WHAT IS CEMENT ?
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In the most general sense of the word, a cement is a binder, a
substance which sets and hardens independently, and can bind
other materials together. The word "cement" traces to the Romans,
who used the term "opus caementicium" to describe masonry which
resembled concrete and was made from crushed rock with burnt
lime as binder.
The most important use of cement is the production of mortar and
concrete—the bonding of natural or artificial aggregates to form a
strong building material which is durable in the face of normal
environmental effects.
Cements that are used for construction fall into two main categories
based on cement properties, hydraulic or non-hydraulic. In addition to
the two main cement forms, there are several different forms of
hydraulic cement. Of the many varieties of hydraulic cement, the
most commonly used cement today is Portland cement.
TYPES OF CEMENT
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Hydraulic cement
An inorganic material or a mixture of
inorganic materials that sets and
develops strength by chemical
reaction with water by formation of
hydrates and is capable of doing so
under water.
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Non-hydraulic cement
Non-hydraulic cement is cement which
cannot harden while in contact with
water, as opposed to hydraulic cement
which can. Non-hydraulic cements are
created using materials such as nonhydraulic lime and gypsum plasters,
and oxychloride, which has liquid
properties. After non-hydraulic cement
is utilized in construction, it must be
kept dry in order to gain strength and
hold the structure. When non-hydraulic
cement is used in mortars, those
mortars can set only by drying out, and
therefore gain strength very slowly. Due
to the difficulties associated with
waiting long periods for setting and
drying, non-hydraulic cement is rarely
utilized in modern times.
PORTLAND CEMENT
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In addition to the two main forms of cement which exist, hydraulic and nonhydraulic, there are also several types of hydraulic cements that can be
made and used in construction. The main form of cement used in
construction worldwide today is the hydraulic cement called Portland
cement. Portland cement is a type of hydraulic cement made by heating a
limestone and clay mixture in a kiln and pulverizing the materials. It is a
fine, grey or white powder that is made by grinding Portland cement clinker,
a limited amount of calcium sulfate which controls the set time, with other
minor constituents. Portland cement is the most common type of cement in
general usage in many parts of the world. The cement is used as the basic
ingredient of concrete, mortar, stucco and most non specialty grout.
Invented in the 19th century, Portland cement has become the staple form
of cement produced and used worldwide. All references to cement
worldwide refer to Portland cement, as it constitutes virtually all cement
produced.
PORTLAND CEMENT
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In addition to the two main forms of cement which exist, hydraulic and nonhydraulic, there are also several types of hydraulic cements that can be
made and used in construction. The main form of cement used in
construction worldwide today is the hydraulic cement called Portland
cement. Portland cement is a type of hydraulic cement made by heating a
limestone and clay mixture in a kiln and pulverizing the materials. It is a
fine, grey or white powder that is made by grinding Portland cement clinker,
a limited amount of calcium sulfate which controls the set time, with other
minor constituents. Portland cement is the most common type of cement in
general usage in many parts of the world. The cement is used as the basic
ingredient of concrete, mortar, stucco and most non specialty grout.
Invented in the 19th century, Portland cement has become the staple form
of cement produced and used worldwide. All references to cement
worldwide refer to Portland cement, as it constitutes virtually all cement
produced.
COMPOSITION OF CEMENT
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The essential raw ingredients of Portland
cement are limestone, 75 to 77%, and alumina
(A12O3) and silica (SiO2) 20 to 25%. The
alumina and silica are commonly found
combined as * clay, which is a silicate of
aluminum (Al2O32SiO2) + 2H2O.. There are
accidental ingredients usually amounting to
about 5%, but these must not include over 3%
of magnesia (MgO).
MANUFACTURING OF CEMENT
PROCESS
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Quarrying
Two types of materials are necessary for the production of cement: one rich
in calcium or calcareous materials such as limestone, chalk, etc., and one
that is rich in silica or argillaceous materials such as clay. Extensive quarry
drilling and analysis are being undertaken to reduce the variability of the
raw material quality. The quality check that starts from the quarry ensures
optimization in the utilization of the reserves. Limestone and clay are either
scraped or blasted from the quarry and then transported to the crusher.
Crushing
The crusher is responsible for the primary size reduction of the
quarried materials. Boulders as big as 1 meter are being crushed to
material sizes less than 80 mm.
PROCESS
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Pre-blending
The crushed materials pass through an on-line analyzer to determine the pile composition. A stacker is then
used to create different piles of materials and to reduce variation in material beds.
Raw grinding and blending
A belt conveyor transports the pre-blended piles into individual bins where a weighing feeder proportions it
according to the type of clinker to be produced. The materials are then ground into the desired fineness by
the raw mill equipment. The powdered raw meal is then transported into a continuous blending storage silo
where variations are further reduced by mixing using aeration.
Finish grinding
From the clinker silo, clinker is transferred to the clinker bin. It passes through the weighing feeder, which
regulates its flow in proportion with the additive materials. At this stage, gypsum is added to the clinker and
then fed to the finish grinding mills. Gypsum serves as a retarder in the too rapid setting or hardening of
cement.
