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INVESTIGATIONS INTO THE INFLUENCE OF LIMESTONE
ADDITIONS TO PORTLAND CEMENT CLINKER PHASES ON
THE EARLY PHASE OF HYDRATION
J Stark
E Freyburg
K Lohmer
Bauhaus-Universitat Weimar
Germany
A B S T R A C T . This paper is concerned with the influence of limestone powder on the
hydration of cement. Differences in dilation and shrinkage of concretes made from cements
with limestone additives prompted an investigation into the effects of the use of limestone in
cement on the process and the products of hydration of the four major cement clinker phases.
In order to do so, separately produced cement clinker phases were hydrated one by one with a
variety of four different limestone powders together with sulfatic additives. By means of Xray diffractometry for phase analysis monocarbonate (MC) was detected, proving the
participation of the calcium carbonate added in the chemical reaction with both aluminatic
phases C A and C AF. It showed that calcium carbonate has an influence on the heat of
reaction and the conversion of the aluminatic phases as well as C S during the early age of
hydration. These effects were noticeably increased solely by extending the specific surface of
the limestone powder.
3
4
3
Keywords: (3-C S, C A, C AF, C S, Cement clinker, Conduction calorimetry, Dolomite
powder, Limestone powder, Monocarbonate, Thaumasite, X-ray diffractometry.
2
3
4
3
Professor J S t a r k is Director of the F.A.Finger-Institute of Building Material Sciences at the
Bauhaus-Universitat Weimar. The main fields of research are the use of binders, the
durability of concrete, structural light-weight concrete, high-performance concrete, and
historic mortars.
D r E F r e y b u r g is a Research/Teaching Fellow at the F.A.Finger-Institute of Building
Material Sciences at the Bauhaus-Universitat Weimar. His main research interests include
the use of binders, the durability of concrete and especially the assessment of damaged
concrete structures.
K L o h m e r is a research assistant at the F.A.Finger-Institute of Building Material Sciences at
the Bauhaus-Universitat Weimar. She specialises on the use of binders, in particular on the
improvement of the properties of cement.
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70
Stark, Freyburg, Lohmer
INTRODUCTION
By German and European standards, except for CEM II/A-L and CEM II/B-L, the addition of
limestone powder is permissible as "subsidiary component" in cements and as "inorganic
substance" in plaster and mortar binders. In these cases limestone powder does not have to
meet any requirements concerning its chemical reactivity.
From various investigations [1,4,5,6] it is known that the addition of even relatively small
amounts -still ranging as subsidiary component- changes the processing features of cement.
It had to be asked whether or not the use of limestone in quantities classified as " subsidiary
components" according to ENV 197 part 1, i.e. about 5 %, accounts for any chemical
reactions besides the purely physical effect of a filler. Therefore it was investigated if in the
presence of very small amounts of limestone detectable chemical reactions do occur and how
they might influence the process of hydration (heat and phases of hydration).
In order to be able to classify possible effects and to identify converted compounds the
complex matter "cement" was abstracted as singular clinker phases.
BASIC M A T E R I A L S AND C O M P O S I T I O N O F MIXTURES
The cement clinker phases C S, C S, C A and C AF were produced, processed and tested
separately. In order to maintain comparable conditions it was defined that each cement
clinker comprises of 100 % of the cement clinker phase investigated. So, the actual
proportions of clinker and additives (or the stoichiometrically precise ratio) were not
considered.
Common to all mixtures was the addition of 6 % sulfatic substance,
corresponding to an S0 -content of 3.4 %. The sulfatic substance contained 50 % natural
anhydrite and 50 % synthetically produced hemihydrate.
3
2
3
4
3
The reference sample contained nothing but one cement clinker phase each and sulfatic
substance.
To all other samples 3 and 6 % limestone powder were added to respectively. As additives
were used: two different types of limestone powder (A) and (B), type (B) of different fineness
(Ba) and (Bb), and dolomite powder (C).
Table 1 shows the specific surface and the calcite/dolomite content of each powder used.
Table 1 Fineness and chemical purity of the stonepowders used
TYPE
SPECIFIC SURFACE [cm /g]
CALCITE CONTENT
A
Ba
Bb
C
13,700
6,800
10,500
11,500
98%
85%
85%
98 % (dolomite)
2
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Influence of L i m e s t o n e on H y d r a t i o n
71
The value for the specific surface of the cement clinker phases ranged between 3,300 and
4,200 cm7g.
By means of calorimetric testing only reference samples and type (A) mixtures containing 3
and 6 % limestone powder were analysed.
All mixtures were produced with a water-to-binder ratio of 0.5.
METHODS OF INVESTIGATION
Calorimetric measurements were run by means of a conduction calorimeter (DCA-06, ToniTechnik). Only the rate of heat evolution was taken under consideration. Each measurement
lasted over a period of 72 hours.
