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2017SpringShotcreteEMag

Table 3: Plastic shotcrete properties Mixture Fiber content Slump Air content, % Temperature kg/m3 lb/yd3 % volume mm in. As-batched As-shot °C °F WP 0 0 0 50 2.0 5.5 4 13 55 WNF 2 3.4 0.15 70 3.0 9 4.3 18 64 WSF 1.35 2.3 0.15 60 2.5 8 4.8 20 68 Note: Specified slump is 3 ± 1 in. (70 ± 20 mm); specified as-shot air content is 3.0 to 6.0%. Fig. 5: Shooting a beehive of plain concrete mixture (WP) 6 in. (150 mm) thick on a vertical plywood panel Fig. 6: Synthetic fiber mixture (WSF) sloughed off plywood panel after being disturbed by cutting off the plywood panel under its own weight. The synthetic fiber mixture (WSF) displayed better performance in that it did not sag or slough off the plywood form immediately after shooting. However, when it was disturbed and when an attempt was made to cut it with a trowel, it sloughed off the plywood form, as shown in Fig. 6. Fig. 7: Measuring thickness of natural fiber mixture (WNF) beehive Fig. 8: Cutting and trimming natural fiber mixture (WNF) with no sagging or sloughing By contrast, the natural fiber mixture (WNF) displayed great adhesion and cohesion and did not sag or slough when built up to the full 6 in. (150 mm) thickness, as shown in Fig. 7. The WNF mixture could be cut, trimmed, and finished without any sagging or sloughing, as shown in Fig. 8. In fact, considerable effort had to be expended by a finisher to dislodge the beehive from the plywood form using a flat spade. It is believed this markedly enhanced adhesion and cohesion is attributable not only to the reinforcing effect of the natural fiber but also due to the hydrophyllic fiber absorbing some of the excess water of workability from the shotcrete and reducing bleeding tendencies in the applied mixture. www.shotcrete.org Spring 2017 | Shotcrete 39


2017SpringShotcreteEMag
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