High Performance Concrete Specifications and Practices for Bridges. A Synthesis of Highway Practice.

摘要

Specifications for concrete to be used in bridge structures have traditionally been prescriptive in nature, meaning that the constituent materials of the concrete and their relative proportions are stated like a recipe for a cake. In the 1990s, FHWA began to introduce the concept of performance specifications, which designate required results rather than means. FHWA suggested eight performance characteristics that could be quantified using standard tests, four related to concrete durability and four related to concrete strength for structural design. The durability characteristics were intended to increase the service life of the concrete, in particular, bridge decks, which have always been the Achilles heel of bridges. The structural design characteristics related to the applications of high-strength concrete, which allows the use of longer span lengths; wider girder spacings and fewer girders; shallower girders; or a combination of these, resulting in more economical structures. This material was called high performance concrete (HPC). State transportation agencies adopted these characteristics for concrete in bridges to varying degrees. State documents for bridges generally include standard specifications, supplemental specifications, and special provisions. The standard specifications document is used for all projects. It may be updated periodically through the use of supplemental specifications or through the issuance of a revised document. Special provisions are issued to define the requirements for specific projects. This last type was used by those states that initially moved forward with the HPC concept. Since then, some states have begun to require HPC in their standard specifications, while others have changed their prescriptive specifications as a result of experience with HPC (although the concrete may not be called HPC). The primary objectives of this synthesis are to document the types of specifications and practices used by state agencies to produce HPC, and to identify specifications and practices reported as having improved concrete performance and those that have not.