Limes

Limes
Building Construction Material

Syllabus
• Lime: Introduction, classification, manufacturing,
slacking, properties, tests, handling, storage and uses

Introduction
• Lime is an important cementing material used in engineering
construction.
• A Cementing material may be defined as that material which has
capacity of holding structural unit to-geather with sufficient
strength.
• Among this group are included lime, natural cements, gypsum,
Portland cement as well as various other synthetic products.

Introduction
• Cementing material: The material which has the capacity of holding
structural units (like bricks, stones, aggregate)
• Examples: Lime, natural cements, gypsum, Portland cement
• Lime is an oxide of calcium, CaO
• Uses: .
• Ordinary buildings, massive monuments, palaces, forts
• As a Reliable and economical cementing material.

Lime : As a Reliable and economical cementing
material

Classification
• Lime is available in the market in three main types which are
Quick lime, Hydrated lime, Hydraulic lime
• Classification: based on its composition
i) Quicklime
ii) Hydrated lime
iii) Hydraulic lime

Classification
Quicklime: also called Fat lime, Rich lime, Pure lime.
• In it CaO is greater than (93%) by weight, remaining being MgO and
very little clay.
• Quick lime is Amorphous (shapeless) white material. It has very
high affinity for water and carbon dioxide.
• It Will Absorb the moisture quickly from atmosphere and converting
itself to a carbonate of calcium,
CaO + CO2 = CaCO3
CaO + H2O = Ca(OH)2
Ca(OH)2 + CO2 = CaCO3 + H2O

Manufacturing Of Fat Lime
• The essential raw material for the manufacturing of quick
lime is a rock called LIMESTONE CaCO3.
• Limestone is a sedimentary rock which occurs in nature in
good abundance forming hill ranges, plateaus.

Classification
Hydrated Lime: It is that lime to which sufficient quantity of
water has already been added at the manufacturing stage to
hydrate (slake) it completely.
• In composition, it is Ca(OH)2, In structure, it is in powder
form, It comes in ready to use form compared to fat lime that has
to be hydrated or slaked before using.
• Lime can also be converted to hydrated form at the place of
construction, the method is called slaking of lime.

Classification
• Hydraulic Lime: It is different in chemical composition form
fat lime in that it contains a definite amount of clay in addition to
CaO, clay content in hydraulic lime may range from 10 to 30% by
weight.
• This clay plus lime composition gives the hydraulic lime a
property of hydraulicity.

Hydraulic Lime
• Hydraulicity: The capacity to set and harden even under water and in the
absence of air as between very thick walls”
• The hydraulic lime is further classified into three sub types on the basis of
hydraulicity of the lime.
• Subdivision based on hydraulicity:
Class A – Eminently Hydraulic: clay content 21-30%, sets under water in 24
hours
Class B – Moderately Hydraulic: clay content 11-20%, sets in water in about
a week
Class C – Feebly Hydraulic: clay content 5-10%, sets under water within a
month or more
Class D – rich in magnesium, suitable only for finishing coats, do not
possess hydraulicity

Classification
• Lime has also sometimes classified on the basis of raw material as
Stone lime, shell lime, and kankar lime.
• Similarly lime is distinguished into building lime and finished
lime.
• The first type is required to possess good strength and ability to
mix with sand. It is used in mortar that are used in walls and
foundations.
• The finished lime however, is required to possess sufficient
plasticity, good color and quick setting property.

Manufacture Of Fat Lime
• Common lime stone has following Constitution:
• Constitution of lime stone rock:
• Calcium Carbonate (CaCO3) – 60 to 65%, The higher percentage of CaCO3, the
better suited for lime stone for manufacturing of fat lime.
• Magnesium Carbonate Mg(CO3)2 – 5 to 30%, It is almost a universal component
of many limestones for making fat lime, its content should not be greater than 5%
• Clay - 10 to 30%, for fat lime its content should be less than 10%, Limestone with
higher clay content are more suited for hydraulics lime.
• Iron, alkalis and sulphates – are present in small proportions in many limestone,
when their total content is less than 5% and the CaCO3 is above 90 % the limestone is
suitable for flat lime manufacturing. But when present in excess amount, these salts
make the lime unsuitable as a raw material.
• Besides Limestone, sufficient quantity of fuel is also required to manufacturing
lime.

