Granulometry of clinker

PCA R&D Serial No. 2967

Clinker Microstructure and Grindability:
Updated Literature Review
by Linda M. Hills

©Portland Cement Association 2007
All rights reserved

KEYWORDS
Alite, belite, C2S, C3S, clinker, content, crystal size, grindability, microscopy, mineralogy, phase
content, porosity, trace elements.

ABSTRACT
Much of the available literature on the relationship between clinker microstructure and
grindability agree that the primary influential factors are alite and belite crystal size and content.
Specifically, smaller crystals and more alite (less belite) result in easier to grind clinker.
Numerous equations are found in literature to predict clinker grindability based on its
microstructure, and although the equations vary somewhat, the relationship to alite and belite
content and size previously described are consistent.
On a related topic, some literature was found on clinker microstructure and grindability with
the focus on the influence of trace elements, this topic arising likely due to the increased use of
alternate raw materials and fuels.

REFERENCE
Hills, Linda M., Clinker Microstructure and Grindability: Updated Literature Review, SN2967,
Portland Cement Association, Skokie, Illinois, USA, 2007, 15 pages.

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TABLE OF CONTENTS
Page
Keywords………………………………………………………………………………….. i
Abstract…...……………………………………………………………………………….. i
Reference…………………………………………………………………………………. i
Introduction………………………………………………………………………….……. 1
Primary Influential Factors……………………………………………………………….. 1
Alite and Belite Size and Content …………..…………………………………….…... 1
Possible Secondary Influential Factors………………………………………………….... 1
Microstructural Properties …………..…………………………………….…............... 1
Chemical Content …………..…………………………………….…............................ 2
Estimating Grindability …………..………………………….……………………….…... 2
Acknowledgements…………………………………………………………..……….…... 6
Bibliographic References……………………………………………………………..…... 6

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Clinker Microstructure and Grindability:
Updated Literature Review
By Linda M. Hills*

INTRODUCTION
In the early 1990’s, Portland Cement Association (PCA) sponsored a literature review to define
the influence of clinker microstructural properties on the difficulty or ease of clinker grinding
(Hills 1995). The updated literature search presented here was requested as a supplement to the
former report, with the purpose of including recent literature and specifically to provide guidance
tools for cement manufacturing personnel. The bibliographic references are attached, with a
summary of the overall conclusions provided below.

PRIMARY INFLUENTIAL FACTORS

Alite and Belite Size and Content
Most of the available literature on the relationship between clinker microstructure and
grindability agree with the conclusions of those of the 1995 PCA report, in that the primary
influences to ease of grinding relate to alite and belite crystal size and content. Specifically,
smaller crystals and more alite (less belite) result in easier to grind clinker. Regarding the
reasoning behind the relationship with alite/belite content, Viggh (1994) offers this description:
alite is more brittle than belite and contains micro-cracks developed during cooling, enabling
easier grinding compared to the round and more plastic belite. In terms of alite size, Viggh
comments that not only are larger alite crystals harder to grind, but the smaller particles resulting
from grinding have a higher surface charge activity, causing agglomeration and increase in
grinding energy requirements. Based on these primary influential factors of alite and belite
crystal size and content on clinker grindability, grindability prediction equations are provided
later in this report.

POSSIBLE SECONDARY INFLUENTIAL FACTORS

Microstructural Properties
Several references include the effect of other microstructural properties on clinker grindability.
Although these parameters are rarely quantified in grindability equations, they are worth
mentioning. These include:

______________________
*Affiliated Consultant, CTLGroup, 5400 Old Orchard Road, Skokie, IL 60077 USA (847) 965-7500,
lhills@ctlgroup.com, www.ctlgroup.com.

