Prediction of swelling pressures of different types of bentonite in dilute solutions

• A model is developed to predict swelling pressures of bentonite-based materials.
• The model takes both crystalline swelling and osmotic swelling into account.
• The model also accounts for disintegration of the montmorillonite particles.
• The model predictions agree well with a great number of experimental results.
• The model is able to predict the water retention curves of unsaturated bentonites.

A mechanistic model is developed to predict the swelling pressure of fully saturated, bentonite-based materials in distilled water or dilute saline solutions over a large range of final dry densities of bentonite. It applies a thermodynamic relationship between swelling pressure and suction to describe the contribution of crystalline swelling, while using a diffuse double-layer model to explain the behavior of osmotic swelling. In addition, it accounts for the demixing of exchangeable cations and the disintegration of the montmorillonite particles into small stacks of unit layers upon water uptake.Comparison of the model predictions with a great number of experimental results of swelling pressures of different types of bentonites and bentonite–aggregate mixtures in both distilled water and saline solutions suggests that the model works excellently in the cases tested. It is found that the water chemistry, the montmorillonite content, the type and amount of exchangeable cations in the interlayers are important in determining the extent to which the montmorillonite particles are delaminated and hence the swelling behavior of saturated, bentonite-based materials.On the other hand, the applicability of the model in predicting the water retention curves of unsaturated bentonites is also tested. The results show that the predicted curves are in good agreement with the measured data and that the montmorillonite particles are more difficult to disintegrate into small pieces in the case of unsaturated bentonites than would otherwise be possible.

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