Changes to the triaxial composition of the hydrated phases (CaO/Al 2O3/SiO2) in the metakaolin/lime system

Article abstract of DOI:10.1111/j.1551-2916.2011.05040.x

This study examines the composition of certain hydrates (calcium silicate, aluminum silicate, and related phases) produced by the pozzolanic reaction of waste-paper sludge that had previously been activated at different temperatures. It summarizes and compares the evolution of the oxide compounds, and records their stability intervals. Changes to their mineralogical composition were analyzed using X-Ray Diffraction, scanning electron microscopy, and energy dispersive X-ray spectroscopy. The hydration products from 1 to 360 days of curing time were CSH gels, hydrotalcite-type compounds (LDH), and stratlingite (C₂ASH₈). CSH gels were employed as substrates for growing other materials and their morphologies were modified from fibrous to hexagonal layers. The composition of the LDH-type compounds observed in the carbonate group varied with changes in curing time. Two LDH-type compound types were identified: (a) with and (b) without magnesium. Stratlingite was the only stable material after long-curing times.

Full text of DOI:10.1111/j.1551-2916.2011.05040.x

J. Am. Ceram. Soc., 95 [3] 1118–1122 (2012)
DOI: 10.1111/j.1551-2916.2011.05040.x
© 2012 The American Ceramic Society
ournal
J
Changes to the Triaxial Composition of the Hydrated Phases
(CaO/Al2O3/SiO2) in the Metakaolin/Lime System
Rosario Garcıa Gimenez,‡,† Olga Rodrıguez,§ Raquel Vigil de la Villa,‡ and Moises Frıas¶
‡Unidad Asociada CSIC-UAM, Departamento de Geologıa y Geoquımica, Facultad de Ciencias, Universidad Autonoma,
C/Francisco Tomas y Valiente, 7, 28949 Madrid, Spain
§Department of Primary Metallurgy and Materials Recycling, National Center for Metallurgical Research, CENIM (CSIC),
Avda. Gregorio del Amo, 8, 28040 Madrid, Spain
¶Instituto Eduardo Torroja (CSIC), C/Serrano Galvache, 4, 28033 Madrid, Spain
This study examines the composition of certain hydrates (cal-
cium silicate, aluminum silicate, and related phases) produced
by the pozzolanic reaction of waste-paper sludge that had pre-
viously been activated at different temperatures. It summarizes
and compares the evolution of the oxide compounds, and
records their stability intervals. Changes to their mineralogical
composition were analyzed using X-Ray Diffraction, scanning
electron microscopy, and energy dispersive X-ray spectroscopy.
The hydration products from 1 to 360 days of curing time were
CSH gels, hydrotalcite-type compounds (LDH), and stratling-
ite (C2ASH8). CSH gels were employed as substrates for
growing other materials and their morphologies were modified
from fibrous to hexagonal layers. The composition of the
LDH-type compounds observed in the carbonate group varied
with changes in curing time. Two LDH-type compound types
were identified: (a) with and (b) without magnesium. Stratling-
ite was the only stable material after long-curing times.
drous silicate phase hydration (C3S and C2S).10 The C–S–H
nanoparticles are responsible for setting the cement paste due
to the electrostatic forces that exist between them.11–13
Aluminate phases are the second most important ones in
the hydration of Portland cement. It is well known that alu-
minum may substitute silicon in C–S–H.14 Therefore, the
C–S–H that occurs in a cement paste will not be pure C–S–
H, but Al substituted-C–S–H referred to as C–A–S–H.15
The pozzolan/lime/water system is very simple and helps
the interpretation of pozzolan blended cement behavior.
Knowledge of the hydration products generated during the
pozzolanic reaction, their morphological characteristics,
chemistry, and structural composition will help determine
whether the pozzolan may be used in cements.
Thus, the purpose of this article is threefold: first, to ana-
lyze the composition of the most important calcium (alumi-
num) silicate hydrates and their related phases, which should
be a useful reference source for others interested in these
phases; secondly, to analyze the evolution of the oxide com-
pounds and finally, to record their stability intervals.
