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1、 Highway IDEA Program Evaluation of Al-Zn-In Alloy for Galvanic Cathodic Protection of Bridge Decks Final Report for Highway IDEA Project 100 Prepared by: Walter T. Young, P.E.,Clem Firlotte, P.E.,Miki Funahashi, P.E., Corrpro Companies, Inc August 2009 INNOVATIONS DESERVING EXPLORATORY ANALYSIS (ID
2、EA) PROGRAMS MANAGED BY THE TRANSPORTATION RESEARCH BOARD (TRB) This NCHRP-IDEA investigation was completed as part of the National Cooperative Highway Research Program (NCHRP). The NCHRP-IDEA program is one of the four IDEA programs managed by the Transportation Research Board (TRB) to foster innov
3、ations in highway and intermodal surface transportation systems. The other three IDEA program areas are Transit- IDEA, which focuses on products and results for transit practice, in support of the Transit Cooperative Research Program (TCRP), Safety-IDEA, which focuses on motor carrier safety practic
4、e, in support of the Federal Motor Carrier Safety Administration and Federal Railroad Administration, and High Speed Rail-IDEA (HSR), which focuses on products and results for high speed rail practice, in support of the Federal Railroad Administration. The four IDEA program areas are integrated to p
5、romote the development and testing of nontraditional and innovative concepts, methods, and technologies for surface transportation systems. For information on the IDEA Program contact IDEA Program, Transportation Research Board, 500 5th Street, N.W., Washington, D.C. 20001 (phone: 202/334-1461, fax:
6、 202/334-3471, http:/www.nationalacademies.org/trb/idea) The project that is the subject of this contractor-authored report was a part of the Innovations Deserving Exploratory Analysis (IDEA) Programs, which are managed by the Transportation Research Board (TRB) with the approval of the Governing Bo
7、ard of the National Research Council. The members of the oversight committee that monitored the project and reviewed the report were chosen for their special competencies and with regard for appropriate balance. The views expressed in this report are those of the contractor who conducted the investi
8、gation documented in this report and do not necessarily reflect those of the Transportation Research Board, the National Research Council, or the sponsors of the IDEA Programs. This document has not been edited by TRB. The Transportation Research Board of the National Academies, the National Researc
9、h Council, and the organizations that sponsor the IDEA Programs do not endorse products or manufacturers. Trade or manufacturers names appear herein solely because they are considered essential to the object of the investigation. Evaluation of Al-Zn-In Alloy for Galvanic Cathodic Protection of Bridg
10、e Decks IDEA Program Final Report For the Period October 2003 to August 2009 Contract NCHRP-100A Prepared for the IDEA Program Transportation Research Board National Research Council Walter T. Young, P.E. Clem Firlotte, P.E. Miki Funahashi, P.E. Corrpro Companies, Inc. 1380 Enterprise Drive, Suite 1
11、00 West Chester, PA19380 August 18, 2009 ACKNOWLEDGEMENTS The Corrpro project team would like to thank the Missouri Department of Transportation for their assistance with this project. Missouri DOT provided a bridge for the trial installation of the bridge deck anode and assisted with the collection
12、 of survey data. TABLE OF CONTENTS EXECUTIVE SUMMARY .1 INTRODUCTION.1 ANODE DEVELOPMENT.2 Anode Mesh, Al-20Zn-0.2In Alloy .2 Extruded Strip Anode 3 Anode Mesh Using Thermal Spray6 BRIDGE INSTALLATION.8 CONCLUSIONS12 1 EXECUTIVE SUMMARY An alloy was developed under FHWA Project FHWA-RD-96-171 for us
13、e as a galvanic anode for the protection of steel reinforced concrete bridge substructures. The alloy consists of 20 percent zinc, 0.2 percent indium with the balance aluminum (U.S. Patent 6,673,309). Indium is the component that keeps the anode active even in dry environments. The anode was designe
14、d to be applied to concrete using thermal spray technology, typically electric arc spray. The recommended thickness of the coating is 12 mils. Based on predicted consumption rates, the alloy is expected to provide 10 to 15 years service life based on a consumption rate of 0.5 mil per year. Since the
15、 first trial system was installed in 1995, this alloy has been installed on more than 15 structures with a total surface area of about 300,000 ft2. The objective of project NCHRP-100A was to develop a galvanic mesh anode for bridge deck application. The concept was to develop an expanded mesh or per
16、forated sheet that would last at least 25 years, be durable for construction, not interfere with concrete overlay bonding and be of a size that is practical for transportation and field installation. This work was planned in two stages. Stage 1 was to develop the anode mesh. Stage 2 was to install t
17、he anode on two bridge decks of 1,000 to 2,000 square feet surface area to evaluate the anode performance and to produce concrete test blocks for anode evaluation in the laboratory and calculate anode consumption rate. The evaluation period for the bridges and test blocks was to be twelve months. In
