Louis N. Triandafilou, Federal Highway Administration
Created in 1997, the Federal Highway Administration’s (FHWA) High Performance Concrete (HPC) Technology Deployment Team (TDT) assists state departments of transportation (DOTs) and other agencies with deploying HPC technology.* In 2003/04, the team conducted a national survey of HPC usage, and the results were summarized in HPC Bridge Views, Issue No. 32. A second survey was made in 2006/07. The results are summarized in this article.
The survey was distributed to all 50 state DOTs, Puerto Rico, the District of Columbia, and the Federal Lands Bridge Office. All 53 agencies returned the survey to the TDT for processing, although some agencies did not respond to all questions. The survey included sections on general usage of HPC, permeability benefits of HPC, strength benefits of HPC, self-consolidating concrete (SCC), lightweight HPC, and usage of various types of corrosion-resistant reinforcing bars.
General Usage of HPC
The recent survey asked about the usage since 2003 of HPC for major bridge components—deck overlays, deck slabs, superstructures, and/or substructures. On average, about 15% of the agencies used HPC for these components in more than 50 bridges, 20% in 10 to 50 bridges, 30% in 1 to 10 bridges, and the remainder not using it at all or not responding to the question.
On a project basis, on average, 16 agencies used HPC on up to 10% of their bridge projects, 19 agencies used HPC on 10 to 80% of their projects, and 15 agencies used HPC on over 80% of their projects.
HPC for Permeability and Strength
Similar to the earlier survey, the recent survey also tracked the agencies’ use of HPC for permeability and strength benefits. Rapid chloride permeability values in the range of 1001 to 2000 coulombs were most commonly specified for overlays, decks, superstructures, and/or substructures.
A compressive strength range of 4001 to 5000 psi (28 to 34 MPa) was most commonly used for decks and substructures. The next most common range was 3001 to 4000 psi (21 to 34 MPa). For superstructures, the compressive strength range of 8001 to 10,000 psi (55 to 69 MPa) was most commonly specified. The next most common was 4001 to 5000 psi (28 to 34 MPa).
Self-Consolidating Concrete
In the recent survey, the reported usage of SCC was categorized by superstructure and other precast members, and by various substructure elements. Eleven agencies responded that they had used SCC in up to 10 bridge superstructures and/or precast members. Three agencies reported using SCC in 11 to 20 bridge superstructures. One agency reported its use in 21 to 30 precast structural members, and one agency reported from 31 to 50 bridge superstructures with SCC.
SCC usage in substructure elements has been much less. Only five agencies reported such usage, in up to 10 bridges over the past 4 years. The usage was for pier caps and columns, footings, piles, and drilled shafts.
Lightweight HPC
As with other data noted above, the earlier survey tracked only generally whether an agency had tried lightweight HPC on an experimental basis, or whether the agency had progressed to the point of developing standard specifications for the technology. The recent survey tracked actual project experience. This time around, 11 agencies told us they had used lightweight HPC in up to 10 bridge decks, and three agencies used the material in the superstructure of up to 10 bridges. Two agencies used lightweight HPC in the range of 11 to 20 decks, and two agencies on more than 50 bridge decks. No agency reported using lightweight HPC in bridge substructures.
HPC Performance Characteristics
The survey obtained results on what HPC performance characteristics were being tested by the agencies. For durability, performance characteristics include freeze-thaw (F/T) durability, scaling resistance, abrasion resistance, chloride penetration, alkali-silica reactivity (ASR), and sulfate resistance. Strength-related performance characteristics include compressive strength, modulus of elasticity, shrinkage, and creep. In addition, flowability can also be specified as a conventional slump value or as a flow for self-consolidating concrete.
Not surprisingly, compressive strength tests were specified by the highest number of agencies with 48 out of 53 reporting their use. The next highest was rapid chloride permeability, tested by 34 agencies followed by shrinkage, tested by 20 agencies. Flowability, ASR, and F/T were grouped fairly close together and tested by 17 agencies. Scaling and sulfate resistance were the least specified tests, and by only six agencies.
Methods of Specifying HPC
The most common methods of specifying HPC for bridges was either by (a) special provision for a particular project, or (b) a combination of special provisions and general specifications. Twenty-two agencies reported the use of Method (a) and 22 agencies the use of Method (b). Only eight agencies used general specifications. Slightly over half the agencies had neither built nor planned HPC bridge projects using end-result, performance-based specifications (ERS). Eleven agencies had one to five bridges either planned or built using ERS. Only one agency had made substantial progress with ERS being used on over 100 bridges.
High-Performance Corrosion-Resistant Reinforcing Bars
For many years, agencies have been experimenting with corrosion-resistant alternatives to epoxy-coated reinforcement for bridge decks. A long-term research study has been performed for the FHWA and the Florida DOT by Florida Atlantic University to evaluate alloys previously identified as candidates for corrosion-resistant reinforcement. Details of the results of this portion of the survey and the remainder of the survey, as well as results of the earlier survey, may be found on the Team’s website at http://knowledge.fhwa.dot.gov/hpc.
Conclusions
The HPC TDT’s survey of 2003/04 showed that almost every agency had either incorporated HPC into their standard specifications, or had at least tried it during the previous 10 years. However, the results were inconclusive as to the extent of HPC usage by each agency. The 2006/07 survey attempted to bridge that gap by soliciting information as to number of bridges constructed with an HPC element, as well as percentages of projects built since the first survey with an HPC bridge element.
The map at the beginning of this article shows that there is still much work to be done if HPC is to successfully impact the new and rehabilitated U.S. bridge infrastructure in the 21st century. An aggressive training effort will still be necessary for the total work force involved with bridge design and construction—engineers, inspectors, and contractors. Undergraduate and graduate school curricula must also adapt to give students the tools needed to understand the behavior of HPC constituent materials.
The 1990s laid the groundwork for HPC technology to develop and blossom into a bona fide bridge material through the efforts of FHWA, state agencies, consulting engineers, the concrete industry, and academia. It is this continuing dedicated partnership that will play a critical role in the widespread use of HPC.
Acknowledgement
The author wishes to express his sincere appreciation to Rodolfo F. Maruri and Claude S. Napier of the FHWA for synthesizing a huge amount of data from the survey in a very timely manner.
* See HPC Bridge Views, Issue No. 19, January/February 2002.