1.constitutents of concrete and cement production
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8/3/2019 1.Constitutents of Concrete and Cement Production
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CEMENT CONCRETE
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Outline
Concrete
History of Cement
Raw Materials
Manufacturing process
Quality Control
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What is Concrete?
Cement Concrete
Cement Paste Phase Aggregate Phase(OPC, PPC....)
Cement+Admixtures+Water Coarse Fine
SP, VMA, SRA...
Mineral + Chemical River Msand
Synthetic Natural Recycled
Pozzolanic + Inert Fillers
FA, slag, silica fume, Metakaolin Light wt. Normal wt. Heavy wt.3
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Why Concrete?
Excellent water resistance
Ease of moulding in to any shape and size Availability of raw materials
Economy (~ Rs 5-6)
Less energy consumption (relatively with steel) Sustainable
Durable
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5.5 billion tonnes of concrete per year
(~ 1 tonne perhuman being)
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Pantheon
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World's largest unreinforced concrete domeRome - 126 AD
Elliptical amphitheatre
Rome - 80 AD
Colosseum
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History of Cement
Lime mortar - Hydraulic Cement - Portland Cement
John Smeaton (Civil Engineer) -1756 - EddystoneLighthouse - discovered that the best limes for
mortar contained a high degree ofclayey matter
Ultimately, this kind of lime was usedin equal quantities withpozzolana
for the construction of Light house
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Portland Cement
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L. J. Vicat: Prepared artificial hydraulic lime bycalcining an intimate mixture of limestone (chalk)and clay principal forerunner to PortlandCement
1824 Joseph Aspdin, while obtaining a patentfor his hydraulic cement, termed it as Portlandcement, due to the resemblance of hardened
cement in appearance and quality of Portlandstone (limestone from Dorset, UK)
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Portland Cement (PC) over the ages Proto PC Calcined mixture of limestone and clay;
no CaO-SiO2 interaction; low burning temperatures
Meso PC C2S clearly evident; some C3S present;
poorly defined flux phases (C3A and C4AF); Aspdins
patented cement falls in this category
Normal PC Controlled production; suitable
proportioned mixture of calcareous and argillaceous
components, as in the modern day cements.
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Raw Materials for Cement
Calcareous material Containing CaCO3 (primarysource limestone); impurities such as iron andalumina are sometimes present
Argillaceous material Containing clayey matter,source of Silica (SiO2), Alumina (Al2O3 )
Gypsum Added in the final stages ofmanufacture as a set regulator
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Cement Production-Schematic
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1400C
800C
Fluidised calciner - 800C
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Process of Manufacturing CementWet Process and Dry process
Wet process Mechanical stirrers for avoidingsedimentation , more uniform mixing, energy
intensive
Dry process higher output, lower powerconsumption
Preheaters for drying and partially calcination of
the rawmeal
Fluidised calciners used to increase the
decarbonation (dissociation of CaCO3)
Dry process with precalciners are the order of the
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Wet Vs. Dry ? When moisture content of raw materials is >
15%, wet blending (in slurry form) is preferred When moisture content < 8%, dry blending is
done
For 8% < moisture content < 15%, dryblending with precalciners used
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Process WetDry
Preheater Precalciner
Kiln length (m) 40 232 40 95 54 110
Output (tons/day) 100 3350 200 3500 1500 8500
Fuel consumption
(kcal/kg clinker)
1000 2200 800 950 800 95
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Cement kiln
Only rotary kilns used nowadays
Typical kilns are long ~ 30 40 m
Length and diameter of kiln also depends on
blending process, output required and energy
Temperature inside kiln varies from 850 (at inlet) to
1450C (at the outlet)
Reactions are not completed inside kiln; some
require cooling to occur
The material comes out of kiln is called clinker
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Cement Clinker
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3 to 25 mm
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Reactions in the kiln Conversion of mixtures of calcium carbonate, silica
and alumina - bearing components to mixture of special
crystalline components capable of reacting with water to
produce controlled setting and strength gain
