Cement-bentonite interaction with different cement materials, 2; Modeling

異なるセメント材料によるセメント-ベントナイト相互作用への影響,2; 解析的検討

安楽 総太郎 ; 川喜田 竜平  ; 花町 優次*; 三ツ井 誠一郎  ; 笹本 広   ; 三原 守弘  

Anraku, Sohtaro; Kawakita, Ryohei; Hanamachi, Yuji*; Mitsui, Seiichiro; Sasamoto, Hiroshi; Mihara, Morihiro

OPCまたはHFSCとベントナイトを接触させた試験において、界面近傍で観察されたベントナイトの変質と二次鉱物の生成を評価するため、コンピュータモデリングコードCABARETを用いた1次元反応性輸送モデルを構築した。OPCとクニゲルV1の接触試験の解析では、OPC中のCaがポルトランダイトの溶解により枯渇し、クニゲルV1中のSiがカルセドニーの溶解により枯渇し、XRDでの観察と同様、界面にC-S-Hゲルが析出することが確認された。80Cの条件では、C-S-Hゲルの析出により界面が閉塞し、拡散とそれに伴うクニゲルV1の変質が制限されることが確認された。HFSCとクニゲルV1の接触試験の解析では、OPCと比較してpHが低いHFSCの間隙水によるクニゲルV1の変質が著しく少ないことが示され、これは実験結果とも一致した。HFSCは、C-A-S-Hゲルとエトリンガイトの溶解によって界面近傍で空隙率を増加させ、クニゲルV1は、カルセドニーのわずかな溶解によって空隙率を増加させるといる解析結果が示された。

To evaluate the observed alteration of bentonite and secondary mineral formation by OPC or HFSC near the interface, 1D reactive transport models were constructed using the Cement And Bentonite Alteration due to REactive Transport (CABARET) computer modelling code. Supporting calculations for initial hydration of OPC or HFSC were conducted using PHREEQC to generate the initial porewater compositions. JAEA's Thermodynamic DataBase for geochemical reaction was used in all calculations. Modeling of OPC and Kunigel V1 interaction resulted in depletion of Ca in OPC by portlandite dissolution and depletion of Si in Kunigel V1 by chalcedony dissolution leading to C-S-H gel precipitation at the interface, which were confirmed by XRD. Clogging of the interface by the precipitation of C-S-H gel at 80C, however, limited diffusion and therefore the alteration of Kunigel V1. Coupling between diffusion coefficients and low porosities requires further data and validation to improve the simulation. The temperature dependence of dissolution rates of the C-S-H gel and chalcedony also needs to be confirmed. Modeling of HFSC and Kunigel V1 interaction showed significantly less alteration of the Kunigel V1 from the significantly less alkaline HFSC porewater, which is also consistent with the experiments. Modelled changes in HFSC resulted in an increase in porosity at the interface by the dissolution of C-A-S-H gel and ettringite, and in Kunigel V1 by the slight dissolution of chalcedony. To evaluate the elevated temperature effect in HFSC hydration, it is important to use a C-A-S-H gel model and to confirm the extents of pozzolanic reaction of silica fume and fly ash, which are currently based on measurements at room temperature.