cement and refractories

2. Introduction
Refractories are materials that can
withstand high temperature without
softening or suffering a deformation in
shape.
REFRACTORIES
ACIDIC
REFRACTORIES
Eg: Fire Clay
Silica
BASIC
REFRACTRIES
Eg: Magnesite
Dolomite
NEUTRAL
REFRACTORIES
Eg: Silicon Carbide
Chromite
Acidic contain Al2O3 & SiO2, Basic contain CaO & MgO
Neutral contain FeO.CrO2 & ZrO2
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3. Acidic Refractory
 A refractory that is composed principally of silica
and reacts at high temperatures with bases such as
lime, alkalies, and basic oxides.
 These are used in areas where slag and atmosphere
are acidic. They are stable to acids but attacked by
alkalis.
 The main components of these refractories are silica
along with alumina (Al2O3).
 The steel industries are the largest consumer of
acidic refractories.
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4. Basic Refractories
 These are used on areas where slags and
atmosphere are basic, stable to alkaline
materials but reacts with acids.
 The main raw materials is magnesia (MgO) is a
very common example. Other examples includes
dolomite (MgCO3 + CaCO3) and chrome-
magnesia (Cr2O3 + MgO).
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5. Neutral Refractories
 These are used in areas where slags and
atmosphere are either acidic or basic and are
chemically stable to both acids and bases. The
common examples of these materials are alumina
(Al2O3), chrome ( Cr2O3) and carbon.
 Normally we have to use acidic and basic
refractories combined but we use neutral bricks to
avoid the reaction.
 The neutral bricks are made of graphite and
chromites.
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6. CHARACTERISTICS OF GOOD REFRACTORY
 Resistance against heat
 Resistance against corrosion
 Should have high fusing temperature
 Ability to withstand high load
 Should be chemically inert
 Should not undergo deformation
 Uniform expansion and contraction
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7. REFREACTORINESS
It is the ability of a refractory material to
withstand the heat without appreciable
softening or deformation under given service
condition.
 Ability to withstand heat without getting
deformed under operating conditions
 It is measured as Softening Temperature
 The softening temperature is measured by
Seger Cone test
 The test is also called Pyrometric Cone test
PROPERTIES OF REFRACTORIES
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8. Pyrometric/Seger Cone Test
 Refractoriness is usually determined by
comparing the behavior of heat on cone of
material to be tested with series of seger
cone of standard dimension.
 The refractoriness is expressed in terms of
Pyrometric Cone (PCE).
 Standard Cones are
 Pyramidal shaped
 have triangular base
 38 mm high and 19 mm long side
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9.  The standard seger cones are assigned
numbers
 The test cone is heated uniformly at 20oC/hr
or 100oC/hr or 150oC/hr or 600oC/hr
 When the test cone softens one of the std cone
also softens
 The serial number of the std cone is noted
 This number is PYROMETRIC CONE
EQUIVALENT (PCE)
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10. Dr. Vishnu P. Sondhiya 10

11. REFRACTORINESS UNDER LOAD (RUL)
 Refractories are used in industrial furnaces have
invariably to withstand varying load of products.
 A good refractory should have high temperature
resistance as well as load bearing capacity that is
strength
 Strength is calculated by REFRACTORINESS UNDER
LOAD (RUL) test.
 The test is performed by applying a constant load of
3.5 or 1.75 kg/cm2 to the specimen of size 5 cm2 and
75 cm high and heating at the rate of 10oC/min in a
furnace.
 RUL is expressed as temperature at which 10%
deformation takes place
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12. OTHER PROPERTIES
Dimension stability
Chemical inertness
Thermal expansion
Thermal conductivity
Porosity
Thermal spalling
Resistant to abrasion or erosion
Electrical conductivity
Heat capacity
Texture
Permeability
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13. Condition leading to failure of
refractory material
 Using a refractory of less refractoryness that of
the operating temperature.
 Using lower duty refractory bricks in a furnace
than the actual load of raw material and
products.
 Using a brick of higher thermal expansion.
 Rapid change in furnace temperature.
 Using heavy weight refractory bricks.
 Using bricks which undergo considerable
volume change during their use at high
temperature.
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14. COMMON REFRACTORY BRICKS
Silica Bricks
Silica bricks contain 90-95% SiO2 and about 2%
lime is added during grinding to furnish the
bond.
Crushed Siliceous rock + 2% Lime+ Water
Thick paste
Mixing
Bricks
Burning in kilns at 1500oC
for 24 hours
Machine pressing
SILICA REFRACTORY
Preparation
(Quartzite)
(Cristobalite)Dr. Vishnu P. Sondhiya 14

