Hot-Dip Galvanized Reinforcing Steel Performance Report
Hot-Dip Galvanized Reinforcing Steel Performance ReportLongbird Bridge Bermuda 1953 - 2020TM
Longbird Bridge Rebar ReportExecutive SummaryOver the nearly seven decades the Longbird Bridge stood,several inspections and corings were conducted to evaluatethe performance of the hot-dip galvanized (HDG) rebarused in the bridge deck. In each of the studies, the averagegalvanized coating thickness was measured and foundto exceed the requirements for newly galvanized rebardespite being exposed to a highly corrosive, tropical marineenvironment in Bermuda. The bridge was exposed to heavysalt-spray from tidal splash zones and was constructed in veryclose proximity to the ocean.In 1995, when the bridge was 42 years old, the HDG rebarcoating thickness was in excess of the requirement for newlygalvanized rebar even though the measured chloride levels were3 to 10 lbs/yd3, well beyond the threshold limit of 1.1 lbs/yd3(0.65 kg/m3) for black rebar. In 2020, after the bridge had beendemolished, analyzed rebar samples showed HDG coatingthickness still in excess of the requirement for new galvanizedrebar after 67 years of service.The performance of the Longbird Bridge, in part, ledBermuda’s Ministry of Works and Engineering (MW&E) toexclusively specify hot-dip galvanized reinforcement in futurebridge projects for more than 50 years and it is still standardpractice today. If it were not for damage from multiplehurricanes over the years, including the devastating finalblow delivered by Hurricane Fabian in 2008, the LongbirdBridge would have provided service for well over 100 years.Concrete Corrosion Costs 20 Billion AnnuallyThe deterioration and subsequent maintenance and replacementof reinforced concrete structures, such as bridges, is estimated tocost more than 20 billion annually in the United States. Thesecosts are increasing by nearly 500 million each year, which hasbecome a major liability for highway agencies. The direct costs ofreplacing and repairing the structures is obvious; however, theindirect costs resulting from traffic delays, business interruption,and structural failures further exacerbates the problem. As aresult, finding a sustainable, corrosion-resistant reinforcingsolution that lengthens the service life of reinforced concretestructures is paramount to decrease the burden these costs placeon society. Hot-dip galvanized reinforcing steel has emerged as aviable solution to this problem.2American Galvanizers Association / International Zinc AssociationInitial ConstructionAbout BermudaThe Longbird Bridge in Bermuda, a swinging asymmetrical steelspan, was built across Castle Harbor by the US Navy in 1953 tofacilitate movements to St. David’s Island near the Kindley NavalAir Station (now the Bermuda L. F. Wade International Airport).The US Navy maintained a military presence in Bermuda fromthe 1940’s to 1995 and constructed many structures as part ofits operations, including the Longbird Bridge. Due to the highchloride environment, hot-dip galvanized steel reinforcementwas used in the concrete approach and bridge deck.Bermuda lies in the northwestern Atlantic Oceanabout 650 miles (1050 km) east of North Carolina.The main Island is about 23 miles (38 km) longand 1.25 miles (2 km) wide at its widest point. Theclimate is frost-free with temperatures ranging from50 F to 90 F (10 C to 32 C) and an average relativehumidity of 80%. No point in the archipelago of sevenmain islands and numerous islets is more than onekilometer from the sea, so salt spray and salt-ladenair create a corrosive, tropical marine environment.The single span concrete approach deck was approximately 18ft (5.5 m) long by 20 ft (6.1 m) wide with 10 in (254 mm) thickconcrete covered by 2 in (51 mm) of asphalt. Deformed, round,hot-dip galvanized #4 rebar was used to construct three layerseach in an upper and lower mat of reinforcing steel. Top andbottom bars were longitudinal at staggered 16 in (406 mm)centers while the middle layer was transverse at staggered 8 in(203 mm) centers. An additional lower mat was constructed inessentially the same manner. Concrete cover over the top matof the reinforcing bars was approximately 2 in (51 mm).The parameters of the concrete mix are unknown; however, itis typical in the construction of bridges, seawalls, and buildingsin Bermuda for concrete to be made with coral aggregates andmixed with seawater because fresh water is a rare resource.This introduces a high initial chloride concentration, amplifyingthe need to protect the steel reinforcement from corrosion.Inspections & StudiesInternational Lead Zinc Research Organization - 1975More than 20 years after the construction of the LongbirdBridge, the International Lead Zinc Research Organization(ILZRO) sponsored studies on the performance of galvanizedreinforcement in concrete bridge decks in the United States,Canada and Bermuda. Concrete cores were drilled and samplesof concrete and HDG rebar were pulled from various structureswww.galvanizedrebar.com3