• Calcinations (process of burning): Lime is manufactured by a process
of burning or calcinations of limestone in suitable types of kilns. The
term calcinations signifies
• “Heating the material at red heat in the presence of air till it decomposes”
Lime stone dissociates when heated at 880⁰ C into its principal
constituents; Calcium oxide and carbon dioxide, as per above reaction which
is reversible.
CaCO3 ( 880⁰ C) CaO + CO2
• It is essential that,
• all the carbon dioxide produced during the reaction is removed quickly
from the kiln:
• the dissociation temperature of reaction (880⁰ C ) is not allowed to come
down during the burning process.

• The Burning of Limestone is carried out either in clamps or in kilns.
• Clamps are temporary, make shift arrangements for burning in an
ordinary manner and at a much lower cost.
• Kilns are, however permanent structures build to carry out the
burning operations at a regular intervals or on continuous basis.

Manufacture Of Fat Lime – Clamp Burning
• It is a common method for obtaining small
supplies of quick lime.
• No permanent construction is needed. A Small part
of ground is cleared and fuel (wood) stacked in
alternate layers with fuel as lower layer.
• If coal is used as fuel, it is mixed with the
limestone instead of stacking in separate layers.
The whole heap is covered with mud plaster and
small holes are left for escape of carbon dioxide. Clamp Burning

Manufacture Of Fat Lime – Clamp Burning
• Clamp is ignited from the base and allowed to keep on burning for 2-3 days.
Burning is discontinued when blue flame disappears at the top and it is allowed to
cool for 2-3 days.
• It is then dismantled. Limestone gets disintegrated into small pieces of small
lumps of CaO or lime. Such lumps are separated from the ash by hand picking.
• Clamp burning is a quick and cheap method for obtaining ordinary type of
lime and not suitable for large supplies of fat lime of good quality because;
• Burning is neither uniform nor complete;
• Some stones may be over burnt and some may be under burnt resulting in
wastage of raw materials;
• There is considerable Wastage of heat generated by burning of fuel. Some of
it escapes from frequent cracking of the plaster on getting heated. Thus this
method is not suitable method of producing fat lime on a commercial scale.

Manufacture Of Fat Lime – Kiln Burning
• Most of the Commercial lime is manufactured by burning limestone in
kilns, they are Permanent structures, kilns used for manufacturing lime
are of great variety and different designs.
• In principle, however they are either Batch type (intermittent) kiln /
Continuous kiln. In the first type of kiln however kilns have to be cooled
every time after burning a batch of limestone. The continuous type however
are kept in operation all the time unless they are required to be stopped for
repair. Further, a kiln may be of mixed type or separate type design.
• Mixed feed (flame type) kiln – fuel and limestone are in a mixed together
batch, burnt lime is obtained mixed with ash and has to be separated from it.
• Separate feed (flare type) kiln – fuel and limestone are not in contact with
each other, fuel is burnt separately, hot gases are allowed to heat limestone
and lime is free from ash.

