Swelling pressure deterioration of compacted GMZ bentonite and its structural damage under heat combined with hyperalkaline conditions

Abstract

ABSTRACT Compacted bentonite as an artificial barrier/backfill material is susceptible to heat when combined with the hyperalkaline conditions of deep geological repositories. In order to investigate the structural damage of compacted GMZ bentonite and its effect on swelling pressure deterioration, X-ray powder diffraction (XRD) and mercury intrusion porosimetry (MIP) tests were performed on bentonite specimens after immersed in hyperalkaline solution at 20–80°C. The results suggest that the increase in the number and pore sizes of macropores, and the decrease in the crystallinity degree of montmorillonite and silicate minerals are extremely obvious, which well characterises the structural damage of compacted bentonite on a microscopic scale. The structural damage parameter is facilitated by heat combined with hyperalkaline conditions. The structural damage of compacted bentonite is more susceptible to variations in the microscopic pore structure and the dissolution of silicate minerals than that of montmorillonite; and the structural damage of compacted bentonite will cause the long-term deterioration of swelling pressure. Hence, the long-term safety of HLW repository should be evaluated taking into account of the structural damage of compacted bentonite caused by heat combined with chemical conditions.