corrosion protection

Corrosion Protection of a Halifax Harbour Bridge: Challenges, Issues and Opportunities

The Angus L. Macdonald Bridge is a 1.3-kilometer-long (4,265-foot-long) cable suspension bridge that carries automotive traffic over the Halifax Harbour between Dartmouth and Halifax. There are four approach spans to the west cable bent on the Halifax end and 12 approach spans to the east cable bent on the Dartmouth end. The bridge was opened April 2, 1955. 

As seen in the September 2019 Edition of the Journal of Protective Coatings and Linings (JPCL) & on

The Macdonald Bridge was originally painted with a lead-based oil alkyd, three-coat paint system. In 1993, because of environmental concerns and availability, Halifax Harbour Bridges (HHB), the organization responsible for operating and maintaining bridges in the Halifax Harbour, transitioned to a zinc-hydroxy-phosphite (Fig. 1). Spot repairs are conducted by a seasonal crew of 30 painters who join HHB for the painting season.

Fig. 1: Localized touch-up on the Macdonald Bridge. Photos courtesy of Halifax Harbour Bridges unless otherwise noted.

Generally, HHB’s painting team performs touch-up painting only, except for the main towers where a single finish coat is applied for color uniformity and aesthetic floodlighting. Although spot repairs to the existing coating system have successfully prevented the spread of corrosion for the most part, corrosion in difficult-to-clean-and-recoat areas is expanding due to the limitations of a maintenance strategy that is based on power-tool cleaning rather than on blast-cleaning. Furthermore, the number of coating layers present and high total thickness on many of the existing steel surfaces places further spot repair and overcoating at risk of catastrophic delamination failure, because the existing alkyd system becomes more brittle with age and seasonal temperature cycling (Fig. 2). As a result, two independent consultants have recommended that the existing coating system on the approach spans, cable bents, towers and main cable of the Macdonald Bridge be completely removed and replaced. Full removal and replacement of the existing coating system will initiate a design life with a new maintenance cycle that will include spot repairs, overcoating and zone repairs, and eventually removal and replacement. HHB wants a durable corrosion-protection system that will provide 25–30 years of service life.

Fig. 2: Pre-blast condition.

HHB recognized that the implementation of the new corrosion-protection program for the Macdonald Bridge approach spans and towers is a significant capital investment estimated at $40 million in 2015. Due to many unknowns, HHB decided to implement the program in multiple phases over six years:

  • Research and development in 2016;
  • Detailed inspection in 2017;
  • Trial/pilot project in 2018;
  • Halifax approach and cable bents in 2019;
  • Dartmouth approach spans in 2020; and
  • Towers in 2021.

The main objectives of the pilot project were as follows:

  • To select and use the most cost-effective coating system that would best protect the bridge and minimize maintenance works;
  • To obtain practical knowledge on challenges, issues and opportunities prior to implementation of major contracts;
  • To refine the estimate of steel repairs—estimated versus actual;
  • To ensure that there is minimal impact on the natural environment;
  • To ensure that there are no safety incidents throughout the project;
  • To minimize negative impact on the neighbors; and
  • To ensure public safety.


In order to gain practical knowledge and information about the application of different protective coating systems on similar bridges, HHB engineers conducted site visits to five bridges on the east coast that have environmental exposures similar to HHB’s bridges and have recently completed or are presently undertaking major paint rehabilitation or replacement projects. From these bridge-site visits, HHB compiled key observations to be considered in planning a complete repainting program.

