15th International Congress on the Chemistry of Cement

Prague, Czech Republic, September 16–20, 2019

СOMPLEX ADDITIVE THE CALCINED MIXTURE OF CLAY AND

LIMESTONE FOR BLENDED PORTLAND CEMENT

Elizaveta Ermilova a, Ravil Rakhimov b, Zagira Kamalova c , Pavel Bulanovd

Department of Building Materials, Kazan State University of Architecture and Engineering, Kazan,
Russian Federation

alizabeta_91@list.ru
brahimov@kgasu.ru
c zlesik@mail.ru
df_lays@mail.ru

ABSTRACT
The predicted increase the world production of blended Portland cement and the dosage of mineral
additives up to 30-40%, lead to an increase the volume of additives production and application.
Resources of currently used mineral additives do not provide the increasing their needs. The complex
additives which differ by the presence of a synergetic effect in the co-introduction of multiple mineral
additives play the great importance in the creation of blended cements. One of the promising directions
is the creation of complex additives based on the combination of calcined clays with limestone. But
sometimes there are clay impurities in carbonate rocks which adversely effect on properties of a
received cements and concretes. At the same time calcium carbonate contained in marl clays during
calcination allows to get high quality pozzolanic material.
The effective complex additive based on the calcined mixture of clay and limestone was the creation.
The optimization of parameters for obtaining the complex additive the mathematical experiment
planning was used. The calcination of mixtures based on the kaolinitic or polimineral clay and
limestone with the calcite content of 99% at a temperature of 720-800 ºС leads to form of C2S, and
also increase the quantity of an amorphous phase. The results of research show the influence of the
complex additive on blended cement stone properties. It has been established that strength of cement
stone with a complex mineral additive depends on the content of kaolinite in initial clay, and on
calcination parameters.
 15th International Congress on the Chemistry of Cement
Prague, Czech Republic, September 16–20, 2019

1. INTRODUCTION

One of the most effective and recognized approaches to solving problems in Portland cement industry
(high energy and resource consumption, polluting emissions) is the development of low clinker
blended Portland cement with mineral additives. The predicted increase the global production of
Portland cement, coupled with the increased dosage of mineral additives up to 30-40 %, leads to an
increase in the volume of additives production and application. In search of alternatives to traditional
mineral additives, recent times have engendered studies of the effectiveness of calcined clay
(Lothenbach B. et al. 2011, Ludwig H.-M. 2015, Nehdi M. 2001, Rakhimov R.Z. et al. 2015, 1st
International Conference on Calcined Clays for Sustainable Concrete 2015). The high efficiency of
metakaolin is proven (Habert G. 2009, Rakhimov R.Z. et al. 2015). However, because of their limited
resources and high cost, the search for affordable mineral additives has been expanded to include a
study of the effectiveness of calcined polymineral clays of widespread provenance containing little or
no kaolinite (Ibausil 2015, Proc. XIV International Congress on the Chemistry of cement 2015).

One of the more promising direction in the creation of complex additives for blended cements is
combinations of calcined clays and limestone (Lothenbach B. et al. 2011, Ludwig H.-M. 2015) in ratio
of 2:1 (clay : limestone) (Antoni M. et al. 2012).

At the same time carbonate rocks contain clay impurities with adverse effects on the resultant cements
and concretes properties. In 1920s, Weiner (Glinit-cement 1935) found that decomposition of the
calcium carbonate in mixture with clay occurs at temperatures lower than 910° C (temperature of
calcite dissociation). Gorland (Glinit-cement 1935) showed that, in the temperature range 660 to 810
°C almost all calcium carbonate contained in spondyl clay (marl clay) decomposed. According to Jung
V.N. (1988) calcium carbonate contained in marl clays in “close mix” with clay particles and during
calcination makes it possible to get the high quality glinite-cement. Ramachandran V.S. (1977) found
that in the temperature range 800 to 900 °C, dicalcium silicate begins to form especially in the mixture
of “clay-CaCO3” with pure oxides. Carbonate impurities dissociation with red-burnt clay composition
occurs at temperatures of 600-830 °C, with a maximum endothermic effect at 760-780 °C
(Voznesensky V.A. 1987).