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• Distribution of belite crystals, i.e. belite formation in clusters will make the clinker harder
to grind compared to clinker with well-distributed individual crystals (Dorn, 1985;
Kilhara, Centurione, Munhoz, 1992; Venkateswaran and Gore, 1991; Laszlo, Opoczky,
and Gavel, 2000; Slim, Tagnit-Hamou, Marciano 1996; Zampieri and Munhoz 1995).
The present author agrees this property to have an influence, especially if the belite is
tightly packed (the result of coarse silica in the raw feed). A method to quantify belite
clustering as Cluster Index was found (Hargave, Venkateswaran, Chatterjee, Rangnekar
1983), which possibly could be incorporated into a grindability equation.
• Porosity (Laszlo, Opozcky, and Gavel 2000). However, numerous references state that
porosity is only a factor in coarse grinding, and not influential when grinding to ordinary
cement fineness (Kilhara, Centurione, Munhoz, 1992; Scheubel 1985; Slim, Tagnit-
Hamou, Marciano 1996; Theisen 1993) .
• Coarsely crystalline C3A. Laszlo, Opozcky, and Gavel (2000) state this property as
negatively influencing grindability.
• Irregular belite morphology and alite with “disintegrated and damaged edges”, as
included by Laszlo, Opozcky, and Gavel (2000), will make the clinker harder to grind.

Chemical Content
Likely due to the increased use of alternate raw materials and fuels, some studies on clinker
microstructure and grindability focus on the influence of these materials, such as trace elements:
• The inclusion of trace elements (Cr, Zn, Ba, Ni, Ti, P) were shown to favorably influence
grindability. The authors credit this improvement to the quantity and property of the
“molten phase” and their inclusion in the silicate minerals, reducing their hardness
(Opoczky and Gavel, 2004).
• The grindability study of clinkers containing transition metal oxides concluded the oxide
could be classified in order of decreasing clinker grindability as follows: MnO, Cr2O3,
Ni2O3, ZrO2, CuO, Co2O3, V2O5, MoO3, TiO2, ZnO. (Tsivilis and Kakali, 1997)
• One study found that clinker grindability became worse as ZnO content increased (Kim,
Chu, Lee, Song, 1997).

ESTIMATING GRINDABILITY
Several references offer equations to estimate or predict clinker grindability based on its
microstructure, as provided in Table 1.

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Table 1. Grindability Estimation Equations from Literature

Equation and Discussion Reference
Relationship between KM and sieve residue at 37 μm
Kilhara,
KM= (C3S%/C2S%)*(100/C3S size)
Centurione,
Where,
Munhoz, 1992
KM = mineralogical coefficient
BL=1251+218AS+239AB+287BS+2.1BC
Where,
Ono 1981
BL = “Blaine fineness” (specific surface area)
AS = alite size, AB = alite birefringence; BS = belite size; BC = belite color
When grinding with 5% gypsum:
P350=23.9+0.42*C3Sn+0.36*C2S amount (with 5% gypsum)
When grinding with TEA as grinding aid:
P350= 30.2+0.34*C3Sn+0.38*C2S amount -11.58*TEA
Theisen 1993
Where,
P350= power consumption in kWh/t for grinding to 350 m2/kg
C3Sn = (C3S%*20)/NC3S /(1-p)
NC3S = number of alite intersections in microscopical line count
p = porosity
Relationship between 1/Px1000 and ln AK Scheubel 1985
Where,
P = power consumption Venkateswaran
Ak = belite corrected alite chord length = C3S%/C3S size - (C2S%*C2S and Gore 1991
size/1000)
Ak Revision to (C3S%/ C3S size)/((C2S %* C2S size)/1000) Venkateswaran
Suggested to have better correlation with grindability in belite-rich clinker and Gore 1991
Relationship between grindability and Bk (alite corrected belite chord length)
Where, Venkateswaran
Bk = (C2S%/ C2S size) -(C3S %* C3S size)/1000) and Gore
Suggested to have better correlation with grindability in belite-rich clinker
P1(kWh/t) = -20.7xInAk+57.9
Where, Viggh 1994
Ak = C3S%/ C3S size - (C2S%* C2S size /1000)
Relationship between KM and sieve residue at 37 μm
KM= C3S%/(C2S%- C3S size) * 100 Zampieri and
Where, Munhoz 1995
KM = mineralogical coefficient

If an arbitrary set of data were applied to these equations, the resulting conclusions would
vary somewhat. However, in each case the best grinding clinker would be that containing high
alite and low belite content with small crystal sizes versus the most difficult to grind clinker
containing low alite and high belite content with large crystals. These relationships between
clinker grindability and crystal size and content are presented in Table 2.

