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2013SprShotcreteEMag

Pool & Recreational Shotcrete Corner Reprinted with permission from the January 2013 issue ofAqua Magazine (www.aquamagazine.com) Perfecting Placement By William T. Drakeley Jr. Casphalt, and glass don’t even come close. process) are superior to other forms of properlyThe reason that shotcrete, both dry and wet(both versions of the “pneumatically applied”oncrete is the construction material usedmost by humankind—wood, stone, brick, In a sense, our world is made out of concrete and mixed concrete application boils down to one I am among those who believe the very best way word—velocity. to apply it, without question, is by way of the When you shoot concrete onto a form or the shotcrete process. earth at 300 to 400 feet per second (90 to 120 m per second), it compacts and becomes dense. The problem is, most people, even those in the pool and spa industry who use shotcrete on a regular basis, often don’t understand the basics of installation, beginning with proper velocity. That starts with an air compressor with enough air volume to deliver the required material at the desired speed. Unfortunately, most companies I’ve come in contact with use compressors that are undersized, delivering, say, 185 cubic feet per minute (CFM) 315m3/hr— not nearly enough capacity to drive the wet mix properly into place. (More on compressor size below.) That’s just one common mistake that compro- mises the end product. Beyond that most basic issue, there are a number of specific measures before, during and after the application process that must be scrupulously observed; otherwise, you’ll wind up with an inferior product that doesn’t provide the structural integrity necessary to create a watertight pool vessel. The ACI has always stated that structural concrete built for water retention or a water environment needs to have a minimum compressive value of 4000 psi 1.3 MPa (ACI-318, ACI-350). With that in mind, let’s dive right into the basics of making the most of pneumatically- placed concrete. Prior To Placement To begin, you must be certain the substrates receiving the concrete are rigid and non-vibrating. That means your forms must not move during application and the soil has to be competent enough to provide a solid support. Your steel and 32 Shotcrete • Spring 2013


2013SprShotcreteEMag
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