Issue link: http://digital.canadawide.com/i/124234
and its roster of projects has included seniors' residences, cultural and community centres, and condo complexes. A few years ago, about 70 to 80 per cent of its projects involved tilt-up, but that has dropped to around 30 per cent, Klaassen says. He attributes this to building code changes to seismic requirements. As a result of an industry habit of trying to keep consulting costs in check, there is a reluctance to pay an engineer more money for some extra research and work that might enable a tilt-up project to meet the more stringent seismic requirements. The result, then, Klaassen says, is that these possibilities have not been explored as much as they might have been, and tilt-up is being shut out as a method for construction of post-disaster buildings. If Canada's building sector is side-lining what Klaassen sees as research opportunities in engineering for tilt-up construction, companies supplying the global sector are not ignoring the potential of UltraHigh Performance Ductile Concrete (UHPdC). Extensive research and development on this cementitious composite material has been undertaken by numerous research groups and engineers worldwide "in hopes to promote UHPdC as an ultimate sustainable construction material for the future," according to a paper published in the International Journal of Civil and Structural Engineering. The paper identified four UHPdC proprietary blends. A fifth, Densit, which was developed in the 1960s, was not identified as current. The others were developed between mid-1990 and 2006, and are, respectively, Ductal, Ceracem, Ducon and Dura. As one might expect, the blends differ from one 16/ april 2013 p12-17Precast.indd 16 another. Ducon uses a mesh system, while Lafarge, which makes Ductal, uses fibres for reinforcement. "Both have their strengths. Others are also working on high-performance concrete," says Don Zakariasen, director of marketing at Lafarge Canada. As research and development continues with UHPdC blends, the drop in price for Glass Fibre Reinforced Polymer (GFRP), in place of steel, is resulting in more widespread use of this product. Although some lab-based research had suggested that GFRP was subject to decay in concrete environments with a strong alkaline component, a 2011 Australian government-sponsored study reviewed the work of three scientific research teams, including a Canadian one and found that "there was no degradation of the GFRP in the samples provided." Zakariasen says that some earlier findings had indicated that GFRP was subject to a loss of structural strength or capacity, but with more widespread use and further development, the product improved, as more applications have been found. "GFRP is a great solution. It's strong and light, and much easier to work with," he says. Malcolm Hachborn, chief engineer at Res Precast Inc., shares Zakariasen's view that UHPdC will soon play a far greater role in a range of construction sectors – from bridge decks to cladding. "With this kind of new material, that means panels are thinner and lighter, so lighter columns and slabs, and less cost to the owner. Also, less shipping costs, so more sustainable, [and] less crane costs," Hachborn says. That, as yet, is still in the future. Today, architects want higher R values in precast panels. It makes sense, says Hachborn, who notes it is a good way to raise the R value of a building's overall envelope system. In recent years, though, sealants for the joints between panels have sometimes been the weak link in a precast cladding system. "Four things deteriorate the sealant: light, temperature, moisture, and movement from expansions and contraction because of the weather cycles," Hachborn says. The solution is a two stage system with an outer and inner sealant. "With a two stage sealant, only the outer one is exposed to all the elements, but the inner one is protected from them. It acts as an air barrier and there is no light, no moisture, an almost constant temperature, so less movement. It's protected from all the four forces that deteriorate it. Movement is still there, but it's less," Hachborn says. Partly due to the increased priority attached to enclosing building floors under construction as soon as possible, in recent years larger panels have been favoured. About 15 years ago, the heaviest panels topped out at around 20,000 pounds. Today, Hachborn says some weigh as much as 45,000 pounds. He expects that these big, more comprehensive panels, which provide a "one-stop-shop envelope" could become a big future trend. Precast proponents might argue that a choice between precast and cast-in-place should be a no-brainer. As Ken Pensack, sales director for engineered solutions at Armtec points out, a hollowcore slab system can be installed "about six times faster" than a cast-in-place one. But there's a twist. "When there's no work, forming contractors lower their prices, so cast-in-place can be cheaper than hollowcore. But when forming contractors are busier, hollowcore might cost relatively less," he says. ■ Precast Concrete 13-04-05 1:54 PM