advance concrete technology

1. QUIZ 3 (RAJENDRA SINGH)
1. Describe in your own words the production of Portland cement.
ANS- Portland cement is the basic ingredient of Portland cement concrete. Concrete is
formed when Portland cement creates a paste with water that binds with aggregates.
Cement is manufactured through a closely controlled chemical combination of calcium,
silicon, aluminum, iron and other ingredients. Common materials used to manufacture
cement are limestone, shells, and chalk or marl combined with shale, clay, slate, blast
furnace slag, silica sand, and iron ore. These ingredients, when heated at high
temperatures form a rock-like substance that is ground into the fine powder that we
commonly think of as cement.
The most common way to manufacture Portland cement is through a dry method. The first
step is to quarry the principal raw materials, mainly limestone, clay, and other materials.
After quarrying the rock is crushed. This involves several stages. The first crushing reduces
the rock to a maximum size of about 150mm. The rock then goes to secondary crushers or
hammer mills for reduction to about 75mm or smaller.
The crushed rock is combined with other ingredients such as iron oreor fly ash and ground,
mixed, and fed to a cement kiln. The cement kiln heats all the ingredients to about 2,700
degrees Fahrenheit in huge cylindrical steel rotary kilns lined with special firebrick. The
finely ground raw material or the slurry is fed into the higher end. At the lower end is a
roaring blast of flame, produced by precisely controlled burning of powdered coal, oil,
alternative fuels, or gas under forced draft. As the material moves through the kiln, certain
elements are driven off in the form of gases. The remaining elements unite to form a new
substance called clinker. Clinker comes out of the kiln as grey balls, about the size of
marbles.
Clinker is discharged red-hot from the lower end of the kiln and generally is brought down
to handling temperature in various types of coolers. The heated air from the coolers is
returned to the kilns, a process that saves fuel and increases burning efficiency.
After the clinker is cooled, cement plants grind it and mix it with small amounts of gypsum
and limestone. The cement is now ready for transport to ready-mix concrete companies to
be used in a variety of construction projects.
Although the dry process is the most modern and popular way to manufacture cement,
some kilns in the United States use a wet process. The two processes are essentially alike

2. except in the wet process, the raw materials are ground with water before being fed into
the kiln.
2. How to measure or calculate the chemicalcomponentsofPortland cement (i.e.,
chemical elements and phases)?
ANS- Portland cement is made up of four main compounds: tricalcium silicate (3CaO ·
SiO2), dicalcium silicate (2CaO · SiO2), tricalcium aluminate (3CaO · Al2O3), and a tetra-
calcium aluminoferrite (4CaO · Al2O3Fe2O3). In an abbreviated notation differing from the
normal atomic symbols, thesecompounds are designated as C3S, C2S, C3A, and C4AF, where
C stands for calcium oxide (lime), S for silica, A for alumina, and F for iron oxide. Small
amounts of uncombined lime and magnesia also are present, along with alkalies and minor
amounts of other elements.
The composition of cement is varied depending on the application. A typical example of
cement contains 50–70% C3S, 15–30% C2S, 5–10% C3A, 5–15% C4AF, and 3–8% other
additives or minerals (such as oxides of calcium and magnesium). It is the hydration of the
calcium silicate, aluminate, and aluminoferrite minerals that causes the hardening, or
setting, of cement. The ratio of C3S to C2S helps to determine how fast the cement will set,
with faster setting occurring with higher C3S contents. Lower C3A content promotes
resistance to sulfates. Higher amounts of ferrite lead to slower hydration. The ferrite phase
causes the brownish gray color in cements, so that “white cements” (i.e., those that are low
in C4AF) are often used for aesthetic purposes.
The Bogue calculation is used to calculate the approximate proportions of the four main
minerals in Portland cement clinker. The standard Bogue calculation refers to cement
clinker, rather than cement, but it can be adjusted for use with cement. Although the
result is only approximate, the calculation is an extremely useful and widely-used
calculation in the cement industry. The calculation assumes that the four main clinker
minerals are pure minerals with compositions:
Alite: C3S, or tricalcium silicate
Belite: C2S, or dicalcium silicate
Aluminate phase: C3A, or tricalcium aluminate

