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Conduction calorimetric studies of ternary binders based
on Portland cement, calcium aluminate cement and calcium
sulphate
David Torre
´ns-Martı
´n•Lucı
´a Ferna
´ndez-Carrasco •
Marı
´a Teresa Blanco-Varela
Received: 6 November 2012 / Accepted: 21 January 2013 / Published online: 12 February 2013
Akade
´miai Kiado
´, Budapest, Hungary 2013
Abstract Different binders of Portland cement, calcium
aluminate cement and calcium sulphate (PC/CAC/C
S)
have been investigated to determinate the influence the
CAC and C
S amount in the reactions mechanism. Several
mixtures were studied, ratios of 100, 85/15 and 75/25 of
PC/CAC with 0, 3 and 5 % of C
S. Conduction calorimetric
technique was used to follow the hydration during 100 h.
The XRD and FTIR techniques were used as support in the
analysis of the hydration products. The results have shown
that the studied ternary systems form an extra amount of
ettringite, and changes in the reactions mechanism with
respect to a PC. The reactions mechanism depends on the
CAC and C
S amount present in the different binders.
Keywords Portland cement Calcium aluminate
cement Calcium sulphate Ternary systems
Ettringite Reaction mechanisms
Introduction
Ternary binders based on Portland cement (PC), calcium
aluminate cement (CAC) and calcium sulphate (C
S) have
different hydration mechanisms than products based purely
on PC or CAC [1]. The typical applications are as tile
adhesives and self-leveling compounds and a possible
requirement profile could be: fast setting, fast strength
development, avoiding conversion of CAC hydrates, reaches
final strength after 1 day, high hydrophilic properties (ready
for early installation) and shrinkage compensation [2]. It has
been reported that the microstructure of these systems is
very complex, only few works are present in the literature
[3–5] that have suggested that the hydration processes are
dependent on PC/CAC and CAC/C
S ratios; however, still
there are some unknowns concerning the hydration mecha-
nism processes in these systems.
The aluminates from PC (Eq. 1) and CAC (Eq. 2)react
with the sulphates. The rapid setting produced in the mix-
tures of PC/CAC is due mainly to the ettringite formation
[3]. Several studies [6–8] have shown that the mechanisms
of these reactions are complex, where any change in the
portions of CAC or C
S modifies these mechanisms. At first
ages the hydration is dominated by ettringite formation.
C3Aþ3C
SHxþð32 3xÞH!C3A3C
SH32 ð1Þ
CA þ3C
SHxþ2C þð32 3xÞH!C3A3C
SH32 ð2Þ
The hydrates formed in PC/CAC mixtures depend on the
portions of the two cements. For low amounts of CAC,
\20 %, the C–S–H gel is the dominant hydrate and the
alumina is present in the form of ettringite, monosulfoa-
luminate or C
4
AH
x
. For these mixtures the metastable
hydrates C
2
AH
8
and CAH
10
have not been detected, so the
conversion of these to C
3
AH
6
is irrelevant. On the other
hand, when the amount of PC is lower than 20 %, the
hydrates obtained are the typical products of normal CAC.
In between these two limits the development of hydrates is
complex, and it is thought to be formed aluminosilicates of
C
2
ASH
8
type [9].
The blended mixture of CAC and C
S are used to
develop materials with dried and fast hardening [9]. The
D. Torre
´ns-Martı
´n(&)L. Ferna
´ndez-Carrasco
Dep. de Construccions Arquitecto
`niques I, Universitat
Polite
`cnica de Catalunya, Diagonal 649, 08028 Barcelona, Spain
e-mail: david.torrens@upc.edu
M. T. Blanco-Varela
IETcc—CSIC, Serrano Galvache 4, 28033 Madrid, Spain
123
J Therm Anal Calorim (2013) 114:799–807
DOI 10.1007/s10973-013-3003-9
main hydration products in these mixtures are ettringite and
aluminium hydroxide according with Eq. 2. When the C
S
is consumed totally, the CA reacts with the ettringite
formed obtaining monosulfoaluminate (Eq. 3)[3].
