3CaO·CaCl₂·15H₂O is considered to be the primary cause of chemical deterioration of concrete induced by CaCl₂. In this study, a method of synthesizing 3CaO·CaCl₂·15H₂O was examined, and the fundamental properties of the synthesized single crystal of the substance were investigated through morphological analysis, X-ray diffractometry (XRD), thermogravimetric/differential thermal analysis (TG-DTA) and differential scanning calorimetry (DSC). It was demonstrated that 3CaO·CaCl₂·15H₂O could be synthesized by using the process of deposition. The synthesized sample was a needle-shaped crystal which was found significantly unstable even in the atmosphere. The heat characteristics of the substance and its chemical reactions accompanying heating were determined. The XRD patterns showed that 3CaO·CaCl₂·15H₂O had a strong preferred orientation.

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 The use of limestone aggregate is expected to increase for its low risk of alkali-silica reaction and effectiveness in reduction of drying shrinkage. Meanwhile, it is known that limestone aggregate tends to generate fine particles during transport. In order to promote proper use of the limestone aggregate, JIS A 5005 "Crushed stone and manufactured sand for concrete" was revised in March 2009, with the regulation on fine particle content in aggregate modified. In this study, the influence of the increased fine particle content in limestone aggregate on the fresh and hardened properties of concrete was experimentally investigated, using aggregate products from different sources with different cement types at various water to cement ratios. It was found that the increase in fine particle content decreased the bleeding ratio and increased compressive strength in normal-strength concrete. On the other hand, no significant effects were found in major strength properties of high-strength concrete, with only minor decrease in workability which was found adjustable with the amount of admixture to be added. These results suggested that the limestone aggregate may be used the same way as the conventional aggregate.

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 The use of ultra high strength fiber reinforced concrete (UFC) with increased tensile strength has been increasing since the publication of recommendations on design and construction of UFC structures by the Japan Society of Civil Engineers (JSCE). UFC is a unique cementitious composite with high tensile strength which enables concrete structure designs without reinforcing bars. Its durability is also very high compared to conventional concrete. UFC is prepared by mixing pre-mix powder with water and superplasticizer and dispersing short fibers in the mixture. The pre-mix powder consists of cement, silica fume, silica fine powder, silica sand and other materials in the optimum proportion. The standard formulation contains short steel fibers (with a diameter of 0.2mm and a length of 15mm) of 2 volume % mixture.
　One of the common problems found with UFC is surface contamination induced by corrosion of the exposed steel fibers on the surface. Corrosion may also occur on steel fibers when they bridge cracks, if present, inside the UFC. In order to provide a solution to this problem, the authors investigated applicability of corrosion-resistant organic fibers with extremely high strength and elasticity, including twisted poly-p-phenylenebenzobisoxazole (PBO) fiber bundles.
　The important findings in this study were as follows: (1) tensile and flexural strengths of UFC were increased by using twisted PBO fiber bundles; (2) shrinkage behavior of UFC containing twisted PBO fiber bundles was the same as that of UFC containing steel fibers; and (3) fracture energy and abrasion resistance of UFC were slightly decreased by using twisted PBO fiber bundles.

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 Non-radioactive concrete waste generated from dismantling of a standard large nuclear power plant is estimated to be about 500,000 tons in weight. Using such waste as recycled aggregate within the enclosure of the plant requires a new manufacturing technology that generates a minimal amount of by-product powder.
　Recycled aggregate has brittle parts with defects such as cracks, pores, and voids in residual paste from original concrete. This study presents a method of selectively removing the defective parts during manufacture to improve the quality of the recycled fine aggregate. With this selective removal method used, the amount of by-product powder can be reduced by half as compared to that by a conventional method.
　The influences of the characteristics of the recycled fine aggregate on the flowability and strength of the mortar using recycled fine aggregate were evaluated by multiple linear regression analysis. The results clearly showed that the flowability was primarily affected by the filling fraction of recycled fine aggregate, while the compressive strength of mortar was primarily affected by the fraction of defects in the aggregate. It was also found that grains produced by a granulator have more irregularities in the surfaces than those produced by a ball mill, providing an increased mortar strength.
　Using these findings from this study, efforts are also being made to develop a mechanical technology that enables simultaneous processing of decontamination and recycling. The granulator under consideration is capable of grinding the surfaces of irregularly shaped particles and may be used successfully, under optimal conditions, for the surface decontamination of concrete waste contaminated with radioactive materials.

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 The purpose of this study is to evaluate the strength properties and durability of polymer cement mortar for road slab repair. It was found that bending strength of the polymer cement mortar was 1.4 times higher than that of steel-fiber reinforced concrete, and that bond strength with steel or concrete was larger than 1.0N/mm². The polymer cement mortar exhibited extremely small shrinkage strain, showing its excellent resistance against shrinkage cracking and good applicability for use to repair crack-prone regions with a large specific surface area per unit volume. Evaluations on freezing and thawing resistance, neutralization rate and chloride ion penetration depth revealed adequate resistance to prevent penetration of deteriorating factors even where its application thickness is small. Moreover, partial damage in existing road slabs repaired using the polymer cement mortar showed no problems including recurrence of deterioration.

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 A large amount of radioactivity was released to the environment during the accidents at the Fukushima Daiichi Nuclear Plant after the Great East Japan Earthquake. Solutions are urgently needed against the environmental contamination by radioactive materials that originated from the accidents. Policies of the Japanese government for the restoration of the environment contaminated with the radioactive materials include the followings: decontamination of the environment; treatment of the radioactive waste; and temporary storage of the contaminants before future transfer to a final disposal facility. The authors developed a concrete container for the safe storage of the waste contaminated with the radioactive cesium generated from the environmental restoration.
　This paper summarizes general characteristics of radiation and radioactive materials, describes characteristics and shielding of the radiation emitted from the radioactive cesium released to the environment by the accidents, and presents design requirements for the concrete container and results of demonstration tests conducted in Fukushima which included a radiation shielding performance test on the container.

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