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Nozzleman Knowledge Fig. 2: Nozzleman initially places material into the panel’s lower corners while close in Fig. 3: As the panel fills, the nozzleman adjusts the Fig. 1: Poor placement techniques have produced sand angle and backs away to avoid displacing in-place lens or encased rebound trapped within test specimen material. Note continuous use of a blow pipe affects placement difficulty. This is primarily due that is properly consolidated. Initially, come close to the placement accuracy required to fill small and direct the nozzle flow into the lower corners elements. Nozzle orientation, angle, material and then build from the bottom. When shooting volume, air flow, slump, and blow-pipe techniques wet-mix shotcrete with a coarse aggregate, use a become more critical when filling small areas. blow pipe to keep the receiving surface free of Whereas nozzle velocity is a primary element rebound or loose sand. As the panel fills, back in material consolidation and compaction, exces- away slowly to keep excess energy from disturbing sive velocity can shove, displace, or fold material previously placed material within the panel until when placing a test panel. Poorly chosen place- it reaches its full thickness (refer to Fig. 2 and 3). ment angles, distance, or incorrect nozzle flow If a nozzleman is unsure of the placement can disturb in-place material within the panel. quality of material within a panel, it should be Internal cracks, voids, laminations, or sand lenses cleaned out and shot again. can result. Additionally, because test panels have After placement, do not trowel, sweep, or formed perpendicular edges, the potential for otherwise work the shotcrete surface. Movement trapped rebound pockets or sand lenses within the by troweling can bring water to the surface or in-place material can intensify if panels are not disturb the test panel’s compaction and consolida- placed skillfully (refer to Fig. 1). tion. Never allow panels to be worked, troweled, Prior to placement of any test panel, nozzlemen or finished. This unnecessary step can affect should ensure that the panel is sufficiently rigid to strength values. Specifications require that after withstand placement pressures without movement. panels are cored, ends of the cores will be pre- Nozzlemen should reduce placement volume and pared for uniformity by the testing facility. make other material adjustments before shooting the panel. Adjust placement equipment to attain a Next Step: Do Not Disturb smooth, controllable nozzle flow that is free of Moving a freshly placed test panel will never slugging or air bursts. Due to the panel’s size, increase its strength; however, it can certainly steady filling, free of irregular, high-energy bursts diminish it. Like any concrete, freshly placed test of material, is crucial to producing a test specimen panels are extremely susceptible to damage from Shotcrete • Summer 2013 49


2013SumShotcreteEMag
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