Patented Post-tension Materials
Words: Gary Otto, Ed PankusLike many other types of masonry applications, post-tensioning offers several systems that integrate the application with specialized hardware and engineering. With all three of the following examples, post-tensioning brings the highly desirable qualities of being faster to build, cheaper in materials and labor, and stronger than traditional masonry.
Post-tension Wall System
Cercorp Initiatives has developed the FlexLock Wall System, a patented post-tension masonry wall system that can be used for loadbearing and non-loadbearing applications. According to the company's web site, this system is completely mortarless and groutless (with the exception of the first course), reduces assembly time, lowers mason contractors' costs, and produces a solid structure with the ability to absorb external forces, such as seismic or wind.
Ed Pankus, Vice President of Commercialization for Cercorp, says that FlexLock can help keep mason contractors competitive to other types of building applications in several ways.
"One way is they are able to put up between 100 block per hour as opposed to 175-200 block per day," says Pankus. "The speed at which it goes up is much more efficient."
Another way that this system helps keep costs down is the fact that it requires one journeyman bricklayer to set the first course, while apprentices can be used to complete the structure.
Although this system is not currently covered by the Masonry Society Joint Committee (MSJC), which is written around rigid, mortared systems, like many other new innovations, mason contractors and professional engineers are getting FlexLock approved by building inspectors through "Alternative Materials and Methods" and "Special Structures."
"We're hoping that in 2005, the MSJC will come up with specific guidelines for mortarless, groutless dry-stack systems within the codes because they don't currently exist," says Pankus.
Fences and Retaining Walls
With many of the same attributes as its loadbearing cousin, post-tension masonry can also be utilized for non-loadbearing fences and retaining walls. Gary Otto, President of Proto II Wall Systems, says that mason contractors should investigate the cost-effective features that post-tension can bring to these applications.
"Due to the strength of post-tensioning, we can produce Proto II in smaller block widths ? four-wide, six-wide and eight-wide units," says Otto. "Four-inch strengths are very similar to that of six- or eight-inch wide block due to the post-tensioning effect. Further, four-inch wide block can be 20-30% cheaper and can lay 20-30% faster.
"Proto II retaining walls eliminate the rebar and the grout, and it can pure post-tension without any grout up to six feet," adds Otto. "You're eliminating costly materials with post-tension rods."
Parapets
Proto II also offers a post-tension parapet system for jurisdictions and clients who wish to conceal rooftop utilities.
"Proto Parapets works well because it's designed to be light, using post-tension rods instead of rebar and grout, and we don't have to brace our parapet system back into the roofing structure," says Otto. "Heavy, conventional rebar/grouted masonry parapets must be 'braced' back into the roof structure, which is very expensive and creates numerous opportunities for roof leaks."
Otto adds that the lighter parapet weight allows structural engineers to downsize their design loads in the building structure below. "You can imagine all of the hundreds of thousands of pounds those [traditional masonry] parapets must weigh. Eight hundred or a thousand feet of wall that can go up 12 feet high ? taking all of the grout out of that is taking off a lot of weight."