Modifying the linear packing model for predicting the packing density of GMZ bentonite pellet mixtures.

In repositories for high-level radioactive waste, bentonite pellet mixtures serve to fill joints between compacted blocks of bentonite and the gaps between these blocks and the concrete lining. Gradation significantly influences the packing density of on-site backfill mixtures. This study specifically examined Gaomiaozi (GMZ) bentonite pellet mixtures, characterized by particle sizes ranging from 0.25 to 10 mm. We systematically categorized these mixtures for packing density testing and modified the linear packing model based on measured values, establishing a model suitable for predicting the packing density of bentonite pellet mixtures. The reliability of the modified linear packing model was evaluated by comparing errors between measured and theoretical values. Using this modified model, we determined the maximum packing density and the corresponding optimal gradation for GMZ bentonite pellet mixtures. The research underscores that the modified linear packing model yields highly accurate predictions, with the error between theoretical and measured packing density staying within 3%. Notably, the maximum packing density recorded for GMZ bentonite pellet mixtures is 0.840. The optimal gradation indicates that pellets with particle sizes of 0.5–0.25 mm should have the largest mass fraction, at 0.45. Additionally, pellets with particle sizes of 10–5 mm have a mass fraction of 0.40, while the mass fractions of pellets with particle sizes of 5–2 mm, 2–1 mm, and 1–0.5 mm are all 0.05. Furthermore, bentonite pellet mixtures featuring the optimal gradation achieve a maximum dry density of 1.88 g/cm³ at a water content of 11.9%, surpassing the maximum dry density achieved by mixtures with Hoffmann and Fuller gradations by 0.02 g/cm³. • Modification of the linear packing model tailored to bentonite pellet mixtures. • Validation of the accuracy of the modified linear packing model using measured packing density values. • Calculation of the maximum packing density and its associated gradation for GMZ bentonite pellet mixtures. • Assessment of the compaction characteristics of bentonite pellet mixtures featuring the optimal gradation. [ABSTRACT FROM AUTHOR]