6CA þC3A3C
SH32 þ16H !3C3AC
SH12 þAH3ð3Þ
The development of hydrates and of mechanical properties
depends on the relative portions of the components and
also on the type of C
S, i.e. hemihydrate, gypsum or
anhydrite. The kind of C
S, and the different dissolution
rates, could be a key for morphology or special distribution
of the hydrates. So for hemihydrate and gypsum (rapid
dissolution rate), the solution would be poor in Al
3?
and
short crystal of ettringite is formed in the surface of CAC
grains. But in the anhydrite case (slow dissolution rate), the
lower dissolution of C
S makes the SO
4
2-
the limit param-
eter and it lead to the growth of long thin needles of
ettringite [10].
In the ternary systems, PC/CAC/C
S, two zones have
been described in the literature. A zone rich in CAC/C
S,
that provide fast hardening kinetics, self drying capacity
and volume variations control. Most of self-leveling scre-
eds, high tech tile adhesives and rapid repair mortar are
based on this technology. The second zone is rich in PC
and is characterized by better hardening profile and
shrinkage compensation, and they would find applications
as fast hardening cement and technical mortars, for repair
concrete and protection utilities [11].
In order to contribute to the understanding on the
hydration mechanisms in these ternary systems on the
richer area of PC in the PC/CAC/C
S ternary system, a
conduction calorimetric analysis was performed studying
selected ratios of PC/CAC with three C
S different per-
centages (0, 3 and 5 %). The X-ray diffraction (XRD) and
FTIR techniques were used to detect the developed phases.
Materials and methodology
Materials
The materials used in this research were a PC type I 52.5R,
Electroland CAC and a commercial C
S from Algiss. The
X-ray fluorescence technique (XRF) was used to determine
the chemical composition of the cements (Table 1). Both
cements and the C
S were analyzed by the XRD (Fig. 1)
technique in order to verify its mineralogical composition.
C
S used is in the form of hemihydrate. According with
recent studies [12], this kind of C
S have a faster dissolution
rate that provides an ettringite formation early.
Methodology
The PC/CAC/C
S compositions selected from previous
works [1,3,4]. Three ratios PC/CAC are selected 100, 85/
15 and 75/25; in order to see the influence of sulphate
content in these mixtures, 0, 3 and 5 %wt of C
S are ana-
lyzed. The pastes were prepared with w/c ratio kept con-
stant at 0.4.
The heat of hydration generated by the different blended
mixture was monitored with a TA instruments TAM AIR
conduction calorimeter, under the following conditions:
temperature 25 C; binder mass 5 g; mixing water mass
2 g. The sample was prepared mixing the blended mixture
and water for 3 min in the vial and after that, it was
introduced into the calorimeter sample compartment. The
measure was recorded during 100 h.
In parallel, exact blended pastes were treated at different
times with acetone/ethanol [13] to detain hydration and
then characterized for mineralogy by means of XRD with a
PANalytical X’Pert PRO MPD difractrometer (model DY
3197) equipped with a secondary graphite monochromator
(CuK
a12
, flat sample) and standard operating conditions of
40 kV and 50 mA; the step side used was 0.020, 1 s per
step, in the 5–60 2hrange., and infrared spectroscopy
analysis with a NICOLET 6700 ThermoScientific spec-
trometer with a detector DGTS CsI. The register was
realized in the region of medium infrared (4,000–
400 cm
-1
) with a spectral resolution of 4 cm
-1
. The
samples for FTIR were prepared using pellets procedure
(1 mg sample/300 mg KBr). Raman spectroscopy was also
used, micro-Raman measurements were performed at room
temperature using an inVia Raman microscope equipped
with a Leica microscope, a CCD camera, and laser at
532 nm with 10 mW laser powder. Typical spectra from
90–4,000 cm
-1
were recorded with a resolution of 4 cm
-1
.
The time acquisition was 10 s and five scans were recorded
to improve the signal-to-noise ratio.
Results and discussion
The rates of heat evolution of PC and CAC cements are
depicted in Fig. 2. It shows typical plot for the PC and
CAC [14]. The PC plot has four stages: dissolution,
induction, acceleration and post-acceleration. In the first
period, C
3
A reacts immediately with water and C
Sin
solution to form an AFt phase. An aluminate rich gel,
probably AFm phases C
4
AH
13
and C
2
AH
8
forms on the
surface and short ettringite rods nucleate at edge of gel and
in solution [15]. At this stage, the degree of reaction of C
3
S
is very small [6], and the C
S in form of hemihydrate may
also react with water to form gypsum. The heat achieves its
800 D. Torre
´ns-Martı
´n et al.
