quantification of hydration phases in supersulfates cements.pdf
TRANSCRIPT
Advances in Cement Research, 2011, 23(6), 265–275
http://dx.doi.org/10.1680/adcr.2011.23.6.265
Paper 900041
Received 26/09/2009; revised 09/08/2010; accepted 04/11/2010
Thomas Telford Ltd & 2011
Advances in Cement ResearchVolume 23 Issue 6
Quantification of hydration phases insupersulfated cements: review and newapproachesGruskovnjak, Lothenbach, Winnefeld et al.
Quantification of hydrationphases in supersulfated cements:review and new approachesAstrid GruskovnjakEmpa, Swiss Federal Laboratories for Materials Science and Technology,Department for Concrete and Construction Chemistry, Dubendorf,Switzerland
Barbara LothenbachEmpa, Swiss Federal Laboratories for Materials Science and Technology,Department for Concrete and Construction Chemistry, Dubendorf,Switzerland
Frank WinnefeldEmpa, Swiss Federal Laboratories for Materials Science and Technology,Department for Concrete and Construction Chemistry, Dubendorf,Switzerland
Beat MunchEmpa, Swiss Federal Laboratories for Materials Science and Technology,Department for Concrete and Construction Chemistry, Dubendorf,Switzerland
Renato FigiEmpa, Swiss Federal Laboratories for Materials Science and Technology,Laboratory for Analytical Chemistry, Dubendorf, Switzerland
Suz-Chung KoHolcim Group Support Ltd, Product Innovation and Support, Holderbank,Switzerland
Michael AdlerHolcim Group Support Ltd, Product Innovation and Support, Holderbank,Switzerland
Urs MaderUniversity of Bern, Institute of Geological Sciences, Rock-Water-InteractionGroup, Bern, Switzerland
Quantification of the progress of hydration of supersulfated cements (SSC) may be approached in two ways: (a) from
recording the increasing dissolution of the slag particles directly, and (b) indirectly from quantifying the formation of
the hydration phases. Image analysis based on backscattered electron imaging in a scanning electron microscope
(SEM), the dissolution of hydrates (EDTA), differential thermal analysis (DTA) and sulfide concentration (SP) were
used to quantify the dissolution of the slag particles; selective extraction of hydrates by sodium carbonate (SE), X-ray
diffraction (XRD) with Rietveld analysis and thermogravimetric (TGA) refinement methods were used to quantify the
amount of hydration products formed. SEM-based image analysis was found to be a direct and promising way for
the quantification of slag particles. With the help of selective extraction by sodium carbonate (SE), it was possible to
quantify the amorphous C–S–H phase in SSC. Mass balance calculations constrained by thermodynamic stability were
used to calculate the amount of reacted slag in the system. XRD Rietveld and TGA methods were used to assess the
amounts of specific hydration products formed in SSC but did not allow an absolute quantification of the amount of
slag reacted. Other methods such as the dissolution of the hydrates by EDTA and DTA were not found to be reliable
due to intrinsic problems.
IntroductionThe activation of ground granulated blast furnace slag (GGBFS)
by sulfates was first described by Kuhl in 1909 (Kuhl and
Schleicher, 1952). Generally, the supersulfated cements (SSC)
consist of 80–85 wt% of slag mixed with 10-15 wt% of
anhydrite and an alkaline activator such as Portland cement
clinker (Taylor, 1997). SSC shows an increased resistance to
sulfate attack and exhibits a lower heat of hydration compared to
ordinary Portland cement (OPC). The main hydration products
are C–S–H phase, ettringite, gypsum and some hydrotalcite can
be observed as well.
Quantification of phases in cementitious systems is mainly
focused on raw materials (Taylor, 1997). There are some common
methods for the quantification of the phase composition in
clinker: quantitative X-ray diffraction analysis by Rietveld refine-
ment (Walenta and Fullmann, 2004), optical microscopy using
point counting, the Bogue method and chemical or physical
methods for the separation of phases (Taylor, 1997).
For a better understanding of the hydration processes in cementi-
tious materials, it is important to quantify the amount of
hydration products formed as a function of time and thus to
determine the degree of hydration. In OPC systems, the progress
of hydration is often monitored by X-ray diffraction (XRD),
measuring directly the consumption of the clinker phases and the
formation of hydrates. In slag systems, the glassy part of the slag
as well as the main hydration product (C–S–H) are XRD-
amorphous, which makes the quantification of the hydration
progress a difficult task.
265
Thus, there is a lack of reliable and efficient methods for the
quantification of the phases in hydrated slag cements, even
though several methods have been applied in a number of studies:
selective dissolution by EDTA for blended cements was briefly
reviewed by Lumley et al. (1996); for supersulfated cements
selective dissolution by EDTA has been used by Matschei et al.
(2005) and Stark et al. (1990). Additionally, the exothermic
reaction from the devitrification process was measured (DTA)
and used to estimate the degree of reaction of slag (Rosina et al.,
1966; Schneider and Meng, 2000; Schramli, 1963).
In the present study, the methods used for slag cement systems
mentioned above were reviewed and compared with each other in
order to determine the degree of reaction in supersulfated cement.
In addition, backscattered electron imaging, Rietveld refinement
of XRD patterns and thermogravimetric analysis have been used
for the quantification of hydration in supersulfated cements.
