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2013FallShotcreteEMag

Pool & Recreational Shotcrete Corner will subside when thawed, and should not be resistant paper. It is commonly used in swimming shotcreted upon. pool forming and works well for creating curved In areas with relatively stiff soils, earth can profiles. An incorrect practice occasionally seen also be used as the one-sided form for the walls is to install a wood form for the pool beam (top of the pool (Fig. 2). Historically, the residential of pool wall), hang the Steeltex down from the pool has been formed in exactly this way, as an wood form, and then simply tie the Steeltex to the efficient means to construct a pool within the steel reinforcing cage with wire, but with no other reach of the burgeoning middle class. This process support (Fig. 4 and 5). As gunning occurs, the can be quite effective, as it requires less time and impact and weight of the shotcrete pulls on the materials spent excavating and forming, with little reinforcing bar and the wood forms above. This backfill. It does, however, require an excavator incorrect support of the Steeltex leads to poor and dig crew who are experienced in this practice. shotcrete practice as the crew tries to save the Again, loose, soft, or fractured soil should be forms by adjusting the shotcrete flow, which can removed to give the shotcrete a solid receiving surface. Loose sands would not be appropriate for forming pool walls because they cannot stand up to create a vertical surface to shoot upon. Other materials are commonly used for the one-sided forming of the walls. If a material is able to be shaped, and is durable and not detri- mental to the shotcrete process, it probably can be used. Rough-cut lumber, framing lumber, pegboard, plywood, and Steeltex® are among these materials; and many times, more than one material is used to allow creation of curves and add stability to the form. Forming materials are used instead of earth for various reasons. The soil may just be too rocky, leaving large voids and caved-in walls during excavation. The structure may be built above existing site grades due to design choices or building on sloping land (Fig. 3). In some cases, pools are excavated without the earth forming crew being on site, requiring forms to Fig. 2: The rocky soil has been trimmed to accept the shotcreted pool shell be built later. The forms must be constructed in such a way as to provide a solid, stable, nonvibrating sur- face for the shotcrete. Once you realize that shotcrete is being shot out of the nozzle at up to 180 ft/s (55 m/s), you start to understand the need for form strength. Ironically, should the forms be weak or loose, the shotcrete crew may try and reduce the amount of compressed air being delivered, so as to “save” the form. But, in doing this, they fundamentally alter the shotcrete process with a detrimental effect on the in-place quality of shotcrete in the finished project. In some areas, the forms must also be strong enough to carry the static weight of the wet shotcrete once in place. A sloping wall or the bottoms of skimmer boxes are two examples that come to mind. Steeltex deserves special mention. Steeltex is a brand name for a thick-gauge welded wire mesh Fig. 3: A significant set of wood forms, well-reinforced, for a negative- covered with a heavy-duty fiberglass/water- edge pool being built above grade Shotcrete • Fall 2013 57


2013FallShotcreteEMag
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