- 2077 Chaitra · 4 marks
Compare montmorillonite and kaolinite
Short answer
Montmorillonite is a 2:1 mineral with weak van der Waals bonding, high isomorphous substitution, high specific surface and CEC, causing strong swelling, high plasticity and compressibility, low permeability and weak wet strength. Kaolinite is 1:1, hydrogen-bonded, low substitution and surface, giving low swelling, good stability, lower plasticity and compressibility, and is generally construction-friendly.
Compare the montmorillonite and kaolinite minerals of clay on the basis of chemical and physical characteristics and how they affect the geotechnical behavior of soil.
| Basis | Montmorillonite | Kaolinite |
|---|---|---|
| Structure | 2:1 (silica - gibbsite - silica) | 1:1 (silica - gibbsite) |
| Layer thickness | About 9.6 Å | About 7.2 Å |
| Bonding between layers | Weak van der Waals; water enters between layers | Strong hydrogen bonds and van der Waals |
| Isomorphous substitution | Extensive (Mg for Al) | Very little |
| Specific surface | Up to 800 m²/g | About 15 m²/g |
| Cation exchange capacity | High (80 - 150 meq/100 g) | Low (3 - 15 meq/100 g) |
| Particle shape | Very thin flakes | Thicker hexagonal plates |
| Liquid limit | 100 - 900% | 30 - 110% |
| Activity | 1 - 7 (active) | 0.3 - 0.5 (inactive) |
Effect on geotechnical behaviour
- Montmorillonite: very high swelling and shrinkage, high plasticity, high compressibility, low permeability and low shear strength when wet. It causes foundation, slope, and pavement problems (black cotton soil); bentonite is used as a sealing material and drilling mud.
- Kaolinite: low swelling and shrinkage, low plasticity and compressibility, higher permeability and good stability. It is generally a favourable soil for construction and is stable on wetting and drying.
✓ Answer checked by Claude Opus 5.5 (high effort)
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