Award of Excellence: Water Structures Category
Concrete Restoration of Three Underground Water Storage Tanks
Submitted by Gale Associates, Inc.
Division of Capital Asset Management
Gale Associates, Inc.
Architectural Building & Restoration
Scituate, Rhode Island
The water storage tanks, constructed in the mid-1980s, are located three stories below-grade beneath a ten-story building in Boston, MA. Each tank measures 58 ft (17.7 m) long x 22 ft (6.7 m) wide x 24 ft (7.3 m) high and have an approximate capacity of 225,000 gal (851,718 L) each when filled. The tanks consist of concrete walls, base slab, and mid-height level concrete beam grids.
Historically, the tanks had been used to store clean water for use by the building’s mechanical air conditioning equipment. Each tank was leaking thousands of gallons every day, causing concern about the possible undermining of the structure.
Examination of the tanks revealed delamination of a crystalline parge coat applied during an earlier repair attempt. The coating was flaking off the surface of the concrete. Reflective cracking through the waterproof coating was widespread. Exposed wire mesh reinforcement was observed at column and beam locations. There was widespread cracking of the surface, with multiple spalls and delaminated concrete at structural steel wide-flange columns. A cementitious paste appeared to have leached from the bottom of several wall cracks.
Due to the amount of surface loss to the concrete, it was decided to apply resurfacing mortar to the entire surface of the tank interior, overlaid with a fiberglass reinforced epoxy coating.
Access limitations, including “confined access” requirements, presented logistical and manpower issues which were addressed jointly between the engineer, owner, and contractor. A variety of different products required a contractor experienced with several different waterproofing techniques. The success of the project has been highlighted by no loss of water and was only achievable by having a team approach between the engineer, owner, and the contractor.