The gray-green limestone from Agios Panteleimonas is studied in this paper after submitting it in special technological analyses in order to determine the possibility for quicklime production. Cubic test specimens with mean 50 mm edge length were calcined at 850, 950 and 1,050~ with 150 rain preheating time and 120 rain retention time at each calcination temperature. At the dissociation temperature of pure calcite (898~ only one half of the initial limestone has been calcined. The dissociation of the specimens started at 740~ and almost completed at 1,050~ Probably, the large edge length of the cubic specimens and the low retention time are responsible for the incomplete calcination at 1,050~ The dry apparent weight of the calcined limestone (1.577 g/cm3), its low shrinkage (0.1-0.3%), the 2% impurities content and the 24% value of the attrition and abrasion resistance, characterize this quicklime and classify it to the high quality products.

1. Materials and Structures/Mat6riaux et Constructions, Vol.32, August-September1999, pp546-551
Technologicalcharacteristicsof the calcinedlimestone
from AgiosPanteleimonas,Macedonia, Greece
N. Kantiranis, A. Tsirambides, A. Filippidis and B. Christaras
SchoolofGeology,AristotleUniversityofThessaloniki, 540 06 Thessaloniki, Greece
Paperreceived:March9, 1999;Paperaccepted:April 26, 1999
ABSTRACT R !~ S U M E
The gray-green limestone from Agios Panteleimonas
is studied in this paper after submitting it in special tech-
nological analyses in order to determine the possibility
for quicklime production. Cubic test specimens with
mean 50 mm edge length were calcined at 850, 950 and
1,050~ with 150 rain preheating time and 120 rain
retention time at each calcination temperature. At the
dissociation temperature of pure calcite (898~ only
one half of the initial limestone has been calcined. The
dissociation of the specimens started at 740~ and
almost completed at 1,050~ Probably, the large edge
length of the cubic specimens and the low retention
time are responsible for the incomplete calcination at
1,050~ The dry apparent weight of the calcined lime-
stone (1.577 g/cm3), its low shrinkage (0.1-0.3%), the
2% impurities content and the 24% value of the attri-
tion and abrasion resistance, characterize this quicklime
and classifyit to the high quality products.
Dans cet article, le calcaire gris-vert d'Agios
Panteleimonas est (tudi~ par rapport a la possibilit( de son
utilisation pour la production de chaux, apr& avoir (t~ sou-
mis a des essais technologiques sp&iaux. Des (prouvettes
cubiques de 50 mm de cSt~ont (t( calcin&s a 850, 950 et
1050~ chauff&s pendant 120 rain a chaque temp&ature,
apr& leurpr&hauffage pendant 150 rain. La dissociation des
(prouvettes a (t( re'ah'se'epar augmentation de la temp&ature
de 740~ a 1 050~ Dans ce cadre, seulement la moiti(
du calcaire initial a (t( calcin& a la temp&ature de dissocia-
tion de la calcitepure (898~ La grande taille des @rou-
vettes et la courte dur& des essais, sont responsables de la cal-
cination incomplete, a la temp&ature de I 050~ La masse
volumique apparente s&he du calcairecalcin~ (1,577g/cm3),
son retraitfaible (0,1-0,3%), le taux d'impuret& (2%), le
coefficient d'attrition (24%) et la r&istance a l'abrasion,
caract&'sent cette chaux rive et la classent comme (tant un
produit de haute qualitY.
1. INTRODUCTION
The principal chemical property of limestone is its
thermal decomposition. It is due to this characteristic
that lime manufacturing was created by the process of
calcination. This process commences on the exterior
surfaces and progresses inwards as the surrounding tem-
perature increases. As the release of CO 2 involves a gen-
eral weight loss of 40-44% the porosity of the material is
increased giving a mass of CaO with a large internal sur-
face area and hence, high chemical reactivity.
There are numerous critical variables in limestone
calcination that can exert a serious effect on lime quality.
In decreasing importance such variables may be [1]:
Degree of calcite crystallinity, types and quantities of
impurities, rate of calcination, calcination duration and
temperature, chemical reactivity, shrinkage etc. Burning
technology and kiln design are also important factors in
determining the quality ofihe lime.
