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Dr. Kimberly KurtisSchool of Civil Engineering

Georgia Institute of TechnologyAtlanta, Georgia

Portland Cement Manufacture

Key Steps

1. Selection and proportioning of raw materials

2. Grinding and blending of raw materials

3. Clinkering

4. Grinding of clinker

5. Addition of gypsum

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Raw Materials

Portlandcement is:

45-60% C3S

15-30% C2S

6-12% C3A

6-8% C4AF

Anhydrite

Calciumsulfate

Gypsum

Aluminum-orerefuse

Bauxite

Cement rock

Clay

Copper slag

Fly ash

Fullers earth

Granodiorite

Limestone

Loess

Ore washings

Shale

Slag

Staurolite

Calcium silicate

Cement rock

Clay

Fly ash

Fullers earth

Loess

Marl

Ore washings

Quartzite

Rice-hull ash

Sand

Sandstone

Shale

Slag

Traprock

Blast-furnaceflue dust

Clay

Iron ore

Mill scale

Ore washings

Pyrite cinders

Shale

Alkali waste

Aragonite

Calcite

Cement-kilndust

Cement rock

Chalk

Clay

Fullers earth

Limestone

Marble

Marl

Seashells

Shale

Slag

SulfateAluminaSilicaIronCalcium

Raw Materials

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Raw Materials

Raw Materials

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CaO-SiO2 Binary Phase Diagram

CaO-Al2O3 Binary Phase Diagram

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Raw Materials

Grinding and Blending

Because the objective is to fuse the raw materials at high temperature,

but with energy conservation, the size of the raw materials is critical.

Feedstock materials with the same chemical composition but different

size fractions can require different firing temps (by as much as 150oC) to

achieve an acceptable degree of reaction .

Therefore the materials must be finely and uniformly ground to achieve

burning at the lowest possible temperature.

- - saves fuel

- - prolongs the life of the refractory (heat-resisting

ceramic material which line the kiln)

- - achieves a more uniform product

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Grinding and Blending

~5~3/4

The more work done by crushing, the less work necessary during

further milling (energy savings)

Grinding and Blending: Wet Process

~1/8 powder (

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Grinding and Blending: Dry Process

Grinding mill Vertical roller mill

800oC

Sintering or Clinkering 1-4% inclined rotary kiln, 1-4 rev./min.

Wet process kilns can be up to 8m in diameter and as long as 230 m.

Typical dimensions are 50-100m long, and 3-10m diam.

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Clinkering: Reactions

Clinkering: Reactions

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Clinkering: Reactions

Production of 1 ton of cement, results in release of ~ 1 ton CO 2.

Clinkering: Reactions

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Clinkering: Reactions

Clinkering: Wet vs. Dry Process Wet process requires 500 lbs of coal to produce 1 ton of

cement (1400 kcal or 5700 kJ energy/kg cement).

Dry process requires less than half as much energy.

Smaller kilns can be used in more modern dry-process

cement manufacture.

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Clinkering: Wet vs. Dry Process

Wet Process

Dry Process

Note 1: Cement Kiln Dust

Release of cement kiln dust (CKD) is carefully controlled

Can be precipitated and used in concreting

Very high alkali content

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Note 2: Fuels Used

Fuel used for cement manufacture amounts to 6-8% of the

worlds fuel consumption!

Since fuel costs amount to about 40-60% of the manufacturing

costs, fuels are often selected on an economic basis, although

other considerations may also be made.

Acquisition of the raw materials represents only 10% of the cost

in comparision.

Fuels used include:

- natural gas (2%)

- oil (7%)

- coal (70%+)

- trash, including wood chips, tires, rice husks, oil-soaked Fullers

earth, etc. (20%+)

Grinding of ClinkerUpon exit from the kiln, the clinker, which is black and glistening, is

cooled and then interground with gypsum.

The rate of cooling affects the degree of crystallization of the material.

Modern cement plants rapidly cool the clinker to retain as much

amorphous material as possible.

Kiln

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Red - C3S

Aqua -C2S

Green - C3A

Yellow - C4AF

Pale green - gypsum

White - free lime (CaO)

Dark blue (purple) - K2SO4Light magenta- periclase

(magnesium containing

phase).

Image is 256 m x 200 m.

Grinding of Clinker

Two-dimensional processed SEM/X-ray image for cement 133 issued by the CCRL

(NIST) in June of 1999.

Griding of Clinker: Influence of Fineness

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Addition of Gypsum

~ 5%Gypsum (CaSO42H2O) is added to prevent flash set ofcement

Slows the otherwise very fast reaction of the C3A phase

Interground with clinker in a ball mill (finish mill)

+

Clinker

Gypsum

Ball Mill

Cement

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Grinding and Addition of Gypsum

Ground cement typically transported in bulk

Can also be sold in barrels or 94-lb. bags (sacks)

Great Web Reference

http://www.cement.org/basics/images/flashtour.html

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Question

Now that we have an understanding of how

cement is produced commercially, how might we

make it in the lab? Why would we want to do so?