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Publication Number: FHWA-HRT-13-060
Date: June 2013

 

Ultra-High Performance Concrete: A State-Of-The-Art Report for The Bridge Community

CHAPTER 1. INTRODUCTION

BACKGROUND

Ultra-high performance concrete (UHPC) in its present form became commercially available in the United States in about 2000.(1) The Federal Highway Administration (FHWA) began investigating the use of UHPC for highway infrastructure in 2001 and has been working with State transportation departments to deploy the technology since 2002. This work has led to the use of UHPC in several bridge applications, including precast, prestressed girders; precast waffle panels for bridge decks; and as a jointing material between precast concrete deck panels and girders and between the flanges of adjacent girders. At the same time, research work has been underway at several universities in the United States.

In Canada, the first UHPC bridge was constructed in 1997.(2) This pedestrian bridge consists of a precast, post-tensioned space truss. At least 26 bridges have been built in Canada using UHPC in one or more components.

In Germany, a 12 million euro research program, begun in 2005, has just been completed.(3) That program, funded by the German Research Foundation, involved 34 research projects at more than 20 research institutes in Germany. The purpose of the program was to elaborate on the basic knowledge so that reliable technical standards could be developed. The goal was to make UHPC a reliable, commonly available, economically feasible, regularly applied material. Several bridges that use UHPC have been built in Germany.

In 2002, the first recommendations on the use of UHPC in structures were published in France.(4) This initial document addressed mechanical properties, structural design, and durability. Since 2002, several bridges have been built in France using UHPC. In 2009, severalpapers published in French recommended updates to the recommendations.(5,6,7) A similar set of design recommendations was developed for use in Japan.(8)

Other countries with bridges using UHPC include Australia, Austria, Croatia, Italy, Japan, Malaysia, the Netherlands, New Zealand, Slovenia, South Korea, and Switzerland. The literature search identified more than 90 completed bridges using UHPC in one or more components. A major research program is currently underway in South Korea to investigate the use of UHPC in cable-stayed bridges.(9) It is obvious, therefore, that UHPC is receiving worldwide attention.

The evolution of UHPC into its present formulation has been a gradual process occurring over many years. Several papers have summarized thisdevelopment. Naaman and Wille identified many of the significant advances in the technology over the last 5 decades.(10) Buitelaar summarized the early developments in the Netherlands and Denmark.(11) Richard and Rossi described the developments in France.(12,13,14)

As part of its ongoing activities to implement UHPC in the United States, FHWA has requested a state-of-the-art report about the research, development, and deployment of UHPC. This document reports what has been done and looks ahead to what needs to be done to achieve appropriate applications in the U.S. highway infrastructure.

OBJECTIVE

The objective of this report is to document the state of the art with regard to the research, development, and deployment of UHPC components within the U.S. highway transportation infrastructure. In addition, because much of the development and initial deployment of UHPC has occurred internationally, the report also documents work completed outside the U.S. highway sector. In addition, the report addresses what is needed to allow future wider implementation of UHPC.

SCOPE

Similar to how Graybeal defines it, this document defines UHPC-class materials as cementitious-based composite materials with discontinuous fiber reinforcement, compressive strengths above 21.7 ksi (150 MPa), pre-and post-cracking tensile strengths above 0.72 ksi (5 MPa), and enhanced durability via their discontinuous pore structure.(1) However, the published literature does not always include sufficient information to determine whether the tested materials conformed to this definition. Unless an obvious reason existed to exclude an article, it is included in this report.

The authors identified more than 600 references relevant to this report. Some topics are described in more than one article by the same or similar combinations of authors. Some articles also provide updates on previous articles on the same topic. For this report, the most comprehensive documents readily available and written in English are used for most of the cited references. The other articles are listed in the Bibliography. Based on this approach, the majority of articles in this report come from the following publications:

The articles published in the proceedings of the international meetings are usually summaries of the research or applications and written in English. As such, the articles do not contain sufficient information for use in developing design guides or specifications. For more details, the articles often refer to a full report written in a language other than English. Use of these reports requires either a comprehension of the other language or an English translation.

TERMINOLOGY

Various terms are used to refer to cementitious-based composite materials with high compressive strength and enhanced durability. These include the following:

In addition, various patterns of hyphens are used to form compound adjectives. For this report, the product is generally called ultra-high performanceconcrete or UHPC unless it is necessary to differentiate the different types. Descriptions of some of the different types are provided by Rossi. (13) Although calling the different types by a single name may not be technically correct, it simplifies understanding the available information.

This report also refers to conventional concrete. Conventional concrete is composed of cementitious materials, fine and coarse aggregates, water, and admixtures. Compressive strengths are assumed to be in the range of 4 to 8 ksi (28 to 55 MPa).

SUSTAINABILITY

Few articles have been published about the sustainability of UHPC compared with the number published about its material and engineering properties. Several authors have addressed the topic because of the increasing requirement to consider sustainability.

Racky determined that the energy and raw material consumption to produce a square reinforced column made of UHPC were 74 and 58 percent, respectively, of the quantities required for a Grade 40/50 (6/7 ksi) column.(15) He also pointed out that UHPC had greater frost and deicing salt resistance, a lower rate of carbonation, and greater chloride resistance than conventional concretes. Consequently, highway structures made with UHPC will have lower maintenance and repair costs in the future compared with conventional concrete bridges. However, sufficient data were lacking to perform realistic life cycle cost analyses.

Schmidt and Jerebic reported that the energy demanded for production of 1.3 yd3 (1 m3) of UHPC was approximately double that for conventional concrete.(16) However, when the total energy demand to construct the Gaertnerplatz bridge using UHPC and steel tubes was compared with the energy demand for an equivalent conventional prestressed concrete bridge, the increase was reduced to 25 percent. The largest component of energy was for the production of the steel tubes. If the steel tubes could be replaced by UHPC tubes, the estimated energy demand would drop by about 50 percent. When the CO2 contributions from construction to the greenhouse effect were considered, the UHPC-steel combination had the largest value, the UHPC tube the lowest, and the prestressed concrete bridge was intermediate.

Sedran, Durand, and de Larrard reported that UHPC called Ceracem could be crushed and separated into sand and fibers.(17) The recycled sand could then be used as a replacement for river sand in self-leveling concrete with no loss of fluidity and no decrease in compressive strength.

Stengel and Schießl reported that the environmental impact of UHPC production was mainly caused by the production of the steel fibers, portland cement, and high-range water-reducing admixtures.(18) The effect of heat curing UHPC was not taken into account. In another study, life-cycle assessments of bridge structures were made using German standard Deutsches Institut für Normung (DIN) ISO 14040 ff.(19,20) The research concluded that the environmental impact of structures made with state-of-the-art UHPC was up to 2.5 times greater than with conventional concrete. The environmental impact could be decreased by reducing the amount of portland cement, steel fibers, and high-range water-reducing admixtures in the UHPC.

COSTS

The initial unit quantity cost of UHPC far exceeds that of conventional concrete. Consequently, applications have focused on optimizing its use by reducing concrete member thickness, changing concrete structural shapes, or developing solutions that address shortcomings with existing non-concrete structural materials. As discussed in chapter 5, UHPC is a very durable product, and structures that use it are expected to have a longer service life and require less maintenance than structures built with conventional concrete.

Piotrowski and Schmidt conducted a life cycle cost analysis of two replacement methods for the Eder bridge in Felsberg, Germany.(21) One method used precast UHPC box girders filled with lightweight concrete. The second method used conventional prestressed concrete bridge members. Although the UHPC had higher initial costs, the authors predicted the life cycle cost over 100 years would be less for the UHPC bridge.

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