CHAPTER THREE
BINDING MATERIALS
DEFINITION
Binders and The Binding Action
BINDERS
are substances that are used to bind inorganic
and organic particles and fibers to form strong,
hard and/or flexible components.
THE BINDING ACTION
is generally due to chemical reactions which
take place when the binder is
⚫ heated,
⚫ mixed with water and/or other materials,
⚫ or just exposed to air.
BINDERS
Types of Binders to be Discussed
Binders
Gypsum Portland Asphalt
Lime
Plasters Cement Cement
BINDERS
Main Groups of Binder
There are three main groups of binders:
➢Mineral binders
➢Bituminous (Asphalt) binders
➢Synthetic binders
BINDERS
Mineral Binders
Mineral Binders
Non-hydraulic binders Hydraulic binders
E.g. Lime, Gypsum
E.g Portland cement
plasters
MINERAL BINDERS
Non – Hydraulic Binders
Non-hydraulic binders only harden in the
presence of air
The most common non-hydraulic binder is
lime.
• Hardening depends on its combination with
carbon dioxide from the air (carbonation), by
which it again becomes calcium carbonate
(limestone).
Non – Hydraulic Binders
Gypsum
✓ is a non-hydraulic binder which occurs
naturally as a soft crystalline rock.
✓ The chemical name is calcium sulfate
anhydrate (CaS04.2H20).
✓ By gentle heating up to about the boiling
point of water calcium sulfate hemi-hydrate
(CaSO4.1/2H2O) is produced, more
commonly known as "Plaster of Paris", which
when mixed with water sets in 10 minutes.
MINERAL BINDERS
Hydraulic Binders
✓ Hydraulic binders require water to
harden and develop strength.
✓ The most common hydraulic binder is
Portland cement.
✓ Hydraulic binders are usually available
in the form of a fine powder.
✓Hydraulic binders must be stored in absolutely
dry conditions, to avoid premature setting and
hardening (pre- hydration and carbonation)
Even humid air can cause hydration.
PART - I
LIME
LIME
Generals
✓ Lime is one of the oldest known cementing
material
✓ Lime is found in many parts of the world in
its natural form as a rock of varying degree
of hardness.
✓ Usually Lime in free state is not found in
nature
LIME
Generals
✓ Lime is mainly composed of calcium
oxide (CaO).
✓ Lime in its pure form associates with CO2
to give white CaCo3.
✓ Lime deposits are generally found mixed
with impurities such as CO2, Fe2 O3, and
MgCO3.
✓ Depending on the impurities, lime
deposits acquire different colors.
✓ It is found by burning limestone at a
temperature of about 800 o c
LIME
Production Of Lime
Lime is produced by burning
the raw material limestone
CaCO3.
✓ Chalk , shell and coral can
have CaCO3 content
exceeding 98 %
✓ Pure mineral dolomite has as
low as 54 %
LIME
Production Of Lime
• Excavation
• Crushing Limestone
• Grinding
• Calcination → Quicklime
• Pulverize quicklime
• Mix with water under pressure → Slaked Lime
• Drying of Slaked Lime
• Pulverizing
• Marketing in bags.
Production of Lime
The Burning Process
The amount of heat applied and the method
of slaking depend upon the product needed,
whether hydraulic or non-hydraulic lime.
The burning process takes place in either:
• Vertical shaft kiln
• Rotary kiln
Production of Lime
The Burning Process
Vertical shaft kiln
The raw materials fed in
at the top & the finished
product drawn off through
an opening at the bottom.
Limestone
~10000c
Lime
Production of Lime
The Burning Process
Rotary kiln
LIME
Classification of Lime
If the temperature is low (around 1000oC), the
resulting product is quick lime /caustic lime/. While if
the temperature increases to 1300 o C, a hydraulic lime
is produced.
The next stage of the production process is mixing the
powder lime with water, and this process is called
slaking.
Depending up on the degree of burning and the water
added at the production stage lime is classified in to
three. These are:
⚫ Quick lime
⚫ Hydrated lime
⚫ Hydraulic lime
LIME
Classification of Lime
Quick Lime
The manufacture of quick lime consists in
burning the limestone in some form of
vertical kilns to a temperature of 10000c.
