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2013SprShotcreteEMag

Fig. 5: Placing overhead wet-mix shotcrete Fig. 6: Completed ceiling and wall rehabilitation operation had to be designed so that, if necessary, unfinished. Ultimately, after we completed the the job site could be vacated and the bore reopened first phase, two additional phases were added to within 30 minutes. To accommodate this require- complete the project. The third phase has not yet ment, all necessary equipment and materials been completed. By placing the 23,600 ft3 mobilized in the roadway were mounted to and (668 m3) of concrete using the wet-mix shotcrete used from trailers or vehicles, enabling them to method, the repairs were completed much faster be removed quickly. All equipment left in the air and more efficiently than possible with other duct had to be fully secured as well. Liquid accel- methods. This construction efficiency and flexi- erator was used in the shotcrete mixture to guar- bility convinced the Maryland Transportation antee that the repair material would reach initial Authority that shotcrete was the method of choice set before traffic resumed in the bore. for the rest of the needed repairs in the tunnel. An unanticipated difficulty arose, as it was found that the water piping and electrical utilities encased in the concrete walls on both sides of the fresh air duct were heavily corroded. Removal of the deteriorated and corroded materials without John Becker is an ACI Certified causing further damage to the equipment while it Nozzleman who, for the last was in use required delicate use of hand tools. 5 years, has worked in many Much of the replacement reinforcing steel used capacities—most recently as on the project went into these areas, as total cor- Project Manager—for Coastal rosion of the existing reinforcement was common Gunite Construction Company (Fig. 5 and 6). based in Cambridge, MD. In The extent of necessary repairs significantly addition to the Fort McHenry increased from the initial estimates the contract Tunnel, he has been involved with many shotcrete for the project was based on, requiring substantial projects large and small, including the $15 million additional work in some areas. Thus, the decision Bonner Bridge Rehabilitation Project in Nags was made to exhaust the original funding Head, NC, and the $5 million Old Mill Creek designated for the project and leave the work Sewer Rehabilitation Project in St. Louis, MO. 16 Shotcrete • Spring 2013


2013SprShotcreteEMag
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