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2015SummerShotcreteEMag

Nozzleman Knowledge shotcreting vertical walls in hot weather allows it even easier, there are devices available that for rapid vertical application because the lower measure these variables and then calculate the lifts set quickly. Although, for overhead work, results automatically. Having the materials needed you may still find accelerators beneficial. for onsite evaporation control is important to Low relative humidity and high wind speed protect the fresh concrete and prevent the rapid also need to be addressed. Many contractors today evaporation of free water when it is deemed nec- are familiar with the graph originally published essary under the conditions outlined in Section by the Portland Cement Association that can now 3.1.3 of the ACI 305 document. One of the be found in the ACI 305.1-14 (Fig. 2). This is a methods for doing this is the application of liquid very useful tool. It not only tells what influences membrane curing compound. Another method is moisture loss, but it also quantifies the effects, water curing, which is simply the continuous with the rate of moisture loss being affected by application of water. For horizontal surfaces the in-place concrete temperature and the flooding works well, if it can be done. With ver- humidity. Using this simple graph will give an tical surfaces, covering the work with clean, used idea of the rate of water loss. For those who want carpets is another way to keep the fresh concrete moist. The big advantage of water curing is the additional benefit of evaporative cooling. In cases where compound cure or water curing are not allowable options due to the necessity of subse- quent work such as staining or adhesive applica- tion, covering with tightly sealed polyethylene sheeting is another option. This membrane will keep the moisture in and mitigate the effect of moisture loss due to wind. When all the various project and material conditions, and their potential for problems, have been taken into account and addressed, the likelihood of a durable, safe and profitable completed project increases tremendously. Ultimately, isn’t that the result the owners, engineers, suppliers, specifiers, contractors, and inspectors who make up the shotcrete industry strive to provide for their clients? References ACI Committee 305, 2014, “Specification for Hot Weather Concreting (ACI 305.1-14),” American Concrete Institute, Farmington Hills, MI, 7 pp. Andrea Scott is the Director of Safety and Quality Control for Hydro-Arch, Henderson, NV. She has over 20 years of experience in the construction industry with a background in special inspection of rein- forced concrete, reinforced masonry, structural steel and welding and non- destructive testing. She is an active member of ASA, currently serving on the Board of Direction Fig. 2: Effect of concrete and air temperatures, relative humidity, and and as Chair of the Safety Committee. Scott is wind speed on the rate of evaporation of surface water from concrete also a longtime ACI member and is the Vice (ACI Committee 305 2014) President of the Las Vegas Chapter – ACI. 34 Shotcrete • Summer 2015


2015SummerShotcreteEMag
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