Introduction of Cement

1. Introduction + Pozzolana Cement
Lecture 1

2. Cement

3.  Cement, in general, adhesive substances of all kinds, but, in a narrower
sense, the binding materials used in building and civil engineering
construction.
 Cements of this kind are finely ground powders that, when mixed with
water, set to a hard mass.
 Setting and hardening result from hydration, which is a chemical
combination of the cement compounds with water that yields
submicroscopic crystals or a gel-like material with a high surface area.
 Because of their hydrating properties, constructional cements, which
will even set and harden under water, are often called hydraulic
cements. The most important of these is Portland cement.

4.  The cement-making process, from crushing and grinding of raw
materials, through roasting of the ground and mixed ingredients, to
final cooling and storing of the finished product.

5.  The origin of hydraulic cements goes back to ancient Greece and Rome.
The materials used were lime and a volcanic ash that slowly reacted
with it in the presence of water to form a hard mass.
 This formed the cementing material of the Roman mortars and
concretes of more than 2,000 years ago and of subsequent construction
work in western Europe.
 The term cement, meanwhile, derives from the Latin word
“caementum”, which meant stone chippings such as were used in
Roman mortar—not the binding material itself.
History of cement

6.  The invention of portland cement usually is attributed to Joseph Aspdin
of Leeds, Yorkshire, England, who in 1824 took out a patent for a
material that was produced from a synthetic mixture of limestone and
clay. He called the product “portland cement” because of a fancied
resemblance of the material, when set, to portland stone, a limestone
used for building in England.
 During the 20th century, cement manufacture spread worldwide. By
2019 China and India had become the world leaders in cement
production, followed by Vietnam, the United States, and Egypt.

7.  The term 'pozzolana' has two distinct meanings. The first one indicates
the pyroclastic rocks, essentially glassy and sometimes zeolitised, which
occur either in the neighborhood of Pozzuoli (the ancient Puteoli of the
Roman times) or around Rome.
 The second meaning includes all those inorganic materials, either
natural or artificial, which harden in water when mixed with calcium
hydroxide (lime) or with materials that can release calcium hydroxide
(Portland cement clinker).
 In this chapter the term 'pozzolana' will be referring to the latter
meaning, definitely wider than the former, and will therefore embrace a
large number of very different materials in terms of origin, composition
and structure.
What is pozzolana or pozzolanic material?

8.  A pozzolan is a siliceous or siliceous and aluminous material that in itself
possesses little or no cementitious value but will, in finely divided form
and in the presence of moisture, chemically react with calcium
hydroxide at ordinary temperatures to form compounds having
cementitious properties.
 It is therefore classified as cementitious material. There are both
natural, artificial, and silica fume pozzolans.
 This materials usually doesn't posses any cementitious properties, but
when it is mixed with water or moisture or lime to undergo reaction
with calcium hydroxide to form compounds possessing cement
properties.

9. History
 The name Pozzolan comes from the town Pozzuoli, Italy.
 Ancient Romans (~100 B.C.) produced a hydraulic binder by
mixing hydrated lime with soil (predominantly volcanic ash)
 Horasan mortar, mixing lime with finely divided burned clay, is
extensively used by Ottomans
 Nowadays, the word pozzolan covers a broad range of natural
and artificial materials.
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10. Pozzolan
 A material that, when used in conjunction with portland cement,
contributes to the properties of the hardened concrete through
hydraulic or pozzolanic activity, or both.
 Natural (Volcanic ash, volcanic tuff, pumicite)
 Artificial (fly ash, silica-fume, granulated blast furnace slag)
 Siliceous or aluminous material, which in itself possesses little or
no cementitious value.
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11.  But will, in finely divided form and in the presence of moisture,
chemically react with calcium hydroxide Ca(OH)2 to form
compounds possessing hydraulic cementitious properties.
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POZZOLANS
Silica&Alumina
(higher amounts)
Iron oxide, calcium oxide,
magnesium oxide,
alkalies
(lesser amounts)

12.  Pyroclastic rocks result from explosive volcanic eruptions which project
minute particles of melted magma into the atmosphere. The rapid
pressure decrease occurring during the eruption causes the gases
originally dissolved in the liquid magma to be released.
 As a consequence, each particle will contain a number of microscopic
bubbles and ducts forming a microporous structure. Simultaneously, the
particles are subject to a quenching process which is responsible for
their glassy state. The material can be deposited either on the ground
or in water. Generally, the ground deposits, which are loose and
heterogeneous, are composed of ashes mixed with fragments coming
from the volcanic duct walls or the base of the volcano.
NATURAL POZZOLANAS
1)Materials of volcanic origin (pyroclastic rocks)

13.  Table 10.1 shows that the chemical composition of incoherent volcanic
pozzolanas varies within wide limits and that silica (and alumina) prevails
over other constituents. The alkali content is rather high with peaks
exceeding 10 per cent (pozzolana from Bacoli, Naples and Rhine trass).

