Section 4, Concrete Structures, of the AASHTO LRFD Bridge Design Specifications, Third Edition permits the use of design concrete strengths above 10.0 ksi when allowed by specific articles. This provision was introduced to allow the results of ongoing research projects to be introduced into the specifications when the research is completed. The eventual goal is to extend all articles of Section 5 to a design concrete strength of 15.0 ksi or higher. To date, revisions based on the FHWA project entitled "Compilation and Evaluation of Results from High Performance Concrete Bridge Projects" and NCHRP Project 18-07 on prestress losses have been approved by AASHTO. Ongoing NCHRP projects that will result in additional proposed revisions are 12-56 on shear, 12-60 on bond and development length, and 12-64 on flexure and compression. When these projects are complete and the results incorporated into the specifications, the major articles in Section 5 will be applicable to concrete compressive strengths of 15 ksi or higher. The next step is to identify the additional research needed so that the whole of Section 5 can be made applicable to design concrete strengths up to 15 ksi or higher. After that, a research program can be formulated to address the necessary topics including those not addressed in the ongoing NCHRP projects.

The project is complete. Recommendations for specification changes were considered by the AASHTO Highway Subcommittee on Bridges and Structures (HSCOBS) during their annual meeting in July 2007 and additional revisions will be considered in 2008.