The aim of this work was to obtain high-performance complex additives for Portland cement based on
calcined mixtures of finely divided carbonate rocks and polymineral clay.

2. EXPERIMENTAL

2.1 Materials and characteristics

All experiments were carried out using OPC CEM I 42.5 N according to EN 197-1 (C3S-68.0; C2S-10.0;
C3A-3.7; C4AF-15). Kaolinitic clay (KC) and polymineral clay (PC) were selected for use. The specific
surface area is 500 m2/kg. The mineral and chemical compositions of the materials are presented in Table
1. Differential thermal curves of selected clays are shown in Figures 1 and 2. Limestone (L) has mineral
composition, by mass%: calcite – 99, quartz – 1.

Table 1. Mineral composition of clays

Mineral composition,
Kaolinitic clay (KC) Polimineral clay (PC)
by mass (%)
Kaolinite 82,3 4,06
Quartz 17,7 35,8
Albite - 14,79
Microcline - 17,4
Montmorillonite - 17,9
Chloride - 4,1
Mica 6,0
 15th International Congress on the Chemistry of Cement
Prague, Czech Republic, September 16–20, 2019

TG,% TG,%
DSK,mW DSK,mW
96 TG 68,5
0 TG 0

95
990 °Ñ 68,5
-10
-20 347 °Ñ
DSK 68,5
94 -20
-40
68,5

93
154 °Ñ -30
-60 67,5
-40
67,0
92 -80 527 °Ñ 580 °Ñ
66,5 -50
-100
91
65,0
197 °Ñ -60
-120
90 64,5 147 °Ñ 887 °Ñ -70
-140
89
64,0 DSK
-80
-160
63,5
-90
88 -180
595 °Ñ 63,0
100 150 200 250 300 350 400 450 500 550 600 650 700 750 800 850 900 950 1000 1050
100 150 200 250 300 350 400 450 500 550 600 650 700 750 800 850 900 950 1000 1050

Figure 1. Simultaneous TG-DTA data the Figure 2. Simultaneous TG-DTA data the
kaolinitic clay polimineral clay

2.2 Methodology
The mixture calcination was conducted in the laboratory chamber furnace SNOL 7.2/1300 with a
vacuum fiber chamber. The heating rate for kaolinitic clay mixture was adopted equal to 10 °C/min,
and that for polymineral clay was 3 °C/min according the previous studies (Ermilova E. Yu. et al.
2017).

The experiments were carried out on sample cubes of cement stone with an edge length of 2 cm. The
physico-mechanical properties of cement stone of normal density were evaluated via variation of
compressive strength, water absorption and average density.

Calcined mixtures were introduced into the OPC in amounts of 20 % of its mass according to GOST
31108-2003 and EN 197-1:2000.

The thermal analysis of mixtures and blended cement stone were carried out using a combined
method of thermogravimetry (TG) and differential scanning calorimetry (DSC) using a thermoanalyzer
(Netzsch STA 449C) under continuous heating (40 to 1000 °C) of samples with a mass of about 35 to
40 mg at a rate of 10 °C/min in a flow (50 ml/min) of air in alundum crucibles. The temperatures of the
thermal effects were determined within an accuracy of ±1 to 3 °C, warmth - ±5 %, weight ±0.01 mg.

Determination the mineralogical composition of thermoactivated mixtures, relevant changes, and

hydration products identification were carried out by means of X-ray phase analysis on an automatic
X-ray diffraction D2 phaser (Bruker Company). For CuKα radiation, monochromatization (λ (Cu-Ka) =
1.54184 A) curved Johansson-type germanium monochromator, the mode of operation of a 40 kV, 40
mA X-ray tube was adopted. The experiments were performed at room temperature in the geometry of
Bragg-Brentano flat samples. Analysis and plotting of diffraction patterns were carried out using the
Bruker Diffrac Eva program.