For high quality lime production the limestone may
present the followingmain demands [2]: CaCO 3 > 98.6%
and SiO2 < 1%. However, limestones with CaCO 3 con-
tent > 95% may produce common lime [3].
The diverse limestone types, based solely on theii
calcination behavior, may be arbitrarily categorized in
the following four groups [1]:
I. Those that fracture and decrepitate readily during pre-
heating and at low calcination temperatures.
II. Those that yield a porous, reactive lime under most
Calcination conditions and that are difficult to overburn.
III. Those that yield a dense, unreactive lime of low
porosity even under the mildest calcining conditions.
IV. Those that yield a porous, reactive lime under mild
temperature conditions and a denser, less porous lime
1359-5997/99 9 RILEM 546

2. Kantiranis,Tsirambides,Filippidis,Christaras
under harder burning conditions.
Category II is a desirable type of limestone since it
can be utilized for more uses. Category IV is slightly
preferable to II because through adjustments in time-
temperature conditions, a lime can be produced for all
purposes. However, the key to such a lime is the kiln, its
design, and operating methods.
2. MATERIALS AND METHODS
The gray-green carbonate rocks from the Agios
Panteleimonas region of Florina, Macedonia, are a
sparitic limestone with mean grain size 0.5 mm and
mineralogical composition: calcite 96%, dolomite 2%,
mica 2% and traces of quartz, feldspars, clay minerals
and opaques [4]. Twenty two cubic specimens of 50 mm
mean edge length of this limestone were calcined at 850,
950 and 1,050~ in order to determine its thermal
decomposition rate, as well as its technological character-
istics. Preheating lasted 150 min, while the retention
time at each selected temperature was 120 min.
Calcination was performed in a Naber-Multitherm
N 11/HR furnace.
From surface and core sites of each calcined test spec-
imen material was taken, ground and analyzed by X-ray
diffraction using a Philips diffractometer with Ni-fil-
tered CuKa radiation. Randomly oriented samples were
scanned over the interval 3-43~20 at a scanning speed of
l~ Semi-quantitative estimates of the abundances
of the mineral phases were made from the XRD data
using universal methods [5, 6].
The technological properties determined were the
dry apparent weight and the uniaxial compression
strength on the initial material and on the test specimens
calcined at different temperatures. Additionally, the
modulus of elasticity, the Poisson's ratio and the attrition
and abrasion resistance on the calcined test specimens,
were determined.
Cubic test specimens were submitted to a point load
test and the point load index (Is) was calculated by the
formula:
Is = p/De
where P = force (N) and D - cubic edge length (ram).
The uniaxial compression strength (Cs) was calcu-
lated by the formula [7]:
Cs = k • Is
where k = constant depending on the cubic edge length.
The elastic parameters may be determined by static
or dynamic methods. In this paper a dynamic method
was used. Thus, the cubic test specimens were subjected
to compression and shear wave pulses. Wave velocity is
calculated from the travel time of the pulse through the
specimen. Specimens may be loaded to approximately
field conditions because both P and S wave responses
increase with compression. Ultrasonic velocities were
measured as compression (Vp) and shear (Vs) according
to the French specification AFNOR NF B 10505. Both
compression and shear wave measurements were made
using a Pundit velocimeter.
The attrition and abrasion resistance of the specimens
calcined at 1,050~ were determined after a 2 min
vibrated sieving applying a modification of the Italian pro-
cedure R.D.2232 [8]. The percentage of material passing
the 10 mm screen openings determines the suitability or
not of the initial material for lime production. The deter-
mination is done on completelycalcined specimens.
3. RESULTS AND DISCUSSION
3.1 Calcination
The value for calcite dissociation is 898~ for 1 atm
pressure for a 100% CO 2 atmosphere [1]. Dissociation
always proceeds gradually from the outside surface
inward. Usually the depth of penetration moves uni-
formly inward on all sides of the stone. Actually, a cer-
tain amount of exterior or surface dissociation can occur
at lower temperatures than the preceding under
favourable conditions, such as low concentrations of
CO 2 with low partial pressures. But for dissociation to
penetrate into the interior of the limestone, higher tem-
peratures are necessary and must be further elevated for
dissociation to occur in the center or core of the stone.
