Cement-bentonite interaction with different cement materials, 1; Experiments
Kawakita, Ryohei
; Anraku, Sohtaro
; Hanamachi, Yuji*; Mitsui, Seiichiro
; Sasamoto, Hiroshi
; Mihara, Morihiro

Cement and bentonite materials are to be used in a repository for the geological disposal of radioactive wastes in Japan. Cement will provide structural support to the repository and will be in close contact with bentonite. Understanding the interactions between these two materials is necessary to improve repository design and ensure long-term safety. Ordinary Portland Cement (OPC) is widely used for construction, however, there are concerns that its high pH
13 porewater could cause significant alteration of bentonite. JAEA has therefore developed a High-content Fly ash Silica fume Cement (HFSC) to lower the pH of cement porewater. Studies on HFSC and bentonite interactions are, however, limited. In addition, elevated temperatures can be expected in the repository by the combination of radiolytic heating and geothermal gradients. Temperature affects mineral reaction rates and their overall stability, but such thermal effects have not yet been studied in detail in the context of cement and bentonite interactions. Laboratory scale experiments were therefore conducted to investigate the interactions between OPC or HFSC and compacted bentonite (Kunigel V1; dry density = 1.37 Mg/m
) at repository relevant temperatures of 50
C and 80
C.