Refinements of the thermogravimetric analysis by manual and
mathematical fitting, as well as a new selective extraction method
using sodium carbonate and a method based on the sulfide
concentration in the pore solution have been developed and
applied to supersulfated cements.
Not all examined methods have provided useful results for
obtaining an estimation of the amount of formed hydration
products, but the combination of some of them is suitable.
Experimental work
Materials
The experiments were carried out with a SSC composed of
85 wt% of a highly reactive (HR) ground GBFS and 15 wt%
natural anhydrite, activated additionally by 0.5 wt% KOH. A
water/solid (w/s) ratio of 0.315 was applied. The hydration of the
pastes was stopped with isopropanol and the powder was dried
for 3 days at 408C.
Pure hydrate phases were used as reference materials. C–S–H
with different C/S ratios was synthesised by mixing Ca(OH)2
(puriss.; Riedel-de Haen) and silica fume (Aerosil 200) with
water, followed by 1 week of rest and subsequent drying for 3
days at 408C.
C=S ratio of 1:0 > 5:6 g Ca(OH)2
þ 6:0 g SiO2 þ 30 ml H2O
C=S ratio of 1:4 > 3:9 g Ca(OH)2
þ 3:0 g SiO2 þ 20 ml H2O
For the production of Al-ettringite, stoichiometric amounts of
CaO and Al2(SO4)3:16H2O (purum p.a.; Fluka) were mixed with
water. CaO was obtained from burning Ca(OH)2 in a laboratory
furnace overnight (, 14 h) at 10008C. After 1 week reaction
time, the ettringite was dried for 3 days at 408C.
For the synthesis of hydrotalcite, the procedure described in
Reichle (1986) was followed. A detailed description can be found
in Johnson and Glasser (2003).
Commercial pure gypsum was used as reference material
(calcium sulfate dihydrate, Fluka, purum p.a.)
Methods
Measurement parameters
The chemical composition of the raw materials used in the SSC
was analysed by X-ray fluorescence analysis (XRF) using a
Philips PW 2400 instrument.
The mineralogical composition of the samples was determined
with XRD by using a Panalytical X’Pert Pro powder diffract-
ometer equipped with an X’Celerator detector on powders ground
to , 63 �m; samples used for Rietveld analysis had been ground
to , 40 �m. Measuring conditions: 40 kV; 40 mA; 2Ł angles 5 to
808; step size: 0.0178; time/step, 20 s; scan speed, 0.18/s; time,
11.5 min/sample. The software applied for the Rietveld refine-
ment method was X’Pert HighScore Plus V. 2.0a from PANaly-
tical. The single crystal structures of the crystalline phases were
taken from the Inorganic Crystal Structure Database (ICSD,
2006).
TGA analyses were performed in alox (Al2O3) cups under N2
atmosphere with powdered samples ground to , 63 �m at a
heating rate of 5 K/min up to the desired temperature (Mettler
Toledo TGA/SDTA 581).
DTA measurements were performed under Argon atmosphere
with powdered samples ground to , 63 �m at a heating rate of
20 K/min up to 11008C (TGA Netzsch STA 409 CD). Alox
(Al2O3) was used as reference material.
Pore fluid of the hardened samples was extracted using the steel
die method (Barneyback and Diamond, 1981) with pressures up
to 530 N/mm2: The solution was stabilised and measured accord-
ing to the procedure described in Gruskovnjak et al. (2008).
Polished and carbon-coated samples were examined by scanning
electron microscopy (SEM) (Philips ESEM FEG XL 30) using
backscattered electron images (BSE) with SEM settings at low
voltage (5 kV) and 100 �m aperture.
Thermodynamic modelling
The Gibbs free energy minimisation program GEMS (Kulik,
2005) was used to calculate the equilibrium speciation of
dissolved species, as well as to predict the kind and amount of
solids precipitating as a function of the amount of dissolved slag.
A description of the basic assumptions and the modelling set-up
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Quantification of hydration phases insupersulfated cements: review and newapproachesGruskovnjak, Lothenbach, Winnefeld et al.
can be found in Lothenbach and Gruskovnjak (2007). The
modelling results are used as a thermodynamically constrained
mass balance approach for the progress of hydration. The solids
precipitated have been calculated as a function of percentage of
hydrated slag.
Quantification methods
Image analysis (SEM method). The same method of backscattered
image analyses based on different grey scale levels was used in
this study as described in Scrivener (2004), but adapted for SSC
pastes in order to identify the amount of anhydrous slag particles.
The magnification used in this study: 10003 and 20003.
Thermogravimetric analysis (TGA method). When analysed with
TGA, overlapping signals occur for the hydration phases C–S–H
and ettringite. Thus, TGA and differential thermal analysis
(DTG) signals were quantified by using reference materials
(Figure 1), similar to the full pattern quantification in XRD.
Synthesised and pure phases were used as reference materials
(see section on ‘Experimental work – Materials’). The TGA and
DTG signals of the reference materials were combined in various
proportions, and these were adjusted until the resulting curve
matched the measured curve of the hydrated SSC samples at the
best. Matching was performed: (a) manually and (b) mathemati-
cally. The mathematical method is based on a Matlab program,
which identifies the local minima in an n-dimensional space
(n ¼ numbers of phases) with the help of the Nelder–Mead
algorithm (Nelder and Mead, 1965). The minimisation criterion
was the mean square difference of the target TGA signal and the
superposed synthetic function.
