With certificates of quality, weight, packing and loading issued by independent inspection agencies, we manufacture
and supply quality clinker conforming to the following standards:
• China’s cement standard GB 175-2007 and clinker standard GB/T 21372-2008;
• American standard ASTM C-150 07;*
• European standard EN 197-1:2000;
• Russian standard GOST 30515-97.
A particular brand, country of origin, etc. are not factors which influence the quality and consistency of the clinkers
which is a big misconception on the side of the Buyers – rather, quality depends on the sequence of the clinker
formation, specification or standards followed, etc., - sulfate and alcali contents of the clinker much affect the
quality of clinker.
Clinkers are of two major colours - white and grey.
Cement clinkers are formed by the heat processing of cement elements in
a kiln. Limestone, clay, bauxite, and iron ore sand in specific proportions
are heated in a rotating kiln at 2,770° Fahrenheit (1,400° Celsius) until they
begin to form cinder lumps, which are also known as cement clinkers.
These are usually ground with gypsum to produce the fine powder later
mixed with liquid to produce cement, although some manufacturers ship
clinkers in their lump form to cut down on dust.
The clinker manufacturing process starts with the extraction of the raw
meal from the homogenization silo to insure that the raw meal is stable and homogenized in order to produce
consistent clinker quality. The preheating of the material takes place in pre-heater cyclones fitted with a pre-calciner
fired with petroleum, natural gas or coal. The calcinations of the material begin during this stage, changing its phase
to the oxide phase for each component to be ready for the burning process. The burning phase takes place in a
rotary kiln. The clinker temperature in the kiln burning zone has to reach 1,500°C and then it is cooled in a cooler by
air which decreases the temperature.
The entire manufacturing process is continuously monitored and
controlled from the central control room.
The clinker is ground with an amount of gypsum to a fine powder in order
to regulate the setting time of cement and to gain the most important
property of cement, which is compressive strength.
Portland cement clinker is the essential ingredient of Portland cement.
Portland cement is obtained by grinding clinker with only minor amounts
of a few other minerals, so its composition does not depart far from
that of clinker. Other cements (i.e. non-Portland cements, for example
pozzolanic cements, blast furnace slag cements, limestone cements and
masonry cements) contain larger amounts of other minerals and have a
much wider composition range.
Although the other potential ingredients may be cheap natural materials,
clinker is made in an energy-intensive chemical process - in a kiln.. Between
one and two billion tons a year of clinker are made world-wide, and the
details of its formation are therefore of great economic significance,
since no viable alternative ingredients for making cement-like materials currently exist.
Unlike many other thermal products (e.g. aluminum, pig-iron), clinker is a fairly complex mixture of different minerals,
and so its production depends on a multi-dimensional control of raw materials and a multi-staged heat treatment.
It has been likened to a “man-made igneous rock”, and an understanding of its structure and chemistry requires the
application of many principles of geochemistry.
Portland Cement Clinker consists essentially of four minerals: alite, belite, tricalcium aluminate and tetracalcium
aluminoferrite and, there are also many other non-essential minerals that occur in small quantities.
The composition of clinker is examined by two separate approaches:
• by mineralogical analysis, using petrographic microscopy and/or x-ray diffraction analysis.
• by chemical analysis, most accurately by x-ray fluorescence spectrometry.
Clinker and Cement analysis
The early analyses were all based upon classical “wet” methods involving
dissolution of the material, then estimating components gravimetrically
– i.e. by precipitating and weighing them – or volumetrically by titration
with a reagent that reacts with the element in question. Without going
into excessive detail, the most important parts of the analysis scheme consisted of:
Dissolving the sample in acid (properly made clinker dissolves in
hydrochloric acid very easily and completely).
• Weigh what little fails to dissolve as “insoluble residue”.
• Reduce the pH to precipitate silica: ignite and weigh it.
• Neutralize with ammonia, precipitating “R2O3” - consisting of most of the
Al2O3, Fe2O3, TiO2, P2O5 and Mn2O3. This is ignited and weighed.
• Add ammonium oxalate to precipitate calcium oxalate: ignite it to CaO
• Concentrate the remaining solution and add ammonium phosphate to
precipitate MgNH4PO4: ignite it to Mg2P2O7 and weigh.
• Redissolve the “R2O3” in acid and separately determine Fe2O3 by selective
precipitation or by a redox reaction.
The last stage was often missed out in early analyses. SO3 was measured on
a fresh sample by precipitation as BaSO4. This was a typical cement plant
analysis: from early times, more scientific investigations performed additional
analysis for Na, P, Cl, K, Ti, Mn, Zn, Sr, Ba, etc. No even moderately accurate
method of analysis for Al2O3 existed until the arrival of XRF in the 1960s.
Reliable alkali metal analysis
remained quite inaccessible until
flame photometry was introduced.
One glaring omission from early
analysis was any estimation of the
amount of “free” or “uncombined”
CaO in clinker. A method was
developed in the USA in 1920s
involving non-aqueous dissolution
and titration of the free CaO using glycols in an alcohol
solvent. A variant finally came into use in Britain after
WWII. For many years prior to this it was often claimed
that there was no free lime in cement - a claim very wide
of the mark. Early manufacturers often “matured” their
cement for several months before daring to sell it, to
give time for the free lime to hydrate.
