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2014FallShotcreteEMag

Pool & Recreational Shotcrete Corner Shotcrete versus Cast-in-Place for Pools By Mason Guarino Sthe pool shell structure in swimming pool chosen prior the start of the shotcrete process.-surface that the shotcrete crew places and finishes as they progress. The desired finish ishotcrete and cast-in-place (CIP) concretehave both been used over the years to create construction. Both shotcrete and CIP can produce The most common finish is a standard rod-cut a good-quality finished product with attention to finish. The rod-cut finish produces a straight material selection and placing quality. Concrete and plumb wall with a rough texture. This placed via the wet-mix shotcrete process rather rough texture is optimum for two reasons: than cast would be slightly modified to allow for second to a gun finish, it is the fastest way to lower slump and increased pumpability. The real finish a shotcrete wall; and it creates a great differences in the two placing techniques stand surface to later bond a tile or marcite plaster out during the pool construction phase. The shot- finish. CIP forms can leave two undesirable crete process can shorten construction time, sig- finishes when the forms are removed. There nificantly reduce formwork requirements, can be either excessive honeycombing that eliminate post-form-stripping concrete surface needs to be repaired prior to the final finish, or touchups, create a monolithic structure, and the forms create a smooth finish that will need eliminate the need for additional steps that CIP to be roughened so the final finish will adhere typically requires. properly. Sometimes finishing the final shot- One of the most time-consuming steps in crete surface will require a little more time the concrete construction process is forming. during placement, as compared to surface Forming adds two steps to the pool construc- touchup of CIP, but that is acceptable because tion process: formwork erection before casting, shotcrete finishing produces the desired final and formwork dismantling and cleaning after finish with a more consistent appearance. casting. CIP forming also requires both sides Swimming pool shells are structural con- of the concrete walls to be formed and the crete components and need to be as strong as forms are much more complex because they reasonably possible. Swimming pools are fairly must be designed to handle the high internal short in length and exposed to moisture pressure created by the fluid concrete filling throughout their life, so they do not experience the forms. In comparison, shotcrete requires excessive shrinkage or temperature movement forming only one wall surface and it is much and do not typically require expansion or con- lighter construction because it withstands much traction joints. Because most swimming pools less pressure. Shotcrete forms only need to be do not require movement joints, they can be rigid enough to handle the force of the shotcrete built as monolithic structures. Shotcrete is the spray being applied without excessive vibra- only way to create a true monolithic structure tion. Because the shotcrete forms are only for a pool, especially large pools. Shotcrete, one-sided and less substantial, much less form- when applied properly, has no construction work is required and the form stripping process joints. Swimming pools can take multiple days is much quicker and with less waste (Fig. 1). to finish and, with proper attention to shooting CIP walls frequently require touchups of the pool floor and walls between sections, can water and air bubble voids, or areas that were be constructed as a complete monolithic struc- not fully consolidated at the surface after forms ture. Large monolithic floors can easily be CIP were removed. This is so common that all and then completed with shotcrete walls to specifications now have a section to cover how create a large monolithic pool. Large pools can it should be done properly. With shotcrete, the easily have 300 to 600 yd3 (229 to 459 m3) just final finished surface is the same exposed in the floor, and with a good flatwork crew, can 42 Shotcrete • Fall 2014


2014FallShotcreteEMag
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