Bohner, Edgar

Kivikoski, Harri

Löija, Mia

Salparanta, Liisa

SKB and Posiva have two different reference methods for production of buffer blocks: uniaxial and isostatic compression, respectively. Both methods have been shown to fulfil current requirements on buffer blocks. Yet the comparisons of performance have not been made by blocks produced of the exact same material. The goal of the project was to test, compare and evaluate the properties of the uniaxial and isostatic full-scale buffer blocks with a diameter of 1800 mm and manufactured from the same bentonite batch by the same predefined parameters and technical properties. The same batch of MX-80 bentonite with a water content of w = 17%, was used for the comparative study. It was the intention to perform the evaluation based on similar conditions, i.e. at the same age, on the same size samples and using the same test methods for both blocks. After all, a full-scale block, manufactured by isostatic compression, could not be made available. Therefore, the testing was done on an isostatic block with a height of 1250 mm and a diameter of 1200 mm, which is 2/3rd of the diameter of the full-scale uniaxial block having a diameter of 1800 mm and a height of 500 mm. From both blocks, several core samples were taken in the vertical and horizontal directions. The core samples were cut to prepare further specimens. The specimens were used to determine their bulk density, water content, compressive and splitting tensile strength and modulus of elasticity. Further tests were performed to determine the humidity adsorption, change in density and cracking behaviour of the bentonite samples when stored in ambient air with different relative humidity. Special samples in the form of a plate were cut from both blocks. The thermal conductivity of the bentonite plates was measured with a heat flow meter. Based on the testing results the properties and the behaviour of both blocks were compared and evaluated in order to provide the basis for a final decision on the future manufacturing technique for buffer blocks

Evaluation of Performance of Uniaxially and Isostatically Compressed Buffer Blocks

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