The major components in clinker are impure but well
crystallized fine (ca. < 50 Qm) crystals of tricalciumsilicate (C3S) and dicalcium silicate (C2S)
Minor in quantity but important crystalline components are
extremely fine crystals of tricalcium aluminate (C3
A)
and calcium aluminate ferrite solid solution (C4AF)
Of greater importance despite minor amount present are
deposits of soluble crystalline components (alkali sulfates
and calcium alkali sulfates) on the surfaces of clinkers
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Kiln reactions - schematic
Mindess and Young, 1981
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Hewlett, 2001
Up to 700 oC: activation of silicates
through removal of water andchanges in crystal structure
700 900 oC: decarbonation of
CaCO3, initial combination of A, F,
and activated silica with lime
900 1200 oC: Belite (C2S) formation
> 1250 oC (more particularly, > 1300oC): liquid phase appears and
promotes the reaction between belite
and free lime to form alite (C3S)
Cooling stage*: molten phase
(containing C3A and C4AF) gets
transformed to a glass; if cooling is
slow, C3A crystallizes out (causes
setting problems), or alite converts to
belite and free lime
Kiln reactions - schematic
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Amorphous vs. crystalline Describes the structure of certain elements and compounds
in the solid state.
A crystalline solid is one in which there is a there is long-
range order or in other words, regular repeating pattern in
the structure. (Eg) diamond, table salt.
An amorphous solid is one which does not have long-rangeorder. In other words, there is no repeat unit. (Eg) Glass,
wax and plastics.
If a liquid cools very quickly, the molecules will not have
time to arrange themselves in the most favorable pattern andso they are locked into a disordered solid.
Properties of an element existing in amorphous form will
differ considerably from the same element existing in
crystalline form (with same chemical composition)18
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Appearance of clinker
Typical PC clinker is composed of
- large irregular crystals that are grains of alite
(C3S),- more rounded smaller crystals that are belite
(C2S), and
- groundmass consisting of the flux p
hases(mixture of ferrite and C3A solid solutions)
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ClinkerClinkers viewed under reflected light in optical microscope
These figures show the important phases of alite (C3S, generally
angular), belite (C2S, generally rounded), interstitial material (C3A andC4AF, light colour regions) and epoxy resin in clinker pores.
Clinker showing in left fig. has
Typical C3S (alite) structure with
Relativelyh
ighproportion ofaluminate hases white areas
In right fig. a zone of high C2S
(belite) content is visible
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Clinker
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In the Left fig. high C2S content
surrounded by C3S crystals
In the Right fig. fine grained,
nested C2S zone with much
porosity in clinker
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Intergrinding with gypsum Final step in cement manufacture
Gypsum added as a set regulator (absence flashset)
Strict control on temperature required
Done in ball mills
Cement of required
fineness produced
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Other issues Cement manufacture today is a highly controlled
process
Closed circuit grinding is preferred
However, there is lot of variation in quality ofcements (between brands, in the same brand,
sometimes in batches produced on the same day!)
Quality control during cement manufacture done
at every stage in the process
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Quality control
Sampling and evaluation should be performed
after excavation from the quarry
before and after blending the feedstock
after formation of clinker
after intergrinding clinker with gypsum
finally before packaging in the bags and drums
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Quality control parametersLime saturation factor (LSF) = C/(2.8S + 1.2A + 0.65F)
where C, S, A, and F are the % amounts of CaO, SiO2,Al2O3 and Fe2O3, respectively
Silica ratio (or modulus) = S/(A + F)
Alumina ratio (or modulus) = A/F
Potential C3S from Bogue formulation
The LSF is particularly important because it dictates the
amount of free lime that will be present in the product. Too
much free lime can cause unsoundness of the cement.
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Some informations
UK 50 kg
US 42.6 kg*
Environmental impact
1 tonne of cement = 1 tonne of CO2 ( ) Depletion of natural resources
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Acknowledgments
The instructor is indebted to Dr. Manu Santhanam
from Indian Institute of Technology Madras forproviding some of the images and illustrations
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