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Table 2. Relationship between Clinker Grindability Ranking and Crystal Size and Content.
Ranking Value is Relative on a Scale of 1 to 4; 1 being Easy to Grind, and 4 being
Difficult to Grind
Ranking Alite content Belite content Alite size Belite size
easiest 1 high low small small
high low large small
2 high low small large
low high small small
high low large large
3 low high large small
low high small large
hardest 4 low high large large

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The relationships outlined in Table 2 are presented visually in Figures 1 and 2.

High alite content = alite
Low belite content
= belite

Small alite Small alite
Large alite Large belite Large alite
Small belite Small belite Large belite

Ranking: 1 2 2 3

Figure 1. Diagram showing relative ease in grindability based on crystal size of clinker with
high alite/low belite content. Ranking system is relative on a scale of 1 to 4; 1 being easy to
grind, and 4 being more difficult to grind.

Low alite content = alite
High belite content = belite

Small alite Large alite Small alite Large alite
Small belite Small belite Large belite Large belite

Ranking: 2 3 3 4
Figure 2. Diagram showing relative ease in grindability based on crystal size of clinker with low
alite/high belite content. Ranking system is relative on a scale of 1 to 4; 1 being easy to grind,
and 4 being more difficult to grind.

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ACKNOWLEDGEMENTS
The research reported in this paper (SN2967) was conducted by CTLGroup with the sponsorship
of the Portland Cement Association (PCA Project Index No. M06-03). The contents of this
report reflect the views of the author, who is responsible for the facts and accuracy of the data
presented. The contents do not necessarily reflect the views of the Portland Cement Association.

BIBLIOGRAPHIC REFERENCES
Altun, Akin, “Effects of kiln systems on microstructure of clinker,” Cimento ve Beton Dunyasi, v. 3,
no. 19, 1999, p. 33-41.
Technical clinkers taken from three cement factories of Turkey have been analyzed by polarizing
microscope. It has been observed that, in Lepol preheating system, the pores in the clinker are
bigger and the alite crystals are smaller. In cyclone preheating system, opposite observations
have been reached. The little amount of water in the Lepol system may cause the differences in
pore sizes. No important differences were observed in sizes, distributions and shapes of belites,
free lime, aluminates and ferrites for all three clinkers. Clinkers having firmer microstructure can
be ground easily and small alite crystals can react with water more easily. Microscopic
investigation of clinkers give pre-information about later treatments such as grinding and
hydration. (In Turkish and English)
Altun, Akin, “Microscopic criteria for quality control of clinker,” Cimento ve Beton Dunyasi , v. 2,
no. 16, 1998, p. 22-32.
In this study, microstructure of clinker phases were investigated by using a microscope and
decisions were made on the quality of clinker. Free CaO amount found by chemical anal. is a
necessary criteria for quality evaluation of clinker but is not sufficient because crystal size and
distribution of free CaO plays an important role in the volume expansion of Ca(OH)2. Hydration
of CaO affects the 28 day strength of clinkers with a high lime saturation factor. Crystal size and
distribution of periclase affect the volume expansion due to brucite formation. Approx. heating
and cooling rates can be determined from structures of alite and belite crystals. Small alite
crystals affect the setting time to a large extent. Pore shape and size give an idea of sintering
grades. A fine microstructure makes grinding easy. Effects of alkalis on the formation of
aluminate and ferrite phases can be observed by microscopy. As a result, the microscope is an
important tool for the quality evaluation of the clinker. (In Turkish and English)
Centurione, Sergio Luiz; Tonhi, Marcelo, “The influence of burning conditions on alite crystal
characteristics,” Proceedings of the International Conference on Cement Microscopy (1995),
17th, p. 232-41
Both size and shape of alite crystals play an important role on grindability and strength
development of Portland cements . Most researchers agree that these characteristics are
conditioned by burning conditions of raw mix in the kiln. In the present work, the same raw mix
was burned in a static furnace under different temps., times of residence and heating rates. The
laboratory clinkers were analyzed through reflected light microscopy to investigate the
microstructural variations in alite crystals. An increase in burning temperature or time of
residence was followed by an increase in the alite crystal size. On the other hand, only under
high heating rate has there been observed an increase, though discreet, in quantity of elongated
crystals.