Selective extraction (SE) method with sodium carbonate. This
method was used previously for the identification of thaumasite in
the presence of ettringite in OPC systems. Van Aardt and Visser
(1975) mentioned a treatment with a 5% sodium carbonate
solution, which decomposed ettringite and left thaumasite un-
changed but the authors gave no further details such as reaction
time used, ratio cement/solution or the fineness of the sample.
This method was applied in this study for the isolation of the C–
S–H phase in supersulfated slag systems (overlapping signals with
ettringite in TGA). It was optimized for this study as follows: 5 g
of the sample (ground to , 40 �m) was stirred in 100 ml of a 5%
sodium carbonate solution for 10 min. The residue was filtered,
stopped with distilled water and dried for 3 days at 408C. The
treated and untreated samples have then been analysed with TGA.
X-ray diffraction analysis (XRD method). Rietveld refinement of
the XRD patterns was first applied to quantify clinker and
unhydrated cements (Rietveld, 1969). Scrivener et al. (2004)
extended the technique to hydrated samples of a typical Portland
cement.
For SSC samples, an internal standard (10 wt% rutile) was added
to determine the mass fraction of the amorphous component. The
amorphous content is composed of the slag particles, the C–S–H
phase and possibly a hydrotalcite-like phase.
Sulfide concentration (SP method). The measured sulfide concen-
trations after 8 h, 1, 7 and 28 days were compared with the
calculated concentrations from the thermodynamic modelling and
used as indicators of the progress of slag dissolution (Gruskovn-
jak et al., 2006). Sulfide is present exclusively in the slag and is
released as the slag dissolves. Small amounts oxidise to thiosul-
fate (S2O32�) and sulfite (SO3
2�). The main fraction, however,
remains in solution and its concentration increases as hydration
proceeds (Gruskovnjak et al., 2008).
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Hydrotalcite
C–S–H (1:1)
Hydrotalcite
Ettringite
Ettringite
C–S–H (1:1)
Figure 1. TG and DTG curves of the reference materials (C–S–H,
ettringite and hydrotalcite) are shown. The hydrotalcite
Mg4Al2(OH)14:4H2O exhibits a two-stage mass loss pattern
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Quantification of hydration phases insupersulfated cements: review and newapproachesGruskovnjak, Lothenbach, Winnefeld et al.
Selective dissolution by EDTA (EDTA method). EDTA extraction
(Erntroy, 1987) is a method for the determination of slag content
in cements by selective dissolution, which is based on the fast
dissolution of the hydration products (C–S–H, ettringite) and
calcium sulfates. The set-up of the experiment is fully described
in Lumley et al. (1996). The calculations were carried out as
described in Stark et al. (1990).
Differential thermal analysis (DTA method). This method is based
on the principle of recrystallisation of the remaining slag
(Schneider and Meng, 2000) in unhydrated and hydrated samples
during heating. The devitrification process liberates heat, which
can be used for the quantification of the unhydrated slag compo-
nents (Lommatzsch, 1956). For the calculation, the unhydrated
sample is used as reference and compared with the hydrated
samples.
Corrections and assumptions
The hydration products analysed by TGA, XRD and SE method
have been corrected for the loss on ignition taken from TG
analyses; ettringite calculated from TGA was additionally cor-
rected for hydrotalcite (Mg4Al2(CO3)(OH)12:4H2O) as the two
peaks overlap to a certain extent. Thermogravimetric analysis of
the hydrotalcite shows a two-stage mass loss pattern (Figure 1).
The first mass loss is due to the dehydration of water molecules
in the interlayer, while the second mass loss is attributed to the
dehydroxylation of sheets (Kannan, 2004). Corrections have been
performed by the weight loss of the hydrotalcite phase between
30 and 2708C which was subtracted from the weight loss of the
C–S–H phase in the same range.
The amount of reacted slag can be calculated from the corrected
amount of formed ettringite assuming that (a) the slag dissolves
congruently, (b) all magnesium is used for the formation of
hydrotalcite, and (c) the remaining aluminium is completely
incorporated into the hydration phase ettringite (it is assumed that
Al incorporated into the C–S–H phase in SSC is negligible). The
amount of reacted slag can also be calculated from the corrected
amount of C–S–H phase formed assuming that (a) the slag
dissolves congruently and (b) all Si is used for the formation of
C–S–H.
For the selective extraction method, the calculations for the
amount of C–S–H phase are based on the assumptions that the
C/S ratio is 1 and that after the treatment 1.1 H2O per Si is
present.
Results and discussion
Raw material
The chemical composition of the HR-slag and the natural
anhydrite used in the experiments is given in Table 1. The
negative loss of ignition of the slag is due to the oxidation of
sulfide. XRD and TGA analyses have shown that the slag consists
of a glassy phase with no detectable crystalline components, and
that the natural anhydrite contains significant amounts of gypsum
(24 wt%), calcite (12 wt%) and dolomite (3 wt%).