I. Introduction
HE benefits of partially replacing Portland cement with
T
alternative cementitious materials are widely acknowl-
edged.1 At present, new pozzolans are under investigation,
particularly in the form of activated paper sludge.2–6
II. Materials and Methods
A
(1) Materials
by-product of the paper industry, waste-paper sludge is val-
ued because of its high content of organic matter (cellulose)
and inorganic compounds, such as clays and calcium carbon-
ate, used in the processes of de-inking, whitening, etc. High
pozzolanic activity due to thermal activation under con-
trolled calcination transforms the clayey materials, mainly
kaolinite, into calcined products, mainly metakaolinite.7
The high pozzolanic activity of this activated waste com-
pared with other industrial by-products traditionally used in
cements (fly ash, silica fume) was first reported by Frıas
et al.8,9
The substances that comprise cement can be divided into
two groups: crystalline and amorphous. In the present con-
text, “crystalline” refers to substances with a sufficiently reg-
ular internal structure, in terms of atomic, ionic, and
molecular arrangements, to enable characterization using
conventional crystallographic methods.
The waste-paper sludge used in this work was provided by
Holmen Paper S.L., Madrid, which uses 100% recycled
paper as a raw material. Its chemical composition by FRX
analysis is CaO (25%), SiO2 (11%), Al2O3 (7%), MgO,
Fe2O3, SO3, TiO2, Na2O, K2O, P2O5 (<1%), and PPC (mass
after calcinations) 54%.
After drying, the paper sludge waste was calcined in an
electric laboratory furnace at 700°C, 750°C, and 800°C for
either 2 or 5 h of retention time. The resulting products were
ground with a mortar and pestle and then sieved to a size of
less than 45 lm. The samples were grouped as follows: cal-
cined paper sludge 1 (CPS1: 700°C/2 h), CPS2 (700°C/5 h),
CPS3 (750°C/2 h), CPS4 (750°C/5 h), and CPS5 (800°C/2 h).
These materials were then mixed with a saturated lime
solution (Ca(OH)2) and cured in an electric oven at 40°C for
1, 7, 28, 90, 180, and 360 days of reaction. Further informa-
tion concerning paper sludge pozzolanic activation may be
found in previous references.16,17
When Portland cement is hydrated, its main component is
calcium silicate hydrate (C–S–H), which results from anhy-
(2) Techniques
The mineralogical composition of the samples was deter-
mined using X-ray diffraction. The XRD patterns were ana-
lyzed using a SIEMENS D-5000 diffractometer (Munich,
Germany), set at 3°–65° and at a scan speed of 2°/min, using
a tungsten cathode and a copper plate anode (CuKa). The
current and voltage intensity applied to the generating X-ray
G. Scherer—contributing editor
Manuscript No. 29607. Received April 17, 2011; approved December 01, 2011.
†Author to whom correspondence should be addressed. e-mail: rosario.garcia@
uam.es.
1118

March 2012
Composition of the Hydrated Phases (CaO/Al2O3/SiO2)
1119
tube were 30 mA and 40 kW, and the divergence and receipt
splits, 1° and 0.18°, respectively.
respectively. The semi-quantitation of crystalline products by
XRD is show in the Tables I and II. Stratlingite is the most
abundant compound when both temperature and residence
time in the oven increased, reaching a composition of 84%
for CPS5 at 180 days (Table II). LDH-type compounds are
stable and abundant at low temperatures (below 750°C with
short residence time), and CPS2 at 7 days is the most favor-
able condition for obtaining these kinds of compounds
(68%).
The semi-quantitative mineralogical components were
obtained using the reflectant powers method,18 whereas the
areas of talc, calcite, stratlingite, and LDH-type compounds
were measured in the diffractogram. The quantitation of
peak areas was determined by means of Gaussian adjustment
and base-line subtraction. These calculations were done using
a conventional math software program. The error in the
semiquantitative analysis using XRD is 10%.
Calcium silicate hydrate (C–S–H) gel is the principal
amorphous hydration product in Portland cement hydra-
tion.20 It presented particular problems, as it was insuffi-
ciently crystalline for the application of conventional
crystallographic methods.
The textural study of the materials was performed using
an Inspect FEI Company Electron Microscope (SEM; 5350
NE Dawson Creek Drive, Hillsboro, OR) with a tungsten fil-
ament source. The powder samples were fixed to a graphite
plate on the metallic slide using a BIO-RED SC-502 super
coater. The study was complemented using SEM/EDX chem-
ical analyses with a lithium-drifted silicon detector and a
DX41 analyzer. Data shown in the tables were the average
value of ten measurements, performed in different fields.