Longbird Bridge Rebar ReportHow does HDG Rebar Protect Steel in Concrete?including the Longbird Bridge. Metallographic examination andpetrographic analyses were performed on the concrete cores toexamine the galvanized coating thickness on the rebar and thechloride concentration in the concrete near the bar surface.Zinc’s chloride-induced corrosion threshold is 2-4 times higherthan black steel. Black steel is passive in alkaline concreteuntil the chloride level exceeds approximately 1.1 lbs/yd3(0.65 kg/m3); the point at which steel becomes depassivatedand starts to corrode. Zinc, on the other hand, can withstandchloride concentration much higher than black steel and thecorrosion of zinc will not initiate until concentrations of atleast 2.2 lbs/yd3 (1.3 kg/m3) have been achieved and in someconditions even up to nearly 4 lbs/yd3 (2.4 kg/m3).Bare SteelHot-dip Galvanized CoatingThe results from the Longbird Bridge analysis revealed anaverage hot-dip galvanized coating thickness of 6 mils (152 µm)despite an extremely high concrete chloride concentration of 1.7to 2.2 lbs/yd3 (1.0 to 1.3 kg/m3) present in the concrete at thelevel of the top mat of HDG reinforcing steel. This concentrationis well above the 1.1 lbs/yd3 (0.65 kg/m3) to initiate corrosionof uncoated steel bars.Even when the hot-dip galvanized coating begins to corrode,zinc corrosion products have the unique property of diffusinginto the concrete matrix opposed to building up pressure atthe surface of the rebar and causing cracking and spalling. Theelemental map (left) is evidence of this migration. Bare steelis represented as orange, the hot-dip galvanized coating isyellow and the white spots in the concrete indicate zinc oxidewhich has migrated away from the galvanized rebar/concreteinterface.ConcreteCoinciding petrographic examination and visual inspectionshowed the bridge was only slightly affected by corrosion andthere were no visible signs of concrete deterioration observedsince its construction 20 years prior.In 1984, during an annual Bermuda Ministry of Works &Engineering (MW&E) inspection, cracks were observed in thesoffit of the approach span. Initially, the cracking was thoughtto indicate deterioration of the reinforcing steel, however, nosignificant rust staining was visible near the cracks. In 1991,the US Navy repaired the bridge as part of a refurbishment ofthe main steel bridge. During the repair, additional inspectionswere performed in the inter-tidal zone, the splash zone andbelow water. Reinforcing bars uncovered during the repairclearly showed the HDG (zinc) coating was still intact thusdisproving initial conceptions the reinforcing steel had begundeteriorating due to corrosion.Construction Technologies Laboratory - 1995In 1995, when the bridge was 42 years old, another investigationwas commissioned by Bermuda’s MW&E and carried out byConstruction Technologies Laboratory (CTL) to determinethe remaining useful life of the bridge. This study was partlyprompted by the prior visual inspection in 1984 and subsequentrepair by the US Navy in 1991. Again, the concrete was cored andsamples of the concrete and HDG rebar were analyzed to gaugethe performance and estimate remaining service life.Longbird Bridge - 20154The Longbird Bridge was put out of service in2008 due to damage from hurricanes.Photomicrograph from 1976 ILZRO report showing 6.9mils (175 µm) of HDG coating thickness in one locationafter more than 20 years of service. Average thicknessacross all measurements in report was 6.0 mils (152 µm).The results of the study (Appendix A) again showed extremelyhigh levels of chlorides in the concrete ranging from 3.05 lbs/yd3(1.8 kg/m3), taken horizontally into the side of the bridge with6 in (155 mm) of concrete cover, to 10.39 lbs/yd3 (6.11 kg/m3), takenvertically into the sidewalk with 1.5 in (38 mm) of concretecover. Despite the elevated chloride concentration levels,coating thickness measurements on the HDG rebar yielded anaverage coating thickness of 7.1 mils (180 µm) on the samplestaken horizontally and 4.9 mils (124 µm) from samples takenfrom the vertical sections.The results of this 1995 inspection confirmed the conclusionsfrom the repair and inspection that was performed by theUS Navy four years prior. The average zinc coating thicknessexceeded the requirement for new HDG rebar galvanized toASTM A767 (Class 1) even though the chloride levels were3-10 lbs/yd3 (1.8-5.9 kg/m3), well beyond the threshold limitof 1.1 lbs/yd3 (0.65 kg/m3) for corrosion to initiate on blackrebar. The performance of the HDG rebar in the LongbirdBridge supports the Bermuda MW&E’s practice of exclusivelyspecifying HDG reinforcement on all bridge projects.www.galvanizedrebar.com5