The larger the limestone fragment, the higher the tem-
perature required for dissociation of the core due to the
increasing internal pressure as the CO 2 gas forces its
escape. The difference between dissociation tempera-
tures of the surface and core may be 150-370~
depending primarily on the fragment diameter [1].
The rate of heating has the greatest influence on lime
quality (i.e. shrinkage, porosity, and reactivity) affecting
more than maximum temperature or retention time.
Preheating temperature rise must be gradual, rather than
shock, followed by a gradual increase in calcination tem-
perature up to the point at which dissociation is com-
plete, thus avoiding further retention time [1, 9]. There
is an optimum calcination temperature and rate of heat-
ing for every limestone that can only be determined by
experimentation.
The preheating of the cubic specimens lasted 150 rain
and the retention time at each selected calcination tem-
perature was 120 min. The rate of heating was
5.7~ 6.3~ and 7~ for the temperatures
of 850, 950 ~:m 1,050~ respectively. The dissociation of
the cubic specimens started at about 740~ Their com-
plete dissociation was attainted at 1,050~ (Fig. 1).
3.2 Loss of weight
In the complete thermal decomposition of 100%
pure calcite, there is a theoretical loss of weight of 44%
as the CO 2 is evolved. This is called lost on ignition.
With dolomite there is a greater loss of weight, since a
pure magnesium carbonate releases 52.2% of its weight
as CO 2 gas. Thus, the greater the MgCO 3 component is
547

3. Materials and Structures/Mat6riaux et Constructions,Vol. 32, August-September 1999
45 ........................................ 1...............................................................
~" 35
zo~ "~'-'] r = 0.~1
lo
5
0 800 830 900 950 I,O00 1,050 I,I00
Caldnatio.tcmpcratm~CC)
Fig. 1 - Correlation diagram of loss of weight versus calcination
temperature.
............. maximum loss of weight (44%) for high calcium lime-
stone
..... dissociation temperature (898~ for pure calcite
Table 1 - Loss of weight and shrinkage
of the calcined specimens
Calcination Initial Final Lossof Shrinkage
temperature(~ weight(g) weight(g) weight(%) (%)
770
850
850
950
950
1,050
1,050
1,050
1,050
1,050
1,050
281.02
324.60
306.65
332.00
325.05
330.55
332.60
338.55
200.93
250.80
262.84
265.45
280.40
259.85
224.10
219.90
189.05
189.95
193.90
113.12
141.85
148.22
5.5
13.6
15.3
32.5
32.4
42.8
42.9
42.8
43.7
43.4
43.6
0.1
0.1
0.1
0.3
0.3
0.3
in dolomitic or magnesian limestone, the greater is the
weight loss.
In Table 1 the loss of weight (%) of the calcined
cubic limestone specimens are given. Applying the
method of least squares on these data it is concluded that
a very good linear correlation exists between the two
variables by the formula: Y = -100.964 + 0.138X, were
Y is the loss of weight (%) and X the calcination tem-
perature (~ (Fig. 1).
The percentage of shrinkage varies between the dif-
ferent carbonate rocks. A few stones at the lowest tem-
perature (927-954~ may expand initially before final
shrinking [1]. The degree of lineal shrinkage increases
proportionately with the total impurity contents of the
carbonates; the greater the impurity content, the greater
the shrinkage. The dilation and contraction is controlled
by crystal size and density, and the calcination tempera-
ture is greater for a highly crystallized limestone than for
a poorly crystalline [9].
Using the above formula and the data of section 3.5.1
the shrinkage of the cubic specimens for the calcination
temperature 1,050~ was calculated (Table 1). It is con-
cluded that the shrinkage of the calcined specimens
increases as the loss of weight increases.
3.4 X-ray diffraction analysis (XRD)
X-ray diffraction analysis of different quality quick-
limes which were produced from the same limestone
showed that their cell parameters were not affected [10].