Hydration products
During the hydration of SSC the formation of C–S–H, ettringite
and hydrotalcite is observed (Figures 2 and 3). Calcite, dolomite,
anhydrite and gypsum originating from the natural anhydrite
added are identified by XRD (Figure 3). The amount of ettringite
and C–S–H increases and in correspondence the amount of
gypsum decreases with hydration time. The amount of calcite and
dolomite (Figure 2) is rather constant during the first 28 days.
The changes in the hydrate assemblage during hydration were
also calculated by thermodynamic modelling (Figure 4). The
calculation indicates the formation of increasing amounts of
ettringite and C–S–H phase, minor amounts of hydrotalcite,
decreasing amounts of gypsum and traces of syngenite and FeS
during the hydration of the slag.
Quantification
A number of different quantification methods were applied to
determine the degree of reaction. The SEM, EDTA and the DTA
methods determine the reacted amount of slag while the other
methods (TGA, SE, XRD, SP) determine the amount of slag
indirectly using the quantity of hydrates formed or sulfide
released combined with mass balance considerations.
Image analysis (SEM method)
The amount of unreacted slag as determined by image analysis
shows a steady decrease as a function of time (Table 2). With
image analysis the amount of slag present is determined directly;
the anhydrous slag can be distinguished from the hydration
products by its grey level as the average atomic number of the
hydration products and the anhydrous material differs sufficiently
HR-slag: wt% Natural anhydrite: wt%
LOI �3.1 12.0
SiO2 32.5 3.6
Al2O3 11.6 0.9
Fe2O3 3.6 0.4
CaO 44.0 34.4
MgO 5.0 4.2
SO3 4.5 45.5
K2O 0.3 0.3
Na2O 0.2 0.1
TiO2 0.8 0.0
Mn2O3 0.1 0.0
P2O5 , 0.01 0.0
Cl , 0.01 n.a
Total 99.6 101.4
Table 1. Element oxides in wt% from XRF data for unhydrated
HR-slag and the natural anhydrite used for the SSC mixtures
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Quantification of hydration phases insupersulfated cements: review and newapproachesGruskovnjak, Lothenbach, Winnefeld et al.
(Figure 5). Nevertheless, care has to be taken that the relatively
small difference in density between the slag particles and
anhydrite does not result in an overestimation of the non-reacted
slag content.
A relatively large error results already from a small variation in
the percentage of slag particles determined by BSE imaging and
thus can have a significant impact on the calculated amount of
the reacted slag.
The initial volume of the present slag in an unhydrated SSC was
calculated from the known amount of the phases present (slag,
anhydrite, gypsum and calcite/dolomite), their density, and the
w/s ratio.
Thermogravimetric analysis (TGA method)
The two TGA results, the manually matched (man.) and the
mathematically fitted (math.) ones indicate that during hydration
increasing amounts of ettringite and C–S–H are formed (Table 3).
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Gypsum
C–S–H
Hydrotalcite Calcite
HR-slag_unhydrated
HR-SSC_1d
HR-SSC_7d
HR-SSC_28d
Dolomite
Figure 2. TG and DTG curves of unhydrated HR-slag and HR-SSC
hydrated for 1, 7 and 28 days
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HR-SSC_1d
HR-SSC_7d
HR-SSC_28d
E
GHt E
E E E
A
G
E AAE
DG
GCG
DA
Figure 3. XRD analyses of HR-SSC hydrated for 1, 7 and 28 days.
E, ettringite; G, gypsum; Ht, hydrotalcite; A, anhydrite; C, calcite;
D, dolomite
Unhydrated slag:
cm2/cm2
Slag reacted:
%
HR-SSC_unhydrated 44 0
HR-SSC_1d 34 � 2 23 � 4
HR-SSC_7d 28 � 2 36 � 4
HR-SSC_28d 24 � 2 46 � 4
Table 2. The amount of unhydrated slag particles from SEM
imaging and the calculated amount of slag reacted after 1, 7 and
28 days of hydration
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g/85
g s
lag
Unhydrate slag
Pore solutionSyngenite
EttringiteHydrotalcite
FeSC–S–H
Gypsum
Figure 4. The amount of pore solution and solids precipitated as a
function of the amount of slag (85 wt%) dissolved based on
thermodynamically constrained mass balance calculations
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Quantification of hydration phases insupersulfated cements: review and newapproachesGruskovnjak, Lothenbach, Winnefeld et al.
The mathematically matched TGA results yield lower amounts of
ettringite, but higher amounts of gypsum and C–S–H phase than
the manually matched.
The obtained quantities of ettringite and C–S–H have been used,
after corrections (see subsection on ‘Corrections and assump-
tions’), to calculate the amount of slag reacted (Table 4). An
increasing reaction of the slag is observed. The amount of slag
reacted is in the case of C–S–H similar to the results obtained by
SEM, while the amount of slag reacted based on ettringite is, at
longer hydration times, considerably smaller (Table 4).
The TGA method can be associated with significant systematic
errors as the presence of four different overlapping hydrates
(ettringite, C–S–H, gypsum and hydrotalcite) observed between
30 and 2008C makes the deconvolution difficult. In contrast to the
XRD patterns there are not several peaks of one phase present,
which could be used for a more precise refinement.