(1) Batch type (intermittent) kiln: A typical
batch type of lime kiln consist of
Permanent brick-walled structure. Its shape
size and design may vary from place to
place.
• Rectangular, Oval or Cylindrical shapes
are common.
• The Walls of kiln are generally lined with
refractory bricks to save them from
disintegration due to repeated heating at high
temperatures and cooling.
• The kiln is provided with Openings for
supply of air, permanent roof may or may
not be there in kiln.
• After loading, kiln is ignited at bottom, fire
travels upwards and takes 3-4 days for
limestone to burn. Thereafter the kiln is
allowed to cool by itself and then unloaded
and cleaned after which it is loaded with
fresh batch of limestone and fuel.
Intermittent Kilns

(2) Continuous kiln:
• The essential feature of a continuous lime kiln is that while It is charged regularly
from one end with the raw material and the end product is taken out regularly
from the other end.
• As such there is No need to cool the kiln every time after burning a batch of
limestone.
• Naturally its Rate of production of lime is higher than other types of kilns.
• Continuous kilns are of various Types such as – shaft kiln, rotary kiln, circular
kiln etc of these the shaft kiln are most popular. They are made in different
design shape and sizes.

(A)Mixed feed (flame type) continuous kiln:
• It may be constructed Partly underground and partly over ground, the kiln
consists of a shaft or a cylinder of suitable dimensions, the essential features of which
are,
• Diameter – in middle greatest, at top intermediate and at bottom least
• Variation in diameter accumulate large amount of limestone in the central part
as it is hottest zone and ensures complete calcinations.
• The shaft is lined internally with refractory bricks
• A grating plate is at the base of the shaft, which is full of holes to allow the burnt
lime pieces to fall down in the collecting chamber. The kiln is provided with a
hopper type of arrangement at the top for loading the charge and also draw gates at
the bottom for withdrawing the lime after it is cooled. The body of kiln is provided
with opening in the lower region for supply of fresh air. It is also provided with
observation holes in the middle region for keeping an eye on the reactions. Openings
are provided for leading the wastage out of the kiln.

• At top hopper type arrangement for loading the
charge and at bottom draw-gates are provided for
withdrawing the lime after cooling.
• At lower region opening is provided for supply of
fresh air, at middle region holes for observation of the
reaction and at top openings is for leading the waste
gases out of kiln
Continuous Flame-type: Mixed Feed Kiln

• Alternate layers of limestone and fuel is placed and then ignited
through burn holes.
• Main calcinations reaction takes place in the central burning zone of
the kiln.
• At uppermost zone charge is heated up which helps in its quicker
calcinations as it slides down.
• When limestone in the burning zone is completely converted to lime, it
slides down and falls into collecting chamber.
• Hot lime dropped in the basal zone is first cooled by introducing fresh air.
• The charging and emptying operations are continued in this manner in a
regular sequence

• The kiln is first loaded with calculated amount of fuel and
limestone in alternate layers.
• It is then ignited through burn holes. Man calcinations reaction
takes place in the central burning zone of the kiln.
• In the uppermost zone, the charge is mostly heated up, this helps
in quick calcinations as it slides down after some time, when
limestone in the burning zone has been completely converted to lime,
the latter slides down and falls into the collecting chamber through the
holes in the grating. Raking holes are used to turn about the
charges during burning.

(B) Separate feed (flare type) continuous kiln:
• Design is similar to mixed feed type it Consists of shaft made
of steel or brick, lined internally with refractory bricks. It
has Bigger diameter in the central zone for burning, intermediate
diameter in the basal zone and small diameter at top for
charging. Such a kiln is provided with Separate fuel chamber
which is located within the main body or outside the kiln. In first
case, fuel chamber is placed in box type around the periphery of
the shaft where fuel is burnt to generate heat which is conducted
into kiln. In second case, fuel is burnt outside the kiln and hot
gases are allowed to enter into kiln.
• In any case, there is no contact between the fuel and the
limestone.
• After calcinations of limestone, it is made to fall in the lower
cooling zone with help of raking rods. The hot lime is cooled
by introducing fresh air in the basal chambers and once it
becomes hot rises upward in the burning zone of the kiln. There
is therefore Better utilization of heat in this kiln.
Continuous Flare-type:
Separate Feed Kiln

Manufacture Of Hydraulic Lime
• Hydraulic lime has a Clay content is ranging from 10-30 % For the
manufacturing of this type of lime, the process depends upon the type of
raw material available.
(A) Natural Hydraulic Lime: This is manufactured from a single raw
material, an impure limestone rich in clay known as Kankar and occur in
nature either in the form of blocks or making lower part of the ground
at many places.
• Kankar contains 10-40 % clay and 60-80 % calcium carbonate.
• Calcinations of kankar is done in clamp or in kiln in similar manner for
fat lime.
• In case of kankar Temperature is raised to higher degree because of
presence of enough clay in it and then cooled and packed.