  1. Some bridges use rock salt for effective snow and ice control, while others use sand (rather than salt). The sand reduces corrosion issues by eliminating the detrimental effect of the chlorides.
  2. A notable amount of rivets and bolts might need to be replaced during the paint job.
  3. During the paint contracts, 10–15% of the painted areas were found to require steel repairs that makes the construction sequence difficult and significantly increases the project’s cost.
  4. Access platforms and enclosures can catch fire and cause structural damage.
  5. Swing stage for underdeck painting was found to be inefficient and caused extra cost for QA inspections. The tendered specs should include a provision stating that the contractor is to provide a safe access system and an efficient work-platform system that is quick to install.
  6. Careful consideration should be afforded to limit the enclosure/containment lengths for aerodynamic stability of the structure.
  7. An on-site abrasive/waste-collection unit and robust system is required for lead abatement with air-monitoring equipment near the jobsite.
  8. Surface preparation: a. Adequate surface preparation is key for the durability of any coating system. b. Various surface preparation requirements for specific areas such as cable bands, steel plates, sharp edges, slip-critical faying surfaces and galvanized steel should be included in the tendered specs to avoid confusion.
  9. Trial blasts for selected areas can be conducted to verify inspection findings and estimate the steel-repair area to minimize contingency.
  10. Other bridge sites were applying an epoxy zinc primer (full coat and stripe), an epoxy intermediate (full coat and stripe) and a urethane finish. Caulking was used in select areas, prior to application of the finish.
  11. Some coatings fade quickly and should be researched before specifying.
  12. A full-time QA inspector/consultant is critical to ensure a long service life of the new coating system.
  13. A QA team (consisting of the owner’s engineer, a full-time resident engineer and coating inspectors) costing 10–15% of the total contract value is considered to be a best-value approach in a coating project.
  14. The QA consultant should conduct daily inspections and submit daily and monthly reports.
  15. Conducting annual paint inspections and producing an inspection manual to standardize inspection results are beneficial practices.
  16. The contract should include provisions stating that the contractor is to provide uninterrupted inspection access for the owner’s representatives or other contractors.
  17. Prior to the acceptance of a repainting program, detailed inspections are beneficial to identify common steel defect types, estimate quantities and prepare typical repair detail to include in tendered specs.
  18. The contractor should provide a detailed cost breakdown in a sealed envelope with the bid for dispute resolution if required.
  19. Non-Conformance Reports (NCRs) are required to identify deficiencies that need to be addressed (for example, excessive paint thickness, inadequate surface preparation prior to the first coat being applied, inadequate or excessive curing between coats, paint overspray and drips contaminating the surrounding property).
  20. Detailed coating specifications and typical steel-repair details should be included in the tendered package. This approach can minimize interruptions to coating work, uncertainties and extras.
  21. Worker and public safety are paramount. Contract specs should include detailed safety requirements and strict clauses. Drug and alcohol policies and routine testing of painters is recommended.
  22. Large bridges should consider implementing multi-phase, multi-year coating contracts.


Design and Specification

The tendered scope focused on 65,000 square feet of paint replacement as a pilot project on the Halifax truss spans and at a selected location on the girder spans. The project involved the shop painting of new steel and galvanized members, and the removal and replacement of the existing coating on the steel. The overall approach for cleaning and painting follows.  

For the shop-coated steel, the specification required abrasive blast-cleaning to SSPC-SP 10/NACE No. 2, “Near-White Metal Blast Cleaning,” and the application of a organic zinc-rich epoxy/epoxy/polyurethane (Z/EP/PU) system. The approved coating materials were from NEPCOAT, List B. All coats were applied in the shop with damages and connections touched-up in the field.

Existing galvanized steel that had been painted was prepared according to SSPC-SP 16, “Brush-Off Blast Cleaning of Coated and Uncoated Galvanized Steel, Stainless Steels, and Non-Ferrous Metals.” The same epoxy intermediate coat and polyurethane finish coat were applied to the galvanized surfaces. If patches of corrosion were present, a spot coat of organic zinc-rich epoxy primer was applied.

The existing steel was pressure-washed and blast-cleaned to SSPC-SP 10/NACE No. 2 (Fig. 3). Soluble salts and pack rust were removed and the same Z/EP/PU system was applied, but with stripe coats of both the organic zinc-rich epoxy primer and the epoxy intermediate coat (Fig. 4). Caulking was installed in areas where pack rust was found.

Fig. 3: The existing steel was pressure-washed and blast-cleaned to SSPC-SP 10/NACE No. 2.
Fig. 4: Zinc primer and stripe coats applied.

For control of the existing lead paint during removal, the specification required a Class 1A containment and ventilation system according to SSPC-Guide 6, “Guide for Containing Surface Preparation Debris Generated During Paint Removal Operations.” Work had to be conducted in compliance with Nova Scotia’s “Occupational Health and Safety Act,” “Lead in the Workplace: A Guide to Working with Lead,” “Environment Act” and “Transportation of Dangerous Goods Act and Regulations;” as well as the Canadian General Standards Board (CGSB) Provisional Standard No. 164-GP-IMP, “Guidelines For Disposal of Contaminated Solids in Landfills,” and OSHA 29 CFR 1926.62 lead and other worker-protection regulations in 29 CFR 1926. Monitoring of the work was required according to applicable sections of SSPC- TU 7, “Conducting Ambient Air, Soil and Water Sampling.”


