THE CONCRETE BRIDGE MAGAZINE

SPRING 2018

ASPIRE is a quarterly magazine published by PCI in cooperation with the associations of the National Concrete Bridge Council. The editorial content focuses on the latest technology and key issues in the Concrete Bridge Industry.

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STATE Maryland by Jeffrey Robert and Justin Mohr, Maryland Department of Transportation Maryland is located on the East Coast of the United States and shares its borders with four states and the District of Columbia. The state is often referred to as “America in miniature,” because of its varied terrain and climates, its role in American history, and the diversity of its residents. Western Maryland is rural and mountainous and experiences heavy snow in the winter. Central Maryland is densely populated, has moderate snowfall in the winter, and experiences extreme heat in the summer. Eastern Maryland has a mix of rural and urban areas, and the Atlantic shoreline is extremely flat. The eastern region experiences minimal snow accumulation but is occasionally affected by hurricanes. The highway system maintained by the Maryland Department of Transportation State Highway Administration (MDOT SHA) has 2567 bridges, including 511 concrete beam/girder superstructures. In general, the MDOT SHA Office of Structures uses concrete superstructures for bridges over any body of water. The type of beam or girder used at a given location depends on the span length. Bridge Specifications and Policies For water crossings spanning less than 55 ft in length, prestressed concrete slab panels are the “go to” bridge type for two reasons. First, this bridge type lends itself to accelerated bridge construction. The superstructures consist of 3- or 4-ft-wide prefabricated, prestressed concrete solid slab elements. Each slab panel must be fabricated using self-consolidating concrete with a required 28-day compressive strength of 8 ksi. Once all the slab panels are set, the slabs are transversely post-tensioned together so the slabs will act in unison. To provide a smooth riding surface, a 5-in.-minimum thickness concrete overlay with synthetic fibers and with either epoxy-coated or polymer-fiber reinforcement is placed. The railing is typically a prefabricated metal railing bolted to the superstructure. The second reason that the slab-type structure is the preferred bridge option for Maryland’s small water crossings is because it can provide a relatively maintenance-free bridge for the life of the structure. MDOT SHA has set the minimum clear cover to the prestressing strands at 3 in., providing extra protection for the one element that could potentially corrode if exposed to chlorideladen water. The structures are also constructed without joints. The elimination of the joints protects the abutments from potential exposure to chloride from roadway deicing salts. The substructures for these shorter bridges vary based on the site location and conditions. Both precast concrete and cast-in-place concrete elements have been used. Every summer, three or four of these slab-type bridges are constructed in Maryland under a complete road closure and detouring of traffic. The prefabricated elements allow for the complete replacement in fewer than 10 weeks, which means the roadway is open to traffic before schools open in the fall. For larger water crossings requiring greater than 55-ft span lengths, MDOT SHA uses precast concrete economical fabrication (PCEF) bulb-tee prestressed concrete girders. Like its prestressed concrete slabs, Maryland’s PCEF girders are fabricated using self-consolidating concrete with a required 28-day compressive strength of 8 ksi. The use of the PCEF girders is common in many states across the country. Some of the policies and practices that MDOT SHA has adopted regarding these beams are described here. In response to the concerns raised during years of field inspections about problematic details, MDOT SHA adopted policies to reduce maintenance requirements for the prestressed concrete girders used in bridges. Prestressing strands are not debonded, and the minimum concrete clear cover on the bottom of girders has

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