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2017SpringShotcreteEMag

Fig. 15: Bench-gun shooting L-shaped wall Fig. 17: View of finished straight wall Fig. 16: Trimming shotcrete to shooting wires with cutting screed (rod) shooting wires. Because of the very cohesive characteristics of the natural fiber-reinforced shotcrete, the finisher using the cutting screed (rod) could follow immediately behind the nozzleman (only a few feet away), cutting and trimming the shotcrete to the shooting wires to control line and grade. Figure 16 shows the finisher trimming the shotcrete to the shooting wires in the straight wall. A finisher with a darby (long wood float) followed right behind the cutting screed operator, closing and smoothing the shotcrete surface. Final finishing with wood hand floats was carried out to provide a stucco-like surface finish appearance. No fibers were found protruding in the finished shotcrete surface. Figure 17 provides a view of the finished face of the straight wall. The nozzleman and finishers were impressed with the enhanced productivity provided by being able to bench shoot the walls to their full height in one pass and, after shooting of the layer, follow immediately behind the nozzleman with finishing operations, without any problems of shotcrete sagging, sloughing, or fallout. The finishers also commented on how easy it was to finish the walls; the natural fiber appeared to act as a finishing aid for the shotcrete. Fig. 18: Stripped face of L-shaped wall is defect-free Shotcrete Examination and Testing A few days after shooting, the plywood forms were stripped from the back side of the aggregate bin walls and the stripped faces of the aggregate bin walls were examined. The walls were observed to be essentially defect-free, with no significant voids from incomplete consolidation, sags, tears, or shadows behind the reinforcing bar. Figure 18 shows the stripped face of the L-shaped wall. Also, examination of the structural shotcrete walls after several weeks of service showed no evidence of plastic or restrained drying shrinkage cracking. In addition to shooting the structural walls, the nozzleman shot a 2 ft x 2 ft x 4 in. (610 x 610 x 100 mm) test panel with Mixture A. The test panel was cured on site until shipment to a testing laboratory in Vancouver for testing. Cores were extracted for testing for compressive strength to ASTM C39, and values of BA and VPV to ASTM C642 at an age of 28 days. The average 28-day compressive strength was 4440 psi (30.7 MPa), which satisfied the specified minimum compressive strength of 4000 psi (27.6 MPa) at 28 days for this project. The average values for BA and VPV were 7.6 and 16.9%, respectively, which satisfied the maximum allowable values of 8% BA and 17% VPV. www.shotcrete.org Spring 2017 | Shotcrete 43


2017SpringShotcreteEMag
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