高压实高庙子膨润土的微观结构特征

采用水汽平衡法和渗析法吸力控制技术,借助压汞仪法(MIP)和环境扫描电镜法(ESEM)等试验手段,在自由和侧限状态下,试验研究了被确定为我国高放废物地质处置库首选缓冲材料的高庙子膨润土水化过程中的微观结构变化特征.结果表明,侧限条件与土中吸力对于高压实膨润土水化过程中的微观结构变化影响明显.在高吸力范围(3～309MPa)内,无论是处于侧限还是自由膨胀状态,高压实高庙子膨润土的含水量随控制吸力变化不大,且2种状态下数值基本一致;而当吸力低于3 MPa时,尤其是当吸力小于1 MPa时,处于不同状态下的土样中,含水量随吸力的变化特征出现了明显的差异.从微观上看,随着控制吸力的降低,自由膨胀状态下,大量的水进入了集合体间的孔隙(大孔隙)中,压实膨润土的体积膨胀主要来自于集合体间孔隙(大孔隙)的膨胀;侧限状态下,内部膨胀力逐渐积累,集合体间的孔隙(大孔隙)被压缩,较小孔隙的数量不断增加,压实膨润土中的孔隙大小趋于均一化.

Characteristics of Micro structure of Densely Compacted Gaomiaozi Bentonite

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.