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Shotcrete FAQs enhanced liquid-tightness or resistance to aggressive environ- a) Will the shotcrete elements installed in separate layers over mental exposures. The test is sometimes used to provide an the entire roof and perimeter wall system act as effectively overall indication of the quality of the shotcrete mixture, par- as elements that have been shotcreted in one layer? ticularly in dry-mix. However, many factors, including admix- b) Will bonding between layers under gravity be a concern tures and aggregate, as well as shotcrete placing, can affect the during the curing process under the dome roof? porosity of shotcrete, so it should not be considered an absolute c) Would alternate types of construction joints be more measure of shotcrete quality. When required, the mean average advantageous in fabrication of the wall and dome roof? of tests on three specimens from a test panel, or from in-place d) Would any admixtures be recommended for this application? shotcrete, should be less than or equal to the specified boiled absorption and/or specified volume of permeable voids limits Answer: at the specified test age with no single test greater than the a) The shotcrete will act as a single layer when it is finished. specified boiled absorption plus 1%. The bond between rough layers of shotcrete is very good. This has been documented in research done at Brigham Question: We are evaluating a school building with a 4 in. Young University. (102 mm) thick dome roof with a diameter of 120 ft (37 m) b) No, bonding will not be a concern because, as indicated bearing on a 5 in. (127 mm) thick perimeter shear wall. The previously, the shotcrete bond between layers is excellent. roof is constructed by anchoring a membrane to the top of an c) No, other types of construction joints are not really viable. exterior finish wall, inflating the membrane, shooting foam This is the best procedure to construct a shotcrete dome. insulation to both the interior wall and membrane surfaces, d)No admixtures are specifically required. Use of silica fume and then shotcreting both the wall and roof structural ele- (microsilica) as a supplemental cementitious material ments. The contractor specifies to shotcrete only half of the may be advantageous in shooting overhead. An experi- concrete thickness of the walls and roof, install the rein- enced shotcrete contractor would identify whether use of forcing, and then shotcrete the remaining wall and roof to silica fume or accelerator are appropriate for their materials finish thickness. and equipment. Sustainability of Shotcrete S strategies. “Sustainability of Shotcrete” is a timely and valuable resource Sustainabilityustainability continues to grow as a driving force in the decision makingof Owners and Specifiers regarding construction materials and placement to promote the shotcrete process and educate potential clients and owners. The of Shotcrete document can also be submitted with project bids to identify and substantiate the sustainability advantages of the shotcrete process. This 10-page, full-color brochure identifies and discusses the numerous shotcrete sustainability advantages and also includes case studies demonstrating these advantages in both new construction and repair. The brochure’s content was originally developed by the ASA Sustainability Committee for use in the United States Green Concrete Council (USGCC) book titled The Sustainable Concrete Guide—Applications. The full book can be ordered from www.concrete.org. Copies of “Sustainability of Shotcrete” can be ordered from the ASA Web site at www.shotcrete.org or by calling 248-848-3780. For orders outside of North America, please contact ASA directly. Order Code: SUSTAIN The brochure is also sold in The brochure is also sold in ASA Members: $4.95 bundles of 10 bundles of 25 Nonmembers: $6.95 ASA Members: $39.95 ASA Members: $69.95 Nonmembers: $54.95 Nonmembers: $99.95 Shotcrete • Winter 2014 71


2014WinShotcreteEMag
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