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Nozzleman Knowledge the formwork, reinforcement, and other surfaces that contact fresh concrete so the temperature of the freshly placed concrete will not decrease below the minimums as placed and maintained found in Fig. 5. There are many techniques for warming formwork, mixing water, concrete materials, and embedded items. This may include one or more approaches, such as heated enclosures, electric blankets, hydronic heating systems, forced air heat, or other acceptable systems. Other methods of accelerating concrete reaching the 500 psi (3.5 MPa) threshold against freezing damage can be provided by concrete mixture acceleration, such as a chemical admixture, decreasing the w/cm, increasing the cement content, pozzolan quantity, cold weather admixtures, or going to a Type III cement (high early). Figure 6 shows the safe differential temperatures for walls as found in ACI 306R-10. Chapters 8 through 11 in ACI 306R-10 provide much greater detail on protection, curing, and acceleration of concrete set and strength, along with many helpful graphs dealing with different exposure temperatures. When setting up a project, one has to weigh the costs for cold weather shotcreting to see if it is worth the money spent. Some projects have no choice and run right through the winter. Safety of the crew comes first; the added wear and tear on the equipment—as well as the winter protection and heating costs—all play an important role in deciding to continue work or shut down for winter. Since shotcrete is just a placement method for concrete protection and curing of shotcreted sections is the same as for concrete in the winter. References ACI Committee 306, 2010, “Guide to Cold Weather Concreting (ACI 306R-10),” American Concrete Institute, Farmington Hills, MI, 26 pp. ACI Committee 306, 1990, “Specification for Cold Weather Concreting (ACI 306.1-90) (Reapproved 2002),” American Concrete Institute, Farmington Hills, MI, 5 pp. ACI Committee 506, 2013, “Specification for Shotcrete (ACI 506.2-13),” American Concrete Institute, Farmington Hills, MI, 12 pp. ACI Committee 506, 2005, “Guide to Shotcrete (ACI 506R- 05),” American Concrete Institute, Farmington Hills, MI, 40 pp. Mustard, J.N., and Ghosh, R.S., 1979, “Minimum Protection and Thermal Stresses in Winter Concreting,” Concrete International, V. 1, No. 1, Jan., pp. 96-101. Ray Schallom III is an underground shotcrete application specialist and President of RCS Consulting & Construction Co., Inc. He has 40 years of experience as a Project Manager, Owner, and Superintendent. Schallom works with State DOT departments with their shotcrete specifications and trains engineering companies’ inspectors in the field of shotcrete. He is a Past President of ASA, past Chair of the ASA Education Committee, and is a member of the ASA Publications, Underground, Marketing, Sustainability, and Pool & Recreational Shotcrete Committees. Schallom is also a member of ACI Committees 506, Shotcreting, and C660, Shotcrete Nozzleman Certification, and ACI Subcommittees 506-A, Shotcreting- Evaluation; 506-B, Shotcreting-Fiber-Reinforced; 506-C, Shotcreting-Guide; 506-E, Shotcreting-Specifications; 506-F, Shotcreting- Underground; and 506-G, Shotcreting-Qualification for Projects. Schallom is a retired ACI Certified Nozzleman in the wet- and dry-mix processes for vertical and overhead applications with over 40 years of shotcrete nozzling experience in wet- and dry-mix handheld and robotic applications. He is an ASA-approved ACI Shotcrete Examiner for wet and dry applications. Schallom is also a member of ASTM Committee C09, Concrete and Concrete Aggregates, and ASTM Subcommittee C09.46, Shotcrete. 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 54 Shotcrete • Spring 2016


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