2 binders material

DEFINITION
Binders are substances that are used to bind
inorganic and organic particles and fibers to
form strong, hard and/or flexible components.
2 HAILEMARIAM GIRMA 11/02/14

THE BINDING ACTION
 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.

TYPES OF BINDERS TO BE DISCUSSED
Binders
Lime
Gypsum Plasters
Asphalt Cement
Portland Cement

MAIN GROUPS OF BINDERS
There are three main groups of binders: -
1. Mineral binders
2. Bituminous (Asphalt)binders
3. Synthetic binders

1. MINERAL BINDERS
Mineral Binders
Non-hydraulic binders Hydraulic binders
E.g. Lime, Gypsum plasters E.g Portland cement

1.1 NON-HYDRAULIC BINDERS
 Non-hydraulic binders are only harden in the
presence of air
 The most common non-hydraulic binder is:-
A. Lime.
B. Gypsum
Hardening of non-hydraulic binder/lime depends on
its combination with carbon dioxide from the air
(carbonation), by which it again becomes calcium
carbonate (limestone).

Cont’d
 Gypsum is a non-hydraulic binder which
occurs naturally as a soft crystalline rock.
 The chemical name is calcium sulfate
anhydrate (CaS04.2H20).

Cont’d
 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.
The common name for calcium sulfate hemi-hydrate
is known as Plaster of Paris

1.2 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. Why?

Cont’d
 On account of their affinity to water,
hydraulic binders must be stored in absolutely
dry conditions.
Why?
Answer:- to avoid premature setting and
hardening (pre- hydration and carbonation).
 Even humid air can cause hydration.

2. BITUMINOUS BINDERS/ASPHALT
 "Asphalt" is a dark brown to black, highly
viscous, hydrocarbon produced from
petroleum distillation residue.
This distillation can occur naturally, resulting in
asphalt lakes, or occur in a petroleum
refinery.

3. SYNTHETIC BINDERS
 Synthetic binders are generally produced by
industrial processes.
They can either be used as adhesives or as
surface coatings and are either applied hot, or
as an emulsion, or with a solvent.

Cont’d
 Synthetic admixtures which bind loose
particles together are mainly resins derived
from plant materials or mineral oil.
 Adhesives are used to stick larger particles,
components, membranes, sheets, boards, tiles, etc.
on another surface.

LIME

General
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.
Lime is mainly composed of calcium oxide (CaO).

Cont’d
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.

Production of lime
 Lime is produced by burning the raw material limestone
CaCO3.
 Chalk , shell and coal can have CaCO3 content
exceeding 98 %
Dolomite mineral has as low as 54 %

Burning process

A. VERTICAL SHAFT KILN
 Raw materials are fed in at the top &
the finished product drawn off through an
opening at the bottom.
Limestone
~10000c
Lime

B. ROTARY KILN
 The raw materials fed in at the top &
the finished product is drawn off at the
bottom continuously.
Limestone
Lime

CLASSIFICATION OF LIME
 Commercial lime is classified into three
groups:-
1.Quick lime (Caustic lime)
2.Hydrated lime (Slaked lime)
3.Hydraulic lime

1. 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

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

2. 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.

Forms of hydrated lime
 Depending upon the amount of water added during the
slaking process, three forms of hydrated lime are
commonly produced:-
a) Dry hydrate, a dry, fine powder, formed by adding just
enough water (Dry-Slaking) to slake the lime, which is
dried by the heat evolved.
b) Milk of lime, made by slaking quicklime with a large
excess of water (Wet-Slaking) and agitating well, forming
a milky suspension;
c) Lime putty, a viscous mass, formed by the settling of
the solids in the milk of lime.

3. 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.

SETTING AND HARDENING OF LIME
 Slaked lime hardens or sets by gradually
losing the water through evaporation and
absorbing carbon dioxide from the air.
 Thus changing back from calcium hydroxide,
Ca (OH)2 to calcium carbonate,
CaCO3 or limestone.

The Lime cycle
CaCO3
Burning
Drying
Ca(OH)2 CaO
Slaking

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 a stabilizer in soil constructions with clayey
soils

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.

GYPSUM PLASTERS

General
 Gypsum is a combination of sulfate of lime with
water of crystallization.
 Gypsum occurs naturally as:
 Hydrous sulfate of lime (Ca SO4
2H2O) which is generally 76% CaSO4
and 24% H2O,
 Anhydrate (Ca SO4).
 Pure gypsum is known as alabaster
and it is a white translucent crystalline
mineral

Gypsum plasters
 Gypsum plasters are used in the arts and
in building construction.
 Gypsum plasters are manufactured by
heating the raw material gypsum at either
moderate or high temperatures the results
being plaster of Paris or hard-finish plaster
respectively.

A. PLASTER OF PARIS
 If some of the water of crystallization is driven
off by incomplete dehydration at a temperature
just above the boiling point of water (1000c), pure
finely ground gypsum, a semi-hydrated plaster is
obtained which is known as plaster of Paris.
(CaSO4.2H2O)+Moderate Heat (CaSO4 .1/2 H2O) +1/2 H2O

Cont’d
Plaster of Paris:-
 is a white powder having a specific gravity of 2.57.
 is also known as low-temperature gypsum derivative
or semi-hydrated plasters (hemi hydrate).
 When mixed with sufficient water to form a plastic
paste, it sets very rapidly (retarder must be added)

Cont’d
Glue, sawdust or blood can be added to Retard the
setting time of the plaster.
Owing to rapidity of setting, its use in structures is
limited to ornamental work.

Complete cycle in gypsum used as plaster
Hydration Moderate heat
`
CaSo4.2H2O
CaSo4.1/2H2O

B. HARD-FINISH PLASTER
Produced by burning gypsum to a
considerably higher temperature .
Hard-finish plaster is also known as anhydrous
plaster or high-temperature gypsum
derivative.
(CaSO4. 2H2O)+High Heat CaSO4+ 2H2O
 This plaster is less soluble with consequent
reluctance to absorb water in the process of
re crystallization.

Other Derivatives of Gypsum
1.Gypsum Ready Mixed Plaster
Is calcined gypsum(CaSo4.1/2H2O) mixed at the
mill with mineral aggregate to serve as a base to
receive various coats.
Contains about 60% of CaSo4.1/2H2O
2.Gypsum Neat plaster
Contains about 66% of CaSo4.1/2H2O by weight.
The addition of aggregate is made on site.

3.Gypsum Wood fibered plaster
Composed of not less than 66% of
CaSo4.1/2H2O and about 1% wood fiber.
4 . Gypsum bond plaster
Used as a bonding scratch -coat over
monolithic concrete.
It contains not less than 93% of CaSo4.1/2H2O
and not less than 2% or more than 5% of
hydrated lime.

 5.Gypsum Gauging Plaster
Is prepared for mixing with lime putty for the
finish coat.
Contains not less than 66% of
CaSo4.1/2H2O

Thank you !!!

2 binders material

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