Construction material lime

Construction Material
LIME
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LIME : THE TIME-TESTED
CHEMICAL
Lime is one of man's oldest and most vital chemicals.
The ancient Romans used lime in building and road
construction, uses which continue to the present day.
From earliest times, lime has been made by heating
limestone (calcium carbonate) to high temperatures.
This process, known as calcining, results in
quicklime, or calcium oxide.
Hydrated lime (calcium hydroxide) is produced by
reacting quicklime with sufficient water to form a dry,
white powder.

LIME : THE CYCLE
CaCO3 CaO CO2
Quick limeCalcium Carbonate
In form of limestone,
seashells, corals, kankar, etc
Burn in kiln
Ca(OH)2
Slaked with water
+H2O
Slaked or Hydrated lime
cementingCaCO3
+CO2H2O
From atmosphere
To atmosphere
Calcining
Slaking

Classification of Lime IS 712-1973
Class-A :
Eminently Hydraulic Lime
Class-B :
Semi-Hydraulic Lime
Can be used for structural works such as
arches domes etc.
Can be used for constructing masonry
Class-C :
Fat Lime
Can be used for Finishing Coat in Plastering ,
white washing, etc. or used for masonry
mortar with addition of pozzolanic material
Class-D :
magnesium / dolomite Lime
Can be used for Finishing Coat in Plastering
and white washing.
Class-E :
Kankar Lime
Produce by burning Lime Nodules ( found in
soil like black cotton soils contain silica) , it
can be use for masonry mortar
Class-F :
Siliceous dolomite Lime It is used generally for undercoat and
finishing coat of plaster

Revival of lime
During the last 25 years, Lime
has enjoyed a steady revival
for repairs to historic buildings.
The soft, porous and flexible
nature of lime mortars and
plasters is now universally
recognized as being vital to
maintain the traditional
breathing performance of old
buildings. In addition, an
increasing number of
architects, engineers,
surveyors and builders are now
beginning to realise that lime
has many benefits to
offer in new construction.

Lime Blocks
Lime is used in developing a range of carbon neutral blocks like:
Block
Image Descriptor and market
Sumatec unfired
clay block
Internal walls where internal thermal
mass is required along with a very low
embodied carbon information
Hemcrete 3N block
Structural block to replace grey blocks
where a negative carbon footprint is
important
Hemcrete thermal
block
Non structural carbon negative block
with excellent thermal properties to be
used as a replacement to cast or
sprayed Hemcrete

Lime –Chemical requirements
IS:712-1973

Lime –Physical requirements
IS:712-1973

Lime KILN
A lime kiln is a kiln used to produce quicklime by the
calcination of limestone (calcium carbonate). The chemical
equation for this reaction is:
CaCO3 + heat = CaO + CO2
This reaction takes place at 900°C (at which temperature
the partial pressure of CO2 is 1 atmosphere), but a
temperature around 1000°C (at which temperature the
partial pressure of CO2 is 3.8 atmospheres) is usually used
to make the reaction proceed quickly. Excessive
temperature is avoided because it produces unreactive,
"dead-burned" lime.

Old lime kiln
The common feature of early kilns was
an egg-cup shaped burning chamber,
with an air inlet at the base (the "eye"),
constructed of brick. Limestone was
crushed (often by hand) to fairly uniform
20-60 mm (1 to 2.5 inch) lumps - fine
stone was rejected. Successive dome-
shaped layers of coal and limestone
were built up in the kiln on grate bars
across the eye. When loading was
complete, the kiln was kindled at the
bottom, and the fire gradually spread
upwards through the charge. When
burnt through, the lime was cooled and
raked out through the base. Fine coal
ash dropped out and was rejected with
the "riddlings".
Old lime kiln, Boscastle, Cornwall

Old lime kiln
Only lump stone could be used, because the charge needed to "breathe" during
firing. This also limited the size of kilns and explains why kilns were all much
the same size. Above a certain diameter, the half-burned charge would be likely
to collapse under its own weight, extinguishing the fire. So kilns always made
25-30 tonnes of lime in a batch.

