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Fig. 11: Typical daily wet-mix shotcrete production panel There are many different size requirements for production panels. This includes both plan dimensions and thickness. For example, a 12 x 12 in. (300 x 300 mm) panel 3 in. (75 mm) deep may cause problems down the road. The panel may not have enough room for removing all the cores required. ASTM testing requires cores not be taken closer than the depth of the panel plus 1 in. (25 mm). So in a 12 x 12 in. (300 x 300 mm) by 3 in. (75 mm) deep panel, the outer 4 in. (100 mm) of the panel can’t be cored, and leaves only a 4 in. (100 mm) square area in the center of the panel. If taking a 3 in. (75 mm) diameter core (the recommended minimum core diameter), you could only get one core out of each panel. Also, the 3 in. (75 mm) thickness doesn’t allow any additional length to square up the ends of the core for testing. I suggest a minimum shotcrete production panel be 24 x 24 in. (600 x 600 mm) by 5.5 in. (140 mm) deep. This is 2 in. (50 mm) deeper than the ASTM C1140 minimum panel size of 24 x 24 in. (600 x 600 mm) by 3.5 in. (90 mm). The added plan dimensions leave enough room to stay well off the edge and other cores for a non-disturbed sample, and the added length allows the lab to square up the end before testing. Remember, the production panel is a sample of the concrete material as shot in-place. If panel sizes are not thought out in advance, you may not be able to get enough cores for the testing at the desired ages. If the panels are damaged in handling or storage, low strength results could result despite the fact that the concrete in-place is perfectly good. Thus, proper sizing, preparation, and handling of production panels are essential to make sure the cores are truly representative of the work. In summary, with all three test panels, planning ahead, educating the team members, good communication, quality concrete mixtures, and shotcrete placement by a qualified and experienced shotcrete contractor with proper equipment and a well-trained crew will make your job run much more smoothly. Chris Zynda is a Past President of the American Shotcrete Association, current President of the Shotcrete Concrete Contractors Association, General Manager with JJ Albanese Concrete—Shotcrete Operations, and an ACI-approved Examiner for Shotcrete Nozzleman Certfication. He is a member of ACI Committees 506, Shotcreting, and C660, Shotcrete Nozzleman Certification, and ASTM Committee C09, Concrete and Concrete Aggregates. Zynda is also an approved Underground Examiner with California Transportation Agency. Production panels are the equivalent of concrete cylinders used to evaluate compressive strength of the concrete material. Because shotcrete cannot be shot into a closed cylinder form, the shotcrete is shot into an open-faced form. Cores taken from the panel are then tested at the appropriate age to establish the strength of the shotcreted concrete. These panels do not contain any reinforcing. ASTM C1140, “Standard Practice for Preparing and Testing Specimens from Shotcrete Test Panels,” provides testing requirements for production test panels. Figure 11 shows a typical production panel. Care must be taken in the handling and storing of production panels. Don’t move the panels and disturb the concrete before they gain adequate strength. Also, don’t expose the panels to environments that are significantly different than the exposed project’s sections (much hotter, colder, or drier). STRUCTURAL SHOTCRETE SYSTEMS, INC. LICENSE #579272 A www.structuralshotcrete.com JASON E. WEINSTEIN, P.E. VICE PRESIDENT 12645 CLARK STREET (562) 941-9916 SANTA FE SPRINGS, CA 90670 FAX (562) 941-8098 14 Shotcrete • Summer 2016


2016SummerShotcreteEMag
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