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A stone wall in France with lime mortar grouting being applied. Right: unapplied. Centre: lime mortar applied with a trowel. Left: lime mortar applied and then beaten back and brushed with a churn brush. Lime mortar or torching [1] [2] is a masonry mortar composed of lime and an aggregate such as sand, mixed with water.
Limestone is extracted from quarries or mines. Part of the extracted stone, selected according to its chemical composition and optical granulometry, is calcinated at about 900 °C (1,650 °F) in lime kilns to produce quicklime according to the reaction: [6]
Stone and brickwork bonded with lime is easier to re-use. Lime acts sacrificially in that it is weaker and breaks down more readily than the masonry, thus saving weaker stone such as sandstone and limestone from the harmful effects of temperature expansion and mortar freeze. It is less dense than cement, thus less cold bridging.
In limestone calcination, a decomposition process that occurs at 900 to 1050 °C, the chemical reaction is CaCO 3 (s) → CaO(s) + CO 2 (g) Today, this reaction largely occurs in a cement kiln. The standard Gibbs free energy of reaction in [J/mol] is approximated as ΔG° r ≈ 177,100 J/mol − 158 J/(mol*K) * T. [4]
Hot limestone is discharged from the shafts in sequence, by the action of a hydraulic "pusher plate". Kilns of 1000 tonnes per day output are typical. The rotary kiln is the most flexible of any lime kilns able to produce soft, medium, or hard burned as well as dead-burned lime or dolime.
The chemistry of these reactions is not completely clear and is still the object of research. [7] First, the limestone (calcium carbonate) is burned to remove its carbon, producing lime (calcium oxide) in what is known as a calcination reaction. This single chemical reaction is a major emitter of global carbon dioxide emissions. [8]
Limestone was also a very popular building block in the Middle Ages in the areas where it occurred, since it is hard, durable, and commonly occurs in easily accessible surface exposures. Many medieval churches and castles in Europe are made of limestone. Beer stone was a popular kind of limestone for medieval buildings in southern England. [109]
Limestone-plastered wall discovered in Pompei. Lime plaster is a type of plaster composed of sand, water, and lime, usually non-hydraulic hydrated lime (also known as slaked lime, high calcium lime or air lime). Ancient lime plaster often contained horse hair for reinforcement and pozzolan additives to reduce the working time.