膨润土受热作用后的水-力性能研究

受核废料衰变热影响，处置库内缓冲层的膨润土会长期处于高温状态。经历持续高温作用后，膨润土的膨胀自愈能力能否得以保持，还没有明确的结论。利用马弗炉维持105 ℃恒温环境，对粉状膨润土持续加热到预定周期；然后，获得不同加热周期试样的水-力性能。结果表明，随着加热时间增长，膨润土水-力性能出现大幅衰减。借助X射线衍射仪测试发现持续加热90 d其晶面间距缩合，出现了硅质氧化物胶结，导致颗（团）粒集聚。其红外光谱和热重特征表明，持续加热作用脱去了蒙脱石层间离子水合水，引起部分Na、Mg离子随水分蒸发而逃逸，两者共同作用导致蒙脱石颗（团）粒发生缩合作用。通过观察其扫描电镜图片也能发现，经过90 d持续加热后，蒙脱石颗（团）粒表面不再层次分明，而是紧密地相互搭接，发生了显著的缩合行为。粒度分布特征进一步证实，膨润土经历90 d加热后，即使浸泡28 d，其颗（团）粒依然未被分散，可初步推断上述缩合行为不可逆。

Hydro-mechanical performances of bentonite respond to heat-treated history

Bentonite, as buffer materials in disposal repository, will be under long term effect of decay heat which released from nuclear waste sealed in the canister. Whether the expansion self-healing ability of bentonite can be maintained after sustained high temperature has not been clearly concluded. The powdery bentonite was heated in muffle furnace at a constant temperature (105 ℃). But the heating periods were different, and the longest one was 90 d. A series of tests was carried out on the heated samples. The results show that the free swelling ratio and swelling pressure decrease dramatically with heated time. X-ray diffraction spectrums of montmorillonite demonstrate that the adjacent lattice distances is shortened, silica oxide cementation occurs after continuous heating for 90 d, which results in aggregation of montmorillonite particles. It can be inferred from infrared spectrum and thermogravimetric testing results that the hydration of interlayer ions of montmorillonite is removed by continuous heating, and some Na and Mg ions escape with the evaporation of water. The combination of the two causes the condensation of montmorillonite particles. This phenomenon is also found by SEM that montmorillonite particles closely linked to each other instead of distinctly stacked as original state. Moreover, this condensation or cluster behaviors are irreversible, which could be confirmed from particle size distribution curves of heated bentonite. Because the clusters of bentonite (heated 90 d) were not dispersed obviously, even after soaking 28 d.