LIME

Lime is calcium containing inorganic material primarily composed of calcium oxide

or calcium hydroxide. Lime is on important building material, has been in use since
ancient times. Lime had been used as an important cementing material for plastering
mortar and concrete work and also for many manufacturing processes.

Properties of lime
The following properties have made lime, an important Engg. Material.
1. It has good plastic properties
2. It gives strength to the masonry, when used as mortar.
3. Its sets and and hardens when its absorbs carbon dioxide from the air.
4. It is easily workable.
5. It has good adhering properties with stone and bricks both.
6. Its shrinkage in comparatively low and hence masonry in lime mortar in more
durable.
7. Absorbs moisture from the air and reacts to form calcium hydroxide.

Uses of Lime
Lime can be used for following purposes.
1. As a binding material in mortar
2. As a binding material in concrete.
3. As an aggregate in form of crushed lime stone.
4. For plastering
5. White washing and also as a base coat for distemper.
6. Used for lime sand bricks.
7. It is also used as component of refractory clay.
8. is used for soil stabilization ( added to weak or expansive soil to increase their load
bearing capacity)
9. is used for improving soils for agriculture purposes.
10. is used for water purification and sewage treatment works.
11. used in combination with cement, to modify the properties of cement
12. Used in the manufacture of steel to remove impurities.
13. is used for the manufactures of glass.
Sources of Lime
Lime does not occur in nature . It is obtained from Lime stone or chalk or Kanker -
which are the usual raw materials from which lime is obtained.
All the materials containing calcareous substances, have calcium carbonate (CaCO3)
as the chief constituent. When calcareous materials are heated, carbon dioxide and
moisture are driven out, leaving behind calcium oxide (CaO), which is called lime.
This process is referred to as calcination. It is done in a lime kiln.
PROCESS
In this process the limestone with high purity (90% calcium carbonate) is crushed into
smaller sizes. The crushed limestone is the introduced into a lime kiln and heated to
temperatures of 900 - 1100oC to form quicklime.
The quicklime is then cooled and stored for further processing. Quicklime is highly
reactive and will absorb moisture from the air turning it to slaked lime. that’s why it is
stored in airtight containers.
CHEMICAL REACTION
Heat
CaCO3 CaO + CO2
(Limestone) (Calcium oxide (Carbon dioxide)
or quicklime)
Some Important terms and definitions:
Calcination: It is the process of heating the limestone to redness in the presence of
atmospheric air. During calcinations, CO2 is driven out and calcium oxide is left as
final product.
Quick Lime: when CO2 is driven out from pure limestone, the resulting product is
lime.
Settling of Lime: When lime converted into paste form is exposed to atmosphere, it
gradually hardens. This process of slow hardening of lime is called setting of
lime.This is different than drying in which evaporation of water takes place. In the
case of hardening, chemical action takes place.
Slaking: Quick lime has large affinity for moisture. Adding water in sufficient
quantity to quick lime in known as slaking. When water is added to quick lime, it
swells and cracks. Lot of heat in also generated and the lime gets converted into
hydrated lime or calcium hydrate otherwise known as slaked lime.
CaO + H2O Ca(OH)2 + Heat
(Quick lime) (water ) (Calcium hydoxide
or hydrated lime
or slaked lime)
During slaking lot of heat is generated with hissing sound. Quick lime requires about
32% of water by volume. But due to various factors like method of slaking, degree of
burning, composition of lime etc, water required for slaking is taken about 2 to 3
times the volume of the quick lime. Rate of slaking is affected by the size of burnt
lime lumps and temp of atmosphere.
Slaking can be done with steam very speedily, under increased pressure in closed
drums.
Hydrated lime obtained in the form of powder is available in the market is packed
bags. When sand and water are added to this, we get lime mortar
Carbonation of lime
This is the process in which slaked lime or cacium hydoxide reacts with carbon
dioxide from the air to form calcium carbonate .This reaction is important in the
setting and hardening of lime- based materials like lime mortar and plaster.
Ca(OH)2 + CO2 CaCO3 + H2O
When slaked lime is used in construction, it remains soft initially. Overtime it absorbs
carbon dioxide from the atmosphere leading to the hardening of lime making it
durable.
Hydraulicity: It is the property due to which lime sets in damp places in the presence
of moisture.
Fat lime: The lime which has high calcium oxide content and depends solely on the
absorption of carbon dioxide for setting and hardening, is called fat lime.
Hydraulic lime: Lime containing small quantities of silica and alumina and/or iron
oxide which are in chemical combination with some of the calcium oxide content,
giving a putty or mortar which has the property of setting and hardening under water,
is called hydraulic lime. i.e. When quick lime is sprinkled with water, the fine powder
obtained is called hydrated lime.
Hydrated lime: A dry powder obtained by treating quick lime with enough water to
satisfy its chemical affinity for water under the condition of its hydration, is called
hydrated lime.
Lump lime: It is the quick lime as it comes from the kiln in the form of lumps.
Milk lime:- It is a thin pourable solution of slaked lime with water.
Lime putty:- It is prepared by stirring hydrated lime in water so as to get thick
creamy consistency and allowing it to stand and mature for a period of about 16 hours
in the case of non-hydraulic lime before using.

