International Concrete Abstracts Portal

SP-228CD This CD-ROM of Special Publication 228 contains the papers presented at the Seventh International Symposium on the Utilization of High-Strength/High- Performance Concrete that was held in Washington, D.C., USA, June 20-24, 2005. The symposium continued the success of previous symposia held in Stavanger, Norway, (1987); Berkeley, California (1990); Lillehammer, Norway, (1993); Paris, France, (1996); Sandefjord, Norway, (1999); and Leipzig, Germany, (2002). The symposium brought together engineers and material scientists from around the world to discuss topics ranging from the latest applications to the most recent research on high-strength and high-performance concrete. In the years since the first symposium was held in Stavanger, there has been worldwide growth in the use of both high-strength and high-performance concrete. In addition to more research and applications of traditional types of high-performance concrete, the use of self-consolidating concrete and ultra-high-performance concrete has moved from the laboratory to practical applications. This publication offers the opportunity to learn the latest about these developments.

A large number of models have been developed recently in an attempt to link the parameters of the Bingham equation to concrete composition [1]. On the other hand, concrete mixture proportioning methods based on a rheological approach usually do not provide direct input of measurable rheological parameter(s) into the proportioning ex-pression. The theories underlying the design methodologies are usually based on a rheological model, but the parameter associated with the rheology of the system (for instance, the magnitude of the relative viscosity) is an adjustable (arbitrary) constant. Consequently, in a broad sense, a universal method for concrete mixture proportioning based on rheological characteristics has not been proposed until now. In this paper, an attempt has been made to associate the rheological quantity involved in an analytical model for mixture proportioning with a measurable rheological characteristic. To do this, the results from evaluation of concrete rheology using a newly developed capillary viscometer are compared with calculated apparent viscosities by the model on a series of concrete mixtures (conventional and self-consolidated). The agreement of the experi-mental results with the theoretical prediction of the model proved to be encouraging. The application of the approach and a new viscometer for self-consolidating concrete technology is believed to be innovative.

Since the 1970’s the concrete industry has seen major developments in high strength/ high-performance concrete (HPC). New materials, design codes and construction methods have enabled us to design and build taller, slimmer, lighter, more attractive and more durable concrete structures. Through research and development and practical applications we have improved our knowledge on strength, ductility, durability, constructability, appearance and other properties to where technology is not the limiting factor, but rather our ability to utilize what we know and to promote our ideas for more sustainable and competitive concrete structures. HPC is now covered by a number of design codes and high-performance structures can be produced almost anywhere with selected local materials and competent workmanship. The volume of available literature on HPC has increased almost exponentially in recent years. Large research and development programmes have been executed and shown to produce remarkable results and provide very satisfactory returns on the investment. HPC still constitutes only a small part of the output of the concrete industry and is largely limited to marine structures, large span bridges and prestigious buildings and to some extent precast components. The market of ordinary structures is still dominated by ordinary concretes with ordinary performance. The paper discusses some aspects related to the evolution of high strength concrete (HSC) and high performance concrete and how the concrete industry, for the benefits of the clients and its own performance and image, needs to more actively utilize the proven HPC technology.

One of the breakthroughs in concrete technology is ultra-high-performance concrete with a steel like compressive strength of up to 250 N/mm2 and a remarkable increase in durability compared even with high-performance concrete. In combination with steel fibres it is now possible to design sustainable filigree, lightweight concrete constructions with or even without additional reinforcement. Wide span girders, bridges, shells and high rise towers are ideal applications widening the range of concrete applications by far. In addition e.g. to some pedestrian bridges heavily trafficked road bridges has been build in France and in the Netherlands. Bridges are already under construction in Germany as well. A wide range of new concrete formulations has been developed to cover an increasing number of applications. Technical recommendations have recently been published in France and in Germany covering material as well as design aspects. The paper will report on the state of research and application of UHPC in Europe, on material and design aspects of UHPC and will present the state-of-the-art based on an International Symposium on UHPC held in Kassel in 2004.

Although highstrength concrete is often times still considered a relatively new material, its development has been gradual and continual over the last 50 years. During this period, many notable changes have occurred and continue to occur in the area of high-strength concrete technology, including the definition of high-strength concrete itself. With the increased knowledge that has been gained with respect to material availability, design methodology, and construction techniques, the feasible realm of high-strength concrete applications has grown dramatically. One of the primary objectives of ACI Committee 363 during the last few years has been to update and republish document 363R, High-Strength Concrete. This synopsis is based on a full report on high-strength concrete to be published by ACI Committee 363 (High-Strength Concrete). Estimated publication time for the new document is early 2006. The objective of the document is to present state-of-the-art information on concrete with strengths in excess of about 55 MPa (8000 psi), but not including concrete made using exotic materials or techniques. In the 1950s, concrete with a compressive strength of 34 MPa (5000 psi) was considered high strength. Today, high-strength concrete is defined as concrete with a specified compressive strength of 55 MPa (8000 psi) or higher. In many markets today, concrete having a specified compressive strength in excess of 69 MPa (10,000 psi) is routinely produced on a daily basis. Although 55 MPa (8000 psi) was selected as the current lower limit, it is not intended to imply that any drastic change in material properties or in production techniques occurs at this compressive strength. In reality, all changes that take place at or above 55 MPa (8000 psi) represent a process which starts with the lower strength concretes and continues into the highstrength realm. Items to be considered in selecting materials include characteristics of cement and supplementary cementitious materials, aggregate properties, and the effects of chemical admixtures, particularly with respect to their water reduction and hydration controlling capabilities. To ensure that required concrete strengths and other desired properties would be obtained, trial mixtures are an essential part of the process. Depending on the appropriate application, mix proportions for high-strength concrete generally have been based on achieving a required compressive strength at a specified age, many times beyond the traditional 28 days. Factors included in selecting concrete mix proportions have included availability of constituent materials, desired workability, and effects of temperature rise. Research data have indicated that the measured modulus of elasticity of high-strength concrete can vary significantly from calculated values based on unit weight and concrete compressive strength. High-strength concrete has shown a higher rate of strength gain at early ages as compared to lower-strength concrete, but at later ages the relative difference is not as significant. Information on creep and shrinkage of high-strength concrete has indicated that the shrinkage is similar to that for lower-strength concrete. However, specific creep is much less for high-strength concretes than for lower-strength concretes. The use of high-strength concrete can have significant impacts on structural design, though changes in structural behavior generally occur gradually as concrete strength is increased. Modifications to standard design equations developed for lower-strength concretes are necessary for determining the strength of axially-loaded columns, axial and flexural strength of eccentrically-loaded columns, loss of prestress in prestressed concrete beams, and minimum reinforcement requirements for flexure, shear, and torsion in reinforced concrete beams. Proposed modifications in each of these areas have been summarized in the 363R document. Significant research has been completed but consensus design e