123
highest value (124.87 W g
-1
). After the heat down in the
induction period, the concentration of Ca
2?
ions in solution
increases, CH and C–S–H (outer product) starts to nucleate.
Ettringite needles grow and nucleate slowly. This period
achieves its lowest value to 1.3 h. The processes lead to a
change from plastic to rigid consistency (set) during
acceleration period, which corresponds to the main reaction
of C
3
S and the fast formation of C–S–H (outer product) and
CH. Ettringite formation starts again and at the end of the
acceleration period, inner C–S–H starts to be formed [16].
At 5.8 h the acceleration period achieve heat of
20.99 W g
-1
. The last stage (post-accelaration period) is
due to C
3
A reacting with AFt to form AFm phases (mo-
nosulfoaluminate). By the other hand, the plot of CAC
hydration shows one process due to CA hydration. This
process is very exothermic occurring at 10.11 h with a
value of 86.30 W g
-1
. Figure 3shows the accumulated
heat for these cements to 100 h.
The CAC effect
The CAC effect in the PC heat hydration is shown in
Fig. 4a. For the 85/15 mixture we can see a new process at
1.4 h and a delayed to acceleration period to 10.5 h, where
the silicates are hydrated. In Fig. 5the FTIR spectra for 1
and 2 h, before and after the new process are shown. The
differences between spectra are due to aluminate compounds
formation. For the 2 h spectrum appears several bands that
are not in the 1 h spectrum. There is a very weak signal
towards 3,672 cm
-1
due to stretching vibrations of free OH
associated with C
3
AH
6
[17]. There is also a weak band on
425 cm
-1
due to AlO
6
octahedral of C
3
AH
6
[18]. Other
bands appear and these can be associated with the alumin-
ium hydroxide as gibbsite [19]; a band on 3,623 cm
-1
is
better defined and there is a shoulder towards 3,531 cm
-1
;
these bands are due to O–H stretching. A weak shoulder
appears on 1,010 cm
-1
due to Al–O bonds of aluminium
hydroxide. Therefore, we assign the new process to calcium
aluminates hydration.
Table 1 Chemical composition of raw materials
CaO SiO
2
Al
2
O
3
Fe
2
O
3
MgO TiO
2
MnO K
2
OP
2
O
5
CP 63.25 19.56 5.04 3.50 1.96 0.22 0.04 0.75 0.06
CAC 36.54 4.83 40.55 15.50 0.50 1.68 0.02 0.05 0.09
10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40
Gff HC
C3
C2
A3
C3
C3
C3 + C2
C3 + C2
C3 + C2
C
A
A
AA
AA
A
A
ff ff
ff
ff
ff
Y
Y
H
H
H
H
H
2
θ
/°
CS
–
CAC
CP
Fig. 1 Diffraction patterns of raw materials C3:C
3
S, C2:C
2
S,
A3:C
3
A, ff:C
4
AF, A:CA, Y:C
2
AS, H:CaSO
4
0.5H
2
O, G:CaSO
4
2H
2
O, C:CaCO
3
0 5 10 15 20 25
0
10
20
30
40
50
60
70
80
90
100
Heat flow/W g
–1
Time/h
CAC
PC
Fig. 2 Plot of rate of heat development for the raw materials
010 20
0
400
Heat/J gr –1
Time/h
CAC
CP
350
300
250
200
150
100
50
30 40 50 60 70 80 90 100
Fig. 3 Total heat evolution of raw materials
Conduction calorimetric studies of ternary binders 801
123
The heat flow development for 75/25 mixture has a
higher delayed in acceleration period, it appears at 23 h
and a new process is visible before, towards 10 h. By
means of XRD we did analysis of the sample at 9 and 11 h
(Fig. 6). In these diffraction patterns how the ettringite is
transformed in AFm phases can be seen. It is due to total
consumed C
S and leading the CA and C
3
A present to react
with the ettringite formed. The process due to aluminate
hydration present in 85/15 composition disappears. This is
probably due to the fact that aluminates react with the
ettringite to form monosulfoaluminate.
