




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Final Evaluation

Based on the evaluation rankings given to the repairs in terms of thevisual inspection assessment, corrosion potential analysis, number of tidal cycles to reach the corrosion threshold value, maxi-mum corrosion rates, crack scoring, ultimate loading, and cost-effectiveness, a comprehensive evaluation matrix was developedtogive a nal scoreto each group. The groups were graded using thescale in Table 4, based on their ranking for each individualcriterion. The scoring scale was designed to distribute the pointswithin the seven groups as uniformly as possible on a zero to 100scale. Once the scores were assigned for each criterion based onTable 4, the evaluation matrix was developed to sum the scoresper category and provide a nal experimental score to all groups(Table 5). The repair with the highest score in the evaluation matrixrepresents the group that offered the best overall performance after the comprehensive evaluation.

The nal evaluation matrix summarizes the performance of allgroups after the comprehensive durability, microstructural, elec-trochemical, structural, and cost-effectiveness analysis. The nalscore suggests that Groups 3 and 5 provide the best alternatives for repairs of corrosion-damaged marine piles. These groups are closelyfollowed by Group 7. A second tier of repairs comprises Groups 2and 6, and the last tier comprises Groups 1 and 4 (normal concretewith spliced FRP). The nalscore of the top threegroupsfar exceedsthat of the rest. There is a difference of 306 points between the thirdand fourth overall place. Also, the nal score of the last group(Group 4) is more than 6 times lower than the nal score of the toptwo groups. This gives an indication of the consistency of theresults throughout this investigation.

Even though the overall assessment included experiments of different natures, the results of this investigation suggest a correla-tion between the corrosion development and the structural perfor-mance of the repairs. The groups with the lowest corrosion rates andlargest number of tidal cycles to surpass the corrosion thresholdvalue proved to be the groups with the best visual inspection ratings,lowest development of cracking, and highest load bearing capacity.The opposite was the case for the groups with the lowest scores inthecorrosion-related experiments.

Conclusions

The speci c conclusions from the project are as follows:1. Spliced glass FRP reinforcement does not appear to provide

substantial bene ts as a corrosion prevention material. The twogroups of repairs using glass FRP presented the most negativecorrosion potentialvalues (most vulnerable to corrosion), equiv-alent to 355 and 392% of the corrosion threshold value.

2. MMFX steel reinforcement produced the best results in termsof the retardation in the development of corrosion. It took 114

tidal cycles for the conventional concrete with MMFX steelrepair to reach the corrosion threshold value. This is 10 timeslonger than the time it took the conventional concrete repair with spliced glass FRP reinforcement to exceed the samevalue. The MMFX steel reinforced piles were the also theonly group that did not develop any cracking throughout durability exposure.

3. The high-performance ber-reinforced concretepatching withHDPE jacketing presented the best long-term performance interms of anticipated service life. This repair developed a cor-rosion rate of 1:16 mil=year and obtained the highest rate out of all groups in the Clear (1989) service life criteria.

4. The crack scoring method developed for this investigationappeared to be an adequate indicator of the performance of repairs. The results obtained with this method where fairlyconsistent with the ranking provided by the visual assessment and the corrosion evaluation experiments.

5. Groups 1, 3, 5, and 7 presented positive results in terms of structuralintegrity, as they exceeded theultimate load capacityof the control group by 14, 44, 20, and 29%, respectively.Groups 2, 4, and 6 were not able to restore the original ultimateload capacity of the piles, with average ultimate loads 9, 17,and 76% lower than that of the control group.

6. Based on the service life approach, the high-performanceber-reinforced concrete patching with HDPE jacket was

the mostcost-effectivesolution for corrosion-damaged marinepile repairs.

7. With a score of 598 points in the nal evaluation matrix,Groups 3 and 5 were the most effective repairs to alleviate theeffects of corrosion damage.

Acknowledgments

The authors thank the National Science Foundation for nancialsupport of theprojecttitled Cost-Effective Repair of Marine Piles,

Table 3. Experimental Corrosion Rates, n corr , and Corresponding Cost-Effectiveness Rank

GroupMax. n corr [m m/year

(mil=year)]Cost-effectiveness

rank

1 2,373 (93.41) 62 1,534 (60.41) 53 59 (2.34) 24 2,450 (96.46) 75 30 (1.16) 16 521 (20.52) 47 132 (5.18) 3

Table 4. Grading Scale for Final Evaluation Matrix

Rank Score

1 1002 833 664 495 326 157 0

Table 5. Final Evaluation Matrix

Category

Group

1 2 3 4 5 6 7

Visual inspection 15 49 83 32 100 0 66Average minimum corrosion potential

15 32 83 0 100 49 66

Time to corrosion threshold 15 32 83 0 66 49 100Maximum corrosion rate 15 32 83 0 100 49 66Crack scoring 15 32 83 49 66 0 100Ultimate load 49 32 100 15 66 0 83Cost-effectiveness 15 32 83 0 100 49 66

Total 139 241 598 96 598 196 547Final rank 6 4 1 7 1 5 3




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on which this paper is based, under the U.S. Mexico InternationalCooperative Program. Gratitude is expressed to Structural Preser-vation Systems, Inc., for providing technical expertise, staff helpwith therepair work, andassistancewith materials;SRI Consultants,Inc., for their technical support and assistance with the corrosionequipment rental, and Dr. Salem Faza of MMFX Steel Corp. for the donation of MMFX steel. Florida Waterproo ng Supplies, W.R.Grace & Co., andSika Corporationare alsogratefully acknowledgedfor their contributions of repair materials.

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http://dx.doi.org/10.1016/S1350-6307(97)00002-2http://dx.doi.org/10.1016/S1350-6307(97)00002-2http://dx.doi.org/10.1016/S1350-6307(97)00002-2http://dx.doi.org/10.1016/S1350-6307(97)00002-2http://dx.doi.org/10.1016/S1350-6307(97)00002-2http://dx.doi.org/10.1061/(ASCE)1090-0268(2005)9:2(136)http://dx.doi.org/10.1061/(ASCE)1090-0268(2005)9:2(136)http://dx.doi.org/10.1061/(ASCE)1090-0268(2005)9:2(136)http://dx.doi.org/10.1061/(ASCE)1090-0268(2005)9:2(136)http://dx.doi.org/10.1061/(ASCE)1090-0268(2005)9:2(136)http://dx.doi.org/10.1016/0008-8846(96)00135-4http://dx.doi.org/10.1016/0008-8846(96)00135-4http://dx.doi.org/10.1016/0008-8846(96)00135-4http://dx.doi.org/10.1016/0008-8846(96)00135-4http://dx.doi.org/10.1016/0008-8846(96)00135-4http://dx.doi.org/10.1016/0008-8846(96)00135-4http://dx.doi.org/10.1016/0008-8846(96)00135-4http://dx.doi.org/10.1016/0008-8846(96)00135-4http://dx.doi.org/10.1061/(ASCE)1090-0268(2005)9:2(136)http://dx.doi.org/10.1016/S1350-6307(97)00002-2

durability-based ranking of typical structural repairs

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