14. 2) Calcined clay
 Clays and the so-called diatomaceous earths are sedimentary rocks
which are capable of combining with lime.
 Table 10.6 shows the chemical composition of some diatomaceous
earths. The silica content increases as the clay mineral content
decreases. The opposite occurs for alumina.
 Diatomaceous earths are highly reactive towards lime owing to their
high content of amorphous silica and high specific surface area. In spite
of the strongly pozzolanic behaviour, the use of diatoms in pozzolanic
cements is hampered by their huge specific surface area which causes
the water demand of cement to increase. Small additions of diatomites
to concrete improve plasticity and reduce bleeding.

16.  They can be used as a partial replacement for the cement, typically in
the range of 15% to 35%, and to enhance resistance to sulfate attack,
control alkali-silica reactivity, and reduce permeability.
 Calcined clays have a relative density of between 2.40 and 2.61.
 Calcined shale may contain on the order of 5% to 10% calcium, which
results in the material having some cementing or hydraulic properties
on its own.

17.  Fly ash, the most widely used supplementary cementitious material in
concrete, is a byproduct of the combustion of pulverized coal in electric
power generating plants. Upon ignition in the furnace, most of the
volatile matter and carbon in the coal are burned off.
 During combustion, the coal’s mineral impurities (such as clay, feldspar,
quartz, and shale) fuse in suspension and are carried away from the
combustion chamber by the exhaust gases. In the process, the fused
material cools and solidifies into spherical glassy particles called fly ash
 The fly ash is then collected from the exhaust gases by electrostatic
precipitators or bag filters. Fly ash is a finely divided powder resembling
portland cement .
Artificial pozzolanas
1)Fly ash

18. Fly ash, a powder resembling cement, has
been used in concrete since the 1930s.
Coal
Power plant

20.  Fly ashes result from the burning of bituminous or subbituminous coal as
well as of lignite. Their chemical composition depends on the mineral
composition of the coal gangue, i.e. the inorganic part of the coal.
 As shown in Table 10.7, the chemical composition of bituminous fly
ashes (class F according to the ASTM classification) varies within rather
wide limits. Silica and alumina prevail, as in natural pozzolanas.
 Fly ash is primarily silicate glass containing silica, alumina, iron, and
calcium. Minor constituents are magnesium, sulfur, sodium, potassium,
and carbon. Crystalline compounds are present in small amounts. The
relative density (specific gravity) of fly ash generally ranges between 1.9
and 2.8 and the color is generally gray or tan.

21.  Ground granulated blast-furnace slag , also called slag cement, is made
from iron blast-furnace slag; it is a nonmetallic hydraulic cement
consisting essentially of silicates and aluminosilicates of calcium
developed in a molten condition simultaneously with iron in a blast
furnace.
 The molten slag at a temperature of about 1500°C (2730°F) is rapidly
chilled by quenching in water to form a glassy sand like granulated
material.
 The rough and angular-shaped ground slag in the presence of water and
an activator, NaOH or CaOH, both supplied by portland cement,
hydrates and sets in a manner similar to portland cement.
2)SLAG

22. Fig. Ground granulated blast-furnace slag
Blast furnace

23.  Silica fume, also referred to as microsilica or condensed silica fume, is a
byproduct material that is used as a pozzolan (Fig. 3-7). This byproduct is
a result of the reduction of high-purity quartz with coal in an electric arc
furnace in the manufacture of silicon or ferrosilicon alloy.
 Silica fume rises as an oxidized vapor from the 2000°C (3630°F) furnaces.
When it cools it condenses and is collected in huge cloth bags. The
condensed silica fume is then processed to remove impurities and to
control particle size.
 Silica fume is sold in powder form but is more commonly available in a
liquid. Silica fume is used in amounts between 5% and 10% by mass of
the total cementitious material. It is used in applications where a high
degree of impermeability is needed and in high strength concrete.
3) SILICA FUME

24. Fig. 3-7. Silica fume powder.
Quartz

25.  The term 'pozzolanic activity' covers all reactions occurring among the
active constituents of pozzolanas, lime and water.
 The term 'pozzolanic activity' includes two parameters, namely the
maximum amount of lime that a pozzolana can combine and the rate
at which such combination occurs.
 Both factors depend on the nature of pozzolanas and, more precisely,
on the quality and quantity of the active phases.
POZZOLANIC REACTION

26.  A pozzolan’s activity refers to both its capacity of binding lime and the
rate at which the binding reaction takes place, therefore, it covers all the
reactions taking place between the active components of the pozzolan,
lime and water.
 The reactivity of a pozzolan depends on its chemical and mineralogical
composition, the type and proportion of its active phases, the particle’s
specific surface area, the ratio of lime to pozzolan, water content, curing
time and temperature .
 In addition, the rate of lime combination increases in the presence of
sulfates such as gypsum and Na2SO4 and other chemicals such as CaCl2.
.