0510
15 20 25
Heat flow/W g–1
Time/h
30 35 40 45 50 0 5 10 15 20 25
Time/h
30 35 40 45 50
0 5 10 15 20 25
Time/h
30 35 40 45 50
0510
15 20 25
Time/h
30 35 40 45 50
300
250
200
150
100
50
0
20
15
10
5
300
250
200
150
100
50
0
20
15
10
5
300
250
200
150
100
50
0
20
15
10
5
300
250
200
150
100
50
0
15
5
Heat flow/W g–1
Heat flow/W g–1
Heat flow/W g–1
100 0 %
85/15 0 %
75/25 0 %
100 0 %
100 3 %
100 5 %
85/15 3 %
85/15 5 %
85/15 0 %
75/25 3 %
75/25 5 %
75/25 0 %
(a) (b)
(d)(c)
Fig. 4 Rate of heat evolution development for the different blended mixtures. aCP/CAC bCP/CS c85/15 d75/25
4000 3800 3600 3400 3200 1200 1000 800 600 400
Wavenumbers/cm–1
Transmitance/a.u.
1 h
2 h
C3AH6
AIO6
AH3
AI–O
Fig. 5 Infrared spectra for 85/15 0 % CS at 1 and 2 h
5 6 7 8 9 10 11 12 13 14 15
11 h
9 h
E
ff
Afm
2
θ
/°
Fig. 6 XDR to 75/25 0 % CS at 9 and 11 h E:ettringite, AFm:
monosulfoaluminate, ff:C
4
AF
802 D. Torre
´ns-Martı
´n et al.
123
In comparison, the three blended mixtures show increase
in the dissolution peak when the amount of CAC is greater
but the main difference observed is the silicates hydration
delay. This effect was seen previously by Gu et al. [8] and
relating with the strength development. They studied
blended mixtures with PC/CAC ratios of 92.5/7.5, 80/20
and 20/80. The delay in the silicate hydration makes lower
strength development. According with Gu this delay is
produced by ettringite layer around the anhydrous grains.
This barrier layer does the hydration as a diffusion process
slower than the normal hydration. The layer is broken when
the ettringite transforms in AFm. In the case of this
research the formation of ettringite layer is visible for
85/15 and 75/25 ratios. In the first, 85/15 ratio, this layer is
little and delays the silicate hydration but not the locks. On
the contrary in the 75/25 sample, the ettringite layer formed
is bigger and until the transformation occurs at AFm pha-
ses, the silicate hydration does not occur.
The total heat accumulated in the hydration reactions is
visible in Fig. 7a. The heat accumulated is higher when the
amount of CAC grows. This effect is due to the extra et-
tringite formation. So for the same heat the blended mixture
with more CAC takes less time. The 75/25 composition has
a plateau at 6 h, due to the barrier layer formation, and the
heat increases again when this layer is broken.
The C
S effect
In Fig. 4b the rate evolution for the composition 100 with
0, 3 and 5 % of C
S are shown. The profiles of the different
plots are similar. The process due to AFt transformation to
AFm present in the composition with 0 % in post-accel-
eration stage disappears when the C
S amount grows. The
extra C
S amount reacts with total C
3
A present, preventing
the reaction between C
3
A and ettringite from occurring.
The acceleration period is also slightly modified, when the
C
S amount grows, this stage is lower.
Previous studies [20] found a delay in the aluminate
reactions when the C
S appearing after the silicate hydration
increased. In this work we have not seen this effect, we
have found a lower heat in the dissolution peak for medium
concentration. The dissolution peak is higher for the 5 %
than 0 %; in the case of 3 % the dissolution peak is lower.
