Louis N. Triandafilou, Federal Highway Administration
Since the initiation of the AASHTO/SHRP Lead States Team concept for high performance concrete (HPC) over 10 years ago, there has been an aggressive effort by the concrete industry, State DOTs, and the FHWA to achieve nationwide implementation of HPC on bridge projects. Outstanding progress has been made in response to the FHWA Executive Director’s 1997 challenge to construct at least one HPC bridge in every state by HPC Bridge Views has reported on many of these projects as well as the efforts of the FHWA’s HPC Technology Delivery Team to keep HPC in the forefront.* Recently, the Team conducted a 14-question national survey to track this progress and other related concrete issues.
On a preliminary basis, the map indicates which states have included HPC in bridge specifications in the last 10 years. Thirty-seven respondents selected HPC for low permeability, 30 for high strength, and 26 for both performance criteria.
As background on why HPC was being used, respondents ranked deck cracking at ages less than 5 years as the most common distress, followed by corrosion of reinforcing steel, cracking of girders and substructure elements, and freeze-thaw damage.
Preliminary results also indicate that, over the past 10 years, 77 percent of the respondents have made changes in their bridge deck curing requirements, 72 percent have made changes in their specified concrete strengths, and 64 percent have made changes in testing and acceptance requirements. Lightweight concrete has been used by 26 percent of the respondents, and self-consolidating concrete used on a limited basis by 36 percent. Admixture usage and specified permeability values are summarized in the tables below.
Deck concrete curing requirements have received much attention, particularly with increased usage of HPC. Seventynine percent of the respondents include these requirements in their specifications. Fifty-five percent are using curing compounds, 49 percent are using a fog mist, 60 percent are using wet burlap for periods of 3 to 14 days, 45 percent use an evaporation rate limit, and 87 percent specify an overall minimum curing time.
In summary, the state DOTs have made an enormous amount of progress over the past 10 years with implementing some form of HPC into their everyday usage on concrete bridge projects. They have taken advantage of the benefits related to higher strengths for prestressed concrete girder elements, and improved durability for reinforced concrete bridge decks. The widespread national use of this technology is consistent with industry, state, and FHWA goals of mitigating congestion and improving safety at construction sites. HPC addresses these goals by extending bridge service life, reducing costly maintenance activities, and lowering life cycle costs.
Further Information
Results are being compiled and will be summarized in detail on a CD for distribution in the near future, plus posting on the Team’s website at: http://knowledge.fhwa. ot.gov/cops/hpcx.nsf/home. For questions or comments about the article, contact the author at [email protected] or 410-962-3648.
The author wishes to express his sincere appreciation to Rodolfo Maruri, Claude Napier, and Eric Spriggs of the FHWA for synthesizing a huge amount of data from the survey in a very short time period for use in this article.