The optimization of compositions and calcination parameters of complex additives was determined by
B3 plan experimentation on a hypercube with three factors.

3. RESULTS AND DISCUSSION

To investigate the possibility of creating complex additives based on calcined mixtures and their
influence on properties of blended cement, the following mixtures were employed:
 mixture of kaolinitic clay and limestone (KC+L);
 mixture of polymineral clay and limestone (PC+L).

The specific surface area of mixtures was 500 m 2/ kg.

 15th International Congress on the Chemistry of Cement
Prague, Czech Republic, September 16–20, 2019

3.1 Differential thermal analysis of mixtures

Research on the thermal reactions occurring in the artificial mixtures of clay and limestone was carried
out using differential thermal analysis.

According to Figure 3, during calcination, the endothermic effect corresponding to the loss of weakly
bound water in KC, as observed at 154 °C, is smoothed (Figure 1).

Figure 3. Simultaneous TG-DTA- DSC data the mixture of limestone and kaolinitic clay

The endothermic effect characterized the polymorphic aragonite transformation into calcite CaCO3 is
observed at 494 °C. Almost invisible, the endothermic effect in the temperature range 580 to 600 °C is
associated with kaolinite dehydration, while for the kaolinitic clay, this effect is clearly expressed
(Figure 1). The deep endothermic effect involving a large loss of mass (27.89 %) is typical for calcite
dissociation, and is observed much earlier in a mixture with clay than in clean calcite according to the
literature (Ramachandran V.S. 1977, Rovnanikova P. et al. 2011). This is confirmed by the results of
researchers (Ibausil 2015, Rovnanikova P. et al. 2011). However, the exothermic effect disappears,
hence characterized the kaolinite transformation into mullite (Ramachandran V.S. 1977, Rovnanikova
P. et al. 2011), which is observed at 990 °C for kaolinitic clay (Figure 1). Thus, the lack of distinct
peaks accompanying the endothermic effect of kaolinite dehydration, and the exothermic effect of
mullite crystallization indicates kaolinite binding in the presence of calcite in different connections.

Thus, the carbonate decomposition in the presence of clay occurs at temperatures below 810 °C. This
confirms the results presented in (Ramachandran V.S. 1977, Rovnanikova P. et al. 2011). The
common clay and carbonate calcination at the temperature range up to 800 °C makes it possible to
obtain qualitatively new thermoactivated material with not only pozzolanic but also hidden hydraulic
properties.

3.2 Optimization the mixture calcination parameters

The optimization of compositions and the calcination parameters of complex additives were
determined by B3 plan experimentation on a hypercube with three factors. The experimental factors
were arranged on three levels. The mathematical processing of experimental data was done
accomplished by a special program written on the VBA setting.

To improve the reliability of the statistical findings, the models’ adequacy was checked against two
criteria: the Fisher criterion and the average relative error criterion. The tabulated value of the Fisher
criterion for all models is Ftab > 19.2. For all models, Fсal(calculation) < Ftab, made them adequate for
 15th International Congress on the Chemistry of Cement
Prague, Czech Republic, September 16–20, 2019

the Fisher criterion. Constructed models were adequate for the average relative error criterion,
because, for them, the relation is Aav < 10 %, which could be used for solving the optimization aspects,
where the value of limestone in the mixture (X1), the calcination temperature (X2), the calcination time
(X3) were determined, after which the maximum strength of the cement paste was reached at 7 days,
R7, and after steam curing RCS. After solving optimization aspects by Newton’s method in
combination with the method of penalty functions, the calcination parameters and the content of
limestone in a mixture were determined for all types of clay. Obtained results are presented in Table 2.