Fig. 8shows the infrared spectrum for 3 % composition at
9 min, after dissolution peak. This spectrum has bands
010 20
Time/h
30 40 50 60 70 80 90 100 01020
Time/h
30 40 50 60 70 80 90
01020
Time/h
30 40 50 60 70 80 90
100
100 01020
Time/h
30 40 50 60 70 80 90 100
400
350
300
250
200
150
100
50
0
400
350
300
250
200
150
100
50
0
400
350
300
250
200
150
100
50
0
400
350
300
250
200
150
100
50
0
(a) (b)
(d)
(c)
Heat/J g –1
Heat/J g –1
Heat/J g –1 Heat/J g –1
100 0 %
85/15 0 %
75/25 0 %
100 0 %
100 3 %
100 5 %
85/15 3 %
85/15 5 %
85/15 0 %
75/25 3 %
75/25 5 %
75/25 0 %
Fig. 7 Plot of total heat accumulated from blended with 0 % CS aCP/CAC bCP/Cs c85/15 d75/25
Conduction calorimetric studies of ternary binders 803
123
associated to ettringite; stretching vibrations of free OH
towards 3,410 and 3,642 cm
-1
[21] and stretching vibra-
tions due S–O in 1,120 and 620 cm
-1
[22]. There are also
bands due to different forms of C
S; for the gypsum there is
stretching vibrations due to S–O towards 600, 670 and
1,141 cm
-1
, stretching vibrations about 3,540 cm
-1
for
O–H and bending vibrations due to O–H in 1,620 and
1,683 cm
-1
. For the hemihydrate there is stretching
vibrations due to S–O towards 1,192 cm
-1
and bending
vibrations due to O–H in 1,620 cm
-1
[23]. There is also a
band on 883 cm
-1
with a shoulder on 842 cm
-1
, these
signals are due to AlO
4
tetrahedral [18]. There is a strong
band present towards 930 cm
-1
, this band is due to Si–O
bonds present in the anhydrous silicate. By means of XRD
the absence of portlandite was checked. So after dissolution
peak there are still reactive phases for ettringite formation.
Therefore, not all aluminate reactions have occurred. This
spectrum is the same for the other compositions at 9 min, 0
and 3 %, there is the same situation after dissolution peak.
Fig. 7b shows the total heat accumulated. We can see a
decrease of the accumulated heat with C
S increase. Prob-
ably due to a less silicate hydration, for the 3 and 5 %
blended mixtures the heat is lower from 10 h when the
principal silicate hydration is exceeded.
Ternary system
The ternary calorimetric study is focused in the ratios 85/15
and 75/25 with 3 and 5 % of C
S. Fig. 4cshowstheheatflow
for 85/15 ratio with 0, 3 and 5 % of C
S. In the composition
with 0 % silicate hydration appears at 11 h, for the compo-
sitions with 3 and 5 % appears at 5 h before the normal PC
hydration. In the composition with 3 % C
Shavetwonew
processes, respecting binary systems. The plot shows a
shoulder after the acceleration stage, at 7.5 h and other
process in post-acceleration stage at 30.5 h. In Fig. 9the
infrared spectra and diffraction patterns made at 6 and 9 h, the
limits time for the first new process, are shown. In the infrared
spectrum we can see differences in the bands associated to
silicates. For the 6 h there is a broad band towards 954 cm
-1
due to stretching vibrations of Si–O [22]. In this band, the
vibrations of the anhydrous phases and the gel C–S–H are
seen. For the 9 h this band is centred in 983 cm
-1
indicating a
lower anhydrous signal and higher contribution of gel C–S–
H. Towards 521 cm
-1
is the band due to bending vibrations
for Si–O-Si associated anhydrous calcium silicates [23]. This
band is lower for the 9 h spectrum.
The second new process is in the post-acceleration stage
at 30.5 h. In Fig. 10 the diffraction patterns for 24 and 48 h,
the limits for this process, are shown. The diffraction lines
due to ettringite down, there is also a decrease in the CA
diffraction. On the other hand, at 48 h monosulfoaluminate
diffraction lines appear. Therefore, this process at 30 h is
probably due to reaction between ettringite and CA to form
monosulfoaluminate. In Fig. 7(c) the total heat accumulated
which is lower when the C
S amount increase are shown.
The heat generated for the 75/25 ratio, with 0, 3 and
5 %, is in Fig. 4d. The profiles are not similar and appear
to be a different process for each composition. So for
composition with 3 % C
S the silicate hydration is earlier
and lower than composition with 0 % C
S. Following the
hydration with FTIR technique the reactions that occur can
be seen.
