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Publication Number: FHWA-HRT-06-115
Date: August 2006

Index, Structural Behavior of Ultra-High Performance Concrete Prestressed I-Girders

CHAPTER 1. INTRODUCTION

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 also are many overall similarities. The Association Française de Génie Civil (AFGC) Interim Recommendations for Ultra High Performance Fibre-Reinforced Concretes 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. In particular, an extensive material characterization study of UHPC was completed in conjunction with the present study.(2) To date, UHPC has been used in the construction of two public highway bridges,(3,4) numerous pedestrian bridges,(5,6) and a wide variety of other projects.(7,8,9) 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®, which is a product of Lafarge. 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 highway bridge girders by characterizing structural behaviors through full-scale girder testing.

1.3 Summary of Approach

The research included an experimental phase and an analytical phase. The experimental phase focused on determining the structural behavior of UHPC prestressed I-girders by completing full-scale girder tests. This testing was conducted on American Association of State Highway and Transportation Officials (AASHTO) Type II prestressed girders. The tests included one flexure test on a 24.4-meter (m) (80-feet (ft) span girder and three shear tests on shorter span girders. These girders did not contain any mild steel reinforcement; thus, the UHPC was required to carry all secondary (i.e., shear, temperature, shrinkage) tensile forces.

In the analytical phase of this research, the results from the experimental phase were analyzed and elaborated upon. This phase included developing a rational philosophy for the flexure and shear design of prestressed UHPC I-girders.

1.4 Outline of Report

This report is divided into eight chapters. Chapters 1 and 2 provide an introduction and relevant background information. Chapter 3 presents the results of the material tests performed on the specimens from the full-scale UHPC girders. Information regarding the fabrication of and experimental method associated with those girders is presented in chapter 4. The full-scale girder test results are presented in chapter 5. Chapter 6 presents analysis and discussion of the experimental results discussed in chapters 3 through 5. A design philosophy for the flexural and shear design of prestressed UHPC I-girders is presented in chapter 7. Finally, chapter 8 presents the conclusions reached as a result of this research program.

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