Selective extraction (SE) by sodium carbonate
The SE method uses again TGA to quantify the amount of C–S–H
formed but uses a selective extraction by sodium carbonate to
completely dissolve ettringite and gypsum leaving C–S–H phase
and hydrotalcite-like phases unchanged as verified by XRD and
TGA, while some additional calcite precipitates (Figures 6(a)–6(c)
and 7(a)–7(c)). The selective extraction enables a more reliable
quantification of the C–S–H phase of SSC, as the TGA signal of
C–S–H does not overlap with ettringite and gypsum any more
although the TGA still has to be corrected for the amount of
hydrotalcite present (Table 4). The results of the SE method are
comparable with the SEM method. However, the data may be
associated with a systematic error, as the incorporated water of the
C–S–H may be sensitive to (a) the C/S ratio of the C–S–H
(Figure 1), (b) the replacement of Si by Al in C–S–H and (c) the
drying method.
Slag particles
Anhydrite
Anhydrite
Figure 5. BSE image of HR-SSC after 1 day of hydration. The
bright particles are slag and anhydrite; the grey area belongs to
the hydration phases and the black area to the pores
Phases HR-SSC_1d HR-SSC_7d HR-SSC_28d
man. /math.: wt% man. /math.: wt% man. /math.: wt%
Ettringite 13/12 � 1 15/11 � 1 17/10 � 1
Gypsum 2/3 � 0.5 2/6 � 0.5 2/7 � 0.5
C–S–H 13/14 � 3 23/29 � 3 25/36 � 3
Table 3. The amount of hydration products (ettringite, C–S–H
and gypsum) from TG and DTG curves in wt% obtained by the
manual (man.) and mathematical (math.) method after 1, 7 and
28 days of hydration
TGA-method TGA-method SE-method SE-method
slag reacted (from
ettringite): wt%
slag reacted (from C–S–H):
wt%
amount of C–S–H:
wt%
slag reacted (from C–S–H):
wt%
HR-SSC_1d 21 � 2 23 � 5 18 � 3 27 � 5
HR-SSC_7d 25 � 2 41 � 6 28 � 3 41 � 6
HR-SSC_28d 28 � 2 45 � 6 34 � 3 52 � 6
Table 4. The results only from the manual method were
corrected and the percentage of slag reacted from the amount
of ettringite and C–S–H was calculated. The corrected amount
of C–S–H in wt% from the SE method was used for the
calculation of the percentage of slag reacted
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X-ray diffraction analysis (XRD method)
The amount of slag reacted is calculated based on the amount of
ettringite determined by XRD, as described above for the TGA
method. The amount of unreacted slag cannot be determined
directly by XRD as a distinction between amorphous C–S–H
phases and the glassy phase of the slag is not possible.
The amount of slag reacted calculated on the basis of the amount
of ettringite formed can be found in Table 5. The amount of
ettringte and of slag reacted corresponds with the results of the
TGA (ettringite) method and at longer reaction times it is
considerably lower than the SEM or SE results.
Sulfide concentration (SP method)
The measured sulfide concentrations (Table 6) can be used to
calculate the amount of slag reacted as only the slag contains
sulfide. The comparison of the measured concentrations with the
modelled concentrations in Figure 8 (dotted vertical lines) shows
that after 1 day of hydration, already 35 wt% of slag has reacted
(Table 6). The further reaction of the slag seems to proceed only
slowly.
However, there are some uncertainties associated with the SP
method: (a) it is not clear whether the sulfide incorporated in the
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C–S–H
Hydrotalcite
Figure 6(a)–(c). TG and DTG curves of HR-SSC hydrated for 1, 7
and 28 days before (HR-SSC) and after (HR-SSC_SE) the selective
extraction with 5% sodium carbonate solution
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EE
GDAE E E
A
A
0
500
1000
1500
2000
2500
HR-SSC_28d
HR-SSC_28d_SE
C
C
DC C C C C
A
E
GHt E
EE
EE
GDAE E
A
A
Figure 7(a)–(c). XRD analyses of HR-SSC hydrated for 1, 7 and
28 days before (HR-SSC) and after (HR-SSC_SE) the selective
extraction with 5% sodium carbonate solution. E, ettringite;
G, gypsum; Ht, hydrotalcite; A, anhydrite; C, calcite; D, dolomite
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Quantification of hydration phases insupersulfated cements: review and newapproachesGruskovnjak, Lothenbach, Winnefeld et al.
glassy phase of the slag dissolves homogeneously, (b) the determi-
nation of aqueous sulfide is associated with a measurement
uncertainty of 20%, (c) the dissolved sulfide may oxidise depend-
ing on the quantity of oxygen present and on the kinetic of the
oxidation reaction. As stated by different authors (Chen and
Morris, 1972; Fischer et al., 1997; O’Brien and Birkner, 1977) the
oxidation of the intermediate products thiosulfate (S2O32�) and
sulfite (SO32�) are very slow under alkaline conditions. In addition,
solid (AFm) phases may act as a sink for sulfides (Vernet, 1982).
