Research On Microstructure Of Compacted Bentonite Block As HLW Buffer

The mixture of Gaomiaozi bentonite and quartz sand has been identified as ideal buffer-backfill materials up to now,of which enormous researches have been done.Laboratory specimen are characterized with regular shape and small size,which can prepared under an exact condition.While the blocks using in practical engineering construction will be manufactured with industrialization equipment into specific shapes.Therefore,it is significant to develop a manufacture technology by industrialized experiments and to study the size effect.Research group under Professor Zhang in Lanzhou University,based on the domestic and overseas available manufacture studies designed a set of machinery compaction equipment,established a double layer barrier conceptual model which are combined by 1/6 sector and 1/12 sector blocks,and suggested the thesis basic sizes of sector blocks.This research selects two kinds of material,loess and bentonite-sand mixture,to compact sector blocks and analyzes the microstructure features of industry blocks via Computed Tomography(CT),Scanning Electron Microscope(SEM)and Mercury Intrusion Porosimetry(MIP)to reveal the immanent cause of inhomogeneity from micro scale.The research mainly contains two parts,including loess compaction test and microstructure test on bentonite-sand mixture block.In the first part,the loess from the Cuiying Mountain,Lanzhou City,it is compacted into 1/12 sector blocks with ?d=1.8 g/cm3 and ?=13%,and then observed by CT scanning to see the internal microstructure features and the density distribution along different directions.Test results show that loess blocks density is distributed in certain regular pattern along different directions,especially along the height direction.The second part is the microstructure research on bentonite-sand blocks,which is compacted into 1/12 sector as two parallel group,characterized with a sand ratio of Rs=30% and different target dry densities and water contents.The compacted blocks are divided into 4×4×4 pieces,among them 4 typical pieces are taken along the height direction to conduct the SEM and MIP tests based on CT tests.The main conclusions can be drawn as follows:(1)According to the CT scanning image,it can be seen that there are obvious aggregates in the block.For one single block,density shows homogeneous changing pattern along different directions.Along the height direction,the density is distributed symmetrically with a middle layer as symmetry point: High density appears at the upper and lower layers while lower density appears at the middle layer.Along the angle direction,the density distribution is homogeneous.Along the radius direction,the density in circle center area is larger than that in the margin area.(2)By the comparison and analysis on the pore size distribution curve from MIP test,it is seen that the pore range becomes smaller with the increase of dry density.The pore range expands rapidly with the increase of water content.(3)Along the height direction within the same block,the pore size distribution curve shows insignificant distribution rules.Among the three blocks with same water content but different dry density,the pore size range and pore structure types decreases inside the blocks as dry density increases,which means the internal pore size is getting uniform with the increase of dry density.Among the three blocks with different water content but same dry density,the pore size range and pore structure types increase inside the blocks as water content increases,which means the internal pore size is getting inhomogeneous with the increase of water content.