27. POZZOLANIC REACTIONS
 Calcium Hydroxide+Silica+Water → “Calcium-Silicate-Hydrate”
(C-S-H)
 C-S-H provides the hydraulic binding property of the material.
Pozzolanic Activity:
 Capacity of pozzolan to form alumino-silicates with lime to form
cementitious products. (How good how effective the pozzolan
is!)

28. FACTORS THAT AFFECT THE ACTIVITY OF POZZOLANS
1. SiO2 + Al2O3 + Fe2O3 content
 The greater amount of these, the greater its activity.
 ASTM C 618 & TS 25 → min “SiO2+Al2O3+Fe2O3” for
natural pozzolans > 70%
 Fly Ash – ASTM
 Class C→ from Lignite or subbituminous coals
(SiO2+Al2O3+Fe2O3>50%)
 Class F→ from bituminous coals and
SiO2+Al2O3+Fe2O3>70%
 Silica fume → SiO2 ≈ 85-98%
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29.  Blast Furnace Slag→ SiO2 ~ 30-40%
Al2O3 ~ 7-19%
CaO ~ 30-50%
2. Amorphousness
 For chemical reaction → pozzolans must be amorphous
 Volcanic ash, volcanic tuff, fly ash, silica fume are all
amorphous by nature.

30.  Clays → contain high amounts of silica & alumina but have a
crystallic structure! (Do not possess pozzolanic activity)
 However, by heat treatment, such as calcining ~700-900°C
crystallic structure is destroyed & a quasi-amorphous
structure is obtained.
 Clay → does not possess pozzolanic property
 Burned clay → possess pozzolanic property
 Blast furnace slag → contain high amounts of silica, alumina & lime
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31.  However, if molten slag is allowed to cool in air, it gains a
crystal structure. * do not possess pozzolanic property.
 However, if it is cooled very rapidly by pouring it into water, it
becomes a granular material & gains amorpousness. *
possess pozzolanic property.
3. Fineness
 Pozzolanic activity increases as fineness increases.
 Volcanic ash, rice husk ash, fly ash, condensed silica fume
are obtained in finely divided form.
 Volcanic tuff, granulated blast furnace slag & burned clay
must be ground
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32.  Pozzolans can be blended with lime (or Portland cement) to produce
blended cements that can replace pure Portland cement commonly
used in building materials such as concrete, masonry block, masonry
mortar, bricks, and other construction units.
 Utilization of natural pozzolans in civil projects include structural
concrete, precast and prestressed elements, mass concrete, concrete
pipes, concrete masonry units, controlled low-strength materials, grout,
mortar.
Lime –Pozzolana reaction and products formation, Applications.

33. 1. Structural Concrete
 The application of natural pozzolans in concrete structures is either in
the form of cement replacement materials or the addition rate of the
natural pozzolan.
 The natural pozzolans enhance concrete plastic properties, increase the
cohesion and workability of the mixture, as a result, reduce segregation
and facilitate consolidation, reduce permeability, and improve durability.
Uses of Natural Pozzolans in Concrete Applications

34.  Natural pozzolans help precast and prestressed concrete elements to
develop high early strength and obtain adequate durability. These are
essential criteria in the construction of bridges, buildings, and parking
garages in which precast and prestressed concrete elements are utilized.
 The high early strength helps early removal of formwork. However, a
high level of durability is necessary for structures that expose to
moderate to severe conditions.
2. Precast, Prestressed Concrete Elements
Fig. 1: Precast Concrete

35.  Nowadays, concrete that is used in the construction of sizeable dams
contains natural pozzolans. It reduces the heat of hydration; as a result,
decreases the thermal stresses within the concrete that can cause
cracking. The heat of hydration reduction.
 Additionally, it improves sulfate resistance and declines the potential for
expansion from alkali-silica reactions.
3. Mass Concrete

36.  The use of a natural pozzolan can provide significant benefits in the
manufacture of concrete pipe. It reduces the quantity of cement and
maintain the necessary workability for pipe manufacturing.
 The natural pozzolans improve the density of concrete pipes; minimize
permeability.
4. Concrete Pipes

37.  Natural pozzolans are used to produce concrete masonry units. It
improves plasticity and cohesion and hence helps in compaction of
concrete used in the production of masonry units.
 Since natural pozzolans reduce concrete durability, the formation of
efflorescence on concrete brick units is decreased.
5. Concrete Masonry Units