3. Ferrite phase: C4AF, or tetracalcium aluminoferrite
Itis important to remember that these assumed compositions areonly approximations
to the actual compositions of the minerals. Clinker is made by combining lime and silica
and also lime with alumina and iron. If someof the lime remains uncombined, (which it
almost certainly will) we need to subtractthis from the total lime content before we do
the calculation in order to get the best estimate of the proportions of the four main
clinker minerals present. For this reason, a clinker analysis normally gives a figurefor
uncombined free lime.
The calculation is simple in principle: Firstly, according to the assumed mineral
compositions, ferritephase is the only mineral to contain iron. The iron content of the
clinker therefore fixes the ferrite content. Secondly, the aluminate content is fixed by the
total alumina content of the clinker, minus the alumina in the ferrite phase. This can now
be calculated, sincethe amount of ferrite phasehas been calculated. Thirdly, it is
assumed that all the silica is present as belite and the next calculation determines how
much lime is needed to form belite fromthe total silica content of the clinker. There will
be a surplus of lime. Fourthly, the lime surplus is allocated to the belite, converting some
of it to alite. In practice, the above process of allocating the oxides can be reduced to the
following equations, in which the oxides representthe weight percentages of the oxides
in the clinker:
BOGUE CALCULATION
C3S = 4.0710CaO-7.6024SiO2-1.4297Fe2O3-6.7187Al2O3
C2S = 8.6024SiO2+1.0785Fe2O3+5.0683Al2O3-3.0710CaO
C3A = 2.6504Al2O3-1.6920Fe2O3
C4AF = 3.0432Fe2O3
Clinker analysis
SiO2 Al2O3 Fe2O3 CaO MgO K2O Na2O SO3 LOI IR Total
21.5 5.2 2.8 66.6 1.0 0.6 0.2 1.0 1.5 0.5 98.9
Free lime = 1.0% CaO

4. It should be stressed that the Bogue calculation does not give the 'true' amounts of the
four main clinker phases present, although this is sometimes forgotten. The results of
the Bogue calculation differ fromthe 'true' amounts (often called the phaseproportions)
principally because the actual mineral compositions differ - often only slightly, but
occasionally more so and particularly in the case of the ferrite phase, from the pure
phase compositions assumed in the calculation. To adjust the calculation for use with
Portland cement, it is necessary to consider first what other materials may be present in
the cement. If the cement is a mixture of clinker and gypsum only, the calcium bound
with the gypsum can be allowed for approximately by deducting (0.7 x SO3) from the
total CaO. Note that this does not allow for any clinker sulfate present as potassium or
sodium sulfate and a small error will therefore be introduced. A similar adjustment can
be carried out for limestone; the limestone content can be estimated by determining the
CO2 content of the cement and calculating the corresponding CaO. If either slag or fly ash
is present, in principle the formula could be adjusted to take it into account, but the slag
or ash composition would need to be known accurately and in practice this is not an
adjustment normally made.
(3.) Describe the most common Portland cement types used in Canada? What are the
components that bring the most important differences amongst them? Please give some
examples.
ANS- There are following types of Portland cement types used in Canada.
Type 1 GU: It is multipurpose cement suitable for all applications not requiring the special
properties of any other type of cement. Used in various applications such as: pavement,
floors, buildings, sidewalks, pipes, masonry blocs, etc.
Type 2 MS (Moderate Sulfate Resistant Cement): It is used to protect concrete against
moderate sulfate attacks. Itis used for common structures or structure elements in contact
with soils or underground water having sulfate concentration higher than normal but not
exceptionally high. Concrete exposed to sea water is often made with MS type cement. It is
also used for mining or industrial applications.
Type 2 MH (Moderate Heat of Hydration Cement): It is especially designed to generate
less heat, and more slowly, than a general use cement. Heat of hydration is a chemical