Either the mixture of clinker and gypsum for Type-1 cement or the mixture of clinker, gypsum and pozzolan
material for Type-P cement is pulverized in a closed circuit system in the finish mills to the desired fineness.
Cement is now piped to cement silos.
Packing and distribution
The cement from the cement silos are packed into bags by rotary packers or loaded as bulk and are
distributed either
PROPERTIES
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CHEMICAL PROPERTIES
Gypsum
(3.5%)
Other
(1.5%)
Tetracalcium Aluminoferrite
(8%)
Tricalcium Aluminate
(12%)
Dicalcium Silicate
(25%)
Tricalcium Silicate
(50%)
SETTING TIME
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Cement paste setting time is affected by a number
of items including: cement fineness, water-cement
ratio, chemical content (especially gypsum
content) and admixtures. Setting tests are used to
characterize how a particular cement paste
sets. For construction purposes, the initial set
must not be too soon and the final set must not be
too late. Additionally, setting times can give some
indication of whether or not a cement is
undergoing normal hydration
•Initial set. Occurs when the paste begins to stiffen considerably.
•Final set. Occurs when the cement has hardened to the point
at which it can sustain some load.
These particular times are just arbitrary points used to
characterize cement, they do not have any fundamental chemical
significance
Test Method
Vicat
Gillmore
Set Type
Time Specification
Initial
45 minutes
Final
375 minutes
Initial
60 minutes
Final
600 minutes
•The Vicat needle test is more common and tends to give shorter times than
the Gillmore needle test.
RAPID HARDENING OF CEMENT
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The Rapid Hardening Portland Cement's better strength performance is
achieved by increasing the refinement of the product. This is the reason that
its use is increasing in India.
Rapid Hardening Portland Cement is manufactured by fusing together
limestone (which has been finely grounded) and shale, at extremely high
temperatures to produce cement clinker. To this cement clinker, gypsum is
added in small quantities and then finely grounded to produce Rapid
Hardening Portland Cement. It is usually manufactured using the dry
process technology.
Rapid Hardening Portland Cement is used in concrete masonry
manufacture, repair work which is urgent, concreting in cold weather, and in
pre-cast production of concrete. Rapid Hardening Portland Cement has
proved to be a boon in the places where quick repairs are required such as
airfield and highway pavements, marine structures, and bridge decks.
•The raw materials required for the manufacture of Rapid Hardening Portland
Cement are: Limestone
I. Shale
II. Gypsum
III.Coke
•The major companies producing Rapid Hardening Portland Cement in India
are:
I. ACC
II. Gujarat Ambuja
III.J K Cement
IV.Grasim Industries
V. Indian Cement Ltd.
MARKET STUDY
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What is OPC Cement?
OPC means Ordinary Portland Cement which contains mixture of Portland
clinker and Gypsum ground to a very fine powder.
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What is PPC Cement?
PPC means Portland Pozzolana Cement. It is manufactured by blending a
mixture of Ordinary Portland cement and Pozzolana materials such as Fly
Ash, in proportions not less than 15% and not more than 35% by weight of
cement. The fineness of PPC will be greater than OPC.
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Difference between OPC and PPC Cement
Addition of Pozzolanic material such as fly ash in the cement manufacture
by 15% to 35% is the only difference between OPC and PPC.
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Duration of curing for OPC and PPC
Duration for curing is same for both OPC and PPC. But the water cement
ratio may be slightly varied. As the cement is attaining full strength at 28
days, concretes made out of both the cements are to be cured for 28 days.
MARKET STUDY
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What are the setting time for OPC and PPC?
Same for both OPC and PPC. i.e. initial setting time 30 minutes and
final setting time 600 Minutes. (10 hours)
Preferable constructions by OPC and PPC
OPC: OPC is categorized as 33 Grade, 43 Grade and 53 Grade. It is
preferably used in Defence Services, Railway Sleeper making and in
lean concrete structures.
PPC: PPC is having better resistance to Sulphate attack and hence it
is preferably used in Sea Shore, Dam constructions and in the earth
work concreting to neutralize corrosion effect of soil and water under
the earth's crest. Due to higher fineness, mostly it is used in
plastering work for smooth finishing.
GRADES OF CEMENT AVAILABLE
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Ordinary Portland cement (opc)
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Opc is available in 2 grades (i) 53 grade (ii) 43 grade
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There is no grade 4 ppc cement
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Ppc1.Nowadays it is used 4 each and every purposes.eg: bridge, buildings construction, road
construction, etc
2. Setting time- slow
3. Its strength increases day by day. Therefore there is no complaint about ppc cement.
4. durability more than opc.
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Opc1.It is used 4 building superstructure, dam, road furniture, panels, beam, Commercial
Buildings, Industrial Constructions, Multi-storied complexes, Cement concrete, roads, Heavy
Duty Floors etc.
2. Setting time faster than ppc
3. Its strength does not increases day by day. What it attend at 28 day, remains the same
throughout..
4. durability not more than ppc.
RATES
The rate of all the standard cements available is
approximately same.
 The rate of Opc and ppc is the same.
 The cost of one bag of cement is Rs 275.
 dealer ------------------retailer-------------------consumer
Rs 232 +12.50% tax
= Rs. 262
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