It is difficult for an owner to prepare a tender document without being familiar with the role of a general contractor and their subcontractors for the contract. A corrosion-protection project contract may have coating contractor as the GC and a steel contractor as a sub or vice versa, which depends on local market conditions, as well as the percentage of steel repair and coating work for the project. To assemble the best team for the project, HHB prepared tender documents that sought a coating contractor and a steel contractor as part of the same team, thereby eliminating concerns about each causing each other delays—with one acting as the GC and the other as a sub, they would be contractually tied and incentivized to work together.

Challenges and Opportunities

The pilot project identified the following challenges and opportunities for improvement when undertaking the painting of the remainder of the bridge.

Unpredictable Weather: Paint must be applied within the manufacturer’s parameters for air and surface temperature, as well as relative humidity. According to the manufacturer’s instructions for the selected product, the surface temperature must be at least 3 degrees C (or 5 degrees F) above the dew point temperature and the condition must be maintained until the coatings have adequately cured prior to exposure to weather. Although containment can prevent surface contamination, the continuous high humidity and low temperature can affect the speed of curing and application of the next layer of coating, slowing down the project.  

Load Restriction on the Bridge: Due to structural constraints, maximum factored design load (dead plus live) of temporary structures is 8 kN/m per truss, which increased the difficulty of erecting scaffolding and limited the available manpower on the bridge. 

Because the existing coating system contained lead (as much as 8.8% by weight) and chromium (up to 1.4%), containment to control releases was required. Wind load on the structure was also restricted, so containment could not be installed continuously from Pier H1 to the Halifax cable bent. Therefore, the project was conducted in several phases, which slowed down production. 

Restricted Working Hours: Due to spatial restrictions at the end of the truss, it was not possible to install temporary batten plates before the removal of end batten plates. Therefore, based on the consultant’s specification, temporary steel bracings were installed immediately after the removal of the end batten plate under calm traffic. This project had no lane closures or bridge closure, requiring the contractor to work from 9:30 am to 3:00 pm, or 7:00 pm to 5:30 am, limiting the window for replacing end batten plates.

Uncertain Amount of Steel Repair Without Blasting: Since the Macdonald Bridge underwent an annual paint touch-up program, multiple layers of coating made it difficult to determine the condition of the steel and therefore, made it challenging to develop repair/replacement criteria for each structural element during tendering preparation. Although consultants provided repair/replacement criteria for components such as batten plates, measurements could not be taken before the contractor erected the scaffolding and actually blast-cleaned. After blasting to bare steel, additional deterioration and section loss were observed, requiring additional repairs. This increased quantities of steel repair relative to the tender estimates as well as additional time on-site.

Inaccessible Blasting Areas: Some areas, such as deck splice joints and rivet heads inside of troughs, were inaccessible due to the bridge design and configuration, and could not be brought to the required level of surface cleanliness (by reasonably practical methods) that was specified in the tender document.

Difficulties of Measuring Dry-Film Thickness on Corroded Faying Surfaces: The corrosion on some faying surfaces made it difficult to obtain accurate readings. For these pitted areas, a QA inspector would need to work closely with the contractor to adopt an acceptable solution.

Dry-Film Thickness Repair Procedure: During surface preparation of faying surfaces, it was necessary to blast the coated surface to ensure the final primer thickness was within in the manufacturer’s tolerance. However, it took a long time to receive the paint manufacturer’s response for the repair procedure. Therefore, in future tender documents, the contractor should be asked to submit a repair procedure and obtain approval from the paint manufacturer before commencing the work.

Galvanized Deck Splatter Removal: Deck panels were galvanized during fabrication and the galvanized splatter was not removed at that time. Sweep-blasting prior to priming did not remove the larger galvanized splatter, and its deterioration can be harmful to new coating systems. Removal of galvanized splatter should be considered for future projects.

Steel-Repair Procedure: A good deal of welding, cutting and removal are involved in steel repair and therefore, a detailed repair-work procedure should be requested in future tender documents.

Paint Manufacturer’s Representative: Because surface preparation and the application of primer and intermediate coats are critical steps, the paint manufacturer’s representative should be present at the early stages of coating work to approve of the surface condition and the methods being used by the contractor. 

Quality Assurance: HHB selected a QA consultant to provide full-time, on-site inspection and testing services that included monitoring, recording and reporting on blast removal of the existing paint system, steel repairs, cleaning, surface preparation, environmental control and application of the new paint system, which consists of the complete section of the Halifax truss spans and a selected area on the adjacent girder spans.


Lessons Learned 

HHB gathered a significant amount of valuable information from the pilot project, including the following.


Curing Time of Coating: Compatibility between caulking and the coating system is necessary. The contractor must confirm with the paint manufacturer that the caulking is compatible with the coating, and must also pay attention to the curing time of the primer and caulking materials, making sure to select fast-curing products. 

