Concrete engineers have developed RCD and CSG methods, which use mixture materials of aggregate, cement and water with lower cement contents than usual concrete. Such materials can be filled and mechanically compacted just like soil structures. On the other hand, geotechnical engineers have developed cemented well-graded gravels as a new backfill material, in order to construct more stable soil structures. These materials are quite similar to each other in their quality of aggregate (or well-graded gravel), mixture ratio of cement and water and compaction methods. They could be classified in the same category, intermediate between concrete and soils while their concepts of mixture design, quality control and construction methods are different. This paper compares these materials, and reports some experimental results on their compaction and strength characteristics.

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In Japan, by the application of countermeasures against alkali aggregate reaction, ASR, such as the restriction of total alkalis in concrete and the use of blended cement with the combination of evaluation methods of alkali reactivity of aggregate such as a chemical method and a mortar-bar method, the majority of ASR has been controlled. However, some problems have remained in these methods when the wide variations of real aggregate, sever conditions for ASR, and increasing usage of alternative aggregates are considered. Besides, the foreign standards that are the basis of Japanese evaluation methods of aggregate are now changing. In this article, recent activities of RILEM TC 191 - ARP, reaction mechanisms of ASR, evaluation methods of aggregate including petrographic evaluation, and problems in these methods are outlined. Based on the information, “Kyushu Standard” in which the application of blended cement is recommended as a standard mitigating method from a realistic point of view is introduced and reasonable countermeasures against ASR are proposed.

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RC column specimens designed by the old codes were tested until they lost axial load carrying capacity. They failed in shear before or after flexural yielding. For both types, the reasons of collapse were studied and equations to give collapse drift were proposed. In addition, model buildings consisting of the tested columns were analyzed to assess their seismic performance during severe earthquakes.

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Heat resistant concrete has been developed to make it possible to design a new type cask that has been designed on the same concept of metal cask for use in high temperature conditions. The allowable temperature of conventional concrete is limited to less than 100 degrees Celsius because most of its moisture is free water and therefore hydrogen, which is effective for neutron shielding, can be easily lost. Our newly developed concrete has chemically bonded water and as a result can be used under the high temperature exceeding 200 degrees Celsius. In addition, the shielding performance of the γ ray is secured because the same density as ordinary concrete is maintained in such a high temperature. By using the developed concrete, the closed type hybrid cask for spent fuel storage has been designed with the safety of a metal cask and the economy of a concrete cask. The experiment of the hybrid cask for real scale casting and for long-term heatproof have been conducted and the results has been reported.

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