盐碱环境下改性膨润土密封浆液的膨胀性能与改性机制研究OA

The chemical environment of strong alkali and high-sodium water in the chamber of the high-level radioactive waste disposal warehouse is one of the primary factors affecting the sealing effect of the joints in bentonite blocks.In this study,a bentonite slurry with improved fluidity and injectability was used as the seam sealing material.Nano-bentonite(diameter d≤20 μm),sodium polyacrylate(PAA)and sodium carboxymethyl cellulose(CMC)were used as improvers to enhance the slurry's sealing performance in complex environments.Through apparent viscosity tests and free expansion rate tests under salt and alkali conditions,combined with XRD,FTIR and SEM analyses,the viscosity,expansion sealing performance and corresponding modification mechanism of modified bentonite slurry were investigated.The results indicate that CMC has the most significant viscosity-enhancing effect on the slurry,and the nano-bentonite-modified slurry exhibits the best swelling performance.PAA can significantly improve the slurry's fluidity,and the modified bentonite slurry with a soil-water ratio of 1꞉4 is recommended as the joint grouting material.The optimum mass fractions of nano-bentonite,CMC,and PAA are 15%,1%,and 15%,respectively.Both CMC and PAA protect the montmorillonite minerals in the core area through surface coating or a network structure,reducing their dissolution in a strong alkali environment and improving the durability and final swelling performance of bentonite in both salt and strong alkali solutions.The modifying effects of the agents rank from strongest to weakest as following:CMC,PAA,and nano-bentonite.On the whole,the permeability coefficients of the three modified bentonite slurries are in the range of 10-10,which meet the basic requirements for preventing seepage in barrier walls and can be used for joint sealing in high-level radioactive waste repositories.