Systematic observations were performed using this device
(Inspect FEI Company; W source, DX4i analyzer, and Si/Li
detector). The analyzer was previously calibrated with a
multi-mineral sample: the USGS standard ADV – 1.19 The
semi-quantitative analyses by EDX were obtained as an aver-
age of 10 values taken in different grains for each power
sample. The results are expressed in oxides (wt%), adjusted
to 100%. From these data, the structural formulas are calcu-
lated considering 14 negative charges for stratlingite C2ASH8
[Ca2Al2SiO2(OH)10·5H2O] and 14 negative charges for like-
compounds LDH (possible structures type C4AC H12
[Ca4Al2(CO3)(OH)12·12H2O], hydrotalcite type [Mg4A-
l2(OH)14·3H2O], or kaolinite type [Si2Al2O5(OH)4]).
The available information21,22 indicates that C–S–H gel
has a layered structure containing calcium silicate sheets in
solid solution with Ca(OH)2 and H2O. Their semi-quantitation
Table I. Variation in the Mineral Phases for All Samples
and All Reaction Times
Mineral (%)
CPS1
CPS2
CPS3
CPS4
CPS5
1 day
Talc
1
13
–
6
57
19
2
51
Traces
5
51
–
3
44
–
Zeolites
LDH-like
compound
Stratlingite
C4AH13
Calcite
–
Traces
85
–
–
18
–
–
47
–
6
39
31
Traces
22
7 days
Talc
2
–
24
2
–
68
5
Traces
7
3
–
53
2
–
–
Zeolites
LDH-like
compound
Stratlingite
C4AH13
Calcite
III. Discussion
Figure 1 shows the XRD patterns corresponding to the
CPS1 (calcined paper sludge at 700°C/2 h) cured at 1, 7, 28,
90, 180, and 360 days of reaction, which provided examples
of all the XRD patterns. These patterns are detailed in
Table I,4 which also shows chlorite and tobermorite among
the trace contents.
Metakaolinite that results from the calcination of kaolinite
paper sludge was only recognized using SEM/EDX, because
it was an amorphous material. The different hydrated phases
identified using XRD in this work were stratlingite (reflection
peaks at 12.58, 4.18, and 2.49 A) and LDH-type compounds.
These materials were identified in two regions: between
2Ө = 11.01°–12.32° (8.03–7.17 A) and 2Ө = 23.14°–24.50°
(3.84–3.63 A) corresponding to (003) and (006) reflections,
–
Traces
74
4
–
25
–
–
88
19
–
25
66
Traces
32
28 days
Talc
1
–
39
1
–
65
1
–
61
1
–
34
1
–
25
Zeolites
LDH-like
compound
Stratlingite
C4AH13
Calcite
3 13
Traces Traces
58
7
–
31
48
–
18
55
Traces
19
21
90 days
Talc
2
–
24
3
–
28
2
–
24
1
–
32
1
–
19
Zeolites
LDH-like
compound
Stratlingite
C4AH13
Calcite
Traces
Traces
74
28
28
23
17
19
39
50
–
17
64
Traces
15
180 days
Talc
3
–
9
2
–
41
1
–
52
2
–
36
1
–
8
Zeolites
LDH-like
compound
Stratlingite
C4AH13
Calcite
3
Traces
85
13
11
33
6
–
41
36
–
26
84
Traces
7
360 days
Talc
2
–
3
–
46
2
–
23
3
–
27
1
–
–
Zeolites
LDH-like
compound
Stratlingite
C4AH13
Calcite
Traces
2
8
3
–
72
33
–
37
53
Traces
47
Traces Traces
96 43
Fig. 1. XRD diffraction patterns for 700°C/2 h at all reaction
times.

´
Journal of the American Ceramic Society—Garcıa Gimenez et al.
´
1120
Vol. 95, No. 3
Variations of the oxides in the CSH gels, produced during
the pozzolanic reaction of the sludges, are shown in Fig. 3.
These are located in a zone where the SiO2/Al2O3 ratio,
rather than CaO/SiO2 (right side of diagram) predominates.