15. Properties
• Color is yellow with brown specks and contain about 25%
pores.
• Show acidic character.
• Resistant to thermal spalling (below 800oC)
• High load bearing strength ( 3.5 kg/cm2 up to 1600oC)
• Light rigid and mechanically strong
Uses
•The main use of silica bricks are roof of open hearth
furnaces, open hearth steal making furnaces, coke oven walls,
roof of electric furnaces, glass furnaces etc.
•Because of their higher thermal conductivity, they are also
used in by-products coke-oven and gas retard lining.Dr. Vishnu P. Sondhiya 15

16. Fireclay bricks are made from finely grounded soft plastic material
fireclay (Al2O3.2SiO2.2H2O) with powdered calcined fireclay
(grog). The exact properties of constituents depend on the type of
bricks to be made. Greater is the percentage of grog, the lesser
will be the spalling tendency. General constitution of the fireclay
bricks ranges from 55% SiO2 and 35% Al2O3 to 55% Al2O3 and
40% SiO2. (K2O, FeO, CaO, MnO etc. also used for balancing the
properties).
Properties
• Depending upon iron content they are light yellow to redish brown in color
•Show acidic character
•Resistant to thermal spalling
•High crushing strength (about 200 kg/cm2)
•Properly fired refractory are hard as steel
Uses
Construction of blast furnaces, stoves, oven, crucible furnaces,
flues, charging doors etc.
FIRECLAY REFRACTORY
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17. High-alumina bricks
High-alumina bricks contain 50% or more of
Al2O3. These bricks are generally made by mixing
calcined bauxite (Al2O3) with clay binder.
Properties: They posses very low coefficient of
expansion, high porosity, great resistance to slags,
very little tendency to spall, high temperature load
bearing capacity, excellent water resistance and
stability in oxidizing and reducing conditions, inert
to the action of gases. They are good refractory but
costly.
Uses: Lining of Portland cement rotary kiln, soaking
pits etc.
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18. BASIC REFRACTORY
MAGNESITE REFRACTORIES
Preparation
Crushed Magnesite grains (MgO) + caustic magnesia or FeO
Ageing for 10 days
Bricks
Burning in kilns at 1500oC
for 8 hours
MAGNESITE REFRACTORY
Properties
•High crushing strength
• Excellent resistant to basic slag but less to acidic slag
•Poor resistance to abrasion and spalling
•Can be used upto 2000oC
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19. DOLOMITE REFRACTORIES
Preparation Calcined Dolomite (CaO + MgO mixture in equimolar ratio)
Silica + water
Bricks
Burning in kilns at 1500oC
for 24 hours
DOLOMITE REFRACTORY
Properties
•Compared to Dolomite less strength, more softness and porosity
•Low resistance to thermal shocks
•They can withstand a load of 3.5 kg/cm2 at 1650 °C
Uses: Dolomite bricks are used for basic electric furnace lining, bessemer convertors.
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20. CARBON REFRACTORY
Preparation
Coke/Graphite + Clay
Firing at 1300-1400oC
CARBON REFRACTORY
Properties • High thermal conductivity
•Excellent resistant to chemicals, spalling and abrasion
•Practically infusible
•Withstand high temperature fluctuations
During firing contact of the bricks with air is minimized by filling the space in-
between the bricks with a mixture of sand and powdered coke.
Uses: Carbon and graphite are widely used as material of
construction of electrodes, lining of highly chemically-resistant
equipments, atomic reactors, electric furnaces and in copper
aluminum, lead smelting furnaces.Dr. Vishnu P. Sondhiya 20

