Manufacture and homogeneity of highly dense bentonite samples

A project study on behalf of Nagra for high radioactive waste disposal in deep geological formations as well as literature studies have shown that bentonite could be a suitable filling and sealing material. The Institute for Foundation and Soil Mechanics of the Swiss Institute of Technology is under contract by Nagra to investigate different bentonites. The investigations concentrate on the Na-bentonite MX-80 from Wyoming, which is foreseen by the Swedes, and on the geographically more favorable Ca-bentonite Montigel from Bavaria. Montigel powder and granulate, which show certain manufacturing advantages, were investigated. Numerous experiments, mostly for manufacturing of sample bodies for swelling experiments, were performed and evaluated with the aim to clarify the condensation properties of bentonites in a highly dense field. Especially the relationship between water content, pressure and attained dry density for the three bentonites: MX-80 (granulate), Montigel (powder) and Montigel K (granulate) were investigated. It was shown that the delivery water contents of the three bentonites favorably lie within the 8-10 % necessary to prepare high density samples with dry densities of about 2.0 Mg/m3. The comparison of the three bentonites shows that both bentonites in granular form allow lower pressures at condensation than the bentonite in powder form. Based on x-ray and pressure porosimetry investigations the high density bentonites are largely homogeneous sample bodies considering their density and pore radius distribution. 15 figs., 2 tabs