Slaked lime - Applications in civil engineering

Lime is a generic term for calcium oxide and/or hydroxide and calcium magnesium oxide and/or hydroxide produced by the thermal decomposition (calcination) of calcium carbonate (limestone, chalk, shells, etc.), or calcium magnesium carbonate (dolomitic limestone, dolomite).

Air lime meets this general definition. It owes its name to the property of the hydroxide to carbonate on contact with carbon dioxide in the air, thus contributing to the strength and durability of mortars.

A distinction is made between calcium air lime, obtained from calcium carbonate, and dolomitic air lime, obtained from mixed calcium and magnesium carbonate. Because of the purity of the limestone from which they are derived, air lime has no hydraulic properties. They should therefore not be confused with hydraulic limes, whose use is essentially reserved for the manufacture of plasters and mortars for the building industry.

The use of air lime in civil engineering is subject to compliance with the European Construction Products Directive, which requires, among other things, compliance with standard NF EN 459: Building Lime. This standard distinguishes two categories of air lime for construction purposes:

• calcium (CL notation), which includes :

  • calcium oxide: CaO,

  • calcium hydroxide: Ca(OH) ₂ ;

• dolomitic (DL notation), which includes :

  • calcium magnesium oxide: CaO.MgO,

  • calcium and magnesium hydroxide: Ca(OH) ₂ .Mg(OH) ₂ .

Air lime does not contain any added hydraulic or pozzolanic components and is available in two forms:

• quicklime (notation Q), which exists as an oxide and reacts exothermically with water;

• hydrated lime – also known as slaked lime – (S notation) essentially in the form of hydroxide obtained by hydration – or controlled slaking – of the oxide. Hydrated lime is available both as a powder and as a suspension in water. In the latter case, a paste, slurry or milk of lime is obtained, from the most concentrated to the most diluted.