5. process started when water is mixed with cement. Moderate heat of hydration cement is
an optional characteristic that is offered to clients. This type of cement can be used in
massive construction such as dams, bridge piers or columns, foundations or thick retaining
walls for which the risk of heat-induced cracking is higher, especially if concrete is to be
poured in warm weather.
Type 3 HE (High Early Strength Cement): It produces high strength in a shorter time,
usually in a week or less. This cement is chemically and physically similar to the general use
cement, except that its particles are grounded morefinely. Itis used when formwork has to
be removed rapidly or if the construction has to be put in service without delay. For cold
weather construction, HE cement reduces curing time.
Type 4 LH (Low Heat of Hydration Cement): It is used in cases where there is a need to
reduce as much as possible the heat generated by the hydration process. This cement
builds its resistance more slowly than other types of cement. It is recommended for
massive concrete constructions such as gravity dams for which heat of hydration has to be
reduced to a minimum. LH cement is usually available for major projects and on special
order.
Type 5 HS (High Sulfate Resistance Cement): - It is used in concrete with high sulfate
exposure, mainly in cases where soil or groundwater has high sulfate content. Strength
from concrete made with sulfate resistance cement will develop more slowly than with the
general hydraulic cement. A low water-cement ratio and a low permeability are essential
for concrete exposed to sulfates.
There are mainly two important components due to which change happens in the all type
of Portland cement which is clear from the table given below.
TYPE 1-55% (C3S), 19% (C2S), 10% (C3A), 7% (C4AF), 2.8% MgO, 2.9% (SO3), 1.0% ignition
loss, and 1.0% free CaO (utilizing Cement chemist notation).
TYPE 2-51% (C3S), 24% (C2S), 6% (C3A), 11% (C4AF), 2.9% MgO, 2.5% (SO3), 0.8% ignition
loss, and 1.0% free CaO.
TYPE 3-57% (C3S), 19% (C2S), 10% (C3A), 7% (C4AF), 3.0% MgO, 3.1% (SO3), 0.9% ignition
loss, and 1.3% free CaO.
TYPE 4-28% (C3S), 49% (C2S), 4% (C3A), 12% (C4AF), 1.8% MgO, 1.9% (SO3), 0.9% ignition
loss, and 0.8% free CaO.
TYPE 5-38% (C3S), 43% (C2S), 4% (C3A), 9% (C4AF), 1.9% MgO, 1.8% (SO3), 0.9% ignition loss,
and 0.8% free CaO.
From above data it is clear that C3S, C2S, C3A, C4AF are the major component in all types of
Portland cement. Whereas other minor components are MgO and SO3 .
4. Describe in yourown words the 5 hydration phasesofPortland cement. Do not
forget to describe the most important products and their roles in the fresh and
hardened material.
ANS- There are 5 phases of hydration.

6. 1. Phase: Pre-induction
2. Phase: Induction (dormant)
3. Phase: Acceleration
4. Phase: Deceleration
5. Phase: Consolidation (Steady State)
Phase 1: Pre-induction
Initial after mixing the cement and water comes into contact with each other, a peak in
temperature happens. The aluminate (C3A) reacts with H2O (Calcium and sulfate ions) to
form ettringite (aluminate hydrate). The release of the energy from these reactions causes
the initial peak.
Phase 2: Induction (dormant)
A result of the reaction described in phase 1 is a surface coating of the cement particles.
This coating keeps increases, but also slows down the reaction (hydration) as the access to
H2O isn’t as good as when the concrete was mixed. The amount of hydrated concrete
keeps increasing on a steady level while the surface of the concrete keeps fluid.
This is why this phase is used for transporting and pouring the concrete, as the concrete
stays on a fluid level. The length of this period depends on each individual concrete mix and
can, therefore, be optimized depending on the application like winter concreting, length of
transport, etc.This phase ends with an initial set of the concrete.
Phase 3: Acceleration
A heat increase happens due to the reaction between calcium silicate (C3S and C2S) which
creates the silicate hydrate CSH (heat increase also caused by other minor reactions). The
creation of CSH also has a major impact on the concrete strength during this phase.