Selective dissolution by EDTA (EDTA method)
The EDTA method aims to selectively dissolve all hydrates and
activators without dissolving the unhydrated slag. TGA/DTG
analyses of the residues after EDTA extraction (Figure 9) indicate
a complete dissolution of the hydration products ettringite,
gypsum and C–S–H. Hydrotalcite, dolomite and calcite, how-
ever, are not dissolved or only to a small extent. In addition,
small amounts of a non-identified hydrate can be observed in the
TGA between 30 and 2308C. While the literature generally just
mentions the dissolution of hydration phases, this study demon-
strates that a large amount of the unhydrated HR-slag dissolves in
the EDTA-solution, which leads to an erroneous quantification of
the amount of slag that has hydrated; 13 wt% (0.063 g of 0.5 g
sample) of the unhydrated slag (without activator) is dissolved
(Table 7). Omitting leads to an overestimation of the amount of
slag reacted at early ages but may be more accurate at later ages
as the fraction of the slag that dissolves during the selective
dissolution may have reacted during hydration. In addition,
corrections for the presence of hydrotalcite (which does not
dissolve in the EDTA extract), lead to another set of values, still
significantly lower than the values estimated by SEM or by SE.
Although the reproducibility of the EDTA method was very good,
the largely different results obtained based on different assump-
tions and the presence of hydrates after the selective dissolution
indicate that this is not an adequate method to determine the
amount of slag reacted.
Differential thermal analysis (DTA method)
The exothermic reaction during devitrification can theoretically
be used to quantify the amount of unreacted slag (Figure 10).
Phases HR-SSC_1d: wt% HR-SSC_7d: wt% HR-SSC_28d: wt%
Amorphous 70.5 � 7 68.6 � 7 68.0 � 7
Ettringite 14.8 � 2 18.0 � 2 19.6 � 2
Anhydrite 5.5 � 1 5.4 � 1 6.5 � 1
Gypsum 7.1 � 1 4.5 � 1 3.0 � 0.5
Calcite 0.0 � 0.5 0.8 � 0.5 0.5 � 0.5
Dolomite 2.0 � 0.5 2.5 � 0.5 2.4 � 0.5
Sum 99.9 99.8 100.0
Slag reacted
(from
ettringite)
24 � 3 30 � 3 33 � 3
Table 5. The results from XRD-Rietveld calculations for each phase
are shown. The amorphous phase is mainly composed of the
glassy phase of the slag, C–S–H and probably some hydrotalcite.
The amount of ettringite was corrected and hence the percentage
of slag reacted was determined
Sulfide concentrations: mmol/l Slag reacted: %
8 h 87 � 17 26 � 3
1 day 175 � 35 35 � 3
7 days 349 � 70 41 � 3
28 days 349 � 70 41 � 3
Table 6. The sulfide concentration after 8 h, 1, 7 and 28 days
were taken as indicators and combined with thermodynamic
modelling to get the percentage of reacted slag
5040302010
Ca
0·00001
0·0001
0·001
0·01
0·1
1
10
0% of slag hydrated
[M]
8 h 1 d 7 d28 d
Si
K
S(-II)
OH�
Na
Stot
S(VI)
Figure 8. The concentration of the dissolved species as a function
of the amount of slag dissolved. The sulfide concentration of the
pore solution was measured after 8 h, 1, 7 and 28 days and used
as an indicator for the dissolution of the slag
272
Advances in Cement ResearchVolume 23 Issue 6
Quantification of hydration phases insupersulfated cements: review and newapproachesGruskovnjak, Lothenbach, Winnefeld et al.
However, the unbiased definition of a clear baseline in the DTA
curve was not possible. A number of baselines are possible to be
drawn as can be imagined from Figure 10 resulting in a wide
range of results. Thus the method does not fulfil the requirements
of a reliable quantification method and is not further discussed.
Comparison of the different methodsFigure 11 compares the results from the different methods that
have been used for the quantification of the amount of reacted
slag.
The TGA, SE, XRD, and SP methods determine the amount of
slag indirectly using the quantity of hydrates formed or sulfide
released combined with mass balance considerations. The inher-
ent assumptions of the mass balance can lead to additional
errors.
1130103093083073063053043033023013090
92
94
96
98
100
30
Temperature: °C
TG: w
eigh
t %
�0·02
�0·01
0
0·01
0·02
DTG
: der
. of
wei
ght
%
Residues afterEDTA extraction
Calcite
DolomiteHydrotalcite
HR-slag
HR-SSC_1dHR-SSC_7d
HR-SSC_28d
Figure 9. Residues of unhydrated HR-slag and HR-SSC hydrated
for 1, 7 and 28 days after EDTA extraction
Residue: g Slag reacted*: % Slag reacted: % Slag reacted†: %
Slag 0.44 � 0.01 13 � 3 0 0
HR-SSC_1d 0.30 � 0.01 27 � 3 17 � 3 20 � 3
HR-SSC_7d 0.27 � 0.01 33 � 3 22 � 3 27 � 3
HR-SSC_28d 0.25 � 0.01 36 � 3 25 � 3 31 � 3
Table 7. The undissolved residue after extraction by EDTA, the
calculated percentage of reacted slag not corrected for the initial
dissolution of anhydrous slag (*), corrected for the initial
dissolution of slag, and corrected for the presence of hydrotalcite
(†) are shown
120011001000900800700600�2·3
�2·1
�1·9
�1·7
�1·5
�1·3
�1·1
�0·9
�0·7
�0·5
500Temperature: °C
DTA
:V
/mg
µ
HR-SSC_unhydrated
HR-SSC_1d
HR-SSC_7d
HR-SSC_28d
51·35 Vs/mgµ
33·57 Vs/mgµ
28·34 Vs/mgµ
20·99 Vs/mgµ
Figure 10. DTA curves for unhydrated and hydrated (1, 7 and 28
days) HR-SSC with manually fitted baselines and the calculated
area under each curve
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Advances in Cement ResearchVolume 23 Issue 6
Quantification of hydration phases insupersulfated cements: review and newapproachesGruskovnjak, Lothenbach, Winnefeld et al.
