Built in 1908, the 262-meter long, 79-meter high (859.6 ft. x 259.2 ft.) Makatote Viaduct is the third-highest rail bridge in New Zealand and a prime historic site. But exposure to the elements — including ~200 rain days per year in a pristine mountain environment — took a toll over its first century of existence. Concerns over the deteriorating paint system, ongoing corrosion of the carbon steel, pooling water, suspect rivets, and a need to boost capacity prompted owner KiwiRail to seek out solutions to keep the viaduct operational heading into its second century.
Given the size, access issues, and the client’s desire to keep the viaduct in service to trains during work, the 15,400-m2 (165,764.2 sq. ft.) project wasn’t one for the faint of heart. Fortunately for KiwiRail, regional infrastructure maintenance contractor TBS Group — led by technical director and Makatote Viaduct project director Graham Matthews — had an ambitious plan in mind.
“We wanted to deliver a coatings life of at least 50 years,” Matthews said. “That was our goal going in.”
The viaduct’s initial coating system was based on red-lead primer (RLP), used extensively during the 20th century due to strong performance characteristics and tolerance to poor surface preparation. However, lead-based alkyd paints are also harmful to the environment — and thus no longer used in many parts of the world. An attempt to overcoat the existing lead-based coatings was made in 1997, but the project was cancelled when only partially complete amid environmental concerns and issues with quality assurance, Matthews said.
In 2010, a reassessment found that the adherence of the RLP to the steel substrate was compromised, which meant it needed to be removed entirely and a new system installed. Moreover, removing the RLP required full enclosure to avoid releasing lead into the atmosphere.
By early 2012, KiwiRail contracted TBS to develop plans for the refurbishment, including routes to strengthen the steel and replace parts of the steel trusses and towers — and of course, to apply a new coating system.
“We went to several major coatings suppliers and asked for proposals on what they thought we should do,” Matthews said. “Our supervisors did all the trials and brushing tests, and we selected Carboline products as most suitable for the work we wanted to do. We ended up choosing an epoxy primer system with a urethane topcoat. We knew we shouldn’t use a zinc primer because of the problems with water pooling.”
“We tried to get the same color as the original structure,” Matthews added. “Actually a bit brighter.”
After the client signed off on the specifications, including a system dry film thickness (DFT) of ~375 microns (14.8 mils), a lump-sum contract was awarded to TBS in June 2014 for the full refurbishment, to be completed by January 2017.
For the project, TBS utilized a crew of ~30 people, comprised of scaffolders as well as mechanical and painting personnel.
Uneven ground and a stream below meant that crane access would not work. As a result, a system of suspending scaffold frames from Layher — the largest at 275 tons and 76 meters (249.3 ft.) high — was constructed to access the piers. Rope access and fall arrest equipment from Safeworx and NZ Safety were used as safety precautions. Each scaffold included a weather-tight enclosure, which helped on two fronts. First, it prevented any of the old lead primer from escaping into the environment. Second, indirect-fired gas heaters were used to warm each area during the cold New Zealand winter, ensuring proper curing conditions, even if the weather outside was freezing.
But before any application could begin, the old coating had to be removed. The crew wore detailed blasting safety gear, including Tyvek overalls using integrated boots with armpit-high leggings and Nova 2 blast helmets supplied by Blast-One, fitted with full-length blouses. They blasted each segment of the viaduct to a surface cleanliness of International Organization for Standardization (ISO) 8501-1 Sa 2½: Preparation of steel substrates before application of paints and related products — Visual assessment of surface cleanliness. Most of the blasting work was done using a No. 6 nozzle, with angle nozzles used on occasion. An abrasive blast plant building was constructed on a nearby concrete pad to allow for abrasive loading by telehandler, and a stationary vacuum recovery unit was positioned within the building to secure the recovered abrasive and load it into a recycler.
But after wrapping up each blasting phase and moving onto coating work, the crew noticed a reappearing problem.
“When we started blasting and painting, what happened was that the primer took a long time to cure when going on at that thickness,” Matthews said. “When we worked on the spans, the undersize of sleepers were exposed. The dust and abrasives from the blasting had gotten up there, and where trains came across, it came showering down on our coats.”
The TBS crew solved the problem by first putting down a Carboline 504 epoxy holding primer at an average of 50 microns (2.0 mils) after blasting and before applying the six-part coating system.
With the holding primer in place, it was then time for full coating application! Wearing disposable overalls, gloves, and half-face respirators while using spray equipment supplied by Blast-One, the crew applied a stripe coat of Carboline’s Carbomastic 615MIO epoxy followed by a build coat to achieve approximately 150 microns (5.9 mils) DFT for the prime coat. The crew put down a stripe coat and full coat of the Carboguard 690 epoxy at approximately 125 microns (4.9 mils) and then Carbothane 133LH urethane at approximately 75 microns (3.0 mils), the intermediate and topcoats respectively.
While as much as 70 percent of the paint was spray applied using airless equipment from Titan, 20 percent of the job required brush application, which comprised at least half of the total man-hours, Matthews recalled. Both the intermediate and top coats required a full stripe coat of every rivet, crevice, and edge to guarantee the film build.
In all, ~15,300 L (4,041.8 gal.) of paint were used on the project, with close to 430 microns (16.9 mils) of DFT. Also, a third-party inspector, Linetech, signed off on all the work.
By October 2016, the crew had finally completed their multi-year assignment. Despite working more than 130,000 hours and dealing with intense oversight from the client, third-party inspectors, and environmental organizations, the job was completed on schedule and without a single lost-time injury.
Most importantly, the $13-million refurbishment project was indeed successful — hopefully enabling the Category One heritage structure in New Zealand to prolong its service life by at least another 50 years.
“We’re a small company, and even for a touchup, you don’t want to go back there for 20 years,” Matthews said. “But our supervisor had worked with this [client] many times, and he knew exactly what we needed to do. So far, every indication is that they’re very happy with it.”
And with that, both the contractor and rail owner were cleared for departure!