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2013SprShotcreteEMag

Pool & Recreational Shotcrete Corner Proper shotcrete placement requires everyone, from the pump operator to the nozzleman, to know his role form installations should be built to structural Otherwise, run plumbing in the floor stone to specifications based on the soil conditions and set avoid vibration during the shoot, and make up to withstand the impact of the concrete as it’s sure the plumbing is pressure-tested. (Consider shot into place. the difference in hassle and cost of correcting One of the ironies here is that by using com- a plumbing problem before the concrete is pressors that don’t deliver adequate velocity, forms installed versus afterwards.) don’t need to be as rigid to prevent movement. That’s what one might call a fool’s paradise, because as stated above, it’s material velocity that produces Wet v. Dry reliable compaction. (Velocity = compaction, Many in our industry believe that either compaction = density, density = strength, strength wet shotcrete or dry shotcrete is superior to = water tightness.) the other. That’s simply not true — both Beyond that rigidity of the substrate, there are methods can produce quality concrete if used a number of other pre-placement issues, all of correctly. The difference is that each method which, if not observed, will result in inadequate can be better for certain types of applications structural integrity. or certain regions of the country. • The excavation site should be free of standing Our firm uses wet mix shotcrete because water. You should have a layer of stone in the we work in high-volume applications most of bottom of the pool to ensure control of subsurface the time, not only building large swimming water movement. pools but also doing work in highway and • Steel should be raised 2 to 3 in. (50 to 75 mm) subway tunnels. Wet mix is better suited for above the floor and away from the sides. The those applications. Dry on the other hand is American Concrete Institute specifies a better suited for smaller applications when minimum 2 in. (50 mm) coverage around you’re starting and stopping more frequently. any concrete encapsulated reinforcement. Dry or wet are equally suited for the swimming (ACI 350-06) pool industry. • Freestanding walls require support mecha- So, the difference is really like the hammer nisms so there is no vibration. These walls and the screwdriver, it depends on the applica- should be secured and fastened properly. tion. But for the record, both wet mix and dry • All plumbing lines should be mounted firmly mix are the best methods of concrete applica- in place if they are to be part of vertical wall. tion, no ifs, ands or buts about it. Shotcrete • Spring 2013 33


2013SprShotcreteEMag
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