This is especially visible in the results of the TGA and XRD
methods. Both XRD and TGA methods give comparable amounts
of ettringite and thus a comparable amount of slag reacted results
from both methods. However, the amount of slag reacted based
on the amount of C–S–H determined by TGA and SE was
significantly higher, as shown in Figure 11.
The ettringite-based TGA and XRD methods rely on a mass
balance of Al (and Mg), assuming a homogeneous dissolution of
the slag and that all Mg dissolved precipitates as hydrotalcite
(Mg4Al2(CO3)(OH)12:4H2O). These methods are highly depen-
dent on the Al and Mg content of the slag, of ettringite, C–S–H
and hydrotalcite present and thus introduce sources of large errors
that propagate into the calculations for the reacted slag. Uptake
of Al in C–S–H or a higher Al/Mg in hydrotalcite would result
in a higher amount of reacted slag.
The C–S–H based TGA and SE methods use the simple
assumption that all silicate from the dissolving slag precipitates as
C–S–H. In addition, SiO2 is one of the main constituents of the
slag studied (Table 1). The values obtained by the two C–S–H
methods (TGA and SE) agree relatively well and are similar to
the amount of slag reacted as obtained by the SEM method (Fig.
11). The more simple assumptions and the large fraction of SiO2
in the slag seem to give more realistic results. However, it has to
be noted that the TGA measurements can be associated with
significant errors as the presence of overlapping hydrates (ettrin-
gite, C–S–H, gypsum and hydrotalcite) makes the deconvolution
difficult. The SE method is expected to provide a more reliable
estimation of the amount of slag reacted.
The SP method shows a very high degree of reaction at the
beginning, which leaves reasonable doubt if the mechanisms of
the dissolution of sulfur are all well enough understood.
In general, a determination of slag reaction by direct methods
(EDTA, DTA or SEM) seems preferable as no mass balance
assumptions are needed. As mentioned above, the results of the
DTA method are excluded in this discussion as they rely on a
baseline, which cannot be defined properly. The results of the
EDTA method depend strongly on the fraction dissolved in the
unhydrated slag and on whether this fraction is considered at
longer hydration times or not. In addition, the presence of
hydrates in the residue leads at later ages to an underestimation
of the amount of slag reacted (see Figure 11). The SEM method
provides a direct measurement of the fraction of slag reacted, is
less prone to suffer from large errors introduced by calculations
and is thus judged to be a reliable method to measure the amount
of slag reacted in super-sulfated slag systems. In agreement with
the findings reported here, SEM based methods have also been
found to be a reliable method to determine the degree of reaction
in OPC–fly ash systems (Ben Haha et al., 2010).
ConclusionsDifferent methods to determine the degree of reaction of slag in
the presence of anhydrite were evaluated and compared. For all
methods a continuing reaction of the slag during the first month
was observed. Image analysis based on SEM provides the most
direct measurement of the fraction of slag reacted. The newly
developed SE method provides a reliable relative estimation of
the C–S–H phases formed in SSC and gives comparable results
to SEM imaging.
XRD and TGA determine the amount and kind of hydration
product. Calculations based on the amount of ettringite, however,
underestimate strongly the degree of slag reaction.
Two commonly used methods, EDTA and DTA, exhibit serious
sources of error and cannot be used for a reliable quantification
of the amount of reacted slag.
Estimation of the slag reaction using sulfide concentrations
overestimates early reaction while underestimating the late reac-
tion.
AcknowledgementsThe authors express their thanks to Holcim Group Support Ltd
for the financial support. The authors would like to thank Walther
Trindler and his team for the help in the lab and especially Luigi
Brunetti for the tremendous preparation of the samples. Thanks
to Oliver Nagel for the pore solution analyses, Annette Johnson
for the hydrotalcite sample, Mohsen Ben Haha for the help with
the image analysis and Paul Hug for the use of the DSC.
REFERENCES
Barneyback RFJ and Diamond S (1981) Expression and analysis
of pore fluids from hardened cement pastes and mortars.
Cement and Concrete Research 11(2): 279–285.
Ben Haha M, De Weerdt K and Lothenbach B (2010)
Quantification of the degree of reaction of fly ash. Cement
and Concrete Research 40(11): 1620–1629.
Chen KY and Morris JC (1972) Kinetics of oxidation of aqueous
sulfide by O2: Environmental Science and Technology 6(6):
529–536.
3528211470
10
20
30
40
50
60
0
Days of hydration
% s
lag
reac
ted
EDTA
TGA_C–S–H
XRD_ettringite
TGA_ettringite
SP
SE_C–S–HSEM
Figure 11. Comparison of the results of all methods discussed as
a function of percentage of slag dissolved
274
Advances in Cement ResearchVolume 23 Issue 6
Quantification of hydration phases insupersulfated cements: review and newapproachesGruskovnjak, Lothenbach, Winnefeld et al.
