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2014FallShotcreteEMag

Shotcrete Corner mild steel tanks or they can produce an explosive To get the optimum performance from any type hydrogen gas. of accelerator, it is very important to keep Alkali-free accelerators are made by two temperatures at a reasonable level. Ideally, different processes. The older, more common concrete temperature should be between 70 and method is to dissolve solid flakes into a fluid using 80°F (21 and 27°C) to attain the optimum high-shear mixing. This produces a high-viscosity accelerator reaction. A 20°F (11°C) decrease in product much like the consistency of thick syrup. concrete temperature will roughly double the The solids tend to segregate out during storage so reaction time and conversely, a 20°F (11°C) accelerators made from solids require fairly increase will half it. continuous agitation. This manufacturing method But you also need to keep the accelerator also uses a higher content of solids, making the temperature at an appropriate level. It should be accelerator slightly more reactive than the lower- above 60°F (15°C) and preferably above 70°F viscosity materials. (21°C). If the accelerator is too cold, it will not The lower-viscosity alkali-free accelerators are work nearly as well. Another problem with most made with liquid chemicals that do not require accelerators is that when they are cold, they high-shear mixing and are usually closer to the become more viscous, which makes it even more consistency of water. Although these are slightly difficult to get it mix evenly into the stream of lower in solids contents, they do not segregate at concrete at the nozzle. all and are often said to better blend into the When using accelerator in wet-mix shotcrete, concrete mixture at the nozzle due to the lower make sure to use a proper dosing pump. Do not viscosity, and often being as effective as the use a diaphragm pump. A diaphragm pump higher-viscosity products. sends slugs of accelerator to the nozzle and if Shotcrete • Fall 2014 45


2014FallShotcreteEMag
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