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2016SummerShotcreteEMag

In Fig. 6, all the cores taken from the test panels were good except for the core shown in Fig. 7, which had a few voids adjacent to the reinforcing bars. All cores were evaluated by the structural Engineer of Record for the project, and based on the results, approved the shotcrete team for this project. When the cores exhibit some voids, closer inspection is required, and the larger cores with more surface area and embedded reinforcement can help give the engineer a better idea of how the shotcrete placed can perform in their structural sections. Core evaluation can be very subjective, as stated previously, and it is extremely helpful to have the engineer doing the evaluation be familiarized with the shotcrete process. My practice, which I’ve used successfully for years, is to submit shop drawings, check for workable mixture designs, use the proper equipment (it takes horsepower to shoot heavy bar), use a qualified crew, and both communicate and involve the special inspector, testing lab, and engineer on the project. I have looked at cores for over 40 years and I have seen some that may look marginal to the inexperienced eye, but when presented to the knowledgeable Engineer of Record, are approved for the proposed project. The team approach with the qualified shotcrete contractor, the testing lab, and informed Engineer of Record really works. Mockup Panels The second type of panel common in shotcrete construction is the mockup panel. These panels are used to show the finish of the final exposed shotcrete surface for review and approval by the owner, engineer, or architect. Mockup panels can vary in size and shape. Often, multiple panels are shot to show the variety of finishes possible for the final project appearance. The mockup panels will be shot with either the wet- or dry-mix process according to the process to be used on the project. Sometimes both processes are used on the same project. Shotcrete finishing can be a very creative vehicle for a talented contractor to express their artistic side. The finish can vary from a plain float finish on a highway wall to a creative carved rock design with a variety of coloring to give the appearance of natural, weathered rock. Figure 8 shows a mockup panel shot with lightweight concrete. The panel is 4 x 4 ft (1.2 x 1.2 m) and 24 in. (600 mm) deep. This is the same thickness as the walls on the project. This mockup used a color additive to help match the existing building and also included a heavy sandblast finish. This is the final finish for all the exterior walls of the project. Production Panels After all the preconstruction and mockup test panels are complete and accepted, and shotcrete may vary in surface area from 50 in.2 (3200 mm2) to over 300 in.2 (19,000 mm2). I suggest a minimum 6 in. (150 mm) diameter core for best evaluation of the shotcrete in congested test panels. This size core will help prevent the core from breaking during the coring operation and will also have more surface area for evaluation. Fig. 6: Cores taken from a 24 in. (600 mm) wall that went to the testing lab for inspection Fig. 7: Irregularities in one of the cores Fig. 8: Lightweight shotcrete mockup panel 12 Shotcrete • Summer 2016


2016SummerShotcreteEMag
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