Longbird Bridge Rebar ReportAmerican Galvanizers Association & InternationalZinc Association - 2020In 2008, the Longbird Bridge was closed due to damage fromhurricanes and subsequently bypassed by temporary twingalvanized steel bridges. In 2020, 67 years after its construction,Bermuda’s MW&E began demolition of the Longbird Bridge tomake way for a new, larger replacement structure.The American Galvanizers Association (AGA) in collaborationwith the International Zinc Association (IZA) worked closelywith the Bermuda MW&E to retrieve samples of both the rebarand concrete as the bridge was being demolished. Concretesamples were unable to be tested; however, it can safely beassumed that the concrete chloride levels would not havedecreased, but rather increased from their elevated states inprevious studies.The salvaged HDG rebar samples were sent to a lab fordetailed performance and metallographic analysis (AppendixB). For each sample, twelve separate test sites were opticallyexamined and the coating thickness at each site was measured.The high and the low readings were discarded and the finalten measurements were averaged. The average of the foursamples ranged from 3.8 mils to 11.6 mils and the average allof the samples together yielded a thickness of 6.0 mils whichexceeds the minimum coating thickness for new rebar in ASTMA767 Class 1 (150µm or 5.9 mils). Visual observation of allthe samples showed that only one small area on one of thesamples had visible rust.Extremely CorrosiveBermuda EnvironmentThe highly corrosive environment wherethe Longbird Bridge provided service wasevidenced while demolishing the bridge.Laborers removed heavily corroded supportbeams from the bridge deck that wereexposed to heavy salt spray from tidal andsplash zones.Longbird Demolition6American Galvanizers Association / International Zinc AssociationThe Bermuda Ministry of Works & Engineeringcompleted the demolition of the LongbirdBridge in 2020. Rebar samples from thebridge were collected and analyzed to determine remaining zinc coating thickness on thebars. An average of 6.0 mils of zinc was foundto exist after nearly 70 years of service.7
Longbird Bridge Rebar ReportConclusionsAppendix AReproduced with permission from David Stark and CTL. Editorial Note: Equivalent SI values included for comparison.Evaluation Of Galvanised Reinforcing Steel In The Longbird Bridge, BermudaThe performance of hot-dip galvanized rebar used in the Longbird Bridgewas studied extensively over its life of nearly seven decades. In the mostrecent, final study in 2020, the average zinc coating thickness measured onthe rebar exceeded the minimum coating thickness required for any typeof new galvanized rebar according to ASTM A767, Standard Specificationfor Zinc-Coated (Galvanized) Steel Bars for Concrete Reinforcement.April1995by David StarkSenior Principal ScientistConstruction Technology Laboratories (CTL), Inc.IntroductionThe present investigation was intended to evaluate the performance of the galvanised reinforcing steel in the Longbird Bridge, after 42years of service. For this purpose, two concrete cores were extracted and forwarded to CTL. These cores were nominally 5-1/2 in (140mm) in diameter and 12 in (300 mm) and 6 in. (150 mm) long. Core No 1 was taken horizontally into the bridge deck from an outerexposed formed surface, while Core No 2 was taken vertically through a curb-sidewalk component of the structure. Core procurementwas done in the fall of 1994.These results show the corrosion benefits of galvanized rebar despite theremarkably high chloride concentration found in the concrete samples.The concrete was mixed with seawater as is/was the standard practicein Bermuda. Thus, the initial chloride concentration is assumed to havebeen at or near the chloride threshold at which corrosion is initiated onbare steel. Chloride concentrations increased over time showing chlorideshad been diffusing into the concrete from ocean tidal and splash action.Scope of WorkThree lines of evaluation were requested to characterise the