7. In the case of for example mass concrete application, it can be very important to monitor
the internal temperature variances, as the concrete temperature during this phase can
increase rapidly to reach internal temperatures like 70-80C (in some cases even higher). It
is normally not recommended to exceed temperatures at around 70C.If high variations
occur; there is a significant risk of cracks!
Phase 4: Deceleration
A maximum temperature has now been reached and the availability of free particles is now
reduced and therefore slows down the temperature increase.This phase often ends with
the desired strength and the formwork around the concrete can now be removed.
Monitoring of concrete maturity and temperature and therefore enable the user with the
exact time where this is possible.
Phase 5: Consolidation (Steady State)
The hydration process is now slowed down and will continue slowly to finish the remaining
available cement and water particles. The formwork is now often removed and the
concrete will now over time (can take a long time) finish the hydration process and reach
final strengths (can take weeks or months).
Properties of hydration products affecting the overall behavior of the cement-
C-S-H, calcium silicate hydrate – It has very poor crystallinity; the exact chemical
compound is variable. The ratio of C/S varies between 1.5 and 2.0 and depends on many
factors; temperature, w/c ratio, impurities, etc. Likewise, measures of the water content
vary considerably.Because of the poor crystallinity, C-S-H develops very small irregular
particles and consequently a very high surface area. In general, the surface area of the
hydrated cement is about 1000 times larger than the unhdyrated cement. Therefore, the
increase in surface area greatly influences physical properties of the C-S-H hydrate.
Considerable work has been done in modeling the structural components of C-S-H, with
much disagreement among scientists. C-S-H is considered a layer structure composed of
calcium silicate sheets randomly connected by strong ionic-covalent bonds. This is the most
important of all the products and is responsible for all the good properties of concrete i.e.
strength, durability, etc.It has been found that the hydration of C3S produces lesser C-S-H
than Ca(OH)2 as compared to the hydration of C2S. Further, the quality and density of C-S-H
produced by C3S is inferior to C2S.
Calcium Hydroxide (Portlandite) -a well understood hexagonal crystalline material.
Crystals are much larger than C-S-H particles and are sometimes visible to the naked eye.
Calcium hydroxide helps in maintaining a pH value of 13 around the reinforcement, which

8. acts as a passiveprotective layer preventing the corrosion of reinforcement. Ca(OH)2 reacts
with CO2 present in the atmosphere and forms CaCO3. Initially, the reaction transpires on
the surface of concrete but gradually penetrates into the mass. If the concrete mass is a
little porous and reduces the pH value of the passive protective layer, it makes the
reinforcement susceptible to corrosion. This type of deterioration is called carbonation of
concrete.
Calcium Sulfoaluminate (ettringite) -These hexagonally-shaped prism crystals are
considerably longer than CH crystals. Large clusters of ettringite needles may be visible in
concrete affected by sulfate attack. Monosulfoaluminate tends to form very thin,
hexagonal plates. It should be noted that this compound is being formed before the
concrete hardens, and hence this primary ettringite formation doesn’t lead to any harmful
effects on concrete. The same compound becomes deleterious to concrete if it is formed
after the concrete has hardened. This is popularly known as Delayed Ettringite
Formation (DEF), which leads to the development of micro cracks in concrete, making it
porous and less durable.
Calcium Aluminate Hydrate- These hydration products do not impart any strength or
unique property to concrete; instead, their presence is harmful to the concrete, particularly
in cases where concrete is prone to sulfate attack.
5.What’s the main difference between Portland cement and supplementary cement
materials (SCMs)? Pleasediscuss on the impact of SCMs on the fresh and hardened state
of concrete.
ANS- SCMs are materials used as a partial replacement of Portland cement to improve
both fresh and hardened concrete properties. The most commonly used SCMs in concrete
mixtures are fly ash (TypeC, Type F), slag cement, and, to a lesser extent, silica fume. These
materials are byproducts of various industries: Fly ash-burning coalin power plants; Slag
cement-smelting iron ore; Silica fume-alloying silicon or ferrosilicon.Supplementary
cementations materials can be used for improved concrete performancein its fresh and
hardened state. They are primarily used for improved workability, durability and strength.
These materials allow the concrete producer to design and modify the concrete mixture to
suit the desired application. Concrete mixtures with high portland cement contents are
susceptible to cracking and increased heat generation. These effects can be controlled to a
certain degree by using supplementary cementitious materials.Supplementary