CaCO3 → CaO+CO2
Classification of Lime
Quick Lime
Is obtained by calcining (burning) the purest
available calcium carbonate
Gives out considerable heat
Swells two to three times of its original volume
upon addition of water
Takes much time in hardening
Is used for plastering and white washing
Is not suitable for being used as mortar
because of its poor strength and slow
hardening
LIME
Classification of Lime
Hydrated Lime (Slaked Lime)
Quick lime can never be used as such for
construction purposes but must be mixed
with water.
CaO+H2O →Ca (OH)2 + heat
This process is called slaking and the
product (calcium hydroxide) is called slaked
lime or hydrated lime
Hydrated Lime
Forms of Hydrated Lime
Depending upon the amount of water added, there
are two types of slaking;
⚫ Wet - slaking and
⚫ dry - slaking,
Wet - Slaking
Lime is slaked or hydrated at the building site by
mixing quicklime, which is delivered in lump form,
with an excess amount of water, and the resulting
slaked lime should be passed through a fine sieve
to remove slow slaking particles
Hydrated Lime
Forms of Hydrated Lime
Dry – Slaking
If the operation is carefully controlled, as it can
be in a factory so that just sufficient water is
added to hydrate the quick lime, the lumps
break down into a dry powder known as dry
hydrate or hydrated lime. It is obtained by
adding almost exactly the theoretical quantity of
water required to change the burnt lime into
hydrate of lime
Cont’d
PRESERVING QUICKLIME
Fresh burned lime has so much
affinity for water that it will quickly
absorbed moisture and carbon dioxide
from the atmosphere and becomes
air- slaked, and loses its cementing
qualities. It must therefore be kept in
dry storage and carefully protected
from dampness until used.
LIME
Classification of Lime
Hydraulic Lime
⚫ Is prepared by burning impure limestone
that contains clay, producing compounds
similar to those present in Portland cement.
⚫ It is stronger but less fat or plastic than non-
hydraulic lime.
⚫ Hydraulic lime is manufactured in the same
way as quick lime, although a somewhat
higher temperature is required in burning.
LIME
Setting and Hardening of Lime
During setting, the hydrated lime Ca(OH)2 loses water through
evaporation and absorbs carbon dioxide CO2 from the atmosphere and
changes back to CaCO3.
The cycle is completed in the chemical changes from the original
limestone, through burning, slaking, and setting, as shown below.
When burnt, the limestone loses its carbon dioxide and becomes oxide
of lime or quicklime.
CaCO3 + heat (around1000oC) CaO + CO2 (heating)
When slaked, the oxide of lime combines with water and becomes
hydroxide, slaked lime, or hydrated lime
CaO + H2O Ca(OH)2 + Heat (slaking)
When setting, the calcium hydroxide loses its water through
evaporation and absorbs carbon dioxide from the air, becoming CaCO 3
or limestone once again.
Ca(OH)2 + CO2 CaCO3 + H2O (drying)
The Lime cycle
CaCO3
Burning
Drying
Ca(OH)2 CaO
Slaking
LIME
Uses of Lime
1. Lime as a construction material
✓ As mortar (lime mortar) mixed with sand
✓ Lime is used in cement mortar to make it more
workable
✓ As plaster (lime plaster)
✓ As a whitewash, when it gives a sparkling white
finished at a very low cost
✓ As lime concrete
✓ As an important constituent of sand – lime bricks
✓ As a stabilizer in soil constructions with clayey soils
LIME
Uses of Lime
2. Lime as an industrial material
In industry, lime finds many applications:
✓ As a flux in the metallurgical industry
✓ As a refractory material for lining
metallurgical furnaces;
✓ As a raw material for the manufacture of
glasses.
3. Lime as an agricultural input
✓ Lime is used for improving the productive
qualities of soils.
✓ It is added to the poor soils to enrich their lime
content.
LIME
Precautions Taken in Handling Lime
In handling lime the following precautions should be taken
1. Should not be exposed to water before slaking.
2. All precaution against fire hazard should be taken.
3. Workers handling lime should be provided with suitable
goggles , respirators, rubber gloves, boots & skin
protective cream.
4. After working with lime, exposed portions of the body
should be washed with abundant fresh water.
6. Workers handling milk of lime, which is hot, should oil
their skin daily to avoid skin burns.
Questions ?
The End
PART - II
Gypsum Plasters