In Fig. 11 the infrared spectra for 9 min, 4, 6 and 24 h
are shown. These times give all the process that occur in
75/25 3 % C
S hydration. After dissolution peak (9 min) the
infrared spectrum has weak bands associated to ettringite;
stretching vibrations due to free OH towards 3,640 cm
-1
,
portlandite has not formed yet and stretching vibrations due
to S–O on 1,120 cm
-1
. There are also strong bands asso-
ciated to different C
S forms. For the gypsum stretching
4000 3800 3600 3400 3200 600 300
Wavenumbers/cm
–1
9001800 1500 1200
Transmitance/a.u.
S–O
O–H
O–H
S–O
δ
υ
υ
υ
Fig. 8 Infrared spectrum of composition 100 with 3 % CS at
9 min
4000 3800 3600 3400 3200 600 400
Wavenumbers/cm
–1
800
1000
1200
Transmitance/a.u.
Si–O
Si–O–Si
δ
υ
6 h
9 h
Fig. 9 Infrared spectra for 85/15 3 % CS at 6 and 9 h
804 D. Torre
´ns-Martı
´n et al.
123
vibrations are due to free OH about 3,532 and 3,406 cm
-1
,
bending vibrations due to O–H on 1,683 and 1,623 cm
-1
,
stretching vibrations due to S–O towards 1137, 671 and
600 cm
-1
. For the hemihydrate a shoulder in 1,197 cm
-1
is due to stretching vibrations S–O and the bending
vibrations in 1,683 cm
-1
are due to O–H. The other bands
present in the spectrum are of anhydrous phases. Hence
after the dissolution peak small amount of ettringite was
formed.
After the process between dissolution peak and induc-
tion period, the infrared of 4 h studied sample do not
present the C
S absorption bands but the stronger ettringite
bands. The broad O–H band move to 3,426 cm
-1
due to
ettringite formation and the sulphate have an only band
centred in 1,120 cm
-1
.
At 6 h, this is on the induction period, the spectrum
shows bands associated to C
3
AH
6
; stretching vibrations of
O–H towards 3,675 cm
-1
and a band at 422 cm
-1
due to
AlO
6
octahedral. The bands associated to gibbsite were
also present: stretching vibrations due to O–H at 3,623
(weak) and 3,534 (broad) cm
-1
. The anhydrous signals of
aluminates at 846 and 450 cm
-1
disappear. The hydration
of silicates begin but is weak, the band due to stretching
vibrations Si–O evolves from 925 towards to 957 cm
-1
.
The 24 h sample is after the acceleration stage. This
infrared spectrum shows the silicate hydration, the band
due to Si–O vibration is in 969 cm
-1
, but before this
hydration there is a process towards 12 h. The infrared
spectrum shows the transformation of AFt to AFm. Still
there are bands associated to ettringite but bands associated
to monosulfoaluminate appear; stretching vibrations due to
S–O towards 1,163 and 1,110 cm
-1
. This reaction, prob-
ably, produces the process at 12 h and unlocking the sili-
cate hydration.
6
48 h
24 h
2
θ
/°
810 12 14 16 18 20 22 24 26 28 30
Intensity/u.a.
EMff EEEE
EEE
E
E
ff
P
P
P
P
C
C
A
A
Fig. 10 Diffraction patterns for 85/15 3 % CS at 24 and 48 h
E:ettringite, P:portlandita, ff:C
4
AF, C:CaCO
3
, A:CA, M:mono-
sulfoaluminate
4000 3800 3600 3400 3200 600 300
Wavenumbers/cm–1
9001500 1200
Transmitance/a.u.
S–O
O–H
δ
υ
6 h
4 h
18003000
24 h
9 minutes
S–O
υ
O–H
υ
AIO6
C3AH6
AH3
AFm
free O–H
Fig. 11 Infrared spectra for 85/15 5 % CS at 9 min, 4, 6 and 24 h
4000 3600 3200 600 300
Wavenumbers/cm–1
9001200
Transmitance/a.u.
S–O
υ
O–H
υ
free
2800
O–H
υ
S–O
υ
3
4
Fig. 12 Infrared spectra for 75/25 5 % CS at 1 h
1000
Wavenumbers/cm–1
Intensity/u.a.
