Award of Excellence: Longevity Category
Montgomery County Underground Garage Restoration
Submitted by Carl Walker, Inc.
Montgomery County of Public Works
Carl Walker, Inc.
Lithko Contracting, Inc.
Flow Services Corporation
The 450-space Montgomery County Administration Building Parking Garage, constructed in 1970, consists of three below-grade parking levels. The overall dimensions of the facility are 181 x 308 ft (55 x 94 m). The total supported slab area measures approximately 94,000 ft2 (8735 m2). The structural slab system consists of 10 in. (25 cm) thick conventionally reinforced concrete two-way flat slabs.
Chain drag sounding indicated extensive top of slab delaminations over 25% of the floor area. Excavation areas revealed over 50% loss of cross-sectional steel area due to corrosion. The concrete was heavily contaminated with chloride and was marginally air entrained.
The county intended to occupy the building for another 30 years. Hydrodemolition was used to remove all delaminated concrete areas and to prepare the remainder of the surface for the new concrete overlay. The innovative repair approach of cathodic protection with a bonded concrete overlay provided a cost-effective long-term approach.
Successful performance for 13 years and counting! The cathodic protection system was set up to be monitored remotely, every quarter, for performance. The successful performance was supported in the field chain drag and sounding reviews in 1998, 2001, and 2004. No areas of corrosion induced deterioration of the top of floor and ceiling was noted and only minimal areas of topping debonding. The installation of a high quality concrete overlay over the poorly air entrained concrete has also prevented any further freezing-and-thawing deterioration.
The project was completed in February 1994 at a construction cost of $1.30 million dollars, 15% below the construction budget.