Journal of Commerce – BC and Alberta’s construction magazine – November, 2002 Planned versatility is the key behind the efficient construction of Vancouver’s tallest concrete building.
Large, complex and enclosed on all sides by construction and future construction during its two- year building process, the 149-metre tall Shaw Tower project has been organized to cope with possible complications.
Concrete mix designs and readymix supplier support are playing a critical role in that flexibility.
Ocean Concrete was awarded the contract to supply the 38,000 to 39,000 cubic metres of concrete.
“Price was a consideration, of course, but we also liked their innovativeness and their proven ability to work with our team,” said Kirk Chen, Ledcor’s project director. “In addition, we were attracted to their environmental ideas, such as recapturing waste concrete.”
Altogether Ocean Concrete has prepared 28 different readymix designs to meet all sorts of forming criteria and contingencies that Ledcor Construction and forming and placing subcontractor Micron Construction Ltd. might face.
Designed, approved and priced, many of these mixes are alternates to the regular readymix designs for the project, but they can be produced on short notice if need arises, said John Rutherford, Ocean’s product development manager. “Basically, we give them options.”
Keeping their options open was also important to Ledcor and Micron as they planned the forming, placing and stripping operations. Located on harbourside fill beside the 30-ft. high downtown escarpment, the Shaw Tower will be enclosed and served by viaduct level streets.
One of these, the Cordova St. Viaduct Extension, is already nearly completed adjacent to the Shaw Tower site on the south side. When work on the new convention centre proceeds just north of the site, viaduct construction along the north and west sides could start.
“Access to this site is subject to modifications,” said Chen. “We’ve got two sides for access now, but that could change.”
Besides offering a wide variety of mixes to help Ledcor and Micron meet specifications and stay on schedule, Ocean Concrete has suggested a number of cost-saving changes. One of these, Ocean WaterGuard Concrete, has eliminated the need for an exterior waterproof membrane around the underground portion of the five-level parkade.
Because the building sits so close to the harbour, a membrane would have been needed to keep water out of the underground parking. In fact, at high tide, the ground water rises 3 ft. above the lowest parkade level. Extreme tides, storms and other conditions could push it even higher.
But with existing structures abutting the tower basement, installing such a membrane would have been difficult and costly. Instead, Ocean Concrete will supply Ocean WaterGuard Concrete, a mix containing a proprietary admixture from Kryton International Inc.
Reacting with water and the cementitious content of the concrete as it cures, the KIM admixture forms crystals that close up the tiny spaces between the mix particles. The crystals block water penetration.
“Concrete is like a rigid sponge,” said Kim Hammer, senior technical representative with Kryton in Vancouver. “KIM fills those pores and capillaries.”
Should any new hairline cracks develop in the future, residual KIM in the concrete wall will react with the incoming moisture to heal those gaps, she said.
Tests have shown that concrete with KIM can hold back hydrostatic pressure with up to 150 ft. of head, said Hammer. In use around the world for 20 years, it’s been primarily used for concrete tanks. The Shaw Tower application is one of its first uses on a major commercial project in Vancouver.
Other cost-saving readymix designs from Ocean Concrete include admixtures to lower the permeability of the concrete in the parking slabs. Because less moisture, chlorides (salt) or other deleterious materials can get in, the need for air entraining is reduced, cutting the cost of the mix.
“Working as a team has greatly assisted this portion of the project,” said Chen. “This is the kind of value-added service that we offer to our clients and what we require from our suppliers, and in this case, it creates a competitive edge for them.”
Ocean Concrete’s diligence and creativity also extends to care of the environment. No more waste pits on construction sites to catch and hold highly alkaline wash water.
Now each truck carries a collector bucket and separation screen. Clean aggregate can be left at the job site while the cement paste is removed. For spill emergencies Ocean Concrete maintains a special environmental truck ready for dispatch.
To avoid wasting excess readymix delivered to the Shaw Tower site, Ocean Concrete has provided Ledcor Construction with a lock block form. Instead of removing and dumping the extra concrete, it is cast into a useful product for earth retaining walls.
Ledcor Construction expects to complete the $150 million Shaw Tower in 2004. Designed by James K. M. Cheng Architects Inc., the 532,000 sq. ft. highrise is a development by partners Ledcor Properties Inc., Westbank Projects Corp. and Shaw Communications Inc.