Characteristics of Microstructure of Densely Compacted Gaomiaozi Bentonite

Abstract:

The microstructure changes of Gaomiaozi bentonite in the process of hydration, which is deemed as the best buffer or backfilling material for deep disposal of high radioactive waste in China are analyzed under unconfined and confined conditions by using mercury intrusion porosimetry(MIP)method and environmental scanning electronic microscopy(ESEM) techniques. Results show that confining conditions and suction greatly influence the changes of microstructure of bentonite. For high suction (3~309 MPa), water content slightly changes with controlling suction under both confined and unconfined conditions, while for low suction (lower than 3 MPa), especially when suction is lower than 1 MPa, there is a significant difference in the relationship between water content and controlling suction under different confining conditions. From the view point of microstructure, as hydration process continues, under unconfined conditions, most of the water enters interaggregates pores and the swelling of compacted specimen mainly comes from the swelling of the interaggregates pores (big pores), while under confined conditions, swelling pressure increases with hydration process, interaggregates pores (big pores) are compacted and quantities of smaller pores increase, resulting in unified pore size in the compacted specimen.

Key words:Gaomaiozi bentonite; microstructure; mercury intrusion porosimetry(MIP) method; environmental scanning electronic microscopy(ESEM) technique