TYPES OF LIME
Lime may be classified in to following
Fat Lime (Non-Hydraulic Lime)
This lime is known as fat lime, because it increases 2 to 2 times in volume, when
slaked. This lime is obtained by burning comparatively pure lime stone. This lime is
also called pure lime, white lime, rich lime or high calcium lime. The lime stone from
which this lime is obtained, should contain about 95% calcium oxide and other 5%
impurities. For setting this lime absorbs carbon dioxide from the atmosphere.
 It slakes quickly and it contains specific properties such as very slowly hardening, a
high degree of plasticity and soluble in water. Fat lime is white in colour.

Uses of fat lime:

  It is used in plastered surfaces for whitewashing.
  It is used as lime mortar (a combination of lime and sand) for plastering and
pointing works.
  It is used as a Lime Surkhi mortar for foundations, thick masonry walls, etc.,
where surkhi is the powder obtained by pounding burnt bricks.

Hydraulic Lime
Hydraulic lime is the lime that contains small quantities of silica, alumina and iron
oxide, which are collectively in the chemical composition with calcium oxide.
It is also known as water lime because it can set under water and become hard even in the
absence of carbon dioxide.

Based on the percentage of the clay, hydraulic lime is available in different forms such
as Feebly hydraulic lime, Moderately hydraulic lime and Eminently hydraulic lime. The
increase in clay content makes slaking difficult and increases hydraulic properties.

Uses of hydraulic lime:

  It resembles cement as it contains 30% of clay and can be used in major civil
engineering works.
  It can set in thick walls where there is no free-flowing of air.
  It forms a thin paste with water.

Poor Lime
This lime contains more than 30% of clay. It slakes very slowly. It forms a plastic paste
with water. This lime is also called as Lean lime or impure lime. It sets and hardens very
slowly compared to other types of limes. It has very poor binding properties and can form
a thin paste with water. It is used for inferior types of works because of its inferior
quality.
 Comparison between fat lime and hydraulic lime

Classification of Lime
Lime has been classifies into following categories.
CLASS A : It is hydraulic lime which is mostly used for construction works and is
nothing but eminently hydraulic lime.
CLASS B: It is semi hydraulic lime which can be used as mortar in masonry works.
CLASS C: It is fat lime, which can be used for plastering or white washing.
CLASS D: It is magnesium lime used for finishing coat in plastering/white washing.
CLASS E: It is Kankar lime which can be used for under coat and finishing coat of
plaster. It is to be supplied in hydrated or quick lime form.
. Class A and E lime are always available in the form of hydrated lime.
. Class B, C and D lime may be available in the form of quick lime or hydrated lime.
 TEST ON LIME
Visual inspection:
If colour is milky white, it is fat or pure lime. If ordinary white, it is fat lime, if colour is
dirty or grey, it is hydraulic lime having lot of coal ash etc.
If lime available consists of lumps, it shows quick lime or unburnt lime.
.
Hcl test:
This test is carried out to classify the lime and also to assess the lime content. Take small
amount of powdered lime in a test tube and note the level of lime, after adding water to it.
The tube is stirred with glass rod and left for 24 hours. If there is lot of effervescence, it is
indicate high %age of CaCo 3. The residue left at the bottom of test tube indicates the
proportion of impurities or hydraulic properties of lime. If thick gel is formed in the test
tube, even after turning the test tube side down, it shows eminently hydraulic lime. If the
gel formed is not very thick and tends the flow out on tilting the tube, it indicates feebly
hydraulic lime.