Erntroy HC (1987) The determination of clinker content of
composite cements. Zement-Kalk-Gips 40(5): 270–272.
Fischer H, Schulz-Ekloff G andWohrle D (1997) Oxidation of
aqueous sulfide solutions by dioxygen Part I: autooxidation
reaction. Chemical Engineering and Technology 20(7): 462–
468.
Gruskovnjak A, Lothenbach B, Holzer L, Figi R and Winnefeld F
(2006) Hydration of alkali-activated slag: comparison with
ordinary Portland cement. Advances in Cement Research
18(3): 119–128.
Gruskovnjak A, Lothenbach B, Winnefeld F, Figi R and Mader U
(2008) Hydration mechanisms of super sulphated slag
cement. Cement and Concrete Research 38(7): 983–992.
ICSD (2006) Inorganic Crystal Structure Database; ICSD. See
http://icsdweb.fiz-karlsruhe.de/index.php (accessed: 20/02/
2006).
Johnson CA and Glasser FP (2003) Hydrotalcite-like minerals
(M2Al(OH)6(CO3)0:5:XH2O, where M ¼Mg, Zn, Co, Ni) in
the environment: synthesis, characterization and
thermodynamic stability. Clays and Clay Minerals 51(1):
1–8.
Kannan S (2004) Influence of synthesis methodology and post
treatments on structural and textural variations in MgAlCO3
hydrotalcite. Journal of Materials Science 39(21): 6591–
6596.
Kuhl H and Schleicher E (1952) Gipsschlackenzement.
Fachbuchverlag GmbH, Leipzig, Germany.
Kulik D (2005) GEMS-PSI 2.1, PSI-Villigen, Switzerland,
available at http://les.web.psi.ch/Software/GEMS-PSI/
(accessed 15/11/2005).
Lommatzsch A (1956) Untersuchung von Hochofenschlacke mit
der Differentialthermoanalyse. Silikattechnik 7(11): 468.
Lothenbach B and Gruskovnjak A (2007) Hydration of alkali-
activated slag: thermodynamic modelling. Advances in
Cement Research 19(2): 81–92.
Lumley JS, Gollop RS, Moir GK and Taylor HFW (1996) Degrees
of reaction of the slag in some blends with Portland cement.
Cement and Concrete Research 26(1): 139–151.
Matschei T, Bellmann F and Stark J (2005) Hydration behaviour
of sulphate activated slag cements. Advances in Cement
Research 17(4): 167–178.
Nelder JA and Mead R (1965) A simplex method for function
minimization. Computer Journal 7(4): 308–313.
O’Brien DJ and Birkner FB (1977) Kinetics of oxygenation of
reduced sulfur species in aqueous solution. Environmental
Science and Technology 11(12): 1114–1120.
Reichle WT (1986) Synthesis of anionic clay minerals (mixed
metal hydroxides, hydrotalcite). Solid State Ionics 22(1):
135–141.
Rietveld HM (1969) A profile refinement method for nuclear and
magnetic structure. Journal of Applied Crystallography 2(2):
65–71.
Rosina A, Smajic N and Dobovisek B (1966) Beitrag zur
Anwendung der differenz-thermischen Analyse in der
Kalorimetrie (Contribution of the application of differential-
thermal analysis in calorimetry). Microchimica Acta 55(4):
626–638.
Schneider C and Meng B (2000) Bedeutung der Glasstruktur von
Huttensanden fur ihre Reaktivitat (Importance of the glass
structure of blast furnace slag for their reactivity).
Proceedings of the 14th ibausil Conference, Weimar, vol. 1,
pp. 1-0455–1-0463.
Schramli W (1963) Zur Charakterisierung von Hochofenschlacken
mittels Differentialthermoanalyse (For the characterization of
blast furnace slag using differential-thermal analysis).
Zement-Kalk-Gips 26(4): 140–147.
Scrivener KL (2004) Backscattered electron imaging of
cementitious microstructures: understanding and
quantification. Cement and Concrete Composites 26(8): 935–
945.
Scrivener KL, Fullmann T, Gallucci E, Walenta G and Bermejo E
(2004) Quantitative study of Portland cement hydration by
X-ray diffraction/Rietveld analysis and independent methods.
Cement and Concrete Research 34(9): 1541–1547.
Stark J, Ludwig HM and Muller A (1990) Zur Bestimmung des
Hydratationsgrades von Schlackenzementen (For the
determination of the degree of hydration of slag cements).
Zement-Kalk-Gips 43(11): 557–560.
Taylor HFW (1997) Cement Chemistry, 2nd edn. Thomas Telford
Publishing, London, UK.
Van Aardt JHP and Visser S (1975) Thaumasite formation:
A cause of deterioration of Portland cement and related
substances in the presence of sulphates. Cement and Concrete
Research 5(3): 225–232.
Vernet CH (1982) Comportement de l’ion S—au cours de
l’hydratation des ciments riches en laitier (CLK) (The
behaviour of the ion S in the course of the hydration of
cements rich in blast furnace slag). Silicates Industriels 47(3):
85–90.
Walenta G and Fullmann T (2004) Advances in quantitative XRD
analysis for clinker, cements, and cementitious additions.
Powder Diffraction 19(1): 40–44.
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