Cement Production
CE 611
Advanced Concrete Technology

Modern cement….
 John Smeaton, while planning the building
of Eddystone lighthouse tower in 1756,
discovered that the best limes for mortar
contained a high degree of clayey matter
 Ultimately, such a lime was used along with
pozzolana in equal quantities

Eddystone Lighthouse Tower
•Completed in 1759
•72 feet tall; 93 steps
•Newer lighthouse
constructed in 1882;
Smeaton’s tower was
moved stone-by-stone to
Plymouth, where it is
still the most major
landmark

Portland Cement
 L. J. Vicat: Prepared artificial hydraulic lime
by calcining an intimate mixture of limestone
(chalk) and clay – principal forerunner to
Portland Cement
 1824 – Joseph Aspdin, while obtaining a patent
for his hydraulic cement, termed it as Portland
cement, upon Portland stone (limestone from
Dorset, UK), which had a high quality and
durability and a similar appearance

Aspdin’s Creation
Kiln for burning
A – Alite, or C3S
B – Belite, or C2S

Portland Cement
• An unusual industrial product produced in huge quantities
in special plants that can produce nothing else
• The product is produced by a combination of unusual unit
operations involving mining, very fine scale blending of raw
materials, very high temperature clinkering reactions,
controlled cooling, grinding, blending, and finally shipping
under controlled conditions
• Chemical composition is maintained within narrow limits
despite huge tonnages

Portland cement production
• Typical plant costs range upwards of $250 million - a
fairly substantial fixed investment.
• Plant must produce continuously to pay off capital
costs
• Plant must also produce continuously to maintain kiln
integrity - 3 shifts per day!
• Plant must comply with severe environmental
constraints
• All this must be done to produce a commodity product
that sells for Rs. 3.2 / kg

Raw Materials for Cement
 Calcareous material – Containing CaCO3
(primary source – limestone); impurities such as
iron and alumina are sometimes present
 Argillaceous material – Containing clayey
matter, source of SiO2, Al2O3 and Fe2O3
 Gypsum – Added in the final stages of
manufacture as a set regulator
 Sometime, ground limestone is also added to
cement

Location of cement plants
 Outskirts of the city
 Primarily, where raw material sources are
easily available
 Necessary infrastructure (power, equipment,
manpower, access) should be available

Schematic depiction of process
www.ieagreen.org.uk/jan46.htm

Pulverization
 Raw material feedstock should be
pulverized to the right size
 Reduces overall power consumption
 Better blending and burning possible with
reduced size of material

Blending of raw materials
• Choice of blending process
- Wet or dry
• Wet process – more uniform mixing
• Dry process – higher output, lower power
consumption
• Dry process with precalciners are the order
of the day

Blending – Wet Vs. Dry
 When moisture content of raw materials is >
15%, wet blending (in slurry form) is
preferred
 When MC < 8%, dry blending is done
 For 8% < MC < 15%, dry blending with
precalciners used
 Wet blending – better blend

Picture of a cement
plant, showing a
precalciner and rotary
kiln

Burning in kiln
• Only rotary kilns used nowadays
• Typical kilns are long ~ 30 – 40 m
• Length of kiln also depends on blending process
• Temperature inside kiln varies from 850 (at inlet)
to 1450 oC (at the outlet)
• Reactions are not completed inside kiln; some
require cooling to occur
• What comes out of kiln is called ‘clinker’

Reactions in the kiln
• The clinkering reactions involve conversion of
mixtures of calcium carbonate and silica and
alumina- bearing components to a 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 m) crystals of
tricalcium silicate and dicalcium silicate

Kiln reactions (continued)
• Minor but important crystalline components are
extremely fine crystals of tricalcium aluminate and
calcium aluminate ferrite solid solution (ferrite)
• Of great importance despite minor amount present
are deposits of soluble crystalline components (alkali
sulfates and calcium alkali sulfates) on the surfaces of
clinkers

From P. C. Hewlett's 'Lea's Chemistry
of Cement and Concrete'
Up to 700 oC: activation of silicates
through removal of water and changes in
crystal structure
700 – 900 oC: dacarbonation of CaCO3,
initial combination of A, F, and activated
silica with lime
900 – 1200 oC: Belite (C2S) formation
> 1250 oC (more particularly, > 1300 oC):
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

www.ieagreen.org.uk/jan46.htm
www.wonjin.co.kr/eng/Item/
cement-rotary-kiln.html
Some cement plants

Intergrinding with gypsum
• Final step in cement manufacture
• Gypsum added as a set regulator (absence
 flash set)
• Strict control on temperature required
• Done in ball mills
• Cement of required fineness produced

Other issues
• Cement manufacture today is a highly
controlled process
• However, there is lot of variation in quality
of cements (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

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,
and finally before packaging in the bags
and drums

Quality control parameters
Lime 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.