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Dei, Shuntaro; Shibata, Masahito*; Negishi, Kumi*; Sugiura, Yuki; Amano, Yuki; Bateman, K.*; Wilson, J.*; Yokoyama, Tatsunori; Kagami, Saya; Takeda, Masaki; et al.
Results in Earth Sciences (Internet), 3, p.100097_1 - 100097_16, 2025/12
Interactions between cement and host rock in geological repositories for radioactive waste will result in a chemically disturbed zone, which may potentially affect the long-term safety. This paper investigates the chemical evolution at the interface between cement (Ordinary Portland Cement: OPC and Low Alkaline Cement: LAC) and mudstone after 11 years of in situ reactions at the Horonobe Underground Research Laboratory. The study combines various analytical techniques to identify the key reactions at the cement-rock interface, including cement dissolution, precipitation of secondary minerals such as calcite and C-(A-)S-H phases, cation exchange in montmorillonite and reduced porosity in mudstone. The study also highlights the effects of cement-mudstone interactions on radionuclide migration, such as reduction of diffusivity due to reduced porosity and enhancement of sorption due to incorporation into secondary minerals in the altered mudstone.
Mochizuki, Akihito; Matsui, Hiroya; Nakayama, Masashi; Sakamoto, Ryo*; Shibata, Masahito*; Motoshima, Takayuki*; Jo, Mayumi*
Case Studies in Construction Materials, 22, p.e04648_1 - e04648_20, 2025/07
Times Cited Count：0The properties of low-pH cement used in the geological disposal of radioactive waste may change through atmospheric carbonation and degradation caused by groundwater during the long-term operation of a repository. In this study, we investigated the effects of atmospheric carbonation and groundwater contact on the chemical, microstructural, and transport properties of shotcrete made from low-pH, high-fly-ash silica-fume cement (HFSC) over a period of 16 years in an underground research laboratory. In both carbonated and degraded zones of the HFSC shotcrete, capillary porosity increased for pores of 
300 nm in diameter, and the total porosity was higher than in undegraded zones. These changes in porosity may be associated with the decalcification of calcium-silicate-hydrate and decomposition of ettringite. Such changes were minor in altered zones of OPC shotcrete, indicating that HFSC shotcrete is less resistant to atmospheric carbonation and groundwater leaching under the studied conditions. However, the hydraulic conductivity in HFSC was low enough to fulfill the specific functional requirements of low-pH cements for geological disposal.
Iwatsuki, Teruki; Shibata, Masahito*; Murakami, Hiroaki; Watanabe, Yusuke; Fukuda, Kenji
Doboku Gakkai Rombunshu, G (Kankyo) (Internet), 75(1), p.42 - 54, 2019/03
In order to clarify the influence of shotcrete in the underground facility on the groundwater chemistry, an in-situ closed test was conducted in the mock-up tunnel at the depth of 500 m. Brucite, Ettringite, Ca(OH) 
, Gibbsite, KCO
, NaCO 
10HO, SiO (a) and Calcite were identified as the dominant minerals affecting the water chemistry. Furthermore, the shotcrete constructed in the tunnel has a reaction capacity which can produce about 570 m
of alkaline groundwater (pH12.4) saturated with Ca(OH). The estimation would improve the accuracy of prediction analysis of the long-term chemical influence of cement materials after the closure of the tunnel.
Fujita, Hideki*; Haga, Kazuko*; Shibata, Masahito*; Mihara, Morihiro
Semento, Konkurito Rombunshu, (61), p.65 - 71, 2008/02
The elution behavior of polycarboxylate type superplasticizer from hardened cement pastes were examined by analysis of organic matter in the pore water and curing water. A small quantity of superplasticizer was eluted and a large quantity remained in the solid. Only lower molecular weight matter was detected in the pore water, and decomposition of polymer under high alkalinity environment or selective elution of small molecule were suggested. Though there was the assumption that the effect of primary organic matter in cement like grinding aid was canceled by blank test, the assumption may need to be reconsidered.
