Effect of synthetic Beishan site water and cement solutions on the mineralogy and microstructure of compacted Gaomiaozi(GMZ) bentonite

Abstract The mineral alteration and microstructure evolution of compacted GMZ bentonite was investigated during the long-term in the Beishan area, a candidate for a high-level radioactive waste repository in China. The compacted GMZ bentonite samples at initial dry densities of 1.5 and 1.7 Mg/m3 were infiltrated by synthetic Beishan Site Water (BSW) and two synthetic cement solutions (Young Cement Water -YCW and Evolved Cement Water - ECW) under constant volume conditions for about 2 months in this study. X-Ray diffractometry (XRD), mercury intrusion porosimetry (MIP) and scanning electron microscope (SEM-EDS) tests were carried out to observe the mineralogy and microstructure of the specimens after experiencing the three types of pore solutions. There is evidence of cation exchange reactions, some zeolites and C-S-H in the GMZ bentonite after the infiltration of alkaline solutions. The hydration of alkaline solutions and mineralogy alteration result in changes to the microstructure of compacted GMZ bentonite. The generated secondary mineral on the surface of montmorillonite leads to the clogging of inter-aggregate pores. In the case of high dry density, this resulted in pore occlusion.