Accurate analysis only started to develop as
“instrumental” techniques became available – and in particular, various spectrometric
techniques that provided
absolutely element-specific data.
Among these, atomic emission and
absorption techniques were used,
but overwhelmingly the most
important is x-ray fluorescence
Even with highly automated
instrumental techniques, accurate analysis of cement
is particularly difficult. The analysis problem is subtly
different from that of most other process materials.
Other major products for which chemistry is important
– for example iron or aluminum – usually consist largely
of a single element or compound in which the other
constituents are only present in minor or trace quantities.
At worst, an alloy may be a simple binary mixture. The
minor constituents can be measured in the knowledge
Clinker and cement analysis
As the binder in many cement products – a little gypsum is sometimes
• It may also be combined with other active ingredients or chemical
admixtures to produce other types of cement including:
• Ground granulated blast furnace slag cement
• Pozzolana cement
• Silica fume cement
• Grind it as an addition to cement manufacturers’ own clinker at their own
Other important aspects
Clinker, if stored in dry conditions, can be kept for several months without appreciable loss of quality. Because of
this, and because it can easily be handled by ordinary mineral handling equipment, clinker is traded internationally
in large quantities.
• Manufacturers also ship clinker to grinding plants in areas where cement-making raw materials are not available.
• Gypsum is added to clinker primarily as an additive preventing the flash settings of the cement, but it is also
very effective to facilitate the grinding of clinker by preventing agglomeration and coating of the powder at the
surface of balls and mill wall.
• Upon treatment with water, clinker reacts to form a hydrate called cement paste. Upon standing the paste
polymerizes as indicated by its hardening.
Clinker Specification / Standards
Chemical parameters based on the oxide composition are very useful in describing clinker characteristics. The
following parameters are widely used (chemical formulae represent weight percentages):
Lime Saturation Factor (LSF)
The Lime Saturation Factor is a ratio of CaO to the other three main
oxides. Applied to clinker, it is calculated as:
LSF=CaO/(2.8SiO2 + 1.2Al2O3 + 0.65Fe2O3)
Often, this is referred to as a percentage and therefore multiplied by
The LSF controls the ratio of alite to belite in the clinker. A clinker with
a higher LSF will have a higher proportion of alite to belite than will a
clinker with a low LSF.
Typical LSF values in modern clinkers are 0.92-0.98, or 92%-98%.
Values above 1.0 indicate that free lime is likely to be present in the clinker. This is because, in principle, at LSF=1.0
all the free lime should have combined with belite to form alite. If the LSF is higher than 1.0, the surplus free lime has
nothing with which to combine and will remain as free lime.
In practice, the mixing of raw materials is never perfect and there are always regions within the clinker where the LSF
is locally a little above, or a little below, the target for the clinker as a whole. This means that there is almost always
some residual free lime, even where the LSF is considerably below 1.0. It also means that to convert virtually all the
belite to alite, an LSF slightly above 1.0 is needed.
The LSF calculation can also be applied to Portland cement
containing clinker and gypsum if (0.7 x SO3) is subtracted from the
NB: This calculation (0.7 x SO3) is based on the ratio of the molar
masses of calcium oxide and sulfur trioxide, ie: 56/80 = 7/10. It
therefore assumes that all the sulfate in the clinker is present as
anhydrite; it does not account for sulfate present as clinker sulfate in
the form of potassium and sodium sulfates, or for water in gypsum,
and the calculation will therefore not be exact.
Neither does it account for fine limestone or other material such
as slag or fly ash in the cement. If these materials are present,
calculation of the original clinker LSF becomes more complex.
Limestone can be quantified by measuring the CO2 content and
the formula adjusted accordingly, but if slag or fly ash are present,
calculation of the original clinker LSF may not be conveniently
Silica Ratio (SR)
The Silica Ratio (also known as the Silica Modulus) is defined as:
SR = SiO2/(Al2O3 + Fe2O3)
A high silica ratio means that more calcium silicates are present in the clinker and less aluminate and ferrite. SR is
typically between 2.0 and 3.0.
Alumina Ratio (AR)
The alumina ratio is defined as:
This determines the potential relative proportions of aluminate and ferrite phases in the clinker.
An increase in clinker AR (also sometimes written as A/F) means there will be proportionally more aluminate and less
ferrite in the clinker. In ordinary Portland cement clinker, the AR is usually between 1 and 4.
The above three parameters are those most commonly used. A fourth, the ‘Lime Combination Factor’ (LCF) is the
same as the LSF parameter, but with the clinker free lime content subtracted from the total CaO content. With an
LCF=1.0, therefore, the maximum amount of silica is present as C3S.
Phases of clinker:
The clinker formation process can be divided into four main steps;
Drying and preheating (20 – 800° C): release
of free and chemically bound water
• Calcination (800 – 1350° C): release of
CO2: initial reactions with formation of
clinker minerals and intermediate phases.
Conversion of CaCO3 to CaO and MgCO3
• Sintering or clinkerization (1350 – 1550°
C): formation of calcium silicates, calcium
aluminates and liquid phase
• Kiln internal cooling (1550 – 1200° C):
crystallization of calcium aluminate and