performance of the galvanised reinforcing steel in the concrete, as follows:If it were not for hurricanes damaging the Longbird Bridge, the hot-dipgalvanized rebar would have easily provided corrosion protection formore than 100 years.Summary Results of Longbird Bridge StudiesYearStudyAverage CoatingThickness mils (µm)Chloride Concentrationlbs/yd3 (kg/m3)1975International Lead Zinc Research Organization6.0 (152)1.7 - 2.2 (1.0 to 1.3)1995Bermuda MW&E / Construction Technology Laboratory7.1 (180)*4.9 (124)**3.05 (1.79)*10.4 (6.11)**2020AGA - Rebar Focus Group & International Zinc Association6.0 (152)N/A****Samples taken horizontally into the side of the bridge with 6 in (155 mm) of concrete cover**Samples taken vertically into the sidewalk with 1.5 in (38 mm) of concrete cover*** Unavailable - It can be safely assumed that the concentration of chlorides would be at least as high as previous studies due to the location of thebridge and the proximity to salt water.1. One core, No. 1, was subjected to petrographic examination in accordance with procedures in ASTM C856, “ StandardPractice for Petrographic Examination of Hardened Concrete.” Both finely lapped and freshly fractured surfaces wereexamined to characterise the quality of the concrete and identify any other features such as abnormal microcracking andsecondary reaction products. Also, depth of carbonation was determined by phenolphthalein applications to freshlyfractured surfaces.2. Determine the total (acid soluble) chloride contents of the concrete at selected depths in the two cores. For this purpose,dry powder samples were obtained using a drill and ¼ in (6.4 mm) diameter bit, and saving the sample obtained frominside a ¼ in. wide outer ring of concrete in the cores. The holes were drilled into the cylindrical faces of the cores to avoidcontamination from previous wet coring. Chloride contents were determined in accordance with procedures in ASTM C1152, “Standard Test Method for Acid-soluble Chloride in Mortar and Concrete.” Non-evaporable water contents also weredetermined for each sample and used to correct for differences in paste-aggregate ratios among the samples.3. Metallographic analysis was done to determine the thickness and compositions of the galvanised coatings on the embeddedreinforcing steel. This was done on one section of steel in each concrete core.Results of the InvestigationThe following sections describe the findings of this investigation.AcknowledgmentPetrographic ExaminationResults of the petrographic examination of Core No. 1 are reported below. The examination was conducted on both finely lappedand freshly fractured surfaces of the core.The American Galvanizers Association and the International Zinc Association would like to thank the Bermuda MW&E for their assistance incollecting the galvanized rebar samples during their demolition of the Longbird Bridge. This report would have not been possible withouttheir cooperation.The coarse aggregate is a crushed dense to porous limestone consisting virtually entirely of calcite. The colour ranges from light toorange-buff. Particles shapes are angular to subangular and blocky to elongate. Maximum particle size is one in (25 mm). The fineaggregate appears to be of the same type of limestone but more consistently of a dense, fine grained texture. Both coarse and fine8American Galvanizers Association / International Zinc Associationwww.galvanizedrebar.com9
Longbird Bridge Rebar Reportparticles are uniformly distributed through the concrete.The concrete is well consolidated with tight, intimate bond between aggregate particles and the hydrated cement paste matrix. Thematrix contains numerous voids, generally in the size range characteristic of intentionally entrained air. These voids are uniformlydistributed through the matrix. A few, somewhat larger, voids are scattered throughout the matrix and are considered entrapped airvoids. The air content of the concrete was estimated at 2.5 to 3.5%.The microscopic examination revealed no abnormal microcracking through the full length of the core, including that due todrying shrinkage or processes that cause progressive deterioration of the concrete. Treatment of freshly fractured surfaces withphenolphthalein indicates no detectable carbonation of the cement paste matrix in the interior of the concrete, nor particularly at theexposed outer surface of the concrete. This surface carries a light grey to while painted coating, beneath which is a dark, dense surfacezone in the concrete where the phenolphthalein caused the appearance of a bronze colour on fractured