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Shotcrete FAQs As a service to our readers, each issue of Shotcrete will include selected questions and provide answers by the American Shotcrete Association (ASA). Questions can be submitted to info@shotcrete.org. Selected FAQs can also be found on the ASA website, http://shotcrete.org/pages/products-services/technical-questions.htm. Question: I have a newly constructed in-ground pool in which Design, Construction, and Monitoring of Soil Nail Walls” for shotcrete was used. The pool has been holding dirty water since additional guidance. Copies of the ACI 506 series documents just after the shotcrete cured. Does the shotcrete have to be are available in the ASA Bookstore: www.shotcrete.org/ cleaned and/or treated before an overlay is applied? BookstoreNet/default.aspx. Answer: To ensure a good bond between the shotcrete shell Question: What is the R-value per inch for shotcrete without and the overlay, the surface should be cleaned and allowed to any integrated insulation? dry before application of the overlay material. Answer: Shotcrete is concrete, pneumatically applied. So the Question: We are using wet-mix shotcrete for culvert linings, same R-value fire ratings for concrete would apply to shotcrete. with an existing corrugated steel plate pipe stream culvert. The The standard is Joint ACI - TMS 216.1, “Code Requirements pipe is 96 in. (2438 mm) long and deteriorated. There is a water for Determining Fire Resistance of Concrete and Masonry diversion, but there is a pressure gradient forcing water through Construction Assemblies.” the voids. Any ideas on leak repair procedures? Question: My company has been using the gunite process Answer: Installing a shotcrete lining requires a somewhat dry (dry-mix shotcrete) for years now. What I have been finding substrate and certainly is not compatible with running water. lately is that a lot more questions are being asked by outside The water needs to be blocked or diverted. safety services, neighbors to our facility, etc., about the health A means of blocking the inflow is to inject a swellable effects of the shotcrete process. I believe that with the new urethane grout through the openings in the existing pipe. The proposed laws dealing with silica, everyone is paying more grout, if done properly, will expand upon contact with water attention to products with sand and cement, and shotcrete has and seal the outside of the pipe. Another means of diverting both. To try to educate myself and to answer these questions I the water is to install drainage material over the inflowing area am on the search for enlightenment and am coming up short. to collect the water and remove it from the pipe. The shotcrete can then be applied over the drainage material. Here is where I am falling short: there is no (or I haven’t found a) general material safety data sheet (MSDS) on shotcrete. Question: I need to find the reference in ACI standards indi- Most MSDSs I have found on the Internet are for proprietary cating the technical and practical reasons why thermal expan- mixtures. I have yet to find an MSDS or any safety info on just sion joints and contraction settings are eliminated in the plain sand and cement mixture. stabilization of nonstructural slopes covered with shotcrete and steel fiber. Can you help? Answer: Shotcrete is a method for placing concrete, so an MSDS for concrete or its constituent components would be Answer: Shotcrete is a method of placing concrete. Fibrous appropriate. MSDS sheets for cement, aggregates, and concrete shotcrete will have very similar, if not identical, properties as are readily available from cement manufacturers, aggregate fibrous cast concrete. Expansion and contraction joints suppliers, and concrete producers, as evidenced by a simple should be similar in shotcrete to those needed in cast concrete. web search. This is the type of issue that can be discussed and ACI 224.3R-95, “Joints in Concrete Construction,” covers effectively addressed by networking with other contractors and joints in many different applications. The closest relevant suppliers in the shotcrete industry. This is a primary benefit of document for eliminating joints is ACI 360R-10, “Guide to actively participating in ASA—you or your organization should Design of Slabs-on-Ground,” where, in Section 8.3, it states: join ASA and attend committee meetings. ASA meetings are “To eliminate sawcut contraction joints, a continuous held three times a year; the next one is in October and is con- amount of reinforcement with a minimum steel ratio of 0.5% current with the ACI Fall 2014 Convention in Washington, DC. (PCA 2001) of the slab cross-sectional area in the direction where the contraction joints are eliminated is recommended.” Question: We are designing a 41 x 60 ft (12 x 18 m), 2.5 to 4.5 This 0.5% reinforcement is consistent with the provisions ft (0.8 to 1.4 m) deep swimming pool. The walls and floor are of ACI 350-06, “Code requirements for Environmental Engi- 8 in. (203 mm) thick with No. 4 (No. 13) bars. We are specifying neering Concrete Structures and commentary,” for the min- shotcrete to build the pool. What should be the minimum imum reinforcement for temperature and shrinkage without spacing for the expansion joint? contraction joints. You can refer to ACI 506 series documents regarding shot- Answer: You need to address this question to a professional crete, and possibly the FHWA SA-96-069R “Manual for engineer who is knowledgeable in the characteristics of shotcrete 56 Shotcrete • Spring 2014


2014SprShotcreteEMag
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