Manufacture Of Hydraulic Lime
(B) Artificial Hydraulic Lime: In this type of lime two source materials are
required – limestone rock, clay.
• Limestone should be free from impurities and clay should not contain any free
silica, oxides of iron, sulphur, alkalis .
• There are two variations of calcinations for the manufacturing of artificial
hydraulic lime depending upon the quality of limestone.
• Calcinations depends upon the quality of limestone.
(i) Limestone is of soft type (e.g. chalk) – such a stone is mixed with clay in
powdered form and burn to red head in any type of kiln and then burnt mixture is
slaked on cooling before marketing
(ii) Limestone is of hard type (e.g. compact limestone) – Calcined in kiln to
obtain quick lime and then cooled and powdered, mixed with clay (10-30 % by
weight) and mixture is converted into ball shaped masses
• These balls are once again charged into the kiln and burnt to red heat so it is known
as Twice Kilned Lime

Properties Of Lime
• Following are the more important properties that determine the
quantity of lime as a building material,
• Physical state: Lime as obtained from kilns is generally in the shape
of solid lump it is termed as lump lime.
• Lime is crushed to obtain powder of required fineness known as
Pulverized lime.

Properties Of Lime
• Slaking of Lime or Hydration: the process of chemical combination of lime
( CaO) with a definite quantity of water so that the end product is hydrated oxide.
• When lime cannot absorb any more water then the process is said to be completed.
The new product, Calcium Hydroxide is formed as per following reaction;
• CaO + H2O = Ca(OH)2
• The above reaction is attended by following processes:
• Evolution: heat is generated of the order of 227 K-Cal/kg of lime
• Expansion: volume extent up to 2-3 times
• Development: hissing and cracking sound due to conversion of water into heat
• Fat lime hydrates in 3-4 hours and hydraulic lime hydrates 1-3 days.
• All limes must be slaked before use in building construction.

Methods Of Slaking
• Tank Slaking (Making Lime Putty): Two brick tanks of suitable
dimensions are constructed adjoining to each other and with a
difference in level.
• The first tank is about 45 cm deep and made at a height, second
tank is 60-75 cm deep and made at a lower level.
• Water is filled in the upper tank to ¾th of its depth. Fat lime is
gradually added to it in small amounts, water is constantly stirred
during the addition of lime.
• The slaking reaction takes place in this tank, which can be
observed by evolution of heat and hissing and cracking sound.
• 3-4 hours for complete hydration
• The lime on reaction with excess water forms milk of lime.
• Screening tap called strainer (with openings of 0.25mm) is opened
and the hydrated lime allowed to pass into the lower tank.
• It is allowed to stay in second day for 2-3 days where it matures
itself to the desired consistency. This is ready as Lime Putty and is
taken out for use of making mortars and plasters.
Tank Slaking

Tank Slaking (Making Lime Putty)

Methods Of Slaking
Precautions
• Only lime should be added to water not water to lime.
• Keep water stirring and hoeing for sometimes more even after the
boiling and hissing sounds are over in the tank.
• Lime Putty should be taken out as soon as it becomes mature in the
tank it should not be allowed to stiffen and harden before use.