19th century limekilns at Froghall
Typically the kiln took a day to load,
three days to fire, two days to cool
and a day to unload, so a one-week
turnaround was normal. The degree
of burning was controlled by trial
and error from batch to batch by
varying the amount of fuel used.
Because there were large
temperature differences between the
center of the charge and the material
close to the wall, a mixture of under-
burned (i.e. high loss on ignition),
well-burned and dead-burned lime
was normally produced. Typical fuel
efficiency was low, with 0.5 tonnes
or more of coal being used per
tonne of finished lime (15 MJ/kg).

A preserved lime kiln in Burgess
Park, London

Modern lime kiln-Shaft kilns
Shaft kilns
The theoretical heat (the standard
enthalpy) of reaction required to make
high-calcium lime is around 3.15 MJ per
kg of lime, so the batch kilns were only
around 20% efficient. The key to
development in efficiency was the
invention of continuous kilns, avoiding
the wasteful heat-up and cool-down
cycles of the batch kilns. The first were
simple shaft kilns, similar in
construction to blast furnaces. These
are counter-current shaft kilns. Modern
variants include regenerative and
annular kilns. Output is usually in the
range 100-500 tonnes per day.

Modern lime kiln- Rotary kilns
Rotary kilns started to be used for lime
manufacture at the start of the 20th century
and now account for a large proportion of new
installations. The early use of simple rotary
kilns had the advantages that a much wider
range of limestone size could be used, from
fines upwards, and undesirable elements such
as sulfur can be removed. On the other hand,
fuel consumption was relatively high because
of poor heat exchange compared with shaft
kilns, leading to excessive heat loss in exhaust
gases. Modern installations partially overcome
this disadvantage by adding a preheater, which
has the same good solids/gas contact as a
shaft kiln, but fuel consumption is still
somewhat higher. In the design shown, a circle of shafts (typically 8-15) is arranged
around the kiln riser duct. Hot limestone is discharged from the
shafts in sequence, by the action of a hydraulic "pusher plate".
Kilns of 1000 tonnes per day output are typical

Lime Mortar
Lime mortar is a type of mortar composed of lime, an
aggregate such as sand, and water. It is one of the oldest known
types of mortar, dating back to the 4th century BCE and widely
used in Ancient Rome and Greece, when it largely replaced the
clay and gypsum mortars common to Ancient Egyptian
construction.
Lime mortar is used as an alternative to ordinary portland
cement. It is made principally of lime (hydraulic, or non
hydraulic), water and an aggregate such as sand.

Hydraulic & Non-hydraulic limes
Hydraulic limes set under water and non-hydraulic limes
need air to carbonate and therefore set. Modern non
hydraulic lime mortars are produced from lime derived from
high calcium lime stones. These lime stones are burnt in
kilns producing quick lime for other industrial uses other
than building.
In the past, countless kilns all over the country burnt lime
stones of varying qualities - many of these lime stones
containing impurities making them unsuitable for today’s
industrial processes but eminently suitable for building due
to their varying degrees of hydraulicity.
All but the kilns burning pure lime stones ceased
production as ordinary portland cement gained widespread
use. However a very small number of kilns are producing
hydraulic lime for the building industry to standards which
are now expected of any building material.

Non-hydraulic limes
Non-hydraulic lime is primarily composed of calcium hydroxide (generally
greater than 95%). Non-hydraulic lime is produced by the heating of
sufficiently pure limestone (calcium carbonate) to between 954° and 1066°C,
driving off carbon dioxide, to produce quicklime (calcium oxide). As well as
calcium based limestone, dolomitic limes can be produced which are based
on calcium magnesium carbonate. This is done in a lime kiln. The quicklime is
then – thoroughly mixed with water to produce lime putty (calcium
hydroxide), or with less water to produce dry hydrated lime. The slaking
process involved in creating a lime putty is an exothermic vigorous reaction
which initially creates a liquid of a cream consistency. This then has to be
matured for between 2 to 3 months - depending upon environmental
conditions - to allow time for it to condense and mature into a lime putty. A
matured lime putty displays a physical property known as "thixotropic" which
means that when a lime putty is physically agitated it changes from a putty
into a more liquid state. This aids its use for mortars as it makes a mortar
easier to work with and apply. If left to stand following agitation a lime putty
will slowly revert from a thick liquid back to a putty state. It is always advised
that a lime mortar should be "knocked up" prior to its use.

