接缝密封材料对缓冲砌块屏障封闭性能的影响

Influence of joint sealing material on the sealing performance of the buffer block barrier

室内制备模拟压实砌块,分别采用膨润土粉末、膨润土泥浆以及微粒膨润土(高密度膨润土颗粒与粉末的混合物)对砌块接缝进行密封,通过室内模拟渗透试验对砌块的膨胀、渗透性能进行研究,并借助X-CT扫描试验、热传导试验以及微观结构分析对砌块接缝的密封程度进行评价。试验结果表明:随着水化时长的增加,砌块核心区膨润土向接缝区孔隙侵入,接缝区膨胀力快速发展,导致砌块轴向膨胀应力的发展速度减缓,产生滞后现象;接缝密封材料类型对砌块体系的水化进程影响显著,膨胀应力发展速率存在差异;接缝的愈合程度与接缝充填材料的初始干密度呈正相关。CT扫描图像表明:水化结束后,密封接缝与砌块已基本"焊接"在一起,而未进行密封的砌块之间仍然存在间隙,并未完全封闭。相较于完整试样,密封接缝区土样的集合体间孔隙尺寸分布范围扩大(3~30μm),泥浆密封试样接缝区土样结构疏松,出现100~500μm的大孔隙,而干缝试样的接缝区则存在多条体积较大的裂隙状二维孔隙。密封可以显著提高砌块体系的各向膨胀能力,改善愈合砌块体系的均质性,密封后的砌块体系抗渗性能以及热传导性能与完整样接近,接缝的不利影响弱化。综合来看,采用微粒膨润土对砌块接缝进行密封,接缝的愈合度最高,砌块的各项工程性能最佳,其次为采用膨润土粉末以及膨润土泥浆进行密封的试样,未进行密封处理的干缝试样愈合效果最差。

An indoor permeability test was conducted to study the sealing performance of joints between the compacted blocks which were backfilled with bentonite powder(P), bentonite particle-powder mixture(P/P) and bentonite slurry(S), respectively. The swelling stress and hydraulic conductivity were monitored during the permeability test. After the test, the homogenization of blocks and sealing degree of joints were evaluated according to the X-CT scanning test, thermal conductivity test and microstructure test. The results show that: with the increase of hydration time, the bentonite in the core area of the block intrudes into the pores of the joint, and the increase rate of swelling stress in the joint zone is higher than that in the axial direction of the block, which leads to the slowing down of the development speed of the axial swelling stress of the block and produces hysteresis. The joint sealing materials have significant influence on the hydration process of the block system, resulting different swelling stress development rates. The sealing degree of the joint is positively correlated with the initial dry density of the joint filling material. The X-CT scanning images show that the sealing joint and the block have been "welded" together after hydration. By contrast, there is still a gap between the blocks with a blank joint, showing a lower sealing degree. The MIP and SEM tests demonstrate that the pore size distribution of inter-aggregates in the joint area lies in the proportion between 3 μm and 30 μm, and a certain number of large pores with a diameter between 100 μm and 500 μm were observed in the joints sealed with bentonite slurry. Some fissure-like 2-dimensional pores appeared in the blank joint according to the SEM picture. Generally, sealing can significantly improve the expansion ability and homogeneity of the block system, and the impermeability and thermal conductivity of the healing block system are close to that of the intact sample. Joint backfilled with bentonite particle-powder mixture shows a better sealing performance, followed by the joint sealed with bentonite powder and bentonite slurry, and the sealing effect of joint without backfilling is the worst.