C–S–H gels in CPS1 (700/2) were calcic at first, but as curing
time increased, the predominant oxide was silica. This cal-
cined sludge has a high content of the oxide CaO, drawn
from the Ca(OH)2 available in the system. As time elapsed,
Table II. Concentration of LDH-Type Compounds and
Stratlingite Determined Using XRD Under All Conditions
Concentration (%)
Stratlingite
LDH-like compounds
1 day
CPS1
CPS2
CPS3
CPS4
CPS5
CPS1
CPS2
CPS3
CPS4
CPS5
28 days
CPS1
CPS2
CPS3
CPS4
CPS5
90 days
CPS1
CPS2
CPS3
CPS4
CPS5
180 days
CPS1
CPS2
CPS3
CPS4
CPS5
360 days
CPS1
CPS2
CPS3
CPS4
CPS5
–
–
–
–
31
–
4
–
19
–
19
Traces
–
–
24
68
7
this concentration fell, but not at
a constant rate; at
180 days, the CaO content was similar to that obtained on
day 1. Al2O3 and SiO2 content remained almost the same
throughout the process. MgO oxide appeared over longer
reaction times.
C–S–H gels in CPS2 (700/5) at all ages showed a higher
content of CaO oxide. Calcium oxide is incorporated at CSH
gels in a way similar to CPS1 sludge. High silica content was
also detected within the range of 7–180 days. The calcic nat-
ure was also confirmed in the CPS3 (750/2) at day 7 of the
reaction, when the Al2O3 content was low; however, over
longer periods of time, the concentrations of CaO, Al2O3,
and SiO2 balanced themselves out, as shown in the triaxial
diagram. The predominant oxides in sludges CPS4 (750/5)
and CPS5 (800/2) consisted of silica with low alumina and
MgO oxide.
53
–
66
3
13
7
48
55
39
65
61
34
25
Traces
23
17
50
64
24
28
24
32
19
Hydrotalcite-like compounds (HT) or double layered
hydroxides (LDH) were identified after 7 days of pozzolanic
reaction, although they were not present in all samples
(Table II). This term is generally applied when carbonate
ions occupy the interlayer spacing. When other interlayer
anions such as nitrate or chloride are dominant, the materials
are referred to as “Hydrotalcite-Type (HT) compounds”.26,27
Calcite content fell after the initial pozzolanic reaction at
28 days of reaction and then gradually increased until the
end of pozzolanic reaction at 360 days. These observations
are explained by the incorporation of the carbonate group in
the hydrotalcite-type phases, in addition to a carbonation
3
13
6
36
84
9
41
52
36
8
2
8
3
33
53
Traces
46
23
27
–
28
phenomenon of portlandite from atmospheric CO2.
Hydrotalcite-like compounds (DLH or LDH) are anionic
clays. These are microporous minerals that have a lamellar
structure and rhombohedric symmetry, comprised of posi-
tively charged hydroxide layers and interlayers of carbonate
anions and water molecules. Growth occurred at the edges,
resulting in the formation of hexagonal plate-shaped hydro-
talcite (LDH-type compounds) crystals [Fig. 2(c)].
The changes in the structural formula from the DLH-like
compounds in accordance with the temperature and the time
in the furnace are shown in Fig. 3. The representation of the
samples is located in the central position of diagram by the
LDH-type compounds in which the three ratios are similar.
These materials are identified in the treatment of 700/2
(CPS1) from 7 to 90 days of pozzolanic reaction. At first,
Ca2+ content per structural formula was high; the concentra-
tion then fell, whereas the Al3+ and Si4+ concentrations
increased. Mg2+ content was low and appeared between 28
and 90 days.
With the increased time in the oven from 2 to 5 h, the
DLH-like compounds were detected from 28 days until
360 days, with variable quantities of Ca2+ content that
reached their maximum concentrations after 180 reaction
days. The same situation was observed at a temperature
change to 750°C for 2 h (CPS3).
The variation was considerable at an activation tempera-
ture of 750°C over 5 h (CPS4). A new majority phase was
identified at 7 days showing LDH-type compounds rich in
Mg2+ content (LDH type II).6 This magnesium proceeded
from the total destruction of the crystalline lattice of the talc
(Fig. 1), which disappeared at this temperature [Fig. 2(d)].