Hydrated lime and lime putty
Non-hydraulic lime is produced in two forms:
1. hydrated lime
2. lime putty.
A frequent source of confusion regarding lime mortar stems from the
similarity of the terms hydraulic and hydrated, however the two terms,
in this context, have different meanings. Hydrated lime is any lime other
than quicklime, so can refer to either hydraulic (hardens underwater) or
non-hydraulic (doesn't harden underwater) lime. Stored lime putty is
always non-hydraulic (since hydraulic putty sets quickly after mixing)
and, as the name suggests, lime putty is in the form of a putty made
from just lime and water.
If the quicklime is slaked with an excess of water then putty or slurry is
produced. If less water is used, then the result is a dry material (any
excess water escaping as steam during heating). This is ground to
make hydrated lime.

Lime putty
Hydrated non-hydraulic lime can be mixed with water to form lime putty.
Before use it is usually left in the absence of carbon dioxide (usually
under water) to mature.
Putty can be matured for anything from 24 hours to many years, an
increased maturation time improving the quality of the putty. There is
however an argument that a lime putty which has been matured for an
extended period eg over 12 months, becomes so stiff that it is less
workable.
There is some dispute as to the comparative quality of putty formed from
hydrated lime compared to that produced as putty at the time of slaking.
It is generally agreed that the latter is preferable.
A hydrated lime will produce a material which is not as "fatty" and often
due to lengthy and poor storage, the resulting lime produced by
hydrated lime will exhibit longer carbonation periods as well as lower
compressive strengths.

Hydraulic lime
In the context of lime or cement, the term 'hydraulic' means to 'harden
under water'.
Hydraulic lime can be considered, in terms both of properties and
manufacture, as part-way between non-hydraulic lime and OPC. The
limestone used contains sufficient quantities of clay and/or silica. The
resultant product will contain dicalcium silicate but unlike OPC not
tricalcium silicate.
It is slaked enough to convert the calcium oxide to calcium hydroxide but
not with sufficient water to react with the dicalcium silicate. It is this
dicalcium silicate which in combination with water provides the setting
properties of hydraulic lime.
Aluminium and magnesium also produce a hydraulic set, and some
pozzolans contain these elements.

Lime stone mines in india

Why Use Lime?
1. Lime Allows Buildings To Breathe
In the search by architects and conservators for building materials
sympathetic to traditional construction, lime was found to be one of
the most important. One of the reasons lime binders are promoted
by the Society for the Protection of Ancient Buildings for repairs is
because they are vapour permeable and allow buildings to breathe.
This reduces the risk of trapped moisture and consequent damage
to the building fabric

Why Use Lime?
2. Lime Provides A Comfortable Environment
Porous and open textured materials such as lime plasters, help to
stabilize the internal humidity of a building by absorbing and
releasing moisture. This makes for a more comfortable
environment and reduces surface condensation and mould growth.

Why Use Lime?
3. The Use Of Lime Has Ecological Benefits
• Lime has less embodied energy than cement.
• Free lime absorbs carbon dioxide in the setting process of
carbonation.
• It is possible to produce lime on a small scale.
• The gentle binding properties of lime enable full re-use of
other materials.
• A very low proportion of quicklime will stabilize clay soils.
• Small quantities of lime can protect otherwise vulnerable,
very low energy materials such as earth construction and
straw bales.

Why Use Lime?
4. Lime Binds Gently With Early Adhesion
The fine particle size of lime, far smaller than cement, is linked to
the root meaning of the word lime, which is 'sticky material'. Due to
the fine particle size, lime mixes penetrate minute voids in the
background more deeply than other materials. They bind gently
and the stickiness gives good adhesion to other surfaces.

Why Use Lime?
5. Lime Mortar Can Protect Adjacent Materials
Lime mortars with a high free lime content are porous and
permeable. These characteristics allow lime mortars to protect
adjacent materials by handling moisture movements through the
building fabric and protecting them from harmful salts. Adjacent
materials frequently affected this way include timber and iron as
well as stone and brick masonry.

