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Post-tension Masonry

One of the most overlooked factors when discussing the shrinking workforce is its relationship to current building technology. For any industry to be successful and remain commercially viable, there has to be a complementary relationship between the technology used and the state of the workforce. Put another way, we need both an efficient method for building masonry structures and, at the same time, a sufficient labor pool to build those structures. Without an adequate balance between these two factors, the industry will be unable to meet market demand, and profitability will decline. Though this may seem rather obvious to those within the industry, the relationship between technology and workforce can provide insights into both the current problem and a realistic solution.

 Like two variables in a simple equation, technology and the workforce each directly affect the total solution that, in this case, is the state of the industry and its ability to meet market demand. By changing one of these variables in relation to the other, the industry is impacted in either a positive or negative way. As a result, there are only two possible ways to positively impact the industry: 1) increase the number of skilled workers in the labor pool; or 2) reconfigure the technology to accommodate the changing labor pool. Of course, in both cases, it is essential to bear in mind that any change must serve the masonry industry. In other words, neither factor can be radically changed so as to create an entirely new industry as in the case of pre-cast and cast-in-place tilt-up construction.

Over the last decade or so, the industry has largely focused on workforce development as a means to maintain its market share. Although little attention has been paid to developing new masonry technologies, one such innovation offering great promise has emerged.

The FlexLock® Solution
The FlexLock Wall System is a multi-patented, post-tensioned masonry wall system developed to configure itself to the changing labor pool. Cercorp Initiatives Inc. specifically designed FlexLock so that mason contractors could use fewer journeymen bricklayers and more apprentices. This enables mason contractors to multiply their existing crews by breaking them down into smaller crews, each capable of doing the work of the previous larger crew. Beyond increasing productivity, smaller crews mean smaller labor costs. This, along with faster build times, translates into greater profitability.

FlexLock construction begins by installing anchors into the footing. Because footings vary, the first course is laid in mortar. This is the only time mortar is used. With the first course in place, all-thread tendon segments are connected to the anchors by means of a coupling. These are typically spaced about 4' on center. The interlocking units are then dry-stacked. A slot in the unit enables the mason to place the block around the tendon without having to lift it over the top. Grout is not used in the vertical cores.

The FlexLock Wall System
This method of post-tensioning is unique to FlexLock. The units are precision ground on the top and bottom to 0.015" preventing point loading, making post-tensioning possible. The system accommodates non-modular construction, jambs, sills, lintels, pilasters, and can be matted to conventional masonry. At the top of the wall, a bond beam is laid, reinforced and grouted with post-tensioning accomplished within, or on top of, the bond unit. Cercorp has extensively tested the FlexLock System and found it to have three to four times the reserve strength of standard masonry.

A Case Study
 To assess both the speed of construction and the composite workforce, Cercorp, working with the engineering firm of Ryan-Biggs Associates and the International Masonry Institute (IMI), built a small test structure. The building, along with some test panels, were constructed with IMI students at their apprentice training facility in Cascade, Md. The instructors began by laying out the first course, after which the students built up the leads and courses. The students were each timed by Cercorp at laying approximately 100-125 units per hour, with material handling being the primary limiting factor. As the walls were laid up, the instructor walked around with a level and dead blow hammer ensuring that the walls were plumb, and window and door opening were in the right place. From this test, Cercorp concludes that FlexLock can dramatically increase productivity.

For the masonry industry to expand its markets, it has to balance the equation between the workforce and technology. The FlexLock Wall System, with its unique post-tensioning technology, enables mason contractors to reconfigure the available labor pool to increase both productivity and profitability.

For more information and availability, visit Cercorp's web site at www.cercorp.com.

Post-tensioning Creates New Options for Contractors and Builders
The idea of using post-tensioning to structurally support masonry fencing in lieu of rebar and grout was unheard of in the mid 1980s. At that time, Proto-IITM Wall Systems had developed and patented a post-tensioned masonry fence system called The Proto-II Wall. This system provided an engineered, stronger and less expensive alternative to conventional masonry fencing. Royce Walls of Phoenix, a masonry fence installing company, was one the first Proto-II Wall Systems' licensees and began installing the system for clients in the Phoenix area in 1986.

In the beginning, Royce Walls faced a lot of doubt and resistance about trying a new and unknown product. However, Royce Walls persevered, and through the years Proto-II Walls became more accepted. The builders who used post-tensioned masonry for their fencing projects found them to be an extremely reliable and cost-saving alternative. The system stood the test of time and outperformed conventional masonry fencing, especially in the severe Arizona monsoons. Today, Proto-II Walls are a well-established and highly regarded masonry fencing product among Arizona builders.

While the Proto-II Walls were a superior and cost-saving fencing product for Royce Walls to provide their customers, they did not have a similar alternative to conventional masonry retaining walls. This became an increasing challenge as the market changed. New projects were moving further into the outlying areas of the Phoenix valley where flat parcels of land were scarce. Also, there had been an increase in builders' requirements to provide extensive drainage control, retention basins and between-lot retaining. As a result, retaining walls had become an extensive part of most masonry fencing projects. In addition, retaining walls were expensive and time-consuming due to the increased excavation, bench out, backfill, concrete, steel, grout and labor required to construct them. Because of material shortages and subsequent price increases, retaining walls became more expensive than ever. As retaining walls became a more common and more costly item on job sites, staying within budget became a bigger concern for builders.

How Does Post Tensioning Work
in Masonry Fencing?

The Proto-IITM Wall is a masonry fence system using standard concrete masonry units. High-strength steel tension rods are connected to rebar in the footing. A steel bearing plate, high-grade nut and Direct Tension Indicator (DTI) washer are installed near the top of wall. The rod, plate and nut assembly are tightened to a specific torque rating, which collapses the DTI to achieve the specified tension within a 3% tolerance. The tensioning results in compression distributed throughout the wall, dramatically increasing its strength and load capacity over conventional grouted masonry walls.

Proto-II Wall Systems responded to the market needs. Through research, development and testing, they expanded from masonry fencing and introduced the Proto-II Retaining Walls. The retaining walls system uses the same post-tension technology and design as the original Proto-II Walls and yields the same post-tension advantages of increased strength and load capacities. While conventional retaining walls require solid grouting, post-tensioning doesn't, creating significant savings in both materials and labor. In addition, the bench out, excavation, footing size and steel are all reduced due to the unique engineering used in the post-tension design. Another advantage is that Proto-II Retaining Walls can be backfilled much sooner than conventional retaining walls, as no cure time is required for the grout. This results in an additional time savings for the customer.

Immediately, Royce Walls began marketing the Proto-II Retaining Walls to their customers. With increased strengths, reduced installation time and up to 40% savings, Proto-II Retaining Walls became an excellent alternative to the conventional retaining walls. As before, Royce Walls experienced some initial resistance from clients in trying a new and unknown product. However, with Royce Walls' trusted experience with post-tensioned fencing and the increased savings with the product, clients' skepticism did not last long. As more builders discover the advantages, post-tensioned retaining walls are becoming an established alternative in the Phoenix market.



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