The maximum concentration of Ca2+ ion was observed at
180 days.
was not possible using XRD, because it was a noncrystalline
compound; however, in this case, we have identified some
peaks relating to CSH gel that suggest a higher degree of
structural order.23 These peaks, which corresponded to CSH
gels type I and II,23 are located at 2h = 29.06°, 31.94°, and
49.9° (Fig. 1). The different hydrated phases had been ana-
lyzed using SEM/EDX at all curing times (1, 7, 28, 90, 180,
and 360 days). The triangular diagrams (Fig. 3) were pre-
pared to facilitate the interpretation of all the results linked
to the stratlingite, LDH-type compounds plotting the Ca2+
/
Si4+, Ca2+/Al3+, and Si4+/Al3+ ratios from the structural
formula and CSH gel concentrations, by plotting the CaO/
Al2O3, CaO/SiO2, and SiO2/Al2O3 ratios, as these are the
main oxides with few exceptions in all of the analyses in
which minor amounts of magnesia are identified (<2%).
SEM revealed that the initial crystalline growth presented
nanometer-sized layers that grew on the sides, although their
growth was conditioned by the lime concentration in the
solution24: High concentrations of lime favored the axial
growth of high CaO/SiO2 in C–S–H25 [Figs. 2(a) and (b)].
The first layers of particles appeared remarkably well orga-
nized, but, as the thickness of the layers increased, so did
their roughness, and they tended to lose order. However,
when aged in lime solutions, these disordered aggregated lay-
ers reorganized themselves to yield flat surfaces. In this
study, the LDH-type compounds and the stratlingite nucle-
ates on the C–S–H gel substrate [Fig. 2(f)]. These gels repre-
sent the first signs of crystallization and all the other reactive
products with a hexagonal appearance grow over them,
which can only be distinguished using SEM/EDX analysis.
Finally, the most aggressive treatment (CPS5) showed cal-
cic LDH-like compounds (LDH type I)6 within the range of
28/180 days with high Ca2+ content (Fig. 3).

March 2012
Composition of the Hydrated Phases (CaO/Al2O3/SiO2)
1121
(a)
(b)
(c)
(d)
(f)
(e)
Fig. 2. (a) C–S–H fibrous gels. (b) C–S–H aggregate gels. (c) Laminar LDH-type compounds. (d) Fibrous LDH-type compounds. (e)
Hexagonal plates of stratlingite. (f) Aggregates with C–S–H gels (□), LDH-type compounds (Δ), and stratlingite (○).
360 days, with constant Al3+ concentration and Si4+ content
increasing as the content of Ca2+ fell, producing practically
the same quantity for the three ions.
When the activation temperature reached 750°C, 2 h
(CPS3), stratlingite was detected from 28 days to 360 days.
Under these conditions, the Si4+ content remains practically
constant, whereas the Al3+ content grew over time, and the
Ca2+ content decreased over time at longer ages (360 days).
The waste-paper sludge that was calcined at 750°C for 5 h
developed stratlingite after 7 days of reaction, remaining
until the end of the study. At first, this phase is rich in Ca2+
ions, whereas Al3+ and Si4+ contents were 1.17 and 0.66,
respectively. From this age onward, the Ca2+ was reduced,
the Si4+ content remained constant, and the Al3+ concentra-
tion stabilized at 1.95 (Fig. 3).
At the highest temperature, 800°C/2 h (CPS5), stratlingite
developed after only 1 day of reaction. It had a rich Ca2+
ion composition and a low Si4+ content, evolving over time
“by means of” a decrease of Ca2+ ions and increase in Si4+
,
with almost constant aluminum. All samples present the stra-
tlingite with a hexagonal morphology [Fig. 2(e)].
Fig. 3. Ratios of different oxides or ions for C–S–H gels, LDH-
type compounds and stratlingite (included the stratlingite type).
In general terms, it could be said that stratlingite forma-
tion is favored by temperature and heating time; at first, stra-
tlingite was rich in Ca2+ ions and poor in Si4+ content, with
values of Al3+ close to 1.95. Later on, the ionic composition
tended to compare between them (equilibrium situation, simi-
lar ionic concentrations). The evolution of this phase is con-
ditioned by Ca2+ and Si4+ ions concentrations (that evolve
in the opposite sense), whereas Al3+ ions concentration fluc-
tuated within a small range.
