Lime and its use
Lime and Aggregates
The lime comes from limestone as quarried in nature. After burning it is transformed into quick lime.
After adding water it turns into slake lime.
1) Crushed limestone is burned by a temperature of over 900 degrees C:
| CaCO3 (s) -> CaO (s) + CO2 (g) |
s = solid; g = gas
In words: Calciumcarbonate (lime) is transformed into calciumoxide (quick lime) and carbondioxide (CO2)
2) After adding water the quick lime transforms into slaked lime:
| CaO (s) + H2O (l) -> Ca(OH)2 (aq) |
s = solid; g = gas l = liquid aq = ....
In words: Calciumoxide (quick lime) plus water turns into Calciumhydroxide (slacked lime).
Aggregates
Slaked lime forms the basis for mortars and plasters.
A mortar is a paste used to bind construction blocks - stones and bricks - and to fill the gaps.
Plasters are paps / slushes that can easily be manipulated, and used for finishing walls and floors, and to make surfaces watertight.
Slacked lime is a binding agent in a mix (an aggregate) of water, sand and/or other inert fillers (like crushed rocks, tiles, brick rubble etc).
Examples:
- Opus Caementicium (often called Roman concrete), the core of many walls, later faced with stones, bricks or marble
- Pozzolana, where vulcanic sand is used from Puteoli / Puzzuoli: mortar often used for underwater works
- Opus Signinum, with broken tiles, plaster to make floors and walls of Roman aqueducts watertight