surfaces. This surface zoneextends to a maximum depth of ¼ in. (6.4 mm) and may represent the application of a surface coating or sealant. It was not presentin, nor typical of, concrete deeper in the core.The core also contained a section of galvanised reinforcing bar, ½ in. (12.7 mm) in diameter and located 2-7/8 in. (73 mm) below thecoated external surface of the core. There was no evidence of corrosion of the steel substrate either on the surface of the steel bar orin the cast of the bar in the concrete. Treatment of the cast with phenolpthalein also revealed no evidence of carbonation. Most of thecast displayed sharply defined features of the embedded steel. However, an ¾ in. (19 mm) long section of part of the cast displayeda frothy texture that may represent either localised inadequate consolidation of fresh concrete along one side of the steel, or reactioncoating with the highly alkaline solutions in the fresh concrete.Chloride ContentsResults of the measurements for total chloride contents, corrected for variations in paste-aggregate ratios among the samples, aregiven in Table 1. Because there were no cement content determinations or mix design data available, results are expressed as massper unit volume of concrete, wherein the unit mass of the concrete was determined in the 1976 investigation (2) to be 3765 lbs./cuyd (2240 kg/m3). Also, all values were corrected for differences in past-aggregate ratios among the seven samples. The thresholdacid-soluble chloride concentration above which corrosion is likely on untreated steel is 0.20% by mass of cement. For a concretecontaining 5
on society. Hot-dip galvanized reinforcing steel has emerged as a viable solution to this problem. 3 to 10 lbs/yd 3, well beyond the threshold limit of 1.1 lbs/yd (0.65 kg/m 3) for black rebar. In 2020, after the bridge had been demolished, analyzed rebar samples showed HDG coating thickness still in excess of the requirement for new galvanized
This specification covers the painting of hot dip galvanized steel other than sheet and wire. The requirements for the painting of hot dip galvanized sheet are contained in ISO 12944 Parts 4 and 5. 7.1 All hot dip galvanized steel to be painted shall be certified as conforming to the required hot dip galvanizing quality standard, prior to painting.
the Inspection of Hot-Dip Galvanized Products Seminar. SUMMARY This paper will address technical issues with the use of hot-dip galvanized steel in bridge construction. Some key technical issues that will be addressed are the slip factor of hot-dip galvanized, painted, and metallized coatings in slip .
1. AASHTO M111, Zinc (Hot Dip Galvanized) Coatings on Iron and Steel Products 2. AASHTO M232, Zinc Coating (Hot Dip) on Iron and Steel Hardware c. American Galvanizers Association (AGA) 1. The Inspection of Products Hot Dip Galvanized After Fabrication 2. Powder Coating over Hot Dip Galvanized Steel, Powder Coating Journal, Feb 2004,
publication Inspection of Products Hot-Dip Galvanized After Fabrication which may be obtained from your galvanizer or the AGA. Iron and steel articles hot-dip galvanized after fabrication may range in size from small pieces of hardware, such as bolts and washers, to large, welded steel assemblies, weighing several tons.
Hot-Dip Galvanizing for Corrosion Protection: A Guide to Specifying and Inspecting Hot-Dip Galvanized ReinforcingSteel Table of Contents: 2004 American Galvanizers Association. The material in this publication has been developed to provide accurate and authoritative information about painting over hot-dip galvanized steel after fabrication.
S Steel, pre-galvanized according to DIN EN 10346 F Steel, hot dip galvanized after fabrication (HDGAF) according to DIN EN ISO 1461 (Replacement according to DIN EN ISO 50 976) SB Steel, black-oxide finish FG Steel, geomet galvanized C COLOR Steel, pre-galvanized and powdercoated DV Steel, w
Unistrut fittings are pressed from hot rolled, pickled and oiled mild steel plate, or strip steel mainly from grade S315MC OR grade S275 mild steel. Stainless steel fittings are available to EN10088-2 grade1.4404 (Grade 316L). FINISHES Hot -Dip Galvanized Channels are Hot-Dip Galvanized in ac
ASME Materials Division 2019 Fall News 5 2019 Awards Nadai Medalist: The Nadai Medal is awarded in recognition of significant contributions and outstanding achievements which broaden the field of materials engineering. The 2019 Nadai Medalist is Ellen M. Arruda, Tim Manganello/ Borg Warner Department Chair of Mechanical Engineering, and the Maria Comninou Collegiate Professor of Mechanical .
