Coating the "Big Dig

Citation

(2002), "Coating the "Big Dig", Anti-Corrosion Methods and Materials, Vol. 49 No. 1. https://doi.org/10.1108/acmm.2002.12849aaf.008

Coating the "Big Dig"

Keywords: Coatings, Polyurea

One of the largest and most complex public works projects undertaken in North America, the Central Artery/Tunnel under construction along the Interstate 90 and Interstate 93 corridors in downtown Boston, Massachusetts, poses unique challenges from a coatings application standpoint.

Slated for completion in 2004, the Massachusetts Turnpike Authority's massive highway project will be an 8 to 10 lane 7.5 mile (12.1 km) expressway - approximately half of which will consist of tunnels - to replace the congested Central Artery, a six- lane elevated highway that opened in 1959. The estimated $14.1 billion project involves 118 separate construction contracts and approximately 5,000 construction workers are presently on the job.

"It is the largest application of its kind in the United States, says Don Moore, technical director of ITW Devcon Engineered Coatings (Danvers, Massachusens). The company provides the Infraseal 200 100 per cent solids polyurea coating system that is being sprayed onto the roofs and walls of underground and underwater tunnel sections for waterproofing. "Because the contractor is applying the coating over all four seasons, the job required some planning to ensure optimal curing at different temperatures. Different primer formulations were developed for varying temperature ranges."

Moore notes that the polyurea coating was chosen because of its application benefits. Polyurea offers a shorter curing time (approximately 2 hours for fight-duty service and 24 - 48 hours for normal or heavy service) and is less sensitive to low-temperature curing. For waterproofing, it can be applied at ambient temperatures of 35F (1.7C) and up. If applied at temperatures below freezing there could be problems due to the formation of ice on the substrate, not material performance.

Surface preparation entails power washing approximately 90 per cent of the overall surface area and grit-blasting some of the horizontal surfaces (the remaining 10 per cent). Moore adds that primers are being applied to all external tunnel surfaces that will be submerged. An additional layer of concrete is being placed atop the polyurea coating on tunnel roofs. Neither the primer nor the polyurea coating contains solvents. MTA reports that the Big Dig's notable attributes include excavating approximately 16 million yd³ of dirt, placing 3.8 million yd³ of concrete, relocating 29 miles of utility lines maintained by 31 separate companies and installing more than 26,000 linear ft of steel- reinforced concrete slurry walls resting on bedrock up to 120 ft below city streets.