Which clay mineral type has high shrink-swell behavior?

• A. 2:1 clays
• B. 1:1 clays
• C. Organic clays
• D. All clays

Answer: (A)

Two-to-one clays, especially smectites like montmorillonite, show the greatest shrink-swell behavior. Their structure has two tetrahedral sheets around one octahedral sheet, creating expandable interlayer spaces that hold water and exchangeable cations. When wetted, water enters these interlayers and pushes the sheets apart, causing swelling; when dried, water leaves and the layers draw back together, causing shrinkage. In contrast, one-to-one clays such as kaolinite have little interlayer space and strong bonds between layers, so they don’t swell much. Organic-clay mixtures can vary, but the pronounced shrink-swell tendency is characteristic of the 2:1 clays.