Table 2. Оptimal parameters for calcination and composition of calcined mixtures

№ Composi The content of Calcined Curing Cement stone properties

tion limestone in the temperatu time,
mixture, % by re, ° C hours RCS, ρ, kg/m3 w, %
МPа
weight

1 OPC - - - 60,0 2095 5,66

2 KC+L 40 812 3,2 56,4 2231 4,69
3 PC+L 15 800 3,1 60,8 2152 4,90

According to the Table 2, the optimal content of limestone additives in calcined mixtures is 40% and
15 %, respectively, for mixtures with kaolinitic and polymineral clays. The optimum content of
limestone in mixture with kaolinitic clay corresponds to the relationship between metakaolin and
calcium carbonate as 2 : 1 corresponding to the mass proportions of the chemical reaction of 1 mole
of alumina calcined clays with 1 mole of calcium carbonate in the presence of calcium ion excess in
aqueous solution to form 1 mol of calcium hydromonocarboaluminate. In the case with polymineral
clay, the calcined temperature reduction associates with an elevated content of alkali oxides causes
acceleration the reaction between active alumina and calcium oxide formed at thermal dissociation.
The optimum temperature of calcination of a mixture with polymineral clay is lower due to the high
content of alkali oxides in the clay.

3.3 Identification the calcined mixture products

Identification the calcined mixture products was effected by XRD. The resulting diffraction patterns
are presented in Figures 4 and 5.

In the calcined mixture of kaolinitic clay KC and limestone L (Figure 4), the estimated content of main
components amounted: calcite (40 %), kaolinite (49 %) and quartz (11 %). The estimated content of
components after calcination became: calcite (80 %), quartz (20 %), kaolinite (undetermined).

The actual content of calcite is 37.1 % (diffraction peaks with interplanar spacings d = (3.036; 2.494;
2.284; 1.875) Å), and of quartz is 59.25 % (diffraction peaks with interplanar spacings d = (4.462; 3,
3.347; 2.459; 2.130) Å), which is indicative of limestone transition into amorphous phases. The
theoretical content of the amorphous phase must be between the amounts contained in KC (30.5 %)
and in L (21.8 %), while the actual amount of content is 45.3 %. Therefore, the amorphous phase
contains not only the amorphized kaolinite, but also new formations from the interaction of kaolinite
and carbonate decomposition products (Ramachandran V.S. 1977). On the XRD pattern, the CaO is
not identified, but there are peaks with interplanar spacings d = (2.844; 2.566; 1.982) Å, corresponding
to β-C2S.

In the mixture of polymineral clay PC and limestone L (Figure 5), the estimated content of main
components amounted: calcite (15 %) and quartz (30 %). The estimated content of components after
calcination became: calcite (38.7 %) and quartz (19.4 %).

The XRD pattern in Figure 5, shows that the absorption line of calcite is absent, and the content of
quartz is 45.47 %, as confirmed by the diffraction peaks with interplanar distances d= (4.262; 3.345;
2.459; 2.284; 2.238) Å. The amorphous phase increases up to 47.2 %, while the calculated
composition limits of an amorphous phase are 21.8-24.7 %. The kaolinite content of the initial clay is
negligibly low, so the amorphous phase contains noncrystallization amorphous new growths. The
 15th International Congress on the Chemistry of Cement
Prague, Czech Republic, September 16–20, 2019

diffraction peaks with interplanar distances d= (3.030; 2.901; 2.628) Å correspond with the formed β-
C2S.

