Abstract: The fractal dimension is determined based on the slope of the double logarithmic curve using synchrotron radiation small angle X-ray scattering (SAXS) and liquid nitrogen adsorption for sodium-based bentonite in Gaomiaozi, Inner Mongolia, as a backfill material for nuclear waste buffering. Based on the FHH (Frenkel-Halsey-Hill) model, the fractal dimension of liquid nitrogen adsorption was calculated. The calculation of bentonite expansion deformation and the required parameters are summarized. Based on the electric double layer model and fractal model of bentonite expansion deformation, the K value of the expansion force parameter of bentonite was calculated by SAXS fractal dimension and liquid nitrogen adsorption fractal dimension. The difference of the calculated expansion force of the fractal dimension measured by the two methods was compared. The results show that the fractal dimensions measured by SAXS and liquid nitrogen adsorption are close, which are 2.600 and 2.636 respectively, and the difference between the two is small. There is a good linear relationship between scattering intensity and scattering vector in the double logarithmic relationship. In the correlation between void ratio and expansion force, the predicted values obtained by the two methods are smaller than the experimental measured values. Under the same bentonite density, the fractal dimension is calculated by SAXS. The predicted value of the expansion strain is greater than the value predicted by the fractal dimension from the liquid nitrogen adsorption test.

Key words: synchrotron radiation, small angle X-ray scattering, Gaomiaozi bentonite, liquid nitrogen adsorption, expansion force