膨润土团粒的压实性能研究

Compaction Properties of Bentonite Agglomerate

高放核废料深地质处置中,膨润土缓冲/回填材料需要满足低渗透性要求,实现阻滞地下水入渗和放射性核素泄漏的目标。增强膨润土防渗能力的常规方法是采用增大压实功提高其密实度,但该方法十分耗时耗能。为此,尝试从调整膨润土团(颗)粒级配角度,探究提高压实度的有效方法。首先,配置不同团粒级配和初始含水率的膨润土试样,再利用压力机压实到45kN;最后,采用液氮冻干法干燥不同状态的试样,通过压汞仪获得其孔隙分布曲线。结果表明:相同压实荷载下(45kN),干密度随含水率呈先增大后减小的整体变化趋势,含水率约为20%时压实效果最佳,其中O-B组合与A-B-3组合具有双峰特征;另外,通过调整团粒级配,压实效果显著提升,最大干密度由1.64g/cm3提高到1.72g/cm3,其中A-B-3团粒组合效果最好。孔隙分布曲线表明,压实荷载只能压缩3.59~0.188μm范围的孔隙,而对26nm左右的孔隙没有影响。当含水率超过20%时,依靠增大压实荷载不能提高其压实度,但当改变团粒组合后,却可以有效提高其压实性能。

Bentonite is able to meet the low permeability requirements.Thus,it was considered as buffer/backfill material in deep geological disposal repository for high-level radioactive nuclear waste.This clay plays a major role in retarding groundwater infiltration and radionuclide leakage.Usually,the infiltration prevention capacity of bentonites can be enhanced through improving compaction degree.The common and direct method for compaction degree improvement is to use high compaction energy,but this 'method is not economical in practice.Therefore,a low energy consuming method for compaction degree improvement was presented through adjusting agglomerate composition.First,the bentonite samples with different agglomerate compositions and water contents were prepared.Then the samples were compacted under force 45kN.Finally,the compacted blocks with different compaction degrees were dried using liquid nitrogen freeze-drying method,and their pore distribution curves were obtained through mercury porosimeter.The compaction results show that,under the same compaction force (45kN),the dry density of the samples increases at first and then decreases with water content increasing.The optimum water content is about 20%.Among them,O-B and A-B-3samples show double peaks in the compaction curves.Compared with O-B assembly,the A-B-3samples are more easily to be compacted,with maximum dry density increasing from 1.64g/cm3to 1.72g/cm3.This phenomenon proves that compacted effect can be improved significantly through adjusting agglomerate composition.The pore distribution curves show that pores with diameters range from 3.59μm to 0.188μm can be compacted effectively,and the compaction loading has little effect on pores with diameters around 26nm.When water content exceeds 20%,there is no useful in improving compacted degree by increasing compacted energy solely.But,the compacted degree can be improved effectively by changing agglomerates size combination.