Why Use Lime?
6. . Lime Renders Can Assist Drying Out By
Evaporation
Dense and impermeable renders can trap moisture within the
building fabric. Trapped moisture is often the agent for various
decay mechanisms. Dense renders used in conjunction with softer
materials or on weaker backgrounds can cause serious problems
by creating local stresses. High calcium lime renders allow
evaporation and reduce the risk of trapped moisture and decay. In
simple terms, the greater the extent of pure lime and permeability
the better this is for the building. This needs to be balanced with
durability, however, and some reduction in permeability may be
necessary to obtain adequate weathering qualities, hence the
advantage of feebly hydraulic limes for external use.

Why Use Lime?
7. Lime Mixes Have Good Workability
The ability of a mortar or plaster to remain smooth and mouldable,
even against the suction it may experience from porous building
materials, is termed workability. Good workability greatly assists
good workmanship, helping to achieve full joints with good bonding
to the other materials. This is what makes lime based mixes such a
pleasure to use. The workability provided by the lime allows the
inclusion of widely graded and sharp aggregates in the mix. These
enhance both the performance and the aesthetic of the finished
work.

Why Use Lime?
8. Lime Binders Can Be Durable And Have Stood
The Test Of Time
When used carefully, lime is
exceptionally durable.
Caesar's Tower at Warwick
Castle has stood the test of
time for over 600 years, and
many cathedrals have stood
longer. An outstanding
example is the Pantheon
Temple in Rome which has a
lime concrete dome spanning
over 43 metres (142 feet).
This has survived for nearly
2000 years.

Why Use Lime?
9. Lime Finishes Are Beautiful
The double refraction of light
through calcite crystals give a
unique aesthetic combining a soft
texture with a lustre that has a
liveliness and delight of its own.
The graceful softness apparent in
lime based materials is a visual
indication of their intrinsic
permeability, workability and soft
binding properties. They can
rapidly develop a rich patina
which has a glowing translucent
quality.

Why Use Lime?
10. Lime Contributes To A Healthy Environment
Lime is caustic and has been extensively used, often in
the form of limewash, for its disinfectant qualities. Lime
is also used for water purification. Lime mortars,
plasters, renders and limewash have been used to
create hygienic surfaces and improve comfort
conditions within buildings for thousands of years.

Why Use Lime?
11. Self Healing
The nature of ground conditions and the elements are
such that all buildings are subject to varying degrees of
movement over time. When buildings made with lime
are subject to small movements they are more likely to
develop many fine cracks than the individual large
cracks which occur in stiffer cement-bound buildings.
Water penetration can dissolve the 'free' lime and
transport it. As the water evaporates this lime is
deposited and begins to heal the cracks. This process
is called autogenous, or self healing.

Why Use Lime?
12. Free Lime Encourages the Growth of Calcite Crystals
Calcite crystals are a different shape to those formed
by the more complex compounds in hydraulic limes
and cements. The crystals form in voids in lime rich
environments. The growth of calcite crystals adds
strength over time and generally provides a more open
and permeable material than the denser eminently
hydraulic and OPC mixes with little or no free lime.

Why Use Lime?
13. Local Limes Enhance Regional Identity And
Diversity
The diversity of limestone types provides variety and
local distinctiveness. Different limes will vary in colour,
texture and setting properties. Local limes have a
regional identity, they give a sense of place and
provide a continuous link with the local aesthetic. Local
colour is the obvious example in respect of
limewashes.

Why Use Lime?
14. Disfiguring By Cement Can Be Avoided By
The Use Of Lime
On site the temptation to use quick and easy solutions
for short term gain can lead to long term problems. The
attraction of using excess cement to be 'safe' is
understandable if not desirable. The fact that it is
plentiful, inexpensive and readily available adds to the
problem. There is a high probability that over-strong
and dense mixes that are not fit for purpose will be
used in excess. The physical damage and unsightly
aesthetic that results from this can be avoided by the
use of lime.

Why Use Lime?
15. Indefinite Shelf Life
Non-hydraulic limes have an indefinite shelf life when
stored without access to air, usually as a putty under
water or in sealed containers. In fact the quality of the
putty improves the longer it is stored.

