Development of low-alkaline cement using pozzolans for geological disposal of long-lived radioactive waste

Mihara, Morihiro  ; Iriya, Keishiro*; Torii, Kazuyuki*

To reduce uncertainties in the safety assessment of a disposal system for long-lived radioactive waste, cement was developed which generates leachates with a lower pH than that of ordinary cement paste. This cement was termed "low-alkaline cement". Large amounts of pozzolans were used to produce the low-alkaline cement from ordinary Portland cement. To reduce the pH values, silica fume was found to be efficient, however large amounts of silica fume reduced the workability of fresh concrete. Therefore, we also used fly ash with silica fume, high-volume fly ash silica fume cement (HFSC). The low pH value and self-compacting HFSC was developed. Two types of HFSC showed high compressive strength, smaller drying shrinkage and lower temperature rise than those of ordinary cement concrete. They can therefore be applied to the structure and filling concrete in the disposal system.