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Material Property Characterization of Ultra-High Performance Concrete

1.1 INTRODUCTION

Ultra-high performance concrete (UHPC) is a new class of concrete that has been developed in recent decades. When compared with high performance concrete (HPC), UHPC tends to exhibit superior properties such as advanced strength, durability, and long-term stability.

Many researchers around the world have developed concretes that could be classified as UHPC. Although there are differences among types of UHPC, there are also many overall similarities. The Association Française de Gènie Civil (AFGC) document Ultra High Performance Fibre-Reinforced Concretes–Interim Recommendations indicates that UHPC tends to have the following properties: compressive strength that is greater than 150 megapascals (MPa) (21.7 kilopounds per square inch (ksi)), internal fiber reinforcement to ensure nonbrittle behavior, and a high binder content with special aggregates.⁽¹⁾ Furthermore, UHPC tends to have a very low water content and can achieve sufficient rheological properties through a combination of optimized granular packing and the addition of high-range water reducing admixtures.

Characterization of the material behaviors of UHPC has progressed to such an extent that the full-scale structural use of this concrete is on the horizon. To date, UHPC has been used in the construction of two public highway bridges,^(2,3) numerous pedestrian bridges,^(4,5) and a wide variety of other projects.^(6,7,8) Research and observations to date indicate that UHPC has the potential to expand the use of concrete into new forms that have heretofore been impossible.

This research program focused on determining the behaviors of UHPC because this information is relevant to the highway bridge industry in the United States. Currently, the only UHPC that is commercially available in the United States is Ductal^®, a product jointly developed by Lafarge, Bouygues, and Rhodia. Therefore, Ductal was the UHPC product used in this research program.

1.2 OBJECTIVE

The objective of this research is to evaluate the potential use of UHPC in the highway bridge infrastructure by characterizing mechanical- and durability-based material behaviors.

1.3 SUMMARY OF APPROACH

The research included a significant experimental phase and an associated analytical phase. The experimental phase focused on determining the material behaviors of UHPC from the testing of over 1,000 individual specimens, with an emphasis toward determining the compressive and tensile behaviors, the long-term stability, and the durability of UHPC. Many of the material characterization tests were completed according to the American Society for Testing and Materials (ASTM) and the American Association of State Highway and Transportation Officials (AASHTO) standard test procedures; however, in some instances these tests were modified or new tests were devised to accurately capture the relevant behaviors of the concrete. The analytical phase of this research combined, analyzed, and elaborated upon the results from the experimental phase. This work included defining behaviors that can be anticipated to occur in standardized concrete tests, as well as developing predictor equations for relating basic properties of UHPC.

1.4 OUTLINE OF REPORT

This report is divided into five chapters. Chapters 1 and 2 provide an introduction and relevant background information. Chapter 3 presents the results of the material characterization study. Chapter 4 presents further analysis and discussion of the research, relating results from various aspects of this study to one another and to the practical engineering disposition of this research. Finally, chapter 5 presents the conclusions of this research program.