3,347
12000
10000
8000
Counts

6000
4000

3,036
2000

4,262

2,284
3,857

2,459

2,094
2,494

1,875
1,913
3,305

2,239
10,120

4,468

3,514

1,982
2,844

2,130

1,928
2,566
0

10 20 30 40
2Theta (Coupled TwoTheta/Theta) WL=1,54060

Figure 4. XRD pattern the calcined mixtures of limestone and kaolinitic clay

3,345
3000
Counts

2000

4,262

3,239
1000

3,195

2,459
4,500

2,129
3,308

2,284
3,788
10,030

2,628
4,042

3,662

2,901

2,239
4,924

3,473

3,030

2,531

1,981
2,164
6,475
0

10 20 30 40
2Theta (Coupled TwoTheta/Theta) WL=1,54060

Figure 5. XRD pattern the calcined mixtures of limestone and polymineral clay

Free calcium oxide absence on the XRD pattern makes it possible to claim that it was completely
bonded by products of clay mineral decomposition, for example, by kaolinite. Partial formation of
silicon and aluminum oxides was also not identified on the XRD pattern. That gives the reason to
assume the possible formation of amorphous calcium silicates and aluminates. Two-calcium silicate
formed at the same time contains approximately equal quantities in all thermoactivated mixtures, so
that the polymineral clay testifies to the possibility of receiving actual complex agents based not only
on kaolinitic, but also polymineral clay.

Since the content of kaolinite in the original clay was negibly small, the amorphous phase contains
amorphous formations. Diffraction peaks with interplanar distances d = (3.030; 2.901; 2.628) Å
correspond with the resulting β-C2S.

Free calcium oxide is missing in Figure 5. This suggests that it was completely bonded by
decomposition products of clay minerals such as kaolinite. Partial formation of silicon and aluminum
oxides, which were also not identified in Figure 5, is also possible. This, in turn, suggests the formation
of weak-base amorphous calcium silicates and aluminates. The fact that the resultant dicalcium
silicate contains approximately equal amounts in all thermoactivated mixtures indicates the possibility
of obtaining an effective additive based not only on kaolinitic, but also polymineral clays.

Increased content of alkalis in clay tends to accelerate the decomposition of clay minerals with
formation of active amorphous silicon and aluminum oxides (Ramachandran V.S. 1977) that can react
with lime of the carbonate and products of its decomposition.
 15th International Congress on the Chemistry of Cement
Prague, Czech Republic, September 16–20, 2019

3.4 Hydration products composition of blended cements with complex additives

As revealed above, cement stone properties changing in dependence on the employed kind of
complex additives are bound with changes in the hydration product composition. The research on
hydration product composition was conducted on cement stone samples at 28 days of age with the
following compositions:
 1. The control sample of OPC;
 2. The blended cement with 20 % of complex additive based on the calcined mixture of
kaolinitic clay and limestone (KC+ L).

In Figure 6, simultaneous TG-DTA-DSC data the control sample OPC cement stone are submitted.

The structure is characterized by larger peaks of unreacted clinker minerals – alite (d = (2.748; 2.609;
2.316; 2.188) Å) and belite (d = (4.655; 2.787; 2.777; 2.293; 2.195; 2.050; 2.028; 1.980) Å). The
diffraction peaks with interplanar distances d = (7.312; 4,260; 3,178; 2,672) Å correspond to calcium
hydroaluminosilicates. The presence of a small content of calcite (d = (3.037; 2.494; 1.913; 1.877) Å)
and the formed ettringite (d = (9.826; 5.934) Å) is observed. The presence of calcium
hydromonosulfoaluminate is characterized by the diffraction peaks with interplanar distances d =
(9.002; 3.432; 2.973) Å. Diffraction peaks with interplanar distances d = (8.225; 3.871; 2.881; 2.208) Å
are characterized by hydrocalcium silicates C-S-H (I).The considerable quantity of portlandite
corresponds to diffraction peaks with interplanar distances d = (4.918; 3.110; 2.630; 1.928) Å.
700

