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2017SummerShotcreteEMag

Fig. 5(a)—Maintain a relatively sharp angle and completely cover reinforcements to encourage rebound to fall free of the work Fig. 5(b)—Close-up reveals what can occur when reinforcement is not properly covered by the nozzleman. Rebound will become trapped by the deposition of additional material if it is not blown free of the work. This is the likely cause of the flaws within t patterns. Maintain a fairly sharp angle along the top of the he test specimen in Fig. 1 bench to encourage rebound to fall free rather than become trapped and fill around reinforcements completely to diminish potential accumulations behind bars (refer to Fig. 5(a) and (b)). HOW TO MAKE A USEFUL BLOW PIPE Want to make a blow pipe? What could be easier? A fitting, a valve, and a few feet of pipe, and we have the perfect blow pipe. Or do we? An effective blow pipe must be capable of continuously keeping a receiving surface free of rebound as material is being applied. Although this task seems simple, the compressed air stream from a blow pipe can easily disrupt the nozzle stream’s compaction and consolidation or disturb in-place material if the blow pipe air stream is too powerful. The blow pipe tip’s shape plays a role in its usefulness. A blow pipe with an open tip can consume a LOT of air and thus a large portion of the air compressor’s total output, potentially leaving insufficient air to accelerate concrete from the nozzle. Even with a relatively low air volume, an open tip will create a narrow, powerful stream that can displace or even blow a hole into freshly placed material during use. The design in Fig. 6 requires far www.shotcrete.org Summer 2017 | Shotcrete 31


2017SummerShotcreteEMag
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