Kaneda, Yoshihisa*; Haga, Kazuko*; Shibata, Masahito*; Kuranaga, Mebae*; Kikuchi, Michio*; Yamamoto, Takeshi*; Kato, Jun; Osugi, Takeshi; Kuroki, Ryoichiro
no journal, ,
Solidified cement and alkali activated materials was made, and used for dissolution test to obtain basic data of solidification on the waste caused by the contaminated water treatment at Fukushima Daiichi Nuclear Power Station.
Kikuchi, Michio*; Yamamoto, Takeshi*; Otsuka, Taku*; Kawato, Takaya*; Kaneda, Yoshihisa*; Shibata, Masahito*; Haga, Kazuko*; Taniguchi, Takumi; Osugi, Takeshi; Kuroki, Ryoichiro
no journal, ,
Summary of the study which is for characterization of Solidified cement and alkali activated materials was carried out due to obtain the data available for applicability evaluation low-temperature solidification on the waste caused by the contaminated water treatment at Fukushima Daiichi Nuclear Power Station.
Mochizuki, Akihito; Matsui, Hiroya; Ozaki, Yusuke; Motoshima, Takayuki*; Jo, Mayumi*; Shibata, Masahito*; Negishi, Kumi*; Sakamoto, Ryo*
no journal, ,
In geological disposal of high-level radioactive waste, retrievability of the waste should be ensured until the closure of repository. It is necessary to evaluate the soundness of open pit of the repository so that safe work is possible. This study aims to quantitatively understand changes in the characteristics of concrete support in the actual underground environment. Test specimens of low-alkaline sprayed concrete that were same as those applied in 350 m gallery of the Horonobe Underground Research Laboratory were prepared, placed in the same gallery, and physical and chemical characteristics of the specimens were investigated periodically. This presentation will report on the overview of the study and parts of results to date.
Shibata, Masahito*; Negishi, Kumi*; Sakamoto, Ryo*; Matsui, Hiroya; Mochizuki, Akihito; Ozaki, Yusuke
no journal, ,
no abstracts in English
Dei, Shuntaro; Amano, Yuki; Sugiura, Yuki; Shibata, Masahito*; Negishi, Kumi*; Yokoyama, Tatsunori; Kagami, Saya; Takeda, Masaki; Mochizuki, Akihito; Sakurai, Akitaka; et al.
no journal, ,
no abstracts in English
Koike, Ayaka*; Ishida, Keisuke*; Mihara, Morihiro; Shibata, Masahito*; Sawada, Kayo*
no journal, ,
no abstracts in English
Kikuchi, Michio*; Yamamoto, Takeshi*; Otsuka, Taku*; Kawato, Takaya*; Kaneda, Yoshihisa*; Shibata, Masahito*; Haga, Kazuko*; Osugi, Takeshi; Sone, Tomoyuki; Kuroki, Ryoichiro
no journal, ,
In order to obtain data to be used in the evaluation of the applicability of low temperature processing to carbonate slurry generated by contaminated water treatment at Fukushima Daiichi Nuclear Power Station, the basic properties of the solidified cement and alkali activated material blended simulated carbonated slurry were evaluated. An overview of the study and some of the results obtained are reported here.
Kaneda, Yoshihisa*; Haga, Kazuko*; Shibata, Masahito*; Osawa, Norihisa*; Kikuchi, Michio*; Yamamoto, Takeshi*; Kawato, Takaya*; Osugi, Takeshi; Sone, Tomoyuki; Kuroki, Ryoichiro
no journal, ,
Solidified cement and alkali activated material blending carbonated slurry were prepared and their dissolution tests were carried out in order to obtain basic data for the low temperature processing of the waste generated by contaminated water treatment at Fukushima Daiichi Nuclear Power Station. An overview of the study and some of the results obtained are reported here.
Higuchi, Keita*; Okubo, Takahiro*; Negishi, Kumi*; Shibata, Masahito*; Tachi, Yukio
no journal, ,
no abstracts in English
Matsui, Hiroya; Motoshima, Takayuki*; Shibata, Masahito*; Sakamoto, Ryo*; Mochizuki, Akihito
no journal, ,
no abstracts in English
