Evaluation and comparison of bentonite surface fractal dimension and prediction of swelling deformation: Synchrotron radiation SAXS and N2-adsorption isotherms method

Abstract

A key parameter for calculating the swelling deformation using fractal model is the fractal dimension. Small angle X-ray scattering (SAXS) and liquid nitrogen adsorption method (Frenkel-Halsey-Hill (FHH) and Neimark thermodynamic method) were employed to determine fractal dimension of four Chinese bentonite. Based on SAXS and the FHH method, fractal swelling deformation model was adopted to predict mechanical behavior. The result suggested that the fractal dimensions of #1, #2, #3 and #4 calculated by SAXS were 2.600, 2.650, 2.530 and 2.780, respectively. The fractal dimensions determined by FHH model were 2.636, 2.579, 2.612, and 2.892, respectively. These minor variations can be associcated with the different the test scales, difference between the open hole, closed hole and interlayer hole, and the different test mechanism. The SAXS method was based on the difference in electron density and can reach the interlayer pores of montmorillonite. It seemed that the reliability and stability of the Neimark thermodynamic method need to be further improved. Swelling deformation calculated by SAXS and FHH method was roughly in accordance with the experimental data. Compared with the liquid nitrogen adsorption method, the predicted value of the SAXS method was closer to the experimental value, which confirm that the fractal dimension calculated by SAXS was more accurate. This fills the gap of using SAXS to predict the swelling deformation of Gaomiaozi CaGMZ bentonite.