- 2070 Chaitra (old course) · 4 marks
Short note: setting action of lime
Short answer
Fat lime sets by carbonation: Ca(OH)₂ absorbs CO₂ to reform CaCO₃, slow and only in air. Hydraulic lime sets by hydration of silicates/aluminates forming interlocking crystals within days, even underwater; later carbonation adds strength. Lime sets slower and weaker than cement.
Write a short note on setting action of lime.
Setting is the stiffening of lime mortar or paste into a hard mass. It happens in two ways.
Fat lime (non-hydraulic): setting by carbonation
Slaked lime paste first loses water by evaporation and then absorbs CO₂ from the air to turn back into calcium carbonate, which binds the sand particles.
The action is slow and starts from the surface inwards, so thick walls take years to harden fully. It does not happen under water or in damp inside.
Hydraulic lime: setting by hydration
The calcium silicates and aluminates formed during burning react with water to form insoluble hydrates which crystallise and interlock, giving strength within a few days, even under water. Later, carbonation of the free lime adds strength.
Lime sets slower and with less strength than cement.
✓ Answer checked by Claude Opus 5.5 (high effort)