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2013SumShotcreteEMag

Shotcrete FAQs smooth for operation of a manlift). The bottom line: hire a Question: We are in the process of designing retaining walls contractor who has experience in conducting such work. that will be supported by either concrete piers or steel piles. We would like to see some typical details on how the reinforcing Question: I would like to know the standard operating proce- is secured to either the piers or piles. dures for cleaning out shotcrete hoses with air and/or water and, in particular, how to keep the hose from whipping when Answer: For concrete piers, the reinforcing steel is generally using air. secured to the piles with reinforcing bar grouted dowels. For steel piles, the reinforcing bar is generally secured with Answer: Shotcrete hoses can be cleaned out using either water Nelson studs. or air. In many instances, the site conditions make cleaning with water not feasible. When cleaning with air, the free end Question: I am evaluating a community in central Colorado or discharge end of the hose should be secured to something that contains shotcrete slope reinforcement ranging from 14 to to ensure that the hose does not whip as the material and 44 ft (4 to 13 m) in height. Assuming the installation met all cleaning ball or rag discharges. required guidelines, what should I anticipate as a useful life for this product? Question: We are working with an architect in New York City on an unreinforced masonry (URM) building where they want Answer: Shotcrete is a method of placing concrete and properly to remove brick to provide a larger storefront opening. I would placed shotcrete should have a service life similar to cast con- like to use the remaining walls to resist lateral forces but the crete. Generally, concrete structures in normal environmental brick is insufficient. We would like to remove one width of brick exposures are expected to have service lives from 50 to 100 years. and apply 4 in. (102 mm) of reinforced shotcrete in its place. With particular attention to materials and construction methods, Can you tell me where I can find applicable code and design some concrete structures, such as the new San Francisco Bay guidelines for this application? Bridge, have been designed for a service life up to 150 years. The first step in achieving a long-lasting, high-quality instal- Answer: Your proposed solution is certainly reasonable and is lation is to engage a highly qualified and experienced shotcrete used regularly. Shotcrete has been used to strengthen both URM contractor. There are many other factors that influence service and tilt-up panels to accommodate enlarged openings. Shotcrete life, including using the right mixture design for the anticipated is a method of placing concrete and the in-place properties would exposure conditions. be the same. The applicable code would be the code you would use if you were to strengthen this wall with concrete. Designs Question: Is there is a manufactured depth gauge that would using the ACI 318 Building Code and Commentary are fully be glued/nailed to the form to allow the nozzleman to physically applicable to shotcrete placement, although compressive tests see how much concrete is being applied to the surface? We for acceptance are secured using cores from shotcrete test panels have a condition where there will be two or three applications per ASTM C1140/C1140M and C1604/C1604M, rather than on the same surface, and I am concerned that the correct depth cast cylinders. is not being applied in each pass. Question: Is there a specification with regard to cold joints Answer: ACI 506R-05, “Guide to Shotcrete,” Section 5.6, on when using shotcrete? Alignment Control (refer to ASA Bookstore: http://shotcrete. org/BookstoreNet/ProductDetail.aspx?itemid=506R-05) Answer: Generally, the interface between sequentially placed gives specific guidance on proven methods to establish the line layers of shotcrete is not considered a cold joint because the shot- and grade of the surface, as well as proper material thickness crete abrasion, velocity of impact, and high paste content make and cover. Common methods are use of ground wires, guide excellent bonding conditions. Cores taken through layers of strips, depth gauges, and depth probes. Please refer to “ASA’s shotcrete on shotcrete often show that it is virtually impossible to Buyers Guide” (http://shotcrete.org/pages/products- ascertain one layer of shotcrete from the next. Please refer to ACI services/Buyers-Guide/index.asp) and contact one of our 506R, “Guide to Shotcrete,” for information on joints in shotcrete. members who provides supplies to the shotcrete industry. Please note: ASA’s technical team provides the answers to submitted questions as a free service. The information is based on the personal knowledge and experience of the ASA technical team and does not represent the official position of ASA. We assume that the requester has the skills and experience necessary to determine whether the information ASA provided is appropriate for the requester’s purposes. The information provided by ASA is used or implemented by the readers at their OWN RISK. 72 Shotcrete • Summer 2013


2013SumShotcreteEMag
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