Simple, solid rectangular prestressed concrete slabs are being used in Maryland to replace structurally deficient bridges on rural collector roads. Most of the replacement bridges are for stream crossings on 20- to 40-foot spans. Three primary factors led the Maryland Department of Transportation (DOT) to choose the precast slab alternative:
- construction time
- high quality of the components
- long service life with low maintenance
Precast concrete presents a structural system that can be completed quickly while minimizing traffic disruption. Maryland DOT officials also have found that precast superstructure slabs offered high quality at an economical cost because producers had quality-control procedures in place for plant production. Finally, bridges that use these precast slabs could remain in service for 75 to 100 years with little or no cost for maintenance. The Maryland DOT chose a system of 3- or 4-foot-wide precast prestressed slab units, placed adjacent to each other and post-tensioned laterally in place. Once the post-tensioning is completed, a cast-in-place riding surface is placed on top, and a safety curb and steel railing are added. Although the solid section may be less efficient structurally than voided slabs, DOT officials chose it for durability. Maryland's experience with voided slabs has shown that they deteriorate quickly in the void area due to chloride-penetration from deicing salt. The solid slab method of construction offers a speed and ease of construction unmatched by alternative methods, according to John W. Narer, design project engineer for the Maryland DOT. Speed of construction helped to reduce overall construction costs, and Maryland highway officials consider the solid slab bridges very economical to build.The included table compares costs of Maryland's precast prestressed slab bridge superstructures.