CLE 513 Advanced Concrete

Technology

Cement Production

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

ProtoPortland cement

Later, William Aspdin (son) MesoPort land cement

Hewlett, 2001

Kiln for burning

A Alite, or C3S

B Belite, or C2S

Aspdins creation

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

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

Gypsum Added in the final stages of manufacture as

a set regulator

Sometime, ground limestone is also added to cement

Mamloukand Zaniewski, 2000

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 pre calciners are the order of

the day

Blending Wet Vs. Dry

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

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 crystals of tri calcium silicate and di

calcium 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

Kiln reactions -schematic

Mindess and Young, 1981

Hewlett, 2001

Up to 700 deg.C: activation of

silicates through removal of water

and changes in crystal structure

700 900 deg.C: decarbonation of

CaCO3, initial combination of A, F,

and activated silica with lime

900 1200 deg.C: Belite(C2S)

formation

> 1250 deg.C (more particularly, >

1300 deg.C): liquid phase appears

and promotes the reaction between

beliteand 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 beliteand free lime

Inter grinding 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

Quality control

Sampling and evaluation should be performed

after excavation from the quarry, before and

after blending the feedstock, after formation of

clinker, after inter grinding clinker with

gypsum, and finally before packaging in the

bags and drums

Quality control parameters

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.