18、 the early stages of the project, it was learned that the aluminum alloy developed under the FHWA program was too brittle to be formed into the desired mesh. Various alternative configurations and alloy variations were tried. The final form consisted of thermally sprayed anode material on an aluminu
19、m mesh or a sheet that was subsequently expanded to form a mesh. Laboratory trials showed that the alloy was an effective anode in providing cathodic protection to concrete embedded rebar. A limited bridge trial was conducted that further proved the constructability and effectiveness of the anode. H
20、owever, problems were encountered that caused the project to be halted pending further research that is beyond the intent of the program. These problems included limited availability of a suitable substrate alloy, gas generation and delamination of the overlay at the anode. INTRODUCTION Since early
21、1970s corrosion has been recognized as one of the major causes to the deterioration of reinforced concrete bridge structures in the United States. The maintenance costs for bridge structures exposed to salt environments have become large expenditures for many bridge owners. Over the last 30 years, c
22、athodic protection (CP) has been proven to be a highly cost-effective technique in controlling concrete deterioration from chloride induced corrosion for existing concrete bridge structures. This message was delivered by the U.S. Federal Highway Administration (FHWA) to local government agencies in
23、mid 1980s that CP is the only method known to stop corrosion regardless of the level of chloride contamination within the concrete structure and it would provide a major economic benefit to the U.S. (Department of Transportation Memorandum, Federal Highway Administration, “Bridge Deck Deterioration:
24、 A 1981 Perspective” FHWA Office of Research, Washington, DC, Dec. 1981). The FHWA further encouraged states to protect existing bridges before they reach the stage where replacement is necessary. The FHWA strongly suggested that CP systems should be used more frequently as a cost-effective means to
25、 extend the useful life of chloride contaminated bridges (Memorandum, Federal Highway Administration, “FHWA Position on Cathodic Protection Systems Revisited” Office of the Administration, Washington DC, May 24, 1994). Since the first impressed current CP system was installed on a bridge deck in Cal
26、ifornia in 1973, the technology has advanced significantly. The majority of CP systems for reinforced concrete structures are of the impressed current type. With impressed current CP systems, an external direct current (DC) power supply, or rectifier, is used to force CP current from the anode throu
27、gh the concrete to the reinforcing steel, resulting in no corrosion activity on the steel surface. 2 The most widely used impressed current CP anode is expanded titanium mesh, which is 4 feet wide by 0.078-inch thick, and the diamond mesh size is approximately 1 in. x 2 in (2.54 cm x 5 cm). The tita
28、nium mesh is unrolled on a deck concrete surface and is fastened to the concrete substrate using plastic fasteners. A concrete overlay is used for good contact and as a riding surface. The disadvantage of the impressed current CP systems is the rectifier, which requires a certain amount of monitorin
29、g and maintenance over the life of the system. If the owner cannot maintain the rectifiers, the corrosion of the reinforcing steel eventually redevelops and damages the concrete. Due to the maintenance difficulties of the rectifiers by many bridge owners, uses of impressed current CP systems have no
30、t been significant in some states and local agencies. Based on such a situation, the FHWA initiated major R however, this alloy might not be a good base metal for long term tests or usage on a bridge. In practice, a purer (99.5% aluminum) sheet (alloy 1350, UNS A91350) was planned for the full scale
31、 bridge trials. However, this alloy is relatively difficult to obtain and ultimately resulted in unreasonable delays in meeting the goals of this project. BRIDGE INSTALLATION We installed a galvanic anode mesh on the shoulder of a bridge deck in Missouri on Interstate 44 over the Little Bourbese Riv
32、er at mile marker 214, between Bourbon and Cuba, MO (Missouri bridge No. A12112EB). The mesh used for the bridge trial was fabricated by thermally spraying aluminum 80 percent zinc 0.2 percent indium anode alloy onto expanded aluminum sheets. Alloy 3003 mesh sheets, 0.060 in (0.152 cm) thick by 4 ft
33、 (1.22 m) by 8 ft (2.44 m) having 1 in (2.54 cm) x 2.75 in (6.99 cm) diamond pattern openings were used. Table 3 presents a description of the anode system and initial operating information. Figures 6 through 8 show the anode at various stages of the installation in the shoulder of the bridge. Figur
