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SP-167 This ACI special publication is a collection of 15 symposium papers that were presented in three sessions at the ACI Fall Convention in Montreal in November of 1995. The authors were asked to present a view of activities on high-strength concrete from work done in their respective countries: Japan, France, Norway, Holland, Germany, Canada and the United States. The following titles are contained within this informative document.

This paper reviews the ACI-318 Building Code requirements concerning the design of slabs post-tensioned with unbonded tendons. The design of a simply supported one-way slab is considered in detail. By taking into account all requirements (in service and at ultimate), it is shown that use of high strength concrete results in savings in the number of tendons or in slab depth when compared to a design in normal strength concrete. Tests up to failure of two similar two-span slabs, one in normal strength concrete (f'c = 40 MPa), the other in high strength concrete (f'c = 75 MPa I reveal a better ultimate load behavior for the high strength slab which exhibited more ductility than the normal strength slab. ACI requirements proved to be adequate for estimating the service load and conservative for predicting the actual carrying capacity.

Prestressed concrete frames are commonly used in bridge design. However, very little is known about their behavior under reversed cyclic loads, particularly when the frame is made of high strength prestressed concrete and is subjected to severe earthquakes. Most bridge codes do not provide the required design guidelines. Results from small scale models of eight prestressed concrete frames (divided into two groups), tested under various displacement histories simulating earthquake forces are presented. The primary curves (horizontal force-displacement relationships) and the hysteretic loops are determined experimentally. Concrete strength are 35 MPa and 52 MPa, for the two groups, respectively, and the effective prestress is 51 percent of the ultimate strength of prestressing steel. It is found that prestressed frames with high strength concrete provide greater ductility and dissipated energy than those with normal strength concrete. The effect of displacement history on the mechanical behavior is significant.

In Japan high strength concrete was first achieved as early as the 1930s. Yoshida reported in 1930 that high strength concrete with 28-day compressive strength of 102 MPa was obtained. This result was obtained by a combination of pressing and vibrating processes without the use of any chemical and mineral admixtures. This method has been applied for production of high strength segments. In the 196Os, superplasticizers were developed in Japan and West Germany which were very effective chemical admixtures to decrease the water content in concrete. With the use of superplasticizers, it became possible to decrease the water to cement ratio while maintaining the workability of the concrete. This technique was applied very widely and many bridges, high-rise buildings, precast concrete members have been produced. In the 197Os, the combined use of superplasticizers and ultra-fine materials such as silica fume, finely ground blast furnace slag or anhydrous gypsum based additives were studied and has been applied to concrete structures until today. Finally, super high strength concrete greater than 120 MPa in compressive strength was achieved with selected materials and special techniques and this kind of concrete has been applied in other industries instead of in the construction industry. This paper summarizes the history and progress of the development of high strength concrete in Japan.

High strength concrete (HSC) is defined by FIP/CEB as “concrete with a cylinder strength above 60 MPa (-87OOpsi) and up to 130 MPa (-18900 psi), the practical upper limit for concretes with ordinary aggregates. It also includes lightweight aggregate concrete with a cement paste of similar properties “. FIP/CEB similarly regards high performance concrete as material with water-binder ratio (w/b) less than 0.40 According to these definitions all concrete installations built in Norway in the 1990s for the oil and gas-fields in the North Sea and most highway structures are built with HSC/HPC. This amounts to about 20 - 25 % of our total domestic concrete production. Norway was the first nation in the world to have HSC with characteristic cube strengths up to 105 MPa (~ 15300 psi) incorporated in its code of design, NS 3473, in 1989. This paper describes the main Norwegian experience by using these qualities in full scale. The presentation is supplemented by some case studies illustrating some typical applications. The main lesson from some 15 years experience is that the introduction of these “hi-tech” concrete grades should be accompanied by a proper upgrading of the workforce’s competence on all levels to ensure the intended quality.