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repeated projects, provided by King, verified that not only could dry-mix shotcrete be air-entrained but also results of freezing-and-thawing salt-scale testing were dramatically improved when compared with non-air-entrained drymix shotcrete. Among the many challenges faced by the contractor on this project was dealing with high-level security throughout the facility. Construction workers, equipment, and material delivery trucks had to pass through mandatory security checkpoints to make sure no illegal contraband was being smuggled into the prison. All workers were required to sign in and out and wait for a security guard to be escorted to the work area. Each work area was monitored by a trained, high-level security team. SCOPE OF WORK The shotcrete portion of the work required removal and replacement of deteriorated concrete on both inside and outside of the perimeter walls. The original scope called for the removal of 32,000 ft2 (3000 m2) of concrete at an average depth of 4 in. (100 mm). Hydrodemolition was used to remove the deteriorated concrete and prepare the concrete surface. This removal method was chosen because it would provide an ideal surface for the shotcrete material to bond to and minimized microcracking that often accompanied the use of conventional mechanical chipping equipment. The original concrete mixture was produced using very large aggregates 1 to 1.5 in. (25 to 38 mm) in diameter. Special attention to the removal was critical to make sure that any large stone that was exposed would stay intact and not loosen because that could potentially create a bonding issue. During the demolition phase, it was revealed that the depth of deterioration was far greater than expected. In some cases, the outside of the perimeter wall had sections that required up to 18 in. (450 mm) of concrete removal. Apparently, the hydrodemolition equipment penetrated much deeper into the poor-quality concrete than originally expected. Thus, a special depth gauge was eventually used to maintain the proper depth of concrete removal. The specification also called for the installation of a 4 x 4 x W2.9 x W2.9 (102 x 102 x MW18.7 x MW18.7) galvanized wire mesh mounted every 20 in. (500 mm) center-to-center. In one particularly large section, approximately 10,000 ft2 (930 m2) of the inside of the perimeter wall, the specification called for removal of the light scaling from the concrete surface and to repair with conventional hand-applied mortar. Geniex initiated conversations with King Shotcrete Solutions to investigate an alternative using the high-velocity dry-mix shotcrete to shoot and finish a thin layer of shotcrete and create the same look as the original construction. The engineer accepted the proposal after it was explained that the extremely strong bond between the shotcrete and the parent concrete would ensure a longer life and help minimize the progression of corrosion that had begun. However, this portion of the work was put off until the next phase of repairs. Fig. 1: Hydrodemolition machine setup Fig. 2: Close-up of hydrodemolition concrete ready for shotcrete Fig. 3: Repairs ranging from 2.5 to 18 in. (64 to 450 mm) www.shotcrete.org Winter 2017 | Shotcrete 23


2017WinterShotcreteEMag
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