Soundness test:
This test is carried out by Lc-Chatelies apparatus. It consists of brass cylinder mould
attached with two long indicators and two glass plates.
The mold is placed on glass plates with 1:3: 12 (Mixture of cement, hydrated lime and
sand). Mortar is prepared by adding water at the rate of 12% of weight of mixture.
The mold is covered at top by glass plate and left for one hour. The distance between
the indicator needles is then measured. The mould is then placed in a damp air
cupboard for 48 hours and subjected to action of saturated steam for 3 hours without
immersing in water. The mould is allowed to cool and the distance between ends of 2
indicators is measured again. The increase is calculated and should not be more than
10mm. I. also specify popping and pitting tests. Pats are prepared by mixing 70 gms
of hydrated lime with 70cc of water and 10gms of plaster of Paris. They are subjected
to steam action and examined for disintegration and pitting. Any of these indications
shows unsoundness of lime.
Test of workability:
By this test workability is estimated. Take handball of prepared mortar and dash it on
the surface on the wall, where it is to be used. The area covered by mortar in relation
to its dished amount gives an indication of suitability of various ingredients in the
mortar.
Fineness of lime
The fineness of lime refers to the particle size distribution of lime powder. Finer lime
reacts more quickly with water and CO₂, ensures smooth application in mortar and
plaster and reduces grittiness in plasterwork.

Testing the Fineness of Lime

1.Sieving Method (for Hydrated Lime and Quicklime)
Weigh 100 grams of lime powder.Place it on a 300 µm sieve (for hydrated lime) or 1.18
mm sieve (for quicklime).Sieve manually or mechanically for 15 minutes.Weigh the
residue retained on the sieve.

2. Sedimentation Method (For Ultra-Fine Lime Particles)

Used when sieve analysis is not practical, especially for very fine lime particles.
Lime is suspended in water, and the time taken for particles to settle is measured.Finer
particles remain suspended longer, indicating a higher degree of fineness.

Freshness Test on Lime

The freshness test determines whether lime (quicklime or hydrated lime) has deteriorated
due to exposure to air and moisture. Lime absorbs carbon dioxide (CO₂) over time,
forming calcium carbonate (CaCO₃), which reduces its effectiveness in construction.

Methods for Testing Freshness

1. Visual Inspection
Fresh Lime
Quicklime (CaO): White, hard lumps that react vigorously with water.
Hydrated Lime (Ca(OH)₂): Soft, fine powder with a smooth texture.

Expired/Stale Lime:
Turns into a dull, chalky material.Feels gritty instead of soft and may have hardened
lumps due to moisture absorption.

2. Slaking Test (For Quicklime)

Fresh Quicklime reacts vigorously with water, producing heat and steam within 5-10
minutes.
Expired Quicklime reacts slowly or weakly, indicating it has partially turned into calcium
carbonate (CaCO₃).

3. Carbonation Test (For Hydrated Lime)

Fresh Hydrated Lime dissolves in acid without effervescence (bubbling).
Expired Hydrated Lime produces bubbles when mixed with dilute hydrochloric acid
(HCl) due to carbonate formation.

4. Strength Test (For Lime Mortar)

Prepare a lime mortar cube (1:3 ratio of lime to sand).Allow it to cure for 7 days.Test its
compressive strength—weaker mortar suggests stale lime.

ASSIGNMENT
Briefly discuss the handling and storage of lime.