6. Lime and its use

Roman Lime Works, Iversheim (Germany)
In the area south of Cologne (Köln, Germany), limestone is present in the ground, in a pure form which could be quarried easily. During construction of a ditch for water-pipes in 1966 six lime kilns from Roman times were discovered in Iversheim. Between 100 and 300 CE lime was fired in this location. The slaked lime was used as building material and was transported by barge across the river Erft. Despite its destruction during the first invasion of the Franks in 270 A.D., production was started up again, until around 300 it was suddenly stopped. See also a Geman flyer.
Inside the ancient lime kilns in Nettersheim
The Nettersheim lime kilns date back to the 19th century and were restored several years ago. Unlike the cyclical production methods of the Romans in Iversheim, in this 'modern' kiln limestone and coal are continuously poured into the top and the finished lime is extracted at the bottom through tapholes. The Limestone Quarry "Kaninhecke" is located behind the kilns and is rich in fossils, which are described on signs for visitors interested in geology.

1. Lime and Aggregates

Slaked lime forms the basis for mortars and plasters, essential building materials, but not only for aqueducts channels.
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.

Mortar is a lime based paste used to bind construction blocks - stones and bricks - and to fill the gaps.
Plasters are lime based 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).
  • Opus Signinum, with broken tiles, plaster to make floors and walls of Roman aqueducts watertight
  • Stucco is a very fine plaster and remained soft and worked for some time, drying slowly to produce a hard and strong plaster which was called stucco duro. It additionally could contain marble and was used for elaborate and fine decorative work.
  • Roman concrete (often called Opus Caementicium), was the core of many walls, later faced with stones, bricks or marble. The Romans made concrete by mixing lime and volcanic rock (pozzolana, vulcanic sand from Puteoli / Puzzuoli). For underwater applications, this mortar was packed into wooden forms. The seawater instantly triggered a chemical reaction. The lime was hydrated - incorporating water molecules into its structure - and reacted with the ash to cement the whole mixture together.

2. (Crushed) Lime

Chemically spoken: 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)

3. Slaked Lime

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 = dissolved in water

In words: Calciumoxide (quick lime) plus water turns into Calciumhydroxide (slacked lime).

4. Additional explication

See the website of the Wabash and Erie Canal Park (US).

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