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Dorn, J. D. “The Influence of Coarse Quartz in Kiln Feed on the Quality of Clinker and Cement,
Proceedings of the Seventh International Conference on Cement Microscopy, 1985, pages 10-23.
Plant and laboratory studies are used as the basis for a discussion of factors that affect the use of
silica and siliceous raw materials in cement manufacture. The effects of silica type, purity and
size on the clinker quality are described. Factors affecting grinding, strength and product quality
are listed. Advantages of separate silica grinding are given. And, finally, a method for
determining quartz size in raw mix is offered.
Gavel, Viktoria; Opoczky, Ludmilla; Sas, Laszlo, “Relationship between technological parameters,
structure and grindability of clinkers,” Epitoanyag, 2000, v. 52, no. 2, p. 34-38.
The effect of chemical and mineral composition, macro and microstructure as well as processing
parameters on the grindability of cement clicker was studied. The microstructure id the main
factor determining the clinker grindability. The clinker structure is determined by the particle
size distribution of the raw material and the clinkering-cooling temperature The physicochem.
characteristics of clinkers with different grindability are presented. (In Hungarian.)
Gavel, Viktoria; Opoczky, Ludmilla, “Effect of certain trace elements on the grindability of cement
clinkers in the connection with the use of wastes,” International Journal of Mineral Processing,
v. 74, Dec. 10, 2004, p. S129-S136.
The effect of certain trace elements - Cr, Zn, Ba, Ni, Ti, P - on clinker grindability was studied.
From the study of commercial and model clinkers, it was concluded that the trace elements
studied favorably influence and improve the grindability of clinkers. The effect of trace elements
is due to the fact that they favorably influence the clinker formation processes (the quantity and
property of the "molten phase") on the one hand, and on the other hand that during clinker
burning they form solid solutions with silicate minerals (alite, belite) and thereby reduce their
hardness. 8 Refs.
Ghosh, S. P.; Mohan, K., “Interrelationship among lime content of clinker, its microstructure ,
fineness of OPC grinding and strength development of hydrated cement at different ages,”
Proceedings of the International Congress on the Chemistry of Cement,10th, Gothenburg, June
2-6, 1997, v. 2, p. 2ii018-4 pp.
A rational correlation among lime content of clinker , its microstructure , fineness of ordinary
portland cement (OPC) grinding and strength development of hydrated cement at different ages
has been established. The study shows that the two most important factors affecting strength
development of hydrated cement are: (i) mineral phase composition and microstructure of clinker
, and (ii) particle size distribution of ground cement. The granulometry of clinker affects its
grindability , measurable in terms of sp. surface, whereas the mineral phase composition and
microstructure of clinker affects the variations in (a) particle size distribution of ground cement ,
and (b) strength development of hydrated cement at different ages.
Hargave, R.V., Venkateswaran, D., Chatterjee, A.K., Rangnekar, B.S., “Assessment of Process
Effects on Clinker Microstructure Through its Quantification” Proceedings of the International
Conference on Cement Microscopy (1983), 5th, p. 99-120.
Although the significance of clinker microstructure in process control is fairly well understood,
the application of the microscopic techniques, firstly, to the evaluation of process effects and
ultimately, to process control has so far been only qualitative, primarily due to the lack of fool-
proof methods of quantification of microstructural features. Except mainly the phase estimation
and, to some extent, the crystal size measurement, all other significant microstructural features
are described qualitatively. Based on a systematic study, reported elsewhere, the prospects of

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quantification of the following parameters have been established by the present authors: a()
phase assemblage, b) stabilization of phase modifications, c) silicate crystal size, d) silicate
crystal morphology, e) clustering of phases. This approach for quantification has now been
extended to compare the microstructural characteristics of clinkers produced in plants adopting
different processes namely: 1) we-process, 2) wet-process with use of floated limestone, 3) semi-
dry Lepol process, 4) semi-dry Lepol process with use of a mineralizer in kiln feed, 5) dry
suspension-precalciner kiln with and without the use of argillaceous corrective materials. For
comparative evaluation of the microstructural variations observed in the clinkers produced by the
above processes the quantified parameters have been juxtaposed so as to ascertain the more
significant variables within the processes as well as between the processes. After identifying the
more significant variables, an attempt has been made to explain the variables by the known
process effects in terms of specificities of raw materials, raw meal preparation, burning and
cooling systems in operation.

