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High-Performance Concretes

A State-of-Art Report (1989-1994)

8.  CONCLUSIONS

This report is a sequel to a previous state-of-the-art report published by SHRP in 1991 and is based on review of selected literature on high performance concrete with particular reference to highway applications. It covers primarily the six-year period from 1989 to 1994 for which the authors have recently compiled an updated annotated bibliography, containing 776 references, which has been published by the Federal Highway Administration (Publication No. FHWA-RD-96-112). More recent information on the subject is obtained directly from a variety of publications including books, technical journals, conference proceedings, and research reports.

It should be emphasized that, unless otherwise noted, much of the information contained in the previous state-of-the-art report is still current and will not be repeated in the present document. Therefore this document should be viewed as a supplement to rather than a replacement for the previous report. For ease of cross-referencing, the organization and format of the present report have been kept nearly the same as the previous state-of-the-art report. Based on the results of the literature review, the following general conclusions can be drawn:

1. The growth of the amount of research and applications of high performance concrete has been phenomenal in the past seven or eight years. High performance concrete has become widely accepted practically on all continents.
2. A generalized definition of high performance concrete seems to have been accepted by the engineering community. Such a definition is based on achievement of certain performance requirements or characteristics of concrete for a given application that otherwise can not be obtained from normal concrete as a commodity product.
3. Based on the results of the SHRP projects, the Federal Highway Administration has developed a sensible classification of high performance concrete according to different levels of performance requirements. Such a classification would enable design engineers to select appropriate performance criteria of HPC for different highway applications in different environmental conditions.
4. Much of the application of HPC remains in the areas of long-span bridges and high-rise buildings. HPC is used more for bridges than buildings in Europe and Japan, while more buildings than bridges used HPC in the U. S. However, the situation is changing. Use of HPC in buildings is increasing abroad and there is a growing interest in using HPC in bridges in the U. S.
5. There is much understanding of selection of materials, proportioning methods and curing control for the production of high performance concrete. However, much less control is exercised on the concrete placement. In this regard, the development of "self-compactable" concrete in Japan is a significant step toward achieving high performance concrete through automation.
6. Increasing emphasis is being placed on concrete durability than its strength. In many applications, high strength concrete is used only because of its high durability quality rather than the need for its strength.
7. There has been an enormous amount of research performed on durabilty of concrete, but without much correlation largely because the property is "material specific" and dependent on test methods. There is an urgent need for new and improved test methods that would provide more consistent correlation between the laboratory and field results so that the data on durability can be better quantified. More research is needed to develop a rational design methodology for durability.
8. Much research continues to be focused on the mechanical properties of high- and very-high-strength concretes and their structural applications. The results of this research are being incorporated into various national codes of practice. However, more information is needed on the behavior of the concrete at its early age and its relationship to the long-term performance.
9. Comparatively speaking, there is a dearth of information on the mechanical behavior of controlled lower strength concrete. Similarly, the need exists for more research on high performance lightweight concrete so that its use can be more widely accepted in practice.
10. The Slurry Infiltrated Mat Concrete (SIMCON) and the delivery system for non-metallic fibers developed by 3M Corporation are two significant recent developments in the area of high performance fiber reinforced concrete.
11. There has been significant interest and development in the use of continuous fiber reinforcement for improving the behavior of cementitious composites and/or concrete. Fiber Reinforced Polymers (FRP) or sometime also referred to as Fiber Reinforced Plastic are increasingly being accepted as an alternative for uncoated and epoxy-coated steel reinforcement for prestressed and non-prestressed concrete applications.