34、e 9 shows the junction box for testing the system. Prior to the mesh installation, silver-silver chloride reference electrodes were placed at anodic sites at the edge of the repair patches. TABLE 3. Anode system description ECORR native, mV SSC* Al-Zn-In thickness, inch per side 0.010 Anode area ins
35、talled, sq ft 553 Reference electrode 1 . Located at top bar at old patch . 302 Reference electrode 2 . Located at bottom bar, old patch 157 Reference electrode 3 . Located at top bar, new patch. 199 Reference electrode 4 . Located at bottom bar, new patch. 135 Initial anode potential, volts . 1.2 R
36、esistance, anode to steel, ohms. 0.3 Initial anode current, mA 1,248 after 15 minutes or 2.25 mA/SFc 1 week anode current, mA 756 or 1.27 mA/SFc * All reference electrodes are silver-silver chloride The mesh was installed on July 22, 2005 and the anode was connected on September 20, 2005. The panels
37、 were light, relatively stiff, and easy to lay out, although excessive bending of the strands caused the coating to flake off. The panels were laid along the outside curb with the 8 foot length extending out from the curb. This reduced the number of connections that needed to be made. The anode shee
38、ts were connected using aluminum fasteners. The connection was coated with Scotchcoat and sandwiched between two pieces of Scotch mastic pads. The anode was kept electrically isolated from the bridge structure to allow current, potential and depolarization measurements, but this might not be necessa
39、ry in actual practice. Plastic Christmas tree fasteners were used to secure the mesh to the deck. For redundancy, two anode lead wire connections were made to the anode mesh using aluminum fasteners coated as described above. The anode mesh held up very well to the construction activity. Concrete tr
40、ucks were able to drive over the anode. During the pour the anode to steel open circuit potential was 1.2 volts. The depth of cover was about 2 inches. One area of concern was that the anode was very active from the alkalinity of the wet concrete and produced gas bubbles from self corrosion. The gas
41、 pushed bleed water to the surface and smoothed out the raked finish. The bubbles occurred about 20 minutes after the concrete covered the anode and continued for 2 hours until the concrete was covered by burlap for curing. These bubbles ceased after a while and did not appear to extend down to the
42、anode; however, this would be unacceptable for a finished concrete surface. Missouri DOT used boiled linseed oil to seal the deck. At some time before the last data set in October 2008, Missouri DOT used an asphalt emulsion sealer on the deck. The system was temporarily energized for five minutes 30
43、 minutes after the pour was complete. Table 4 presents the initial operating characteristics. The anode was permanently activated after the concrete cured for about 60 days and the junction box was installed. 9 TABLE 4. Initial anode operating data, 30 minutes after concrete poured. Voltage: 1.2 vol
44、ts to a silver-silver chloride reference electrode Current: 0.6 amps (1.08mA/sfc) on 553 sf. RC 1 Polarized 315 mV more negative than the static of -199 mV (top mat) RC 2 Polarized 250 mV more negative than the static of -194 mV (bottom mat) RC 3 Polarized 285 mV more negative than the static of -25
45、7 mV (top mat) RC 4 Polarized 170 mV more negative than the static of -170 mV (bottom mat) FIGURE 6. Anode mesh prior to being set against curb and overlay application. Note white wire which went to the junction box. FIGURE 7. Installed anode mesh prior to overlay application. Black squares are coat
46、ed connections between anode sheets. The white wire goes to the junction box, 10 FIGURE 8. Overlay placement on anode. FIGURE 9. Anode junction box showing 4 reference electrode terminals, shunt, structure wire and disconnect switch for instant-off potential readings. Current, depolarization data an
47、d observations were taken periodically since the anode installation either by Corrpro or Missouri DOT personnel. The first depolarization test was taken September 27, 2005 and the latest test 11 occurred on October 3, 2008. Figure 10 summarizes this data. Figure 10 plots the number of days in test v
48、s. depolarization after at least 2 hours in millivolts (mV) at each test electrode on the left axis and current density expressed as milliamperes per square feet (mA/SFc) of concrete surface area on the right axis. The temperature at the time of the test, anode-to-structure instant-off potential and
49、 whether the deck was wet or dry at the time of measurement is indicated. 0 50 100 150 200 250 300 1611019324929749070410911092 Days in Test Depolarization, mV 0 0.5 1 1.5 2 2.5 3 Current Density, mA/SFc TE 1, top mat, old patch TE 2, bottom mat, old patch TE 3, top mat, new patch TE 4, bottom mat, new patch Current density 90* 986* -* - 837 - 65 640 dry 95 923 humid 22 85 dry 40 885 dry 80 420 wet 81 955 dry 70 540 dry Enviornmental Conditions * Atmpspheric Temp, F * Anode to structure instant-off, V SSC * Deck conditions 70 - dry No depol data FIGURE 10