What is lime?
When calcareous material (Caco3) is heated, Co2 & Cao are formed. The CaO is called lime. Lime is mainly composed of a higher percentage of calcium oxide and some percentage of silica and alumina (in the form of clay).
The lime formed by the decomposition of CaCo3 is quick lime. Quick lime has a great affinity for moisture. The process of adding water in sufficient quantity to quick lime is known as slaking.
CaCo3 = Cao + Co2 (Quick lime)
Cao + H2o = Ca (OH)2 ( Hydrated lime ) (slacked lime)
Uses of lime in construction
- Lime is used for the manufacture of cement.
- It is used in mortar and plastering work on walls & ceilings.
- Fixing walls, floor tiles & other journey works.
- It is used as a flux in the manufacture of steel.
- It’s used in the manufacture of paint.
- It’s used in stabilizing soil.
- It’s used as lining in the furnace.
Lime has been used as a cementing material since time immemorial. In Nepal and India up to today, lime has been extensively used for many types of structures like a wall, roads, etc. Lime does not occur in nature in a free state.
Types of lime in civil engineering
- Hydraulic Lime
- Non-Hydraulic Lime
The lime which set under water is called hydraulic lime. Hydraulic lime is prepared from impure limestone and set through hydrolysis, a reaction caused by water.
The lime which does not set under water is called non-hydraulic lime. Hydraulic lime is prepared from pure limestone, and pure calcium carbonate, and tends to be in the form of putty. Non-hydraulic lime is formed by carbocation.
General Classification of Lime
1) Fat/Rich/Pure/White/Quick lime
- Having 95% Cao and 5% clay
- Setting & hardening actions are slow.
- Soluble in water, white colour.
- Possess a high degree of work ability & plasticity.
2) Hydraulic lime
- Having 70% Cao & 30% clay
- Grayish white in colour.
- It is set underwater in absence of air.
- It does not dissolve in water.
- Slaking action is slow.
- Hydraulic lime is used in underwater construction.
Classification of lime Depending on the content of silica & alumina
- Feebly hydraulic lime = Less than 15% clay
- Moderately hydraulic lime = 15 – 25% clay
- Eminently hydraulic lime = 25 – 30% clay
4) Poor lime
- It contains more than 30% clay.
- Slaking action is very slow.
- Poor binding property.
- Its sets & harden slowly.
- It’s used for inferior types of work.
Properties of lime
- Lime is easily workable
- Provides strength to the masonry
- Posses good plasticity
- Offers good resistance to moisture
- Stiffens early
- Provides low shrinkage.
Differences between fat lime & hydraulic lime
|S.N||Fat lime||Hydraulic lime|
|1.||Contains 95% limestone and 5% clay mineral.||Contains 70% limestone & 30% clay.|
|2.||Milky white in colour.||Grayish white in colour.|
|3.||Slaking action in fast.||Slaking action is slow.|
|4.||It sets in the presence of air.||It sets in the absence of air underwater.|
|5.||Setting & hardening action is slow.||Setting & hardening action is fast.|
|6.||Produce a hissing sound.||Does not produce a hissing sound.|
|7.||Shrinks a lot on drying.||Shrinks less on drying.|
|8.||It’s used for whitewashing, lime plastering, lime mortar, etc.||It’s used for lime concrete work underwater.|
|9.||It dissolves in water.||It does not dissolve in water.|
Q.1) What type of lime is used for soil stabilization?
Ans:- Quick lime is used for soil stabilization because it has high strength and plasticity.
Q.2) What type of lime is used for underwater construction?
Ans:- Hydraulic lime is used in underwater construction because It does not dissolve in water.