Hills, Linda M., “The Effect of Clinker Microstructure on Grindability: Literature Review
Database”, Portland Cement Association, PCA SN 2026, 1995.
Since a substantial amount of energy expended at a cement plant is needed for clinker grinding,
improvement in clinker grindability would increase grinding efficiency, thereby improving
energy consumption. The ease with which clinker is ground depends, amo9ng other variables,
on its microstructural properties, such as porosity, composition, and crystals size. To employ
conclusions from past studies on the relationship between clinker microstructure and
grindability, related literature was reviewed. Information gained from the review was developed
into a database format to make it easily accessible and useful. In addition to the databases, this
report includes a summary and reference list. Extended bibliographies are available. Although
the primary purpose of the report was to investigate the influence of clinker microstructure, the
effects of other characteristics such as clinker te3mperature, cooling rate, and clinker size, which
were discovered throughout the project, are also included in the report. This report was
produced for use by cement plant personnel to better understand and optimize clinker
grindability.

Hills, Linda M., “The influence of clinker microstructure on grindability : Results of an extensive
literature review,” Proceedings of the International Conference on Cement Microscopy (1995),
17th, p. 344-52.
A review, with 2 refs. The ease with which a clinker is ground depends, among other variables,
on its microstructural properties. An extensive literature review of this relationship has been
completed to provide a troubleshooting guide for the cement industry. Conclusions concerning
the influence of twenty-seven parameters on clinker grindability are discussed. These parameters
include the size, content, morphol., and color of microstructural phases, as well as various
aspects of porosity and miscellaneous categories such as clinker size distribution, temperature,
and cooling rate. The effect of some of the parameters on grindability are well agreed upon, such
as the pos. influence of increased alite content and small alite crystal size. The effect of other
parameters are not so clearly determined, including liquid phase content and pore volume.
Kihara, Yushiro; Centurione, Sergio L.; Cunha Munhoz, Flavio Andre da, “An approach to the
prediction of portland clinker grindability and strength by microscopy,” International Congress
on the Chemistry of Cement, 9th (1992), v. 6, p. 182-8.
Grindability and cement strength development are influenced by the raw mix characteristics and

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the portland clinker manufacturing process. The clinker microstructure anal. brings important
technological data for monitoring the stages of cement manufacture and for prediction of the
potential grindability and strength. A laboratory method for clinker grindability and 28-day
cement strength prediction was developed based on microscopic parameters obtained by
reflected light microscopy and on clinker fineness data.
Kim, K.; Chu, S.; Lee, H.; Song, S., “effect of ZnO on the hydration reaction and physical properties
of cement,” Journal of the Korean Ceramic Society, v. 34, no. 4, 1997, p. 399-405.
With increase of ZnO content, heat of hydration decreased. For specimens containing more than
0.6 wt% ZnO, the compressive strength of cement cured for 28 days could not be measured
because setting had not occurred. With the increase of ZnO content, Blaine specific surface area
of cement decreased and the residue of 45 micron and 90 micron increased when the cement was
ground. That is, grindability became worse as ZnO increased in clinker. The difference of colour
as a function of ZnO content could not be observed, but with excess ZnO added the colour
became more white and reddish yellow. 12 refs. In Korean.
area; surface area; technical1; zinc oxide additive; zinc oxide content.
Moore, C. W., “Portland Cement Clinker Grindability and Work Index,” American Ceramic Society
Bulletin, v. 74, no. 8, 1995, p. 80-85.
The relative grindability of Portland cement clinker and the Bond grindability index, the causes
of the differences in the grindability and the precision of the laboratory test for the work index
were determined. Chemical analyses of the clinker samples were undertaken and a microscopic
examination, using the Ono technique, was used. 10 refs.
Odigure, J. O., “Grindability of cement clinker from raw mix containing metallic particles,” Cement
and Concrete Research, v. 29, no. 3, 1999, p. 303-309.
The grindability of cement clinker is greatly influenced by the quantity of liquid phase produced.
The use of by-products can significantly increase the liquid phase content and consequently
influence not only the clinker formation processes but also the grindability of the clinker
produced. The influence of Fe2O3 on the potential grindability of cement clinker produced from
raw mix containing metallic particles was studied by optical and electron microscopy. The
controlled introduction of such an industrial by-product was shown to encourage increased
formation and growth of microcracks on the mineral crystal surfaces and consequently enhance
the grindability of clinker produced. 18 refs.
Ono, Yoshio, “Microscopical Observation of Clinker, for the Estimation of Burning Condition,
Grindability and Hydraulic Activity” Proceedings of the International Conference on Cement
Microscopy (1981), 3rd, p. 198-210
Microscopical observation of clinker and cement gives us much knowledge on the history of
thermal reaction in a rotary kiln and the temperature curve in a kiln. The properties of clinker,
which are closely related with the burning condition, such as grindability of clinker and strength
of cement can be estimated from the microscopically characters. The temperature curve of
clinker-burning can be drawn approximately from the four terms, namely burning rate, maximum
temperature, keeping time and cool rate. Microscopical four terms, alite size, alite birefringence,
belite size and belite color, respectively change by the above burning four terms. If clinker is
burnt by long flame, zone structure and dots in alite might be replaced with alite size, and
raggedness of belite surface and dots in belite might be replaced i3wth belite color. The strength
of cement principally depends on the hydraulic modulus, alkali sulfates, fineness, freshness, and
so on, have an important effect upon the strength at early age, 3 and 7 days. However, the effect