4,918
600

2,630
500

2,777
2,748
2,787
400
Counts

2,609
300

3,037

1,928
2,653
3,110

2,108
2,672
2,881
200

2,195
3,056

1,980
2,293
3,391

2,188
3,308

2,973
7,312

2,050

1,913
3,178
3,571

1,986
2,028
3,246
7,818

2,165
2,279
9,002

3,432

2,316
2,445

1,894
8,225

2,409
4,655

3,662

2,541

1,877
3,871
9,826

4,113

2,494

2,208
4,250

2,239
5,639

2,341
5,934

2,362
100
0

10 20 30 40 50
2Theta (Coupled TwoTheta/Theta) WL=1,54060

Figure 6. XRD pattern the control sample from the OPC cement stone

In Figure 7, the simultaneous TG-DTA data the control sample OPC cement stone is presented. The
observed endothermic effect with the maximum at 70 °C can be bound with loss of free water from a
cement stone (Rovnanikova P. et al. 2011). Nearby, there is another effect (100 to 125 °C) that is not
absolutely accurately expressed on DSC and that binds with loss of adsorption water (Rovnanikova P.
et al. 2011). The small endothermic peak in the temperature range 125 to 150 °C is caused by
ettringite dehydration. The endothermic effect with a maximum at 461 °C and a 1.86 % loss of weight
characterizes the calcium hydroxide decomposition (Ramachandran V.S. 1977). The loss of weight in
the temperature range 480-630 °C is 2.87 %. The endothermic effect with a maximum at 680 °C is
followed by a 4.82 % loss of weight and characterizes the decomposition of lime carbonate formed
during hardening (Ramachandran V.S. 1977).
 15th International Congress on the Chemistry of Cement
Prague, Czech Republic, September 16–20, 2019

Figure 7. Simultaneous TG-DTA- DSC data the control sample from the OPC cement stone

Compound kaolinitic clay and limestone calcination (Figure 8) leads to a considerable decrease in the
formed portlandite content (d = (4.909; 3.852; 2.631) Å) – more than twice as much in comparison with
sample 1.
2,631
3,031
400

3,347

2,745
2,790
300

4,909
Counts

3,291

1,927
200

1,820
2,106
2,885

2,284

2,194
3,112

2,970

2,452

2,091

1,912
2,697

2,493

2,056
2,411

2,185
4,249

1,983

1,875
7,549

3,396
3,852

2,428
3,572

3,184

1,904
2,374
3,783

2,545
3,650

2,028
1,996
2,130
10,011

2,161
7,264
8,091

2,341
2,314

2,239
5,825
9,003

4,637
4,475

4,095
100

9,719

5,588
0

10 20 30 40 50
2Theta (Coupled TwoTheta/Theta) WL=1,54060

Figure 8. XRD pattern the blended cement stone with 20% of complex additive based on the
calcined mixture of kaolinitic clay and limestone

The considerable part, slightly smaller in comparison with sample 1, consists of unreacted clinker
phases of alite (d = (2.745; 2.697; 2.341) Å) and belite (d = (2.790; 2.452; 1.983) Å). The considerable
content of calcite (d = (3.031; 2.493; 2.284; 2.106) A) testifies to the insufficiently high temperature of
calcination and its incomplete decomposition during calcination of the mix. Traces of formed ettringite
(d = (9.719; 5.588) Å) were found. The diffraction peak with the interplanar distance d = (7.264; 3.783)
Å corresponds to calcium hydroaluminosilicates.

Peaks characterizing the existence of calcium hydromonocarboaluminate are represented with an

interplanar distance d = (4.249; 3.182) Å. The diffraction peaks with interplanar distances d = (8.091;
2.885; 1.875)∙Å correspond to the formation of hydrocalcium silicates C-S-H (I). The presence of
calcium hydromonosulfoaluminate is observed (d = (9.003; 2.970) Å), as well as for sample 1.
 15th International Congress on the Chemistry of Cement
Prague, Czech Republic, September 16–20, 2019

