Abstract
Conventional cementitious materials as tunnel supporting materials are utilised in the construction of the final repository for spent nuclear fuel. However, the use of cementitious material releases alkaline ions from pH12 to pH13 plumed into groundwater. Such a high pH is detrimental to the performance of the bentonite functioning, which may possibly enhance the dissolution and alteration of the fracture buffer and filling materials. Instead, low-pH cementitious materials are being developed for use in geological repositories. This study is aimed at evaluating the usability of low-pH cementitious materials containing 40% silica fume or composites blended with 20% silica fume and 40% fly ash. Engineering properties were analysed and verified through experimental research using the flow, compressive strength, pH measurement and hydraulic conductivity. Test results show that the replacement level with 40% of silica fume or 20% of silica fume and 40% of fly ash was suitable for the mixture of low-pH cementitious. Compared to the compressive strength and water permeability of ordinary cementitious, those of low-pH cementitious enhanced better engineered performances at the age of 91 days. The information is contributed us to establish the long-term durability and environmental requirements of disposal repositories in Taiwan.
Highlights
On the basis of preliminary feasibility assessment report for the spent nuclear fuel final disposal technology in 2009, canister design in Taiwan being studied with consideration to the preliminary design of a disposal concept using the Swedish canisters having the KBS3type copper canisters
Low-pH cementitious materials had a lower amount of the C/S ratio of C-S-H, which enhances their sorption capacity of alkalis and reduces their equilibrium pH [8,9,10]. Owing to their fineness and chemical compositions, silica fume and metakaolin are much more reactive in the formulation of low pH cementitious materials and the suitable replacement of cement is in the range of 25% to
This study aims to identify appropriate mix designs for low-pH cementitious materials for suitable materials including silica fume, slag and fly ash
Summary
On the basis of preliminary feasibility assessment report for the spent nuclear fuel final disposal technology in 2009, canister design in Taiwan being studied with consideration to the preliminary design of a disposal concept using the Swedish canisters having the KBS3type copper canisters. Compared to the compressive strength and water permeability of ordinary cementitious, those of low-pH Investigations of silica fume, fly ash and slag to partially replace cement have been carried out to produce low alkalinity, high workability and low heat cementitious materials [2,3, 7].
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