9

at later age, 28 days, is rather small. Therefore, 28 days strength can be practically evaluated
from microscopical observation. The grindability of clinker is closely related with the burning
condition. Although, the mechanism of grinding is not clear, statistic analysis between
grindability and burning condition, and microscopical four terms, gives us distinct regressive
equation. The regressive equation seems to be limited to a kiln. In order to obtain a universal
equation, the microscopical terms might be more carefully selected.
Opoczky, L; Gavel, V., “Effect of certain trace elements on the grindability of cement clinkers in the
connection with the use of wastes,” International Journal of Mineral Processing, v. 74, Dec. 10,
2004, p. S129-S136.
The effect of certain trace elements--Cr, Zn, Ba, Ni, Ti, P--on clinker grindability was studied.
From the study of commercial and model clinkers, it was concluded that the trace elements
studied favorably influence and improve the grindability of clinkers. The effect of trace elements
is due to the fact that they favorably influence the clinker formation processes (the quantity and
property of the ''molten phase'') on the one hand, and on the other hand that during clinker
burning they form solid solutions with silicate minerals (alite, belite) and thereby reduce their
hardness.
Sas, Laszlo; Opoczky, Ludmilla; Gavel, Viktoria, “Knowing clinker microstructure - a possibility to
influence grindability through technology,” Proceedings of the International Conference on
Cement Microscopy (2000), 22nd, p. 215-224.
Based on the complex study - chemical-mineral composition, macro and microstructure ,
grindability -, of about 200 com. clinkers it was shown that the grindability - easy, medium and
heavy grindability - of a clinker with a given mineral composition is influenced to a major extent
by the microstructure of the clinker. The microstructure of clinkers is, however, also influenced
by production parameters, mainly by raw meal grinding fineness and homogeneity, and by
clinker burning and cooling intensity. The microstructure and microhardness of each clinker
phase - and ultimately clinker grindability - is influenced also by the type of fuel used, the trace
elements incorporated into the crystal structure, etc. By knowing these relationships it will be
possible to influence clinker grindability and thus the energy used for grinding.
Scheubel, B., “Microscopically Determinable Parameters and their Relationship to Kiln system and
Clinker Grindability,” Proceedings of the International Conference on Cement Microscopy
(1985), 7th, p. 131-153.
Twenty-six types of industrial clinker from 25 different plants were analyzed by means of linear
analysis and the established stereological parameters related to the kiln system and the clinker
grindability. It was found that the kiln system influences the particle-size distribution of the
alites and, therefore also affects the grindability of the clinker due to the mean chord length of
the alites. Other relationships to the clinker grindability which are frequently the subject of
discussions in the specialist literature could not be confirmed with the analyzed samples,. These
included the porosity, the content of fusible matter and the specific surface of the pores. When
the 26 samples of clinker were examined, the specific alite content proved to be the only
parameter which independently from the kiln system allows for a definite statement as regards
the clinker grindability.
Slim, Freddy; Tagnit-Hamou, Arezki; Marciano, Everaldo Jr., “Use of optical microscopy on raw
meal fineness optimization,” Proceedings of the International Conference on Cement
Microscopy (1996), 18th, p. 21-32.
In this paper we present the results of a study on the effect of raw meal fineness (80% and 86%

