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.

Ultra high strength concrete (UHSC) is undoubtedly an engineered high-tech material, which can be seen as the latest step in the concrete technology development. It is characterized by extraordinary mechanical properties, e.g. high compressive and tensile strength as well as large elastic modulus. For the development of ultra high strength concrete the compressive strength was the relevant factor, therefore suitable mixes normally contain large quantities of cement and silica fume (³ 700 kg/m³), special aggregates and chemical admixtures. Consequently the material costs of this concrete type are very high. The aim of this investigation was to develop different UHSC-mixes in order to minimize the material costs. Furthermore, normal mixing and compacting intervals were used, so that the concrete can be easily handled on site, including pumpability. This paper outlines an experimental program and its results for the development of economic mixes for UHSC. Altogether 69 different mixes were tested on the fresh and hardened properties. Especially the cement type has a significant influence on the workability and the ultimate strength. It could also be shown that a strength of 150 N/mm² can be reached with a maximum cement content of 500 kg/m³.

The addition of polypropylene fibers was considered as an effective remedy to mitigate explosive spalling failure mechanism that usually happened to high-strength concrete exposed to high temperature. However, the melting of polypropylene fibers inside the cement matrix tended to greatly reduce the residual properties of the heated concrete. As the possibility of reusing heated concrete will depend on its residual properties, it is of a great interest as to have both good explosive spalling counter effect and better residual properties on the concrete after being subjected to high temperature. On the other hand, steel fiber-reinforced high-strength concrete had shown better residual properties on heated high-strength concrete, even though the explosive spalling counter effect was not as effective as polypropylene fibers. This paper presents the effect of using both polypropylene and steel fibers, called hybrid fibers, on the residual properties of high-strength concrete subjected to high temperature. The residual properties being investigated in this experimental research will include compressive strength, splitting tensile strength, and permeability. Test results showed the effectiveness of hybrid fibers in mitigating the explosive spalling and reducing the properties loss on high-strength concrete subjected to elevated temperature.

The U.S. Federal Highway Administration recently constructed the first Ultra-High Performance Concrete (UHPC) vehicle bridge in North America. This prestressed concrete road bridge is composed of two bulbed double-tee girders, each having a 2.4 m deck width and a 0.84 m girder depth. The bridge spans 21 m. Structural optimization of the prestressed concrete girder/deck combination indicated that this pi-shaped section was an efficient girder for 21 to 30 meter spans. Fabrication and construction of this bridge is discussed.

The objective of this paper is to study the effects of the elevated internal temperature on the strength development and microstructure of high performance concrete with 40 % fly ash in mass structures. The concrete walls were designed using three different depths, being 1.5 m, 0.8 m, and 0.3 m. Temperature histories at different locations in the walls were recorded and the strength development of concrete at those locations was measured. In addition, the change of the degree of hydration, hydration products, and microstructure development of concrete at the different locations were investigated. Test results indicated that high elevated temperatures in mass concrete structures with fly ash significantly accelerate the strength development of concrete at the early ages, while the long-term strength development is decreased. The long-term strength loss is caused by the reduction of the degree of hydration and increased the total porosity and amount of smaller pores. The use of fly ash in mass concrete structure reduces the detrimental effect of high curing temperature on the strength development of concrete.