The simultaneous TG-DTA data the blended cement with 20 % complex additive based on the
calcined mixture of kaolinitic clay and limestone are presented in Figure 9. Endothermic effects with a
maximum at 79 °С are observed there, similar to what is also observed at control sample 1 and which
bounds with loss of free water, and to the effects at 100 to 125 °C that are caused with partial
dehydration of hydrosilicates such as C-S-H (I). The endothermic effect with a maximum at 152 °C is
specific for ettringite dehydration, the hydrosilicates C 2SH2 and C2S3H2 or the hydroalumosilicates
(Rovnanikova P. et al. 2011). Portlandite decomposition is followed by an endothermic effect with a
maximum at 461 °C. The endothermic effect in the temperature range 669 to 708 °C characterizes the
hydrocalcium silicates such as C-S-H (I) decomposition (Ramachandran V.S. 1977). The endothermic
effect at 708 °C characterizes the decomposition of lime carbonate formed during hardening. The
decomposition of unreacted limestone proceeds with an endothermic effect at 733 °C. The slight
endothermic effect at 850 °C is characteristic for C-S-H (I) (Ramachandran V.S. 1977).

Figure 9. Simultaneous TG-DTA-DSC data the blended cement stone with 20% of complex
additive based on calcined mixture of kaolinitic clay and limestone

The content of portlandite in the sample with the complex additive declines by a factor of nearly 2 in
comparison with the OPC sample, the fact that suggests good pozzolanic properties the calcined
mixtures. According to NTCC (2014) & Rovnanikova P. et al. (2011) surface reactions are formed
between calcium carbonate and portlandite, leading to hardening of the stone structure. In the sample
2, the formation of hydrosilicates С-S-H (I) is observed. The undecomposed limestone acts like a
substrate for the formation of hydrated clinker mineral compounds.

The XRD pattern points out that the hydromonosulfoaluminate contained in the control sample, is
absent in a sample with the complex additive. In place of it, however, calcium
hydromonocarboaluminate is observed in sample 2.

The loss of weight in the field of low-temperature endothermic effects increases with the introduction
of complex additive in comparison with the control sample. It confirms the formation of accreting
amounts of calcium hydrosilicates and hydroaluminosilicates of various composition, and of
hydrocarboaluminate in samples with high limestone content.

4. CONCLUSIONS

The calcination of mixtures based on kaolinitic or polymineral clay and limestone with a calcite content
99 % at a temperature of 720-800 °C leads to the formation of C2S, and increases the quantity of
amorphous phase. At the same time, no free CaO is identified on the XRD pattern of calcined
 15th International Congress on the Chemistry of Cement
Prague, Czech Republic, September 16–20, 2019

mixtures, hence demonstrating its binding by products of clay mineral decomposition - kaolinite for
example - in new growths like C2S or CA, and new growths in amorphous phase. The formation of
accreting amounts of calcium silicates and aluminates in the calcined mixtures makes it possible to
receive the complex additives for blended cement, replacing up to 20 % of OPC with no loss of
durability.

The optimum parameters of calcined mixtures based on kaolinitic or polymineral clay and limestone
arrived at by the method of mathematical experiment planning depend on the chemical and
mineralogical composition, the physical and technological properties of the raw materials, and on the
degree of component dispersion.

The introduction of complex additives based on calcined mixtures of clays and limestone leads to the
formation of an accreting amount of calcium hydrosilicates and hydroaluminosilicates of various
composition, and of hydrocarboaluminate in samples with high carbonate content, hence decreasing
the quantity of ettringite and portlandite.

5. ACKNOWLEDGEMENTS

This research received no specific grant from funding agencies in the public, commercial or not-for-
profit sectors.

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Ermilova EYu, Kamalova ZA, Rakhimov RZ, & Stoyanov OV (2015). Blended Portland cement with
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Ermilova EYu, Kamalova ZA, Rakhimov RZ, Stoyanov OV, Hantemirov AG, Gabbasov DA, &
Akhtariev RR (2017). The investigation of the influence of rate of temperature rise the thermoactivation
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