800 600 400 200
AIO6
Fig. 13 Raman spectra for 75/25 5 % CS at 12 h. In the CS the S
have a overlap
Conduction calorimetric studies of ternary binders 805
123
The plot generated for the 75/25 binder show a different
profile than others with 5 % C
S. The principal process due to
silicate hydration is advanced and provides more heat (5.20 h,
10.46 W g
-1
). These values are similar to a PC normal. For
the first hour the ettringite formation is evident in this IR
spectrum (Fig. 12).Between12and20hthereisaprocess.
Both infrared spectra and diffraction patterns show no dif-
ferences between one process to another. For this case use
Raman spectroscopy which appreciate differences. In the
Raman spectrum at 12 h (Fig. 13) we can see a band towards
353 cm
-1
. This signal is due to AlO
6
present in the C
3
AH
6
.
Hence this process may be due to aluminate hydration.
In Fig. 7d the total heat accumulated which is lower when
the C
S amount increases is shown. The binders with 0 and 3 %
of C
S have a plateau towards 10 h due to monosulfaoalumi-
nate formation. This process is not in the composition with 5 %
of C
S because the amount of calcium sulphate is higher.
Reaction mechanisms
Reaction mechanisms that occur in these mixtures are
different and depend on the initial portions in the system.
Binary system PC/CAC
In this system there are two situations; low or high CAC
amount. In the case of low amount of CAC, the first process
is the ettringite formation due to the reaction between the
aluminates of CAC with the C
S present in the PC (Eq. 4).
CA þ3C
SHxþð38 3xÞH!C3A3C
SH32 þ2AH3ð4Þ
When the C
S is consumed, the rest of aluminate present in the
system reacts with the water (Eq. 5). In this system the
formation of metastable forms (hexagonal) is not detected, and
only stable form (cubic) is present. Reason for that can be the
heat released due to the previous explained reactions. Garces
[24] found this effect, when CAC mortars were cured to
elevated temperatures. Finally the silicates hydration occurs.
CA þ12H !C3AH6þ2AH3ð5Þ
Moreover when the CAC amount is high, the first process
is the same; ettringite formation (Eq. 4). The next process
is the AFm formation (Eq. 6), unlocking the silicate
hydration (Eq. 7).
6CA þC3A3C
SH32 þ16H !3C3AC
SH12 þAH3ð6Þ
C3SþH!CSHþCH ð7Þ
Binary system PC=C
S
In this binder the ettringite formation is the first process.
The ettringite is formed by the reaction between C
3
A and
C
S (Eq. 8). The next process is the silicate hydration
(Eq. 7). Due to the extra contribution of C
S the AFm
formation does not occur.
C3Aþ3C
SHxþð32 3xÞH!C3A3C
SH32 ð8Þ
Ternary system PC=CAC=C
S
In these binders there are several situations. If the PC is the
main compound, with the CAC and C
S amounts low; the
hydration development is similar at normal PC hydration.
The process generated are: ettringite formation, silicate
hydration and AFm formation.
In the case CAC amount is high and C
S amount is low;
the first process is the ettringite formation (Eq. 4). The next
is the AFm formation (Eq. 6), unlocking the silicate
hydration (Eq. 7).
The last case is when the CAC and C
S amounts are high.
One more time, the ettringite formation (Eq. 4) is the first
process. The following process which occurs is the silicate
hydration (Eq. 7). Finally the aluminate hydration (Eq. 5)
occurs with unreacted aluminates present in the system.
Conclusions
Based on the experimental results, it could be concluded that
the initial amount of calcium aluminate cement and calcium
sulphate play a key role in the hydration of PC/CAC/C
S
mixtures, and especially affect the formation of ettringite.
The following conclusions can be drawn from the
present research:
•The mechanism of reaction depends on the amount raw
materials put in the different binders.
•The CAC addition produced a delay in the silicate
hydration due to aluminate hydration or ettringite
formation. It depends on CAC amount.
•When the C
S amount grows there are no changes in the
Portland hydration and the only difference is an extra
amount of ettringite.
•Depending on CAC and C
S amount present in the
system, the reactions occur before or after. The main
being ettringite formation.
Acknowledgements The authors thank the support for this research
by the MICINN (Ministerio de Ciencia e Innovacio
´n) with the
BIA00767-2008. The authors also want to thank the IEM-CSIC for
ease when making Raman measurements.
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