'Lime stabilisation' of expansive (black cotton) soil improves its properties by:
Choose the correct answer
Lime adds water to clay increasing workability
Flocculation (immediate) + pozzolanic C-S-H cementation (long-term) — reduces PI, swell, and increases strength
Only increasing density of soil
Making clay more plastic
Correct Answer
B. Flocculation (immediate) + pozzolanic C-S-H cementation (long-term) — reduces PI, swell, and increases strength
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Lime stabilisation: quick lime (CaO) or hydrated lime Ca(OH)2 added to expansive clay. Reactions: (1) Immediate — flocculation (Ca²⁺ replaces Na⁺/K⁺ on clay surfaces, changes clay from dispersed to flocculated), pH increases to > 12 → reduces plasticity, improves workability; (2) Long-term — pozzolanic reaction (Ca(OH)2 + silica/alumina from clay → C-S-H, C-A-H) → increases strength. Lime: 3–8%.
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