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2013SprShotcreteEMag

Pool & Recreational Shotcrete Corner • All of these preparations should be inspected and verified prior to the shoot. What happens if you get these basic measures wrong? If you have movement of a pipe or a piece of steel, you’ll leave a shadow or gap in the concrete which increases porosity and permeability. This can also lead to cracking. In that scenario, even if the shotcrete applicator has done everything correctly, delivering concrete that measures 4000 psi 1.3 MPa on a compression test, the flawed preparation results in an unsound structure, which in turn leads to surface failures or water loss. Bottom line: Proper substrate, plumbing and steel preparation are essential to create a reliable concrete shell, no exceptions! During The Shoot Let’s assume everything is right prior to the shoot, all verified and built to spec, the substrate is dry, free of debris, etc. Unsurprisingly, the application process also comes with an important checklist. • First, be sure you have the proper equipment for the shoot. As mentioned at the outset of this discussion, undersized compressors represent one of the most common mistakes. Be sure the unit you’re using can deliver that all-important (and highly recommended) 250 CFM (425 m3/h) minimum for wet (shotcrete), or 700 CFM (1200 m3/h) for dry (gunite). You can never really have too big a unit, because to compensate, you’ll merely have to either step back or turn down output. Inadequate CFM is always, always the problem! In addition, you have to be sure the pump for wet mix or gun for dry mix respectively have the capacity or ability for the shot process. • Equipment setup is crucial in that you want it as close to the shoot as possible. When you close the gap between the pump and where the material comes out of the nozzle, everything works better and more efficiently. In the pool industry we’re doing small-line pumping, meaning we’re working with 2-inch (5 cm) hoses, pumping or gunning between 8 and 10 yd3 (6 to 8 m3) of concrete per hour. When you are forced to shoot for distances of more than 100 ft (30 m), you have to account for the loss of velocity that takes place due to the friction inside the hose, as well as diminishing air pressure and changes to the concrete mix that After placement, the success of the project depends on crucial details occur over long distances. including “cutting” the interior structures to their exact specified shapes When the wet mix concrete is pumped a long and wetting the concrete as it cures distance and the heat from friction builds, the 34 Shotcrete • Spring 2013


2013SprShotcreteEMag
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