1.Constitutents of Concrete and Cement Production

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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1.Constitutents of Concrete and Cement Production

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