Portland Cement Manufacture
Dr. Kimberly Kurtis
School of Civil Engineering
Georgia Institute of Technology
Atlanta, Georgia
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
Raw Materials
Portland
cement is:
45-60% C3S
15-30% C2S
6-12% C3A
6-8% C4AF
Calcium
Iron
Silica
Alumina
Sulfate
Alkali waste
Aragonite
Calcite
Cement-kiln
dust
Cement rock
Chalk
Clay
Fuller’s earth
Limestone
Marble
Marl
Seashells
Shale
Slag
Blast-furnace
flue dust
Clay
Iron ore
Mill scale
Ore washings
Pyrite cinders
Shale
Calcium silicate
Cement rock
Clay
Fly ash
Fuller’s earth
Loess
Marl
Ore washings
Quartzite
Rice-hull ash
Sand
Sandstone
Shale
Slag
Traprock
Aluminum-ore
refuse
Bauxite
Cement rock
Clay
Copper slag
Fly ash
Fuller’s earth
Granodiorite
Limestone
Loess
Ore washings
Shale
Slag
Staurolite
Anhydrite
Calcium
sulfate
Gypsum
Raw Materials
Raw Materials
Raw Materials
CaO-SiO2 Binary Phase Diagram
CaO-Al2O3 Binary Phase Diagram
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
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 (<90um)
• After crushing, powders are mixed with water (35-50% by mass)
• Slurries of varying composition are mixed in specific proportions
Grinding and Blending: Dry Process
800oC
Grinding mill
Vertical roller mill
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.
Clinkering: Reactions
Clinkering: Reactions
Clinkering: Reactions
• Production of 1 ton of cement, results in release of ~ 1 ton CO2.
Clinkering: Reactions
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.
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
Note 2: Fuels Used
• Fuel used for cement manufacture amounts to 6-8% of the
world’s 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 Fuller’s
earth, etc. (20%+)
Grinding of Clinker
•Upon 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
Grinding of Clinker
Red - C3S
Aqua - C2S
Green - C3A
Yellow - C4AF
Pale green - gypsum
White - free lime (CaO)
Dark blue (purple) - K2SO4
Light magenta- periclase
(magnesium containing
phase).
Image is 256 µm x 200 µm.
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
Addition of Gypsum
• ~ 5%Gypsum (CaSO4•2H2O) is added to prevent “flash set” of
cement
• Slows the otherwise very fast reaction of the C3A phase
• Interground with clinker in a ball mill (finish mill)
Clinker
Cement
+
Ball Mill
Gypsum
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
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?