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performance in a full-scale field trial, with ready mixed concrete batching, mixing, and supply, in a structural shotcrete application. The evaluation was carried out at the Jos. J. Albanese yard in Santa Clara, CA. Two different wet-mix shotcrete mixture designs commonly used by them in the Bay Area were modified by the addition of the natural hemp-based fiber, and used to construct two structural shotcrete walls for aggregate storage bins. The actual shotcrete mixture designs used are proprietary and so are not reproduced in this paper. Both mixtures had the same portland cement content and contained 15% fly ash by mass of cement. The main difference between the two mixtures was Mixture A had a 3/8 in. (10 mm) pea gravel coarse aggregate and the second mixture, Mixture B, had a 0.5 in. (13 mm) crushed granite coarse aggregate. The natural hemp-based fiber was supplied in 1 lb (0.45 kg) shreddable bags and added to the concrete truck during batching and mixing. The fibers were incorporated into the mixtures at addition rates of 1.5 lb/yd3 (0.89 kg/m3) for Mixture A and 3.0 lb/yd3 (1.8 kg/m3) for Mixture B. Figure 12 shows Mixture B being discharged from the concrete truck chute into the pump hopper. An 8.0 yd3 (6.1 m3) load of Mixture A was supplied at a slump of 3.5 in. (90 mm). A 7.0 yd3 (5.4 m3) load of Mixture B was supplied at a slump of 3.0 in. (75 mm). The shotcrete temperature for both mixtures was 76°F (24°C) and the ambient temperature was around 72°F (22°C) at the time of shooting. Both Mixtures A and B were highly cohesive and pumped and shot well, without any signs of fiber clumps or remnants of the water-shreddable bags being evident during shotcrete discharge, pumping, and shooting or in the as-shot structural walls. The shotcretes were pumped to the nozzle where compressed air was added to pneumatically project the shotcrete at high impacting velocity onto the receiving surface, using the Reed C50 pump shown in Fig. 13. Structural Shotcrete Walls Construction Two structural shotcrete walls, one L-shaped and the other straight, were formed and shot. The L-shaped wall was approximately 16 ft (4.9 m) long and 6 ft (1.8 m) high. The straight wall was approximately 20 ft (6.1 m) long and 4 to 5 ft (1.2 to 1.5 m) high. Both walls were 18 in. (450 mm) thick and were reinforced with a double mat of No. 6 (No. 20M) reinforcing bar. Figure 14 shows the L-shaped wall. The walls were constructed as extensions to aggregate storage bins in the Jos. J. Albanese yard and provided a good opportunity to evaluate how the natural fiber-reinforced shotcrete behaved during shotcrete application, finishing, and subsequent field performance. Both shotcrete mixtures were observed to be very cohesive and the ACI Certified Nozzleman doing the shooting could bench shoot (stack) the structural shotcrete to the full height in both walls without any sagging, sloughing, or fallout. The shotcrete was applied to just cover the outer layer of reinforcing bar. A blow-pipe operator worked alongside the nozzleman, blowing out any accumulations of rebound and overspray from the areas about to receive shotcrete. A finish coat of the shotcrete was then applied from the top down, to build the walls out to their full thickness. Figure 15 shows bench-gun shooting the L-shaped structural wall. Shooting wires had been installed to control line and grade and the nozzleman shot the final layer to just cover the Fig. 12: Natural fiber-reinforced shotcrete (Mixture B) being discharged from concrete truck chute into pump hopper; note highly cohesive nature of mixture Fig. 13: Reed C50 pump used to pump wet-mix process shotcrete Fig. 14: Formwork and reinforcing bar for L-shaped wall 42 Shotcrete | Spring 2017 www.shotcrete.org


2017SpringShotcreteEMag
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