The last compound under study—stratlingite—could only
be detected at 28 days in CPS1, with a prevalence of Ca2+
content. In Fig. 3, stratlingite is located in an opposite area
with Ca2+/Si4+ ratios that are greater than the Si4+/Al3+
the ratios. The increase in activation time from 2 to 5 h
(CPS2), caused the stabilization of this phase from 28 to

´
Journal of the American Ceramic Society—Garcıa Gimenez et al.
´
1122
Vol. 95, No. 3
8M. Frıas, R. Garcıa, R. Vigil de la Villa, and S. Ferreiro, “Calcination of
art Paper Sludge Waste for the Use as a Supplementary Cementing Material,”
Appl. Clay Sci., 42 [1.2] 189–93 (2008).
The activated sludge that has been described in this article
is very well adapted for use as a pozzolan, as has been dem-
onstrated by the product’s stability and stratlingite formation
that followed calcination in the furnace.7
9M. Frıas, O. Rodrıguez, I. Vegas, and R. Vigil, “Properties of Calcined
Clay Waste and its Influence on Blended Cement Behavior,” J. Am. Ceram.
Soc., 91 [4] 1226–30 (2008).
10H. F. W. Taylor, Cement Chemistry. Acad. Press, London, 1990.
11A. Nonat, “The Structure and Stoichiometry of C-S-H,” Cem. Concr.
Res., 34 [9] 1521–8 (2004).
IV. Conclusions
12C. Plassard, E. Lesniewska, I. Pochard, and A. Nonat, “Investigation of
the Surface Structure and Elastic Properties of Calcium Silicate Hydrates at
the Nanoscale,” Ultramicroscopy, 100 [3–4] 331–8 (2004).
The activation of paper sludge at different temperatures and
different times in the furnace resulted in products with
important pozzolanic properties due to the presence of meta-
kaolinite.
The hydration products from 1 up to 360 days of hydra-
tion were C–S–H gels, LDH-type compounds, and stratling-
ite.
C–S–H gels are the compounds used as substrate for
growing other materials. Their morphologies changed from
fibrous to hexagonal plates.
LDH-type compounds were formed between layers in the
carbonate group, and their composition changed with curing
time. Two types of LDH-type compound structures were rec-
ognized: with and without magnesium.
13C. Plassard, E. Lesniewska, I. Pochard, and A. Nonat, “Nanoscale Experi-
mental Investigation of Particle Interactions at the Origin of the Cohesion of
Cement,” Langmuir, 21 [16] 7263–70 (2005).
14J. J. Thomas, D. Rothstein, H. M. Jennings, and B. J. Christensen, “Effect
of Hydration Temperature on the Solubility Behaviour of Ca-, S-, Al-, and Si-
Bearing Solid Phases in Portland Cement Pastes,” Cem. Concr. Res., 33 [12]
2037–47 (2003).
15G. Renaudin, J. Russias, F. Leroux, C. Cau-dit-Coumes, and F. Frizou,
“Structural Characterization of C–S–H and C–A–S–H Samples—Part II:
Local Environment Investigated by Spectroscopic Analyses,” J. Solid State
Chem., 182 [12] 3320–9 (2007).
16I. Vegas, M. Frıas, J. Urreta, and J. T. San Jose, “Obtencion de una adic-
ion puzolanica a partir de la calcinacion controlada de lodos de destintado de
papel: estudio de prestaciones en matrices de cemento,” Mater. Construct., 56
[283] 49–60 (2006).
Stratlingite was shown to be the stable material over long-
curing times.
17R. Vigil de la Villa, M. Frıas, M. I. Sanchez de Rojas, I. Vegas, and R. Garcıa,
“Mineralogical and Morphological Changes of Calcined Paper Sludge at Different
Temperatures and Retention in Furnace,” Appl. Clay Sci., 36, 279–86 (2007).
18L. Schultz, “Quantitative Interpretations of Mineralogical Composition
from X-Ray and Chemical Data for Pierce Shale,” US Geol. Surv. Prof. Pap.,
391-C, 31 (1964).