This means that the molecular geometrics of the crystal
is invariable and the tension of calcination does not affect
the molecular structures but only the intercrystalline
spaces.
Material both from surface and core of each test spec-
imen and each selected temperature was ground and
analyzed by XP,.D. The results are given in Table 2,
where a gradual transformation of calcite to quicklime
and of MgCO 3 component of dolomite to periclase, as
well as the dissociation of the aluminum silicates, is
observed. It should be noted that the breakdown of
muscovite starts about 600~ under 1 atm pressure [11].
The study of XRD patterns of the calcined speci-
mens showed clearly the formation of a non crystalline
phase during calcination. This phase recognized as a
wide reflection at the interval 10-15 ~ 20. The semi-
quantitative estimation of the percentage of the non
crystalline phase with XRD analysis is quite difficult.
However, comparing our XR.D patterns with others
taken from materials that are 100% non crystalline (i.e.
amorphous SiO2 or obsidian), an estimated value of the
percentage of the non crystalline phase that formed dur-
ing calcination in our specimens, is suggested (Table 2).
3.3. Shrinkage (S)
Shrinkage is referred to the process of shrinking of a
carbonate specimen which is calcined at different tem-
peratures. The shrinkage (%) of each calcined specimen
was calculated by the formula:
S = 100x 100/Ds- (100- L)/DL
100Ds
where D s = bulk density of limestone (g/cm3), DL =
bulk density of quicklime (g/cm3) and L = loss on igni-
tion (%) of limestone.
Table 2 - Semi-quantitative mineralogical composition
(wt. %) of the specimens analyzed
C L Pe M F A
Surface/850~ 89 tr 5 tr 6
Core/850~ 95 2 3
Surface/950~ 90 tr 2 tr 8
Core/950~ 90 tr 2 8
Surface/1,050~ 93 tr 7
Core/1,050~ 8 92 tr tr tr
C = calcite, L = lime, Pe =periclase, M = muscovite (+talc), F =feldspars,
A = non crystalline phase, tr = traces.
548

4. Kantiranis,Tsirambides,Filippidis,Christaras
It should be noted that the studied limestone did not
contain any non crystalline phase.
3.5 Technological characteristics
3.5.1 Dry apparent weight
The dry apparent weight of the original limestone was
measured 2.734 g/cm3 and of the completely calcined
specimens 1.577 g/cm3. A significant decrease (58%) of
the dry apparent weight is noted because ofthe calcination.
It is obvious that this change is accompaniedby simultane-
ous porosity increase in the calcined specimens. The mea-
sured value 1.577 g/cm3 is between 1.3 and 1.8 g/cm3
which interval corresponds to high quality quicklimes [1].
3.5.2 Compression strength (Cs)
The point load index and uniaxial compression
strength results are given in Table 3, both for the initial
material and for the cubic test specimens calcined at dif-
ferent temperatures. For comparison the range values of
compression strength for limestones and marbles are
given in the same Table [12].
The graphical presentation of the uniaxial compression
strength values calculatedby the point load test and the cal-
cination temperature, shows that between these two para-
meters a very good linear correlation exists (Fig. 2).
Applying the method ofleast squareson these data it is con-
cluded that the two parameters correlate linearly by the for-
mula: Y = 164.706 - 0.153X, whereY = uniaxial compres-
sion strength (MPa) and X = calcination temperature (~
This formula is valid for 850~ < T < 1,050~
without excluding its extension to lower or higher
temperatures.
3.5.3 Elasticparameters
The ultrasonic velocities Ve and Vs, as well as
the dynamic modulus of elasticity (Ea) and
Poisson's ratio (vd)results are given in Table 4. The
measurements are performed on cubic specimens
with mean edge length 50 mm (min 31 mm - max
65 mm) which were calcined at 850, 950 and
1,050~ The elastic moduli Ed and vd of the cal-
cined specimens were calculated using the follow-
ing formulas:
3Vp2 4Ms2
Ed =cxDxVs2 x
Vp2 -Vs 2
Vp2 - 2Vs2
andvd=2(Vp2 Vs2 )
where c = constant depending on the units used
(for SI - 1000.6), D = dry apparent weight of the
material (g/cm3) and Vp, Vs - velocities of P and
S waves (m/sec).
