Page 16

2013SprShotcreteEMag

Fort Mchenry Tunnel Miscellaneous Structural Repairs By John Becker AMcHenry Tunnel in Baltimore, MD, was (50 mm) cover over the reinforcing steel,Gunite using the wet-mix shotcrete method. Theshotcrete needed to maintain a minimum of 2 in.t the time of its construction, the widestunderwater tunnel in the world, the Fort opened to traffic in 1985. It houses Interstate necessitating that it be built out past the surface Route 95 as it travels under the Baltimore Harbor of the existing concrete sections in most places. and is operated and maintained by the Maryland It was given a fine brush finish. Because of the Transportation Authority. In 2011, Coastal Gunite inconsistent and limited access times for construction, Construction Company was given the task of a preblended, dry material bag mixture provided repairing spalled and delaminated concrete areas by US Concrete Products was batched on site. of the two southbound bores on the underside of Batching on site also allowed Coastal Gunite to the road deck and other areas in the fresh air duct accurately optimize the water-cement ratio (w/c) that runs beneath the roadway (Fig. 1 and 2). for the placement needs. Minimizing exposure of the ventilation fans to Because of the high volume of material and dust was a prime concern during the execution of short working time available, the debris generated these repairs. The bulk of the concrete was from the hydrodemolition and shotcrete activities removed using hydrodemolition by Rampart had to be handled and removed using small equip- Hydro Services with a rig specially designed to ment and a great deal of labor through the few maneuver and work in the small space of the duct. available manholes (Fig. 3 and 4). Wastewater The repair areas ranged in depth from 1 to 6 in. generated by the hydrodemolition and shotcrete (25 to 150 mm) depending on the extent of the activities had to be collected and properly treated deterioration and corrosion present. The to prevent negative environmental impact. hydrodemolition process also roughened the The Maryland Transportation Authority existing concrete surface sufficiently such that no provided traffic control for the project. All work additional roughening was required. was done at night and required the closing of one As another way to minimize dust, the damaged bore of the tunnel at a time. Because the tunnel concrete of the structure was replaced by Coastal is such a vital traffic artery, the entire repair Fig. 2: Underside of road deck prior to Fig. 1: Mobile shotcrete equipment in tunnel (work is underneath road deck) rehabilitation activities 14 Shotcrete • Spring 2013


2013SprShotcreteEMag
To see the actual publication please follow the link above