21. Chromite Bricks
Chromite bricks are made by firing at 1500-1700
°C crushed chromite (FeO2.Cr2O3) mixed with a
little clay as binding material.
Properties: Chromite bricks are neutral in character.
Hey posses high density, resistance to acidic as well
as basic slags and moderate resistance to spalling.
They can be used up to 1800 °C and their
refractoryness under a load of 3.5 kg/cm2 is 1430 °C.
Dr. Vishnu P. Sondhiya 21

22. Gypsum Plaster
 Gypsum is a crystalline mineral of hydrated calcium sulphate
(CaSO4•2H2O). Gypsum is colorless or white, is not highly
water-soluble and is not at all hard. A mixture of gypsum and
water can be poured; the gypsum hardens as the water
evaporates. In art gypsum is mainly used in the partly
dehydrated form of plaster of Paris (2CaSO4•H2O) to make
casts of objects.
PREPARATION
 plaster of Paris is prepared by heating gypsum
(CaSO4.2H2O) at 120°C in rotary kilns, where it gets
partially dehydrated.
 The temperature should be kept below 140°C otherwise
further dehydration will take place and the setting
property of the plaster will be partially reduced.
 Gypsum plaster, or plaster of Paris, is produced by
heating gypsum to about 120°C.
2CaSO4·4H2O + Heat → 2CaSO4·H2O + 3H2O
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23. PROPERTIES
 It is a white powder. When mixed with water (1/3 of its
mass), it evolves heat and quickly sets to a hard porous mass
within 5 to 15 minutes. During setting, a slight expansion
(about 1%) in volume occurs so that it fills the mould
completely and takes a sharp impression. The process of
setting occurs as follows:
 The first step is called the setting stage, and the second, the
hardening stage. The setting of plaster of Paris is catalyzed by
sodium chloride, while it is reduced by borax, or alum.
Uses
 In surgery for setting broken or fractured bones
 For making casts for statues, in dentistry, for surgical
instruments, and toys etc
 In making black board chalks, and statues
 In construction industry
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24.  A cement is a binder, a substance that
sets and hardens independently, and
can bind other materials together.
 Material with adhesive and cohesive
properties
 Any material that binds or unites
essentially like glue

25. Cement Chemical Composition
Cement Compound
Weight
Percentage
Chemical Formula
Tricalcium silicate 50 % Ca3SiO5 or 3CaO.SiO2
Dicalcium silicate 25 % Ca2SiO4 or 2CaO.SiO2
Tricalcium aluminate 10 % Ca3Al2O6 or 3CaO .Al2O3
Tetracalcium
aluminoferrite
10 %
Ca4Al2Fe2O10 or
4CaO.Al2O3
.Fe2O3
Gypsum 5 % CaSO4
.2H2O
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26. Raw Materıals Of Portland Cement
1) Calcareous Rocks (CaCO3 > 75%)
 Limestone
 Marl
 Chalk
 Marine shell deposits
2) Argillocalcareous Rocks (40%<CaCO3<75%)
 Cement rock
 Clayey limestone
 Clayey marl
 Clayey chalk
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27. 3) Argillaceous Rocks (CaCO3 < 40%)
 Clays
 Shales
 Slates
 Portland cement is made by mixing
substances containing CaCO3 with substances
containing SiO2, Al2O3, Fe2O3 and heating
them to a clinker which is subsequently
ground to powder and mixed with 2-6 %
gypsum.
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28. CLINKER GYPSUM
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29. Functions of the ingredients of cements
 Lime is the principal constituent of cement. Its
proportion must be properly regulated. However
excess of lime reduce the strength of cement . On the
other hand presence of lesser amount of lime than
required also reduce the strength of cement and make
it quick setting.
 Silica imparts strength to cement.
 Alumina makes the cement quick setting. (due to
excess weakness of cement increased)
 Gypsum helps to retard the setting action of cement. It
actually enhance the initial setting time of cement.
 Iron oxide provides color, strength and hardness to the
cement.
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30. PRODUCTION STEPS
1) Raw materials are crushed, screemed & stockpiled.
2) Raw materials are mixed with definite proportions
to obtain “raw mix”. They are mixed either dry (dry
mixing) or by water (wet mixing).
3) Prepared raw mix is fed into the rotary kiln.
4) As the materials pass through the kiln their
temperature is rised upto 1300-1600 °C. The
process of heating is named as “burning”. The
output is known as “clinker” which is 0.15-5 cm in
diameter.
5) Clinker is cooled & stored.
6) Clinker is ground with gypsum (3-6%) to adjust
setting time.
7) Packing & marketting.Dr. Vishnu P. Sondhiya 30

