11. Lime

Lime is an ancient construction material used in Sri Lanka. This is mostly used in Anuradhapura and Polonnoruwa. The lime paste is used in Sigiriya.

These days cement has replaced the Lime in most cases but in some instances to obtain better finish of building in the inside, the Lime is used.

11.1 Raw Materials of Lime

The raw materials for lime are derieved from the following

1. Limestones
2. Seashells
3. Coral Reefs
4. Dolamite

Raw lime also contains contaminents such as MgCO[3], Al[2]O[3],SiO[2]. The standard for Lime is, SLS:552 (1982).

1 CaCO[3]         -->    CaO + CO[2]
2 CaMg(CO[3])[2]  --> CaCO[3]+ MgO + CO[2]

The quicklime is obtained by heating pure limestones, seashells to 900° C. Pouring/Spraying water on the quicklime produces Hydrated Lime Ca(OH)2 or Slake Lime.

11.1.1 Hydration of Lime

During this procedure, Calcium Oxide is exposed to water. By doing this,

1. Cracks form
2. Engorges to large space
3. Gains granularity of powder
4. Subsequent levels of heat and steam release

   CaO + H2O —> Ca(OH)2

This operation is normally handled in Kilns straight after obtaining Quick Lime. The unburnt or overburnt lime must be removed before this procedure.