10

passing a 200 mesh (75 μm) sieve) on quality of the final product. To achieve this, chemical and
microstructural anal. were performed as well as phys. tests on cement. This study shows that the
thermal energy consumption required to clinkerize an 80% fineness raw meal increases vs. the
86% raw meal fineness. The raw meal with the 80% fineness is harder to burn. The resulting
clinker with the 80% raw meal fineness is harder to grind into cement than the 86% raw meal
fineness sample. The 86% raw meal fineness strengths in mortars and concrete (with same
slumps) is slightly higher than the resulting cement of the 80% fineness raw meal.
Theisen, Kirsten, “Estimation of Cement Clinker Grindability”, Proceedings of the International
In our laboratory the grindability of cement clinker is determined by grinding clinker plus
gypsum while measuring the power consumption necessary for obtaining a certain fineness. The
power consumption corresponds well with plant results. A relationship has been developed
between the specific power consumption determined during the grinding test, and an estimate
using microscopy measurements combined with results from a normal clinker analysis. The
microscopy measurements are easy to perform on polished sections using an ordinary optical
microscope. The grindability can be estimated for clinker from different plants, but special care
should be taken with certain types of clinker.
Tsivilis, S.; Kakali, G., “Study on the grindability of portland cement clinker containing transition
metal oxides,” Cement and Concrete Research, v. 27, no. 5, 1997, p. 673-678.
The effect of transition metal oxides on the grindability of clinker was studied. Grinding was
performed in a laboratory mill for times ranging from 15 to 90 min. The specific surface area of
the ground material was determined using the Blaine method. The oxides could be classified in
order of decreasing clinker grindability: MnO, Cr2O3, Ni2O3, ZrO2, CuO, Co2O3, V2O5, MoO3,
TiO2, ZnO. XRD analysis and optical microscopy confirmed the results. 5 refs.

Venkateswaran, D., and Gore, V.K., “Application of Microstructural Parameters to the Grindability
Prediction of Industrial Clinkers” Proceedings of the International Conference on Cement
Microscopy (1991), 13th, p. 60-70.
The various microstuctural parameters measured on a number of industrial OPC linkers have
been correlated with their grindability values such as Bond Work Index and grinding energy
determined in a standard laboratory ball mill. The validity of “specific alite content” suggested
in the literature for the assessment of grindability has been tested on the Indian clinkers which
are typically produced in thigh ash coal-fired kilns. The merits and limitations of microstructural
approach to the prediction of grindability have been discussed and possible improvement in the
prediction has been suggested.

Viggh, Erik O., “Estimation of grindability of portland cement clinker,” World Cement, v. 25, no. 10,
1994, p. 44-6, 48, 66-7, 73-4.
The grinding of clinker to make cement requires a great deal of energy. The microstructure of the
clinker nodules has a decisive role as to how easy it is to grind. Data from microscopy and
laboratory grinding of clinker shows the influence of the amount and size of the individual
crystals on predicted grindability. The study reveals the pos. influences of alite content and the
neg. effect of belite content on the grindability of samples from different plants. The change in
cement quality parameters such as strength development, setting time, dry-powder flowability,
etc., are discussed in terms of clinker microstructure grindability.

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Zampieri, Valdir A.; Munhoz, Flavio A. C., “Mechanical strength and grindability of portland
clinkers with different mineralogical characteristics,” Proceedings of the International
Mech. strength and grindability of portland cements are closely related to clinker mineralogical
and microstructural characteristics. This report presents the results of experiments carried out on
four industrial Brazilian clinkers. It has been found that homogeneous clinkers , alite enriched,
with few clusters of belite, and with smaller and more reactive alite crystals, show the best
strength evolution and grindability behavior.

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Granulometry of clinker

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Granulometry of clinker