31. Dr. Vishnu P. Sondhiya 31

32. Manufacturing of Portland Cement
Argillaceous Material
(Clay)
Calcarious Material
(Lime)
Washing Grinding
Proportioning
DRY PROCESS WET PROCESS WATER
Fine Powder Slurry
ROTARY KILN
Clinker
GYPSUM (2 - 3 %)Cooling Grinding
PORTLAND CEMENT
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33. Raw materials are ground to powder and blended
Burning changes raw mix chemically into cement clinker
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34. REACTIONS IN THE KILN
 ~100°C→ free water evaporates.
 ~150-350C°→ loosely bound water is lost from clay.
 ~350-650°C→decomposition of clay→SiO2 & Al2O3
 ~600°C→decomposition of MgCO3→MgO & CO2
(evaporates)
 ~900°C→decomposition of CaCO3 → CaO& CO2
(evaporates)
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35.  ~1250-1280°C→liquid formation & start of
compound formation.
 ~1280°C→clinkering begins.
 ~1400-1500°C→clinkering
 ~100°C→clinker leaves the kiln & falls into a
cooler.
 Sometimes the burning process of raw materials
is performed in two stages: preheating upto 900°C
& rotary kiln
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36. SETTING AND HARDENING OF CEMENT
INITIAL SETTING : Hydration of C3A, C2S, C3S
Gel Formation of C4AF
3CaO.Al2O3 + 6 H2O 3CaO.Al2O3.6H2O
2CaO.SiO2 + 4 H2O 2CaO.SiO2.4H2O
3CaO.SiO2 + 6 H2O 3CaO.SiO2.6H2O
4CaO.Al2O3.Fe2O3 + 7 H2O 3CaO.Al2O3.6H2O + CaO.Fe2O3.H2O
FINAL SETTING AND HARDENING : Hydrolysis of C3S, C2S
2[3CaO.SiO2] + 6H2O 3CaO.2SiO2.3H2O + 3Ca(OH)2
2[2CaO.SiO2] + 4H2O 3CaO.2SiO2.6H2O + Ca(OH)2
When cement is mixed with water to a plastic mass called
cement paste, hydration reaction begin, resulting in the
formation of gel and crystalline products.
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37. ROLE OF CEMENTING MATERIALS
1) GYPSUM : INITIAL SETTING TIME RETARDER
C3A + 6H2O C3A.6H2O + HEAT
C3A + x H2O + y CaSO4. z H2O C3A.yCaSO4.z H2O
Insoluble calcium sulphoaluminate
Quick hardening property
Gypsum
2) Silica / CaO: Imparts srengths
3) Alumina : Imparts strengths, Makes the cement quick setting
4) Fe2O3 : Imparts Grey color, strength and hardness
5) SO3 : Imparts soundness
6) Alkalies (MgO, Na2O, K2O): Lower the clinkering temperature
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