Fire-Retardant Materials for Scaffolding: Fire-retardant materials must be used. Some typical fire-retardant materials used in containment construction are ASTM E-84 Class A/Class 1 flame-retardant plywood and 20-mil tarps that meet the NFPA 701, “Standard Methods of Fire Tests for Flame Propagation of Textiles and Films.”

Salt Contamination: Although salt is effective for melting snow, in order to avoid chloride contamination, sand was used during this project with chloride tests conducted daily in certain spots.  


Clarification of Scope Change and Quantity Change: Because an accurate quantity estimate of steelwork is not possible, the tender document should specify the difference between scope change and quantity change, and address how to deal with any delay induced by an increased quantity of work.  

Painter Certificate: There should be a specific clause in the tender to clarify the qualifications of the painters and QC personnel in order to ensure the competency of workers.

Use of Language: Careful use of formal contractual language is important to ensure that the owner’s expectations are met by the contractor.

Annotated Photos: One must use caution when including photos in tender documents to explain locations because photos may lead a contractor to think that they represent the full scope of work. A clause should clearly state that the pictures are for illustrative purposes only and do not represent the locations of the entire scope of work.


Critical Path and Benchmarks: Although the contractor submitted progress reports to HHB prior to biweekly meetings, comparing the work actually completed to work scheduled, HHB was not given a notice of the severity of the work delay at early stages. Therefore, it is critical to have up-to-date project schedules with key benchmarks and a critical path analysis to demonstrate the impact of changes on the schedule prior to the change being approved and the work beginning.

Construction Sequence

Pre-Blast Site Visit: Because the quantity of steelwork in the tender document is a rough estimate, it is hard for a contractor to decide how many steel-repair items to order beforehand. In this case, construction work may be delayed by the delivery of materials. Therefore, it is necessary to have a pre-blast site visit after scaffolding is set up to give the contractor a sense of how many steel-repair items may be required so that the fabrication process can begin. Therefore, when the blasting is finished, the contractor can start doing the steelwork while conducting more detailed observations and ordering materials as needed.  

Conflict Between Cure Time and Steelwork: Based on the coating manufacturer’s Class B certification, it took more than three days for the chosen primer to cure before making connections, so the installation of new batten plates was put on hold. Because only one batten plate can be replaced at a time in one truss member, the process of batten-plate replacement became very time-consuming. The contractor should be aware of the time required for each plate and organize the steelwork accordingly. Design of future repairs should also recognize the difficulties in quickly making assemblies when a Class B connection is required, and limit their use where possible. 

Caulking and Coating Procedure: Caulking was originally intended to be applied before the final coat on designated crevice areas; however, due to the long curing time required and an effort to maximize productivity, caulking was permitted to be applied after the final coat, followed by a stripe coat of finish after the caulking cured, in some selected areas. Both methods are acceptable practices, but the advantage of the way it was ultimately done, is that if the caulking cracks, there is an extra coat under it to protect the steel.


There are many unique challenges related to bridge corrosion-protection projects and therefore, adequate research, investigation and planning is important to implement a successful coating program. HHB found it very useful to visit other bridges and similar projects to learn and adopt best practices. Implementing a pilot project provided a significant amount of valuable information on project specs and scope, construction means and methods, erection sequence, productivity, QC and QA, schedule and contract performance, and a reduction of financial risk.

This article will be presented at SSPC Coatings+ 2020.


Kenneth A. Trimber is the president of KTA-Tator, Inc. He has over 45 years of experience in the industrial painting field. Trimber is a NACE-certified Coating Inspector, an SSPC Protective Coatings Specialist, an SSPC C-3 Supervisor/Competent Person for the Deleading of Industrial Structures and is certified at a Level III nuclear coating inspection capability in accordance with ANSI N45.2.6. He is a past president of SSPC, a member of the Standards Review Committee and is chairman of the SSPC Commercial Coatings Committee, SSPC Surface Preparation Committee and the SSPC Containment Task Group. Trimber is also past chairman of ASTM D1 on Paints and Related Coatings, Materials and Applications, and authored The Industrial Lead Paint Removal Handbook.

Ahsan Chowdhury came to Canada as a professional engineer and immigrant in 2007, after 10 years of engineering experience in planning, designing and maintaining of high-profile infrastructures in Bangladesh. He received a Master of Engineering degree from Concordia University in Montreal and began his bridge engineering career with HHB in 2010.

Chowdhury is a member of the TRB Standing Committee on Testing and Evaluation of Transportation Structures AFF40 and many other technical committees throughout Canada and the U.S.