Acknowledgments
19K. Govindaraju, Compilation of Working Values and Samples Description
for 383 Geostandards (Geostandards Newsletter special issue) Vandoeuvre, Les
Nancy, France, Vol. XVIII, 158 pp, 1994.
The authors are grateful to the Spanish Government for financial support pro-
vided to this research (Projects ref: MAT 2003-06479-CO3 and MAT2009-
10874-C03) and also to Holmer Paper S.L. Madrid and to the Spanish Cement
Institute (IECA) for their help with this research.
20R. Garcıa, R. Vigil de la Villa, O. Rodrıguez, and M. Frıas, “Study of
Hydrated Phases Present in Calcined Paper Sludge (Metakaolinite)/Saturated
CaO Dissolution System Cured at 40°C and 28 days of Reaction,” Mater. Sci.
Eng. A, 527 [16–17] 3936–41 (2010).
References
21I. G. Richardson, “The Calcium Silicate Hydrates,” Cem. Concr. Res., 38,
137–57 (2008).
1V. M. Malhotra, “Fly Ash, Silica Fume, Slag and Natural Pozzolans in
Concrete” In Proceeding of the Second International Conference, Madrid,
Spain, ACI SP 9–1, 1986.
22R. J. M. Pellenq, N. Lequeux, and H. van Damme, “Engineering the
Bonding Scheme in C-S-H: The Iono-Covalent Framework,” Cem. Concr.
Res., 38, 159–74 (2008).
2P. Banfill and M. Frıas, “Rheology and Conduction Calorimetry of
Cement Modified with Calcined Paper Sludge,” Cem. Concr. Res., 37 [2] 184–
90 (2007).
23C. A. Love, I. G. Richardson, and A. R. Brough, “Composition and
Structure of CSH in White Portland Cement-20% Metakaolin Pastes
Hydrated at 25°C,” Cem. Concr. Res., 37, 109–17 (2007).
3M. Frıas, M. I. Sanchez de Rojas, O. Rodrıguez, R. Garcıa, and R. Vigil
de la Villa, “Characterisation of Calcined Paper Sludge as an Environmentally
Friendly Source of Metakaolin for Manufacture of Cementitious Materials,”
Adv. Cem. Res., 20 [1] 23–30 (2008).
24H. F. W. Taylor (Ed.), Cement Chemistry. Academic Press, London, U.K.,
1997.
25S. Gauffinet-Garrault and A. Nonat, “Hydrated Layer Formation on Tri-
calcium and Dicalcium Silicate Surfaces: Experimental Study and Numerical
Simulations,” Langmuir, 17, 8131–9 (2001).
4M. Frıas, O. Rodrıguez, R. Garcia, and I. Vegas, “Influence of Activation
Temperature on Reaction Kinetics in Recycled Clay Waste-Calcium Hydrox-
ide Systems,” J. Am. Ceram. Soc., 91 [12] 4044–51 (2008).
5O. Rodrıguez, “Valorizacion de un residuo industrial procedente de la
industria papelera como material puzolanico”; Ph.D. Thesis, Universidad
Autonoma de Madrid, Spain, 2008.
26G. P. Gillman, “A Simple Technology for Arsenic Removal from Drinking
Water Using Hydrotalcite,” Sci. Total Envir., 366, 926–31 (2006).
27L. Du, B. Qu, Y. Meng, and Q. Zhu, “Structural Characterization and
Thermal and Mechanical Properties of Poly (Propylene Carbonate/MgAl-
LDH Exfoliation Nanocomposite via Solution Intercalation,” Comp. Sci.
Technol., 66, 913–8 (2006).
6R. Vigil de la Villa, O. Rodrıguez, R. Garcıa, and M. Frıas, “Mineral
Phases in an Activated Kaolinitic Waste Blended Cement System,” Appl. Clay
Sci., 50, 137–42 (2010).
28Q. Tao, Y. Zhang, X. Zhang, P. Yuan, and H. He, “Synthesis and Char-
acterization of Layered Double Hydroxides with a High Aspect Ratio,” J.
7R. Garcıa, R. Vigil de la Villa, I. Vegas, M. Frıas, and M. I. Sanchez de
Rojas, “The Pozzolanic Properties of Paper Sludge Waste,” Constr. Build.
Mater., 22 [7] 1484–90 (2008).
Solid State Chem., 179 [3] 708–15 (2006).
h