9. cementitious materials such as fly ash, stag and silica fume enable the concrete industry to
use hundreds of millions of tons of byproductmaterials that would otherwisebe landfilled
as waste. Furthermore, their use reduces the consumption of Portland cement per unit
volume of concrete. Portland cement has a high energy consumption and emissions
associated with its manufacture, which is conserved or reduced when the amount used in
concrete is reduced.
There are some examples of SCM.
 Fly Ash is a byproductof coal-fired furnaces at power generation facilities and is
the non-combustibleparticulates removed fromthe flue gases.Theamountof fly ash in
concrete can vary from5% to 65% by mass of the cementitious materials, depending on
the sourceand composition of the fly ash and the performancerequirements of the
concrete. Characteristics of fly ash can vary significantly depending on the sourceof the
coal being burnt.
 Ground GranulatedBlast Furnace Slag (GGBFS) is a non-metallic manufactured
byproductfroma blast furnacewhen iron ore is reduced to pig iron. The liquid slag is
rapidly cooled to formgranules, which are then ground to a fineness similar to portlancl
cement. Ground granulated blast furnaceslag used as a cementitious material should
conformto the standard specification,ASTMC989. Slag is used at 20% to 70% by mass
of the cementitious materials.
 SilicaFume is a highly reactive pozzolanic material and is a byproductfromthe
manufactureof silicon or ferro-silicon metaL It is collected fromthe flue gases from
electric arc furnaces. Silicafume is an extremely fine powder, with particles about 100
times smaller than an average cement grain. Silica fume is available as a densified
powder or in a water-slurry form. Dueto its extreme fineness special procedures are
warranted when handling, placing and curing silica fume concrete.
 Natural Pozzolans: Various naturally occurring materials possess, or can be
processed to possess pozzolanic properties. Thesematerials are also covered under the
standard specification,ASTMC 618. Naturalpozzolans aregenerally derived from
volcanic origins as these siliceous materials tend to be reactive if they are cooled rapidly.
Impact of SCMs on the fresh and hardened state of concrete-
FreshConcrete: In general, supplementary cementitious materials improvethe
consistency and workability of fresh concrete becausean additional volumeof fines is
added to the mixture. Concrete with silica fume is typically used at low water contents
with high rangewater reducing admixtures and these mixtures tend to be cohesiveand
stickier than plain concrete. Fly ash and slag generally reduce the water demand for
required concrete slump. Concrete setting time may be retarded with some
supplementary cementitious materials used at higher percentages. This can be
beneficial in hot weather.The retardation is offset in winter by reducing the percentage
of supplementary cementitious material in the concrete. Because of the additional fines,
the amountand rate of bleeding of these concretes is often reduced. This is especially
significant when silica fume is used. Reduced bleeding, in conjunction with retarded

10. setting, can causeplastic shrinkagecracking and may warrantspecialprecautions during
placing and finishing.
Strength - Concrete mixtures can be proportioned to producethe required strength and
rate of strength gain as required for the application. With supplementary cementitious
materials other than silica fume, the rate of strength gain might be lower initially, but
strength gain continues for a longer period compared to mixtures with only portland
cement, frequently resulting in higher ultimate strengths. Silicafume is often used to
produceconcrete compressivestrengths in excess of 10,000 psi[70 MPa]. Concrete
containing supplementary cementitious material generally needs additional
consideration for curing of both the test specimens and the structureto ensurethat the
potential properties are attained.
Durability - Supplementary cementitious materials can be used to reduce the heat
generation associated with cement hydration and reducethe potential for thermal
cracking in massivestructuralelements.These materials modify the microstructureof
concrete and reduce its permeability thereby reducing the penetration of water and
water-bornesalts into concrete. Watertight concrete will reduce various forms of
concrete deterioration, such as corrosion of reinforcing steel and chemical attack. Most
supplementary cementitious materials can reduce internal expansion of concrete due to
chemical reactions such as alkali aggregate reaction and sulfateattack. Resistance to
freezing and thawing cycles requires the useof air entrained concrete. Concrete with a
proper air void systemand strength will performwell in these conditions.
The optimum combination of materials will vary for differentperformancerequirements
and the type of supplementary cementitious materials. The ready mixed concrete
producer, with knowledge of the locally available materials, can establish the mixture
proportions for the required performance. Prescriptiverestrictions on mixture
proportions can inhibit optimization and economy. While severalenhancements to
concrete properties are discussed above, these are not mutually exclusive and the
mixture should be proportioned for the mostcritical performancerequirements for the
job with the available materials.