The influence of the stone powder content was determined concerning the time and peak
value at which a maximum in heat evolution is reached. Furthermore, these maxima
determined served as an indicative to limit the hydration period prior to X-ray analysis.
Before being analysed by means of XRD, the samples have been mixed for 90 seconds and
were then stored quasi-adiabaticly. The hydration was stopped by grinding the sample in
isopropanol and subsequent rinsing with acetone. The samples were dried at 40 °C; to
examine them a X-ray diffractometer was used ( D 5000", Siemens). The results were
evaluated qualitatively and semi-quantitatively, the latter by measuring and comparing peak
values of certain reflections.
M
The d-values of the reflections are listed in Table 2.
Table 2 d-values of certain reflections
COMPOUND
REFLECTIONS [nm] (d-value)
Cement clinker mineral
C,S: 0.276; 0.218; p-C S: 0.219; 0.287;
Portlandite
Anhydrite
Calcite
Dolomite
Gypsum
Thaumasite
Ettringite / AFt-phase
Monosulfate (MS) / AFm-phase
Monocarbonate (MC)
C AH /C (A,F)H
C A H /C (A,F) H
C A: 0.191; C AF: 0.181; 0.205; 0.725
0.49
0.35
0.209; 0.228; 0.303
0.289
0.761; 0.761; 0.428
0.966
0.973 / 0.56; 0.973
0.223; 0.893
0.378; 0.756/0.757
0.23; 0.513/0.515
0.287 - 0.289; 0.796 - 0.834
2
3
3
x
6
y
3
z
6
x
y
z
4
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72
Stark, Freyburg, Lohmer
RESULTS AND I N T E R P R E T A T I O N
Conduction Calorimetry
With the C S samples an exothermal effect of 5 J/g-h was indicated within minutes after the
samples were exposed to water which has to be explained with the moistening of the solid
material. A second exothermal effect of about 20 J/g-h was observed after 10 to 12 hours. If
limestone powder had been added the exothermal maximum occurred up to one hour earlier,
as illustrated in Figure 1.
3
During the period of observation the (3-C S samples did not show any exothermal effect
besides the one due to moistening.
2
—~~"~"
C S
-
C S + 3 % LST. A
-
-
3
- SAMPLE
3
CJS +
4
8
12
16
20
6%
LST. A
24
T I M E OF HYDRATION [ H ]
Figure 1 Course of heat emission of C S samples
3
All C A samples are of very high reactivity during the first minutes of hydration. The heat
release of this effect was found to be reduced if limestone powder had been added. A slight
acceleration is suggested.
3
Figure 2 illustrates the course of heat emission of C A samples during the first minutes of
hydration.
3
The reduction in heat release is evident. This could be attributed to a "thinning" of the
reactive substance i.e. the clinker phase with "inert" filler as well as to a formation of
compounds involving calcium carbonate. The latter is supported by the results of the X-ray
analysis (see next chapter).
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Influence of L i m e s t o n e on H y d r a t i o n
10
20
30
40
50
73
60
time of hydration [minutes]
Figure 2 Course of heat emission of C A samples
3
Regarding C AF samples three exothermal effects were detected. The first one corresponds
to the C A effect, but it occurs later, lasts longer and is less intense than the one of the ironfree calcium aluminate. A second and third effect was observed during the following five
hours.
4
3
Figure 3 illustrates the course of heat emission of C AF samples containing no limestone and
3% of stonepowder respectively.
4
100
time of hydration [h]
Figure 3 Course of heat emission of C AF samples
4
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74
Stark, Freyburg, Lohmer
The addition of limestone powder prompted an acceleration of the reaction, so that all three
effects occurred earlier. The first effect then was, as with the C A samples, less intense but in
the following two effects the samples containing limestone tended towards a higher rate of
heat release.
3
X - r a y Diffractometry
The influence of limestone additives on the hydration of C S, as described in other
publications, could be explained mineralogically by means of X-ray diffractometry. In the
presence of limestone (3 and 6%) an intensified conversion of C S was observed, especially
in the beginning.
3
3
A related acceleration in the formation of portlandite could not be established.
Figure 4 illustrates the different conversion of C S in samples containing no and 6%
limestone powder respectively after two and 24 hours, taking the reflections of 2-0=32.07 and
41.1 (d-value=0.276 and 0.218) as examples.
3
Occasionally, some thaumasite was found; its presence was proven through analysis by
means of SEM of samples hydrated for five days.
This suggests at least the possibility of a chemical reaction of siliceous and sulfatic phases
with calcium carbonate, as discussed by some. Yet, it can not be excluded that atmospheric
carbon dioxide penetrated into the fresh samples (small volume, large surface) and
participated in a chemical reaction.
