NMR study of C-A-S-H structures

Hanamachi, Yuji*; Walker, C.*; Sasamoto, Hiroshi; Mihara, Morihiro

NIMS Bisai Kozo Kaiseki Purattofuomu Riyo Hokokusho (Internet), 2 Pages, 2023/12

A High-volume Fly ash Silica fume Cement (HFSC) has been considered as the use of concrete support of drift in deep disposal of radioactive wastes. JAEA has been carried out experiments and modeling studies to evaluate chemical stability of C-A-S-H gel synthesized which would be believed as the dominant component of the HFSC. For the modeling purpose, it is necessary to evaluate the chemical composition both of C-A-S-H gel synthesized and accompanied minerals in the experiment. In the year of 2020, Al and Si NMR measurement were performed to identify Al and Si distribution in the sample and chemical composition of C-A-S-H gel was derived. However, it was impossible to derive the C-A-S-H gel composition having the expected Al/Si molar ratio since there were several accompanied minerals produced in the experiment due to the short term of immersion. This time similar approach to derive C-A-S-H gel composition is adopted using NMR measurement for the sample of longer time (6 months).

Evolution of the reaction and alteration of mudstone with ordinary Portland cement leachates; Sequential flow experiments and reactive-transport modelling

Bateman, K.; Murayama, Shota*; Hanamachi, Yuji*; Wilson, J.*; Seta, Takamasa*; Amano, Yuki; Kubota, Mitsuru*; Ouchi, Yuji*; Tachi, Yukio

Minerals (Internet), 11(9), p.1026_1 - 1026_23, 2021/09

https://doi.org/10.3390/min11091026

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

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

no journal, , 

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.