In this paper, the change of component materials of concrete is discussed. As for cement, its qualities have been improved by means of manufacturing technology. But the qualities of aggregates are getting worse for lack of their resources, and the durability of concrete has been lowered. In order to improve them, various kinds of admixture are developed and used is almost all cases now.

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5 kW and 20 kW CO₂ laser continuously operating at 10.6, μm were successfully used to cut various kinds of concrete. The output power of the laser, the position of the focal spot, the speed of the laser spot on the material, the species and pressure of the gasses used to assist the cutting were changed as parameters in this experiments. This paper describes the results of these experiments. From the results, it is concluded that the laser beam will be used to cut various types of concretes in the near future, though some difficulties must be solved for actual application.

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Okaya elevated highway bridge, which crosses Okaya city at the height of 60 meters from the ground, is a rigid five span continuous frame prestressed concrete bridge. The concrete volume in the main girders of the bridge is about 15,000 cubic meters. In the absence of an adequate amount of sound aggregate and the difficulties in performing the construction work at elevated levels, the possible application of superplasticized concrete was investigated. The objective was to reduce water content of the concrete without having to use ordinary high strength concrete of dry consistency. It was established both from the laboratory tests and site application that the use of superplasticized concrete meet the quality requirements.

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The 30 storied highrise condominium building in “Park City Shinkawasaki” is the highest reinforced concrete building in Japan. This building is a frame structure above ground line and was constructed by using “HiRC System” developed by Kajima Corporation. The exterior columns of the lower parts of this building were used the confined reinforced concrete columns with centrated core bars, which are improved “Kajima Spiral Column” and high strength concrete having a design strength of 420 kgf/cm² was placed. This report describes the outline of this building and the results of quality control of high strength concrete having design strength between 420 kgf/cm² and 360 kgf/cm².

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For the first time, mass underwater concrete with S. C. A. (Segregation Control Admixture) was used for a substructure of a bridge on laying-down Caisson method. The underwater concrete with S. C. A. has the following advantages. First, it keeps strength deterioration under water at minimum. Second, it is uniform in quality; that is good for execution of work. Third, it hardly makes water turbid, for it is controlled to prevent segregation under water. The present paper refer mainly to the result of examination on such as the flow gradient, temperature rise of the concrete caused by heat of hydration, execution efficiency of the concrete plant, and so on.

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