FIELD TEST : HEAT OF
HYDRATION OF QUICK LIME
This simple test can also be performed ‘in the field’ with easily portable
items. Though it is primarily for comparing the reactivity of quicklimes,
especially for monitoring the burning conditions in a small lime kiln, the
maximum temperature reached through the exothermic (heat
producing) reaction of quicklime with water is a good indicator of the
quality of the lime, at least in terms of the available CaO. The rate at
which the temperature rises is an indicator of how reactive it is.
 Apparatus
• No. 7 mesh sieve (2.83 mm)
• Thermos flask
• Thermometer reading to at least 100°C.
• Clock or watch with seconds hand.
• Scale to weigh 50 g to ± 0.5 g
• A pestle and mortar or other means of crushing the quicklime to pass
the No.7 mesh.

HEAT OF HYDRATION
Method
Take several lumps of fresh quicklime, break them with a hammer
on a clean surface, cone and quarter to get a representative
sample of small fragments. Grind 100–200 g of this with a pestle
and mortar, so that it just passes through a No.7 mesh sieve. Into a
thermos flask put 170 ml of water at the normal prevailing water
temperature, which in tropical countries may be 23°C. Carefully
weigh out 50.0 g of the No.7 mesh quicklime, put it into the thermos
flask, start the stop watch and begin gently stirring the mixture. At
one-minute intervals, record the temperature of the water and
continue doing so for 24 minutes. Note the maximum temperature
(and the time it was reached). By comparing the maximum
temperature, and the hydration curve of temperature against time,
with those obtained with samples of quicklime of known available
lime content, the quality of the sample can be compared and an
estimate made of its available CaO content, as well as its degree of
reactivity.

TESTING OF LIME
Determination of available lime by the rapid
sugar test (using hydrochloric acid)
 Apparatus
• 300 ml flask• 100 ml burette, with stand. •
Balance capable • No.100 mesh sieve. (0.15 mm).
 Materials
• CO2 free distilled water, if available.
• Hydrochloric acid • Methyl orange indicator.
• Phenolphthalein indicator.
• Sucrose – granulated sugar is satisfactory – 15
g.

TESTING OF LIME
 Method Take 0.5 g of 100 mesh lime and brush it into a 300
ml flask containing 20 ml of CO2 free distilled water and
stopper the flask. Swirl and heat to boiling for 2 minutes. Add
150 ml of water and at least 15 g of sucrose. Stopper the
flask, shake at intervals for 5 minutes and allow to stand for
30 minutes to 1 hour. Add 2 drops phenolphthalein, wash
down stopper and sides of flask with distilled water, then
titrate in the original flask with the standard HCl solution. Add
about 90% of the estimated amount of acid before shaking
the flask and then complete titration, with the final acid being
fed slowly until the pink colour disappears.
 Note the reading: 1 ml of the acid solution is equivalent to
1% available lime expressed as CaO.

Loss on ignition test (LOI)
 The LOI test. can be conducted at regular intervals
during production to monitor the relative degree of
calcination. It should be accompanied by a
thorough visual inspection. It is also used in the
testing stage to compare LOI of limestone from
different deposits.
 Apparatus:
-Container of fixed volume (20 or 50 litres), such
as a bucket.
-Scale of sufficient size to weigh the above
volume.

Method.
1. Weigh container (Wb).
2. Weigh the container filled with a representative sample of
limestone feed (Wf).
3. Weigh the container filled with a representative sample of
quicklime lumps (Wa), Or
Conduct the above weighing exercise several times (5 will
suffice) with different batches of limestone feed and
quicklime lumps to determine average figures for (Wf) and
(Wa).
4. Calculate the % weight lost on ignition using the following
formula:
 (Wf -Wa)/(Wf-Wb) X 100 % weight lost in ignition (% LOI)

 The %LOI can be compared with a standard LOI figure
calculated under precise laboratory conditions to
establish the relative degree of burning, or if this is not
available the theoretical value can be used. The
volume of quicklime which has been used in the
weighing exercise must be inspected to determine to
what degree the limestone is overburnt.

If firing is conducted correctly there should be no, or a very
little, underburnt stone, but this should also be checked for.
 Overburnt quicklime lumps can be distinguished by:
 a) A difference in colour compared to lightly burnt lumps.
 b) A relative difference in weight between lumps of
approximately the same size. Overburnt material will be
heavier than lightly burnt material.
 c) Shrinkage due to overburning may cause cracks to
appear.
 d) When tapped lightly with a hammer overburnt lumps will
produce a sharp ringing tone compared to the tone produced
by a lightly burnt stone

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