The mean values of the elastic parameters of the ini-
tial material were Ed= 60.7 MPa and vd = 0.364.
Between the dynamic modulus of elasticity and the
calcination temperature a very good linear correlation
Table 3 - Point loading index (Is) and uniaxial
compression strength (Cs) of the specimensanalyzed
Is(N/mm2) k Cs (MPa)Calcination
temperature(~
In. mat.1
85O
950
1,050
1,050
1,050
4.47 23.5
1.72 21.0
0.74 23.0
0.22 22.5
0.19 22.8
0.22 20.5
105
36
17
5.0
4.3
4.5
Limestones 35.3 - 373.0
Marbles 62.0 - 227.6
k co~cient dependingon theedgelengthCthe cubicspeamens,
t - initial material.
, ~o.
m
.~ 20-
~ 15-
7~
o
100 It~O 900 9SO 1,~ 1,050 1,1~
Cakimtioa~mperamn~(~
Fig. 2 - Correlation diagram of uniaxial compression strength
versus calcination temperature.
Table 4 -Dynamic moduli of elasticity (Ed) and
Poisson's ratios (Vd) of the calcined specimens
Calcination Specimen
temperature(~ thickness(m)
85O
850
850
950
950
950
1,050
1,050
1,050
1,050
1,050
1,050
1,050
1,050
1,050
0.051
0.045
0.050
0.060
0.048
0.065
0.048
0.031
O.050
0.038
0.050
0.048
0.045
0.048
0.050
Vp = P wave velocity, V = S wave velocity.
V~Vs Ed vd
(MPa)
1.71 3.967 0.208
1.71 3.654 0.206
1.72 3.864 0.200
1.83 1.771 0.283
1.88 1.507 0.284
1.84 1.670 0.281
2.07 0.823 0.347
2.04 0,858 0.343
2.11 0.585 0.355
2.43 0.604 0.398
2.47 0.453 0.402
2.49 0.543 0.403
2.07 0.861 0.347
2.20 0.726 0.369
2.33 0.477 0.388
exists (Fig. 3). Applying the method of least squares it is
concluded that these two variables correlate linearly by
the formula: Y = 16.4442 - 0.0151X, where Y = dynamic
modulus of elasticity (MPa) and X = calcination tempera-
ture (~
549

5. Materials and Structures/Matdriaux et Constructions,Vol. 32, August-September1999
4.5,
4.0 1 g
3.]
,.a ,.o~
~ ,.5-1
,.ot
o.o [
Calcinationtcraperat.~ (~
,,100
Fig. 3 - Correlation diagram of dynamic modulus of elasticity
versus calcination temperature.
0.45
0.40- 80
i o.3o~ y=4).51~.~[
9 [r=o.~~
0.20
0.15
,~ ;,0 d0 d0 ,.~ ,.'0~
Caldrationlempcratm~(C)
1,100
Fig. 4 - Correlation diagram of dynamic Poisson's ratio versus
calcination temperature.
Between the dynamic Poisson's ratio and the calcina-
tion temperature a very good linear correlation is noted
(Fig. 4). Applying the least squares method a very good
linear correlation is taken as the following formula
shows: Y - -0.51685 + 0.000846X, where Y = dynamic
Poisson's ratio and X - calcination temperature (~
It should be noted that the above formulas are valid
only for the temperature interval 850-1,050~ but
extension of this function to lower or higher tempera-
tures must not be excluded.
Ultrasonic velocity is not only an indication of the
above two moduli but additionally is a very good index
for rock quality and weathering determination [13-16] as
well as for the determination of rock anisotropy [17].
Decrease of the dynamic modulus of elasticity is fol-
lowed by increase in the rock porosity [18].