Methods Of Slaking
• Platform Slaking (For powder slaked lime): water-tight
platform of masonry or cement-concrete
• Fat lime is spread in the form of a thin layer of about 15
cm height.
• Small quantity of water is sprayed.
• During the water-sprinkling process, lime heap is turned
over and over again using spades.
• When apparent slaking is complete (as indicated by absence
of further hissing and cracking sound), no further water is
added.
• The heap is covered with boards so that any further heat
liberated on slacking is used by the lime for its complete
disintegration.
• It is left for 24 hours during which time slaking may be
completed.
• Lime is turned into a powder form of hydrated lime which is
screened through 0.25 mesh sieve and ready for use of
making mortars and plasters.
Platform Slaking

Slacking of Hydraulic Lime
Slacking of Hydraulic Lime
• It is done by following three methods
• Platform slacking
• Slacking under pressure
• Slacking by hydrators
• The basic difference in the slacking of Fat lime and Hydraulic lime
lies in the fact that the latter is generally slow slacking and require less
water as compared to fat lime.

Properties Of Lime
Plasticity: It is defined as the ability of the lime to spread evenly during application
it is observed that;
• Limes contains some magnesium oxide – more plastic, spread smoothly and easily in
comparison to Limes rich in calcium oxide
• Limes rich in calcium oxide – pure fat lime, hard to work, sticky and stiff quickly
Sand carrying capacity: When lime is used in mortar or plaster sand has to be mixed
with it due to following reasons ;
• To control shrinkage of lime on setting
• To prepare a properly plastic mix of desired strength
• Limes mix with the definite quantity of sand is known as sand carrying capacity of
lime.
• Calcium limes are said to have good sand carrying capacity than magnesium limes

Properties Of Lime
• Setting: The setting of fat lime in free state or in mortar is
essentially a chemical process which involves following reactions
(a)Dehydration – loss of water from the hydrated lime by evaporation
Ca(OH)2 = CaO + H2O
(b) Carbonation – combining of atmospheric carbon dioxide into lime,
forming once again the original material i.e. limestone
CaO + CO2 = CaCO3
The net result of setting is that it us again converted into hard
substance, calcium carbonate this carbonate act as a binding material
when used as mortar.

Properties Of Lime
• Setting: The setting of hydraulic lime is a complex process. This is
due to the fact that hydraulic lime contains besides oxides of
calcium and magnesium, silicates and aluminates of calcium and
some oxides of iron.
• During their setting these compounds get further hydrated and
form crystalline structure. It is for this reason hydraulic lime can
set under water also. It is more like Portland cement then fat lime.
• Hydrated fat lime sets slowly compared to pure fat lime.
• Rate of setting of hydrated lime can be increased by drying air and
charging it with CO2.
• Shrinkage takes place in lime on setting which can be overcome by
mixing sand or surkhi.

Handling And Storage Of Lime
• Handling and storage of lime: Lime in its raw form requires careful handling
to avoid accidents and losses
(i) Quick lime – should be protected from water, as it will start getting hydrated
with the evolution of heat that can cause burn injuries of various serious nature.
• If it is stored in wooden barrels and it comes in contact with water, so much
heat may be evolved to burn barrel, store house or the wagons/trucks in which it is
being transported.
(ii) Fat lime – must be protected from direct contact with atmospheric moisture and
carbon dioxide which starts setting and gets converted to a useless hard material
having no binding properties.
• It is therefore required to convert the lime into lime putty as soon as possible and
stored into a compact heat covered with a thick layer of lime dust which saves the
attack of moist air.
(iii) Hydraulic lime – safer in transport and can be stored for longer period as
compared to fat lime.

Handling And Storage Of Lime
• Precautions to handle lime:
• Workers handling lime must be asked to use goggles,
respirators, rubber gloves and gum boots for protection of
eyes, respiratory system, hands and feet respectively.
• Thorough bath should be taken after working with lime.
• Any inflammable material should never be kept near a heap
or bag of lime or where lime is being hydrated to avoid any
accidental fires.

