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2014SumShotcreteEMag

Concrete Institute: CP-60 (02), Nozzleman Cer- tification; 506R, “Guide to Shotcrete”; and 506- 4R, “Guide to Evaluating Shotcrete.” These publications defined the intended strengths and characteristics of properly placed concrete and completed the process of education we’d begun when our meeting started. But while the project team knew a good bit more now than they had before, they were still hesitant to go out on a limb—either for me or for shotcrete—so I ended up taking that big step for them. In retrospect, my proposal was really quite bold: We would guarantee that the pool would reach a defined minimum-acceptable concrete strength in 28 days and that the shell would be demonstrably watertight before finish applica- tion—all without any water- or damp-proofing agents. If those criteria were not met, we would rip the pool out and proceed anew with cast-in- place materials. Basically, they couldn’t lose and had lots to gain, so the design team ultimately awarded the job to us and the shotcrete process we advocated. On Site at Last By that time, the old facility had been razed, leaving all of us to start with a blank slate. Many trades were to be working on site for the duration of the project, so one of the primary challenges was working with and around the scheduling of other activities—a calendar that involved sporadic stops and starts. As it turned out, we were first to get going, based on the concept that whoever goes deepest goes first. We began with extensive excavation, The finished pool is a triumph on all levels—and testimony to the fact that and then installed a drainage/dewatering system shotcrete, when applied (as it should be) according to basic concrete- to take care of any potential issues with the water industry standards and procedures, produces non-porous, ready-to-finish table. Next, we installed a base of gravel atop surfaces that truly hold water which we began installing construction forms, steel, and pool plumbing. We started in the radius sections where the All forms included solid, non-vibrating mem- walls and floor met to establish critical transition bers to eliminate the possibility of inviting any points, then shot the floor in sections. We chose voids or shadowing in shotcrete application. to work with the wet-shotcrete process rather than Once that was complete, we installed the steel the dry-shotcrete (gunite) process because we had reinforcement for walls and floors that were to some control over the environment, and could be 12 in. (305 mm) thick with offset, double easily apply a high volume of material without mats of No. 5 and No. 4 (No. 16 and No. 13) straining our finishers and while achieving the bars set at 12 in. (305 mm) on center. We used specified minimum strengths. PVC chairs and wheel spacers for proper rein- Once in the pool, we consolidated and leveled forcing bar separation and full concrete cov- off each shot section with a power screed and then erage, and set guide wires for elevations, the applied a light broom finish. Everyone was well multiple levels of the bond beam, the floor’s aware that the pool was to be lined with 1 in. slope, and the walls’ radiuses. (25 mm) square tiles, so critical tolerances were In all, the application required 350 yd3 (268 m3) maintained throughout. After each day’s shoot, of material applied in 7 days of shooting spread we’d place soaker hoses to keep the concrete in a out over ten days in all. The mixture design was saturated condition. This allowed the mix water to set to achieve a minimum strength of 4000 psi stay within the concrete matrix, thus encouraging (28 MPa) after a 28-day wet cure. optimal strength gain with no surface evaporation. Shotcrete • Summer 2014 13


2014SumShotcreteEMag
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