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Influence of L i m e s t o n e on H y d r a t i o n
75
Because of the low reactivity of P-C S no influence of the limestone additive could be
observed.
2
Besides the slight increase in the conversion of C A when limestone was added, the reaction
of calcium carbonate with both aluminatic phases was established. Calcium aluminate
monocarbonate hydrate as well as calcium ferrite monocarbonate hydrate was detected, its
amount increasing in relation with the supply of more calcite.
3
Figure 5 is an X-ray diffraction pattern depicting the different formation of monocarbonate in
varying C A mixtures after four days of hydration.
3
--Theta - Scale
Roentgenlabor F .A.Finger-I nst
itut f .Baustoffkunde W
e
i
m
a
r -UHI
- 16-Sep-1998 14:08
MC = M o n o c a r b o n a t e
1 = C A - S a m p l e without Lst.
3
2 = C A + 3 % Limestone A
3
3 = C A + 6 % Limestone A
3
MC
MC
3
MC
aJLa
H
1
6
Figure 5 X-ray diffraction pattern of monocarbonate in C A samples
after four days of hydration
3
There were no apparent differences between the two types (A) and (B) of limestone used.
When dolomite powder (C) or the more coarse type (Ba) was used less monocarbonate was
formed, especially in C AF samples, due to a lower reactivity of the additives.
4
Figure 6 illustrates that fact with the help of the monocarbonate reflections at 2-0 = 11.68 and
23.5 (d-value = 0.757 and 0.378).
The detection of monocarbonate in samples with dolomite stonepowder added was possible
using the same d-value. In that, the peak changed into the shape of a "shoulder" at d =
0.757nm, as depicted in Figure 7.
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76 Stark, Freyburg, Lohmer
2-Theta
£3 I
-
.
.
Scale
.
.
.
Roentgen 1abor
.
F .A . F i n g e r - l n s t i t u t
lleimar
-UNI-
1&-Sep-1998
14-09
,
:
10
f .Bans tof fkunde
12
14
16
18
20
22
24
Figure 6 X-ray diffraction pattern of C AF samples with 6% stonepowder each
after four days of hydration
4
2-Theta
-
Scale
R o e n t e n 1abor
F .A . F i n g e r - l n s t i t u t
9
f .Baustoffkunde
Weimar
-UHI -
lb-Sep-1998
14
09
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O
Q L_,
r
_,
,
(
,
10.9
,
,
,
!
,
11.0
,
,
,
(
,
11.1
,
,
,
!
,
,
11.2
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11.3
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11.4
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11.5
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11.6
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11.7
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,—,
11.8
,
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11.9
Figure 7 X-ray diffraction pattern depicting monocarbonate in C AF samples
with limestone (A) and dolomite (C) powder
4
The above mentioned influence of limestone powder on the second and third exothermal
effect during the hydration of C AF samples could not be investigated by means of phase
analysis. Detection was possibly hindered by the formation of minor amounts of calcium
aluminate ferrite sulfate hydrate phases as well as by not yet appropriately gentle enough
ways of preparation.
4
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Influence of Limestone on Hydration 77
CONCLUSION
It was established that the addition of 3 and 6% limestone powder indeed influences the early
phase of hydration of C S, C A and C AF.
3
3
4
The finding that thaumasite is formed in an early stage by reaction of C S with the sulfatic
substance and possibly with limestone powder (at least, the C S reaction is accelerated in the
presence of limestone powder) may be exploited by purposefully producing this "rising"
mineral to control the shrinkage of concrete from early on comparable to ettringite.
3
3
The conjecture that the thaumasite found originates from the reaction of the source materials
and is not formed during carbonation is currently being reviewed.
If existing unspecified concrete has to be identified with respect to its original binding agent,
these results indicate that monocarbonate may have been formed primarily, not only by
carbonation of ettringite.
REFERENCES
1.
FREYBURG, E, STARK, J, SPRINGENSCHMID, R AND MANGOLD, M. EinfluB
der Zementeigenschaften auf die Hydratationswarmeentwicklung und die ReiBneigung
des Beton. Wissenschaftliche Zeitschrift der HAB Weimar, 1993, Vol. 39, No. 3, pp
149-155.
2.
INGRAM, K, D, AND DAUGHERTY, K, E. Limestone additions to Portland Cement :
Uptake, Chemistry and Effects. 9. International Congress on the Chemistry of Cement
(ICCC), 1992.
3.
PERLT-SCHUSCHNIG, E. EinfluB von Kalksteinmehl auf die ReiBneigung von jungem
Beton. HAB Weimar, Master Thesis 1993.
4.
SCHIEL, T. Eigenschafiten von jungem Beton bei Einsatz von Kalksteinmehl,
Silicastaub und unterschiedlichen Zuschlagen. HAB Weimar, Master Thesis 1994.
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