3.5.4 Attrition and abrasion resistance
The specimens calcined at 1,050~ were sieved for
2 min in a vibrated sieve with openings 10 ram. The
percentage of the material passing the 10 mm screen
openings, is calculated. Suitable for calcination lime-
stones must present percentages of passing material for
vertical kilns < 30% after the application of the above
procedure on specific test specimens [1]. It is noted that
the sieving must be done on completely calcined speci-
mens. Fine-grained material blocks the exit openings of
steam reducing thus the efficacy of calcination.
However, in rotary kilns this fact has non significance.
The smaller (until 1 cm in diameter) the carbonate frag-
ments, the faster and more economic the calcination
process in a rotary kiln.
The percentange of the calcined material <10 mm in
grain size of the studied limestone was 24%. Although
this value is considered acceptable for manufacturing of
this natural stone, detailed study must be followed before
the complete quality data are defined.
4. CONCLUSIONS
From the loss of weight measurements of the cal-
cined specimens it was found that a positive linear corre-
lation exists with the calcination temperature. Also, it
was found that in the dissociation temperature of pure
calcite (898~ our specimens show 23% loss of weight
(Fig. 1), which means that only one half of the initial
material has been calcined at this temperature. Therefore
the influence of the total impurities to the calcination
progress is very important. Although the initial material
may be considered pure (total impurities 2%), their pres-
ence increases very much the temperature for complete
calcination. The unavoidable presence of some impuri-
ties introduces another parameter to lime burning. In
practice, the concentration of lime is vitiated by about
four times its percent of total impurities as a result of the
fluxing effect during calcination [1]. So for 2% total
impurities in the limestone studied there is a loss of
nearly 8% free CaO in the quicklime. This loss is mini-
mized at lowest calcination temperature levels. Another
interesting conclusion that results from Fig. 1 is that the
dissociation of'our specimens starts at about 740~ This
is due probably to the organic matter which is present at
0.8% [4]. At 1,050~ the specimens did not calcine
completely (8% of the calcite remained unaffected in the
core), probably because of the large sized test specimens
and the low retention time at this temperature9
The shrinkage of the calcined specimens at 1,050~
was found about 0.1 to 0.3%. This observation com-
bined with the pureness of the initial material, means
that a high quality quicklime is produced.
The presence of non crystalline material in the speci-
mens at different calcination temperatures probably is due
to the liquefaction of the impurities and to the imperfect
crystallization of the quicklime because of the rapid
decrease of the temperature after the removal of the cal-
cined specimens from the furnace where the calcinations
took place. At the same time, the XRD study of the cal-
cined specimens showed their gradual calcination from
the surface to core as the temperature increases (Table 2).
The &y apparent weight of the calcined specimens at
1,050~ (1.577 g/cm3), the very low shrinkage (0.1-
0.3%) and the limestone high purity (total impurities
2%), classify the produced quicklime as a high quality
product. The calcined limestone of this study showed
that it belongs between the II and IV categories, because
of its high purity and very low shrinkage. These factors
mean high porosity and chemical reactivity of the pro-
550

6. duced quicklime. However, further study is needed for
more reliable conclusions.
Between uniaxial compression strength and calcina-
tion temperatures a negative linear correlation exists
(Fig. 2). As the calcination temperature increases the
compression strength decreases greatly. The correlation
is effective for 850~ _<T _<1,050~ not excluding
extension at lower or higher temperatures under special
conditions.
The dynamic modulus of elasticity (Ed) and the
dynamic Poisson's ratio (Vd)show a negative and positive
linear correlation respectively with the calcination tem-
perature (Figs. 3 and 4). At higher temperatures the
modulus of elasticity decreases, while the Poisson's ratio
increases, which is due to the structure weakening of the
cubic specimens.
The attrition and abrasion resistance is a parameter
which characterizes the behavior of the completely cal-
cined material inside the vertical kiln as the fragments
grind and impact each other. A material to be suitable
for calcination in a vertical kiln must permit < 30% of
the calcined material to pass a screen with 10 mm open-
ings after a 2 rain vibrated sieving.
Although the percentage of the passing material the
10 mm screen openings is by average 24%, extra analyses
are needed before any final proposal is made concerning
the standardization of quality data of the studied lime-
stone from Agios Panteleimonas.
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