Cary Kopczynski & Co.
Encapsulated anchors are a little more complex and much more dur…
Experts do not believe a wider adoption of encapsulation would present problems on the jobsite. Here’s what a few said. Read More
“There was some resistance, originally, to encapsulation due to its cost,” says Kopczynski. “But in the Pacific Northwest and other markets where I work, the average cost for hard construction is $220 per square foot. So adding 3 or 4 cents per square foot to this figure, which is the cost of encapsulation, is not a big deal. Once folks see the actual numbers, resistance decreases. And now, with encapsulation, the perception of PT is improving with clients and the public at large.”
Still, even a small cost can be a sticking point in an industry where every penny counts, explains Cagley. “The fabricators are competing against other systems. So while the increase may be small, it still might seem disadvantageous to add anything at all to the cost.” Yet Cagley also sees fabricators who are telling designers that encapsulation should be performed, “so there is a push from several directions. When the PTI Technical Advisory Board began promoting encapsulation, fabricators saw the benefit of promoting it as well.”
Ultimately, improving the performance of unbonded tendons will be beneficial to the PT industry as a whole. A wider implementation of encapsulation “will improve durability and quality, and therefore market share,” says Rashid Ahmed, P.E. and vice president of Walker Parking Consultants, a parking consulting and parking design firm that performs work across the globe.
While many are optimistic that elevated structures will eventually achieve almost universal strand and anchor encapsulation, there is less confidence that the practice would spread to slabs-on-ground (SOG). “I have seen no pressure to make this happen,” says Cagley. “It was not originally proposed [by PTI].”
Furthermore, “there are different codes for SOG,” says Pawan Gupta, P.E. and senior restoration project manager at Walker Parking Restoration, a subsidiary of Walker Parking Consultants.
“SOG is nonstructural. It is a wearing surface,” says Kopczynski. Still, he sees situations in which faulty cables snap and come through the concrete slab and believes that the quality gain achieved through encapsulation is worth the small added cost. “There are only a few cables in a house. So you are looking at an additional cost for encapsulation of $100 to $150 for a $500,000 house,” he says.
The fact that there is no life safety issue with SOG, according to Neff, may also slow the rate of encapsulation adoption in SOG construction. “Some feel, however, that because the cost is small and there is some payoff, it should be used. And as encapsulation becomes more standard, it lowers costs and also people get used to it,” he said.
In the SOG market, as in the elevated-structure market, the use of encapsulation is regional. States with wet soils, such as Texas and California, experience ground heave, so those areas make extensive use of cables in slabs. States with brackish groundwater, or high concentrations of chlorides or sulfites, also make wider use of encapsulation. So while areas with exposure have a relatively high rate of encapsulation, percentages estimated as high as 30%, nationwide percentages were estimated to be closer to 5%.
“Soil issues always drive the decision of whether or not to encapsulate,” according to Price. “And litigation has brought awareness.”
Perry McArthur, a manager at Suncoast Post Tension Ltd., has seen an increase in the inclusion of encapsulated systems in SOG construction in the Phoenix area. While the percentage of new home slabs using encapsulation still is not high, this region would have previously seen numbers near zero. McArthur estimates that several years ago, only one subdivision out of 300 would have used encapsulation. Now its use has spread to new neighborhoods, affecting about a dozen out of every 300 subdivisions. Soil testing is driving that increase.
“Traditionally, engineers have gotten soil reports from geotechnical experts, but those reports did not always include chloride data,” says McArthur, who sees many cases in which engineers are pushing back and returning the reports, requesting the inclusion of chloride test results. “Those data are what will determine the use of encapsulation,” he says.
Even though the transition to encapsulated anchor systems is just ramping up, it has already improved the perception of PT and increased the use of the building system. Encapsulation will make PT a more resilient building solution. “Encapsulation will increase the service life of the concrete,” says Carol Hayek, chief technical officer of CCL USA, an international provider of post-tensioning systems. “And that is good for sustainability.”
All updates should make their way into the building codes within five years or so. “Post-tensioning is definitely getting more popular,” says Baxi. “Encapsulation is the new normal, and it is the right thing to do.”
Kristin Dispenza is a writer for Constructive Communication Inc.
