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2015FallShotcreteEMag

Choosing Your Wet or Dry Shotcrete Equipment Wisely By Raymond Schallom III Cbuy the wrong equipment just because the system, were developed for spraying plaster,-Low-velocity applications, which are sometimes specified and advertised as a shotcreteontractors just getting into the shotcretebusiness or inexperienced contractors may specification calls for it or a good salesman talks stucco, fireproofing, and the replacement for the them into it. The seasoned, experienced shotcrete hand-applied hawk-and-trowel method of 1 in. contractor already has the equipment for their (25 mm) thick or less vertical patching with no proficient crews and knows what system (wet or reinforcement. The low-velocity method cannot dry) will work best for the project. Experienced pump any type of macro- or microfibers through shotcrete contractors and crews know that pneu- the machine or through the nozzle tip, does not matically applied concrete material projected at have the material velocity to wrap around the high velocity onto the surface will flow around the reinforcement properly, and has a limited reinforcing bars and has excellent surface bond. pumping distance from the pump to the nozzle of 150 ft (46 m) before it starts to wear on the rotor. The low-velocity system cannot spray overhead without having the nozzle 2 to 4 in. (50 to 100 mm) from the surface and cannot properly encase reinforcement vertically or overhead due to the lack of material velocity. Fig. 1: Fireproofing nozzle setup Figures 1 through 3 show different plaster and fireproofing nozzles and a rotor stator pump, which only pumps fine aggregate mixtures to cut down on the rotor wear. The air hose to the nozzle is typically 3/8 in. (9 mm) ID diameter with a 1/4 in. (6 mm) ID pipe into the tip of the nozzle for adjusting a splatter type spray pattern held at 2 to 4 in. (50 to 100 mm) from the surface. Not enough air volume (cfm) is able to pass through the 3/8 in. (9 mm) hose and 1/4 in. (6 mm) pipe to increase the speed of the material to reach a high-velocity spray pattern. Fig. 2: Plastering nozzle setups The article “Proper Selection of Equipment and Nozzle for ACI Shotcrete Nozzleman Certi- fication”1 talks about what ACI recognizes as the correct nozzle setup and equipment required for nozzleman certification. The American Concrete Institute (ACI) C660 Shotcrete Nozzleman Cer- tification Committee put together the CP-60(09),2 “Craftsman Workbook for Shotcrete,” which covers the equipment, nozzle setup, and distance from the receiving surface. The ACI Shotcrete Subcommittees have written many documents over the years which outline the areas discussed Fig. 3: Rotor stator pumps were designed for previously. ACI documents2-6 also provide guid- plaster, stucco, fireproofing, and later to replace ance on selecting the correct high-velocity shot- the hawk and trowel for patches vertically 1 in. crete equipment and nozzle setup. There is even (25 mm) thick with no reinforcement. These a section on air requirements for both wet and nozzles and pump are not recognized by ACI as dry shotcrete in ACI 506R-05,4 Table 3.1, and shotcrete equipment Sections 3.4, 3.4.1, and 3.4.2. 10 Shotcrete • Fall 2015


2015FallShotcreteEMag
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