Uses Of Lime
• Uses of lime: Lime is very useful material that finds extensive
applications in building construction, industry and agriculture.
(a) As a construction material: Lime was used as main binding
material in all types of construction till 19th century. Even now lime
can compete with Portland Cement in many types of construction.
• as a mortar (lime-mortar) mixed with sand or surkhi.
• as a plaster
• as a whitewash which gives sparking white finish at a very low cost
• as a lime-concrete similar to cement concrete made by mixing lime, sand
and coarse aggregate in proper proportions
• as sand-lime bricks which are quite popular in many countries

Uses Of Lime
(b) As an industrial material: In industries lime find use as
• A flux in the metallurgical industry
• as a refractory material for lining metallurgical furnaces
• as a raw material for the manufacture of glass
(c) An agricultural input:
• Lime is used to to improve productive qualities of soil and added
to the poor soils to enrich their lime content
• Lime has also been used for soil stabilization.

Comparative Study Of Fat Lime And Hydraulic Lime
Properties Fat Lime Hydraulic Lime
Colour White colour Greyish white
Composition CaO with subordinate amount of clay CaO with 10-30% clay
Slaking
qualities
(i) Slakes vigorously
(ii) Enough heat is liberated that creates
hissing and cracking sounds
(iii) Expands 2-3 times
(iv) Slaking time 3-4 hours
(i) Slakes gently
(ii) Not much heat is liberated, so no hissing
sounds
(iii) Expands 1-2 times
(iv) Slaking time 24-48 hours
Setting Setting involves absorption of carbon dioxide
from atmosphere resulting in calcium
carbonate.
It cannot set under water as it does not have
property of hydraulicity
Has double setting action. CaO content may set
as fat lime and clay forms hydrated aluminates
and silicates of calcium similar to cement on
setting.
It can set under water as it has property of
hydraulicity
Strength Not very strong in mortar so may not be used
where high strength binders are required
Quite strong mortars so can be used in
foundation and wall in place of Portland cement
Uses White-washing, plastering, making mortars
Use as a flux in industry and for soil
improvement
Use for making mortar in load bearing
construction for underground and over-ground
superstructures

Tests For Lime
Building lime required to satisfy a number of tests before it is
approved for use in construction work.
1. Chemical Composition: Lime is tested To determine ratio of
different components such as CaO, MgO, SiO2, AlO2 and iron oxides.
• The limits of component should be as per IS:712-1973
2. Fineness: To determine the fineness of grain size by sieve analysis
• The residue is weighed after the test and should not exceeds the
specified limits.

Tests For Lime
3. Soundness: It is defined as The capacity of lime to resist expansion
on setting
• It is tested with the help of Le Chatelier apparatus.
• Lime is mixed with sand and water and filled in mould of the
apparatus.
• The distance between the indicator points is noted and after one hour
placed in a steam boiler for three hours.
• After the boiling action, the distance between the indicators is noted
once again.
• Difference between the two readings gives a measure of soundness
which should be within prescribed limit.

Tests For Lime
4. Setting Time: The time that elapses between the preparing of lime
paste of standard consistency and setting of the same paste after it has
been filled in a standard mould (Vicat Mould) to a minimum specified
depth.
• Initial setting time: The time that elapses from the gauging to the
penetration of the Vicat needle in the paste up to a specified depth –
35mm
• Final setting time: The time that elapses from the gauging to a time
when Vicat needle can no more penetrate the paste (because it is
already set) and makes only a mark on the surface.

Tests For Lime
5. Strength: Tested by preparing specimens of standard sand-lime
mortar,
• For compressive strength – average of 12 specimens, tested on
standard testing machine on specimens taken after 14 days and 28
days
• For transverse strength – average of 6 specimens, tested on standard
transverse strength testing machine
• The setting time and strength tests are recommended for
hydraulic limes only.

Tests & Specifications for Lime IS: 712:1973

References
• Building Construction : Dr B.C. Punmia
• Civil Engineering Material : Prof. Singh
• Internet Web Sites

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