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2014FallShotcreteEMag

Shotcrete FAQs formwork design, unbalanced loading on the dome by shooting you have engaged an engineer, we would suggest you follow very thick sections adjacent to sections not yet shot would be his advice and he should determine the thickness required. a potential concern. Providing a row of dowels around the stem wall to tie the For more information on the performance of shotcrete in shotcrete to the wall should eliminate any significant separation layers, you can review a recent article in Shotcrete magazine, between the shotcrete and the stem wall. Shrinkage of concrete “Shotcrete Placed in Multiple Layers does NOT Create Cold between the walls may cause some minor hairline cracking, Joints,” at www.shotcrete.org/media/Archive/2014Spr_ but nothing to allow ingress of rodents or insects. TechnicalTip.pdf. Question: We have a client who is looking to make a relatively Question: I am searching for criteria/guidelines or ratings on deep cut in a mixture of soils and rock (approximately. 50 ft what different profiles are achieved by shotcrete. I am hoping 15.2 m high, maximum; the structures will be placed on a there are installed shotcrete profile requirements with respect pad at the bottom of the cut). We are looking to provide a to final surface roughness. We manufacture a waterproofing shotcrete facing for the entire cut area. system and are often asked to be installed over shotcrete, to The upper portion of the cut will be in soil; therefore, the which we have no objections. However, I am hoping there are design of a soil nail wall with temporary and permanent facing criteria/guidelines/ratings on achieved profile of the finished in the soil region seems to be relatively straightforward using surface. For example: The concrete industry often talks about design guidance in FHWA publications, Geotechnical Engineering roughness achieved by shotblasting and the surfaces getting Circular #7, and some software programs. Significant portions to various degrees between CSP-1 to CSP-9. of the exposed cut face, however, consist of nondurable bedrock Is there a criteria/guideline/rating system, or something (claystone). We want to stabilize this area with shotcrete to similar with shotcrete? Here is the link to what I am talking prevent weathering and the generation of overhang conditions about: http://shotblastinc.com/industry-guidelines. where the claystone is overlain by a more durable sandstone. I have been unable to find design procedures or guidance Answer: Shotcrete is a method of placing concrete. The surface on specifying shotcrete (thickness, reinforcement type, etc.) and texture of roughness varies considerably depending on the whether or not rock bolts should be used. If so, how do you application and the abilities of the installer. The surface can select the size, spacing, resin type, etc.? vary from a rough nozzle finish to a smooth trowel finish and many variations between these two extremes. In buildings, the Answer: Soil and rock stabilization is an excellent application typical finishes are wood float, rubber float, or trowel finish. for shotcrete. However, ASA as an association does not provide The owner and the architect determine what finish will be engineering design. We recommend consulting with a geotechnical required and generally specify the finish in the construction engineer familiar with the local geology and soil conditions to documents. The documents which might be of help to you are evaluate potential lateral earth forces from the claystone. Once ACI 506R, “Guide to Shotcrete,” ACI 301, “Specifications for potential loads are established, a consulting engineer experienced Structural Concrete,” and ACI 117, “Specification for Tolerances with shotcrete in soil nailing applications will be able to design for Concrete Construction and Materials.” the soil nail facing. You can check our online Buyers Guide at www.shotcrete.org/BuyersGuide to find a consulting engineer Question: An inspection report on our home indicated there experienced with shotcrete. was evidence of past rodent infiltration. An engineering consulting firm recommended that, to prevent rodents from burrowing Question: I need to know about use of carbon fiber in shotcrete. underneath the foundation, we have a contractor apply shot- Would you please inform me about some resources? Is carbon crete across the entire crawlspace bottom, then have a 2 oz. fiber suitable for shotcrete? (60 mL) vapor barrier installed on top of it. The barrier would be glued or taped up the sides of the crawlspace. Answer: We would suggest that you refer to an ACI document, As there is some shrinkage of the concrete during the curing ACI 506.1R, “Guide to Fiber-Reinforced Shotcrete” (available process, I would expect creatures could later emerge between here: www.shotcrete.org/BookstoreNet/ProductDetail. the shotcrete and crawlspace sides. Have you heard this type of aspx?itemid=506108). Carbon fibers are suitable for use in shotcrete application in a crawlspace as a structural pest barrier? shotcrete in suitably designed mixtures. What thickness should the shotcrete be? Is this use of shotcrete effective? Are there any potential drawbacks to using shotcrete Question: I own a home on a very busy street and the house in this way, such as possible problems with the house later on? placement borders the street, approximately 75 ft (23 m) from the curb. Traffic flow has increased over the past year, and I Answer: Shotcrete is a method of placing concrete and the have tried all suggested and approved soundproofing wall properties of shotcrete are equivalent to those of cast concrete. systems with varied results. The type of work you are describing is done in many cases with It would seem that a shotcrete product sprayed within a wall the shotcrete process and is commonly called “ratproofing.” As cavity would work great. My assumption is that I would need 64 Shotcrete • Fall 2014


2014FallShotcreteEMag
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