Kenichiro Nakarai

INSTIGATION ON MECHANISM OF LONG-TERM STRENGTH DEVELOPMENT OF CARBONATED CEMENT-TREATED SAND

The mechanism of the long-term strength development of carbonated cement-treated soils was experimentally investigated. The unconfined uniaxial compressive strength of the carbonated specimen of the cement-treated soil was larger than that of the non-carbonated specimen cured in the sealed condition. In the carbonated specimens, the strength of the specimen carbonated in the air was larger than that of the specimen carbonated in the accelerated camber. The effect of the carbonation method on the strength was analyzed. Then, it was found that forms of carbonated C-S-H gel has significant effect on the strength development rather than the amount of reacted CO₂ and chemically bound water. In the case of the specimen containing bentonite, the strength of the carbonated specimen cured in the air was almost same as the strength of the specimen cured in the sealed condition. It was caused that the carbonation prevented the additional increase of the strength by pozzolanic reaction.炭酸化したセメント系砂質改良土の長期強度発現メカニズムを解明するために各種試験を実施した。セメント系砂質改良土を炭酸化すると、封緘養生に比べ、一軸圧縮強さが大きくなった。炭酸化方法により強度発現に違いが有り、促進炭酸化養生よりも気中養生を施した場合に強度が増進した。各種分析結果から、炭酸化したときの強度の増進にはCO2含有量や結合水量よりも炭酸化したC-S-Hの形態が影響している。ベントナイトを混合した場合、封緘養生と気中養生の長期強度は同等であった。これは気中養生では炭酸化に伴い、ポゾラン反応が阻害されたためであると考えられる。

EFFECT OF MOISTURE CONTENT AND PONDING CONDITION ON PENETRATION AND LEACHING OF CESIUM IN MORTAR

The accident at the Fukushima Daiichi Nuclear Power Plant resulted in a huge amount of radioactive cesium spreading widely. It is important to decontaminate the radioactive cesium and dispose the radioactive waste safely as soon as possible. The sorption properties for cement materials have already been investigated by several researchers. However, the studies on the mass transfer considering the time histories of moisture contents in the concrete under cyclic drying and wetting conditions are very few. Therefore, this study aims to investigate the cesium behaviors such as adsorption, penetration in the cyclic dying and wetting conditions, and leaching in mortar. As a result, it was observed that cesium was hardly adsorbed on cement hydrates as well as aggregates prepared in this study, while significantly adsorbed on zeolite. In addition, in mortar specimens processed with water saturation, 80％ of cesium existing in the whole area of specimens was soluble. On the other hand, in dried specimens, 80％ of existing cesium were soluble only in the inner area of the specimen, but in the surface area, 60％ of the penetrated cesium was soluble in the surface. The authors thought that large amounts of the cesium were fixed as insoluble at the surface, and it was caused by carbonation of the specimen. Furthermore, it is easy to leach cesium from mortar, so that cesium is easily transported in the specimen under cyclic drying and wetting condition.福島第一原子力発電所の事故により、広範囲に拡散した大量の放射性物質を適切に除染するとともに、汚染された災害廃棄物を適切に処理、処分することが求められている。そこで本研究では、モルタル中でのセシウムの吸着、浸透、溶出挙動を把握することを目的とした。実験結果から、セメントや各種細骨材にセシウムは吸着しにくく、飽水処理したモルタル供試体では、供試体表面および内部ともに80％ものセシウムは可溶性として存在していた。一方で乾燥させた供試体の表面付近では60％のセシウムが非可溶性であり炭酸化の影響が示唆された。