Fuel 88 (2009) 1533–1538
Contents lists available at ScienceDirect
Fuel journal homepage: www.elsevier.com/locate/fuel
Review article
Reactions of fly ash with calcium aluminate cement and calcium sulphate Lucía Fernández-Carrasco *, E. Vázquez Department of Construction Materials, Universitat Politècnica de Catalunya, ETSECCPB, c/Jordi Girona 1-3, E-08034 Barcelona, Spain
a r t i c l e
i n f o
Article history: Received 22 July 2008 Received in revised form 12 February 2009 Accepted 17 February 2009 Available online 9 March 2009 Keywords: Fly ash Portland cement Calcium aluminate cement Calcium sulphate Hydration
a b s t r a c t The hydration processes in the ternary system fly ash/calcium aluminate cement/calcium sulphate (FA/ CAC/C$) at 20 °C were investigated; six compositions from the ternary system FA/CAC/C$ were selected for this study. The nature of the reaction products in these pastes were analysed by X-ray diffraction (XRD) and infrared spectroscopy (FTIR). At four days reaction time, the main hydration reaction product in these pastes was ettringite and the samples with major initial CAC presented minor ettringite but calcium aluminates hydrates. The amount of ettringite developed in the systems has no direct relation with the initial components. Ó 2009 Elsevier Ltd. All rights reserved.
Contents 1. 2. 3.
4. 5.
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Experimental . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Results. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.1. X-ray diffraction (XRD) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2. Infrared spectroscopy (FTIR) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Conclusions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1. Introduction In manufacturing processes, cement industry requires the consumption of large amount of energy which also imply important greenhouse gas emissions 5% of CO2 emissions emitted to the atmosphere are caused by this sector. The CO2 causes about 6– 29% of the greenhouse effect on earth [1]. Actually, one of the strategies, that have been adopted in order to reduce the negative impact of cement industry on the environment, is the reduction of the clinker factor [2].
* Corresponding author. Tel.: +34 93 405 4247; fax: +34 93 401 7262. E-mail address:
[email protected] (L. Fernández-Carrasco). 0016-2361/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.fuel.2009.02.018
1533 1534 1535 1535 1535 1536 1537 1538 1538
From the point of view of sustainability, the use of by-products in cement and concrete industry does have significant environmental benefits. The incorporation of additions to clinkers gives up a huge spectrum of blended cements that have been noted not only for its properties of reducing energy consumption and CO2 emission (RECCE) but also for its well known durability properties [3]. In this context, the supplementary cementitious materials (SCMs), such as fly ash, allow the concrete industry to use millions of tonnes of by-products, by reducing the consumption of Portland cement per unit volume of concrete. Fly ash has been used as a puzzolanic material to enhance physical, chemical and mechanical properties of cements and concretes [4]. The waste recycling has become an increasing concern in recent years due to current interest in sustainable development and increasing landfill costs. In the construction context, some new
1534
L. Fernández-Carrasco, E. Vázquez / Fuel 88 (2009) 1533–1538
developments by using by-products as unique cementitious material have raised a new range of materials with special properties: ‘‘alkaline cements” [5]. However, the activation of by-products, such as fly ash, involves alkali activation methods; in which the reactions lead to the breaking down of the glass phases at an elevated temperature curing and an alkaline environment required in order to accelerate the reactions [6–9]. Advanced materials research has recently focused on ettringite rich products [10]. One use of calcium aluminate cement is as a precursor to the formation of ettringite (Ca6Al2(SO4)3(OH)12 26H2O); blending CAC cements with anhydrite or gypsum is required for ettringite development [11]. Some properties and expansion phenomena in these ettringite rich materials from PC/CAC/C$ systems, have been recently evaluated [12,13] but still some new knowledge on expansion mechanisms needs to be developed. Products based on ettringite have a broad range of uses: formulations with water contents near the minimum requirement to ensure plasticity are widely used in proprietary floor screeds and repair materials. Compressive strength depends on formulation but it is comparable with those achieved by sulphate-free CAC cements [14]. An alternative method to obtain ettringite based cements is the use of clinkers based on sulphoaluminate, C4A3S, but only little information is available in the bibliography [15,16]. In order to reduce the clinker factor in ternary systems, the present research study alternate ternary systems to develop new ettringite rich materials by the incorporation of fly ash instead of Portland cement as raw material. Several compositions of the ternary components –FA/CAC/C$ – have been evaluated in terms of mineralogical and micro structural characterization.
Table 2 Portion of raw materials. System
CAC
FA
C$
S1 S2 S3 S4 S5 S6
20 30 40 40 80 90
70 60 40 20 10 5
10 10 20 40 10 5
C$ 0.00 1.0
0.8
0.25
0.6 0.50 4
0.75
0.4 3
5
0.2 2
1
6
1.00
CAC 0.00
0.25
0.50
0.0 1.00 FA
0.75
Fig. 1. Formulations of the ternary system studied.
2. Experimental
Fig. 2. XRD of fly ash. Q = quartz, M = mullite.
S1
S2
S3
Lin (Counts)
A fly ash (Type F according to the ASTM classification), an Electroland calcium aluminate cement and, calcium sulphate 2-hydrate (Panreac PRS-CODEX) were used in this research as raw materials. A PHILIPS PW 2400 X-ray fluorescence spectrometer with a PW 2540 VTC sample changer was used to determine the chemical composition of the materials (see Table 1). Mineralogical composition of the raw materials was determined by an X-ray diffractometer (XRD) with a Siemens D500 instrument and an FTIR- Bomem MB-120 Fourier transform infrared spectrophotometer with a frequency range of 350–5000 cm1 were used. Six working mixtures were prepared by blending the solid raw materials. The portion of raw materials used is shown in Table 2, and the ‘‘water/binder” ratio was kept constant throughout at 0.6. The Fig. 1 shows the studied compositions in the ternary system FA/CAC/C$. The pastes produced were subject to the prescribed curing condition: ambient temperature (20 °C) in an atmosphere with high relative humidity (approximately 97%) and the curing time was four days. In summary, this study covered six cementitious matrices. The mineralogical and microstructural characteristics of these matrices were studied by XRD and FTIR.
S4 C2 ASH 8
S5
Table 1 Chemical composition of raw materials.
CAC Fly ash a
C3 AH 6 AH 3
L.O.I.a
Al2O3
CaO
SiO2
Fe2O3
MgO
K2O
Na2O
0.36 1.27
40.52 25.84
34.89 5.93
2.94 41.49
12.91 20.76
0.5 1.22
0.06 1.37
0.14 –
L.O.I.: loss on ignition.
6
10
20
CA
30 40 2-Theta - Scale
S6
50
Fig. 3. X-ray diffractograms of mixtures S1 (top) to S6. (E = ettringite, G = gypsum and Q = quartz).
1535
L. Fernández-Carrasco, E. Vázquez / Fuel 88 (2009) 1533–1538 Table 3 XRD identification of crystalline phases in matrices. Sample
CA
Q
C$
C3AH6
C2ASH8
C4AHx
AFm
AH3
Ettringite
S1 S2 S3 S4 S5 S6
o o
+ o o o o o
++ –
+
+ + +
+ +
+ +
+ +
++ +" +++ +++ + o
Q = quartz, + present, absent, o traces.
Fig. 4. Diffraction patterns for S5 and S6 samples between 8 and 13° 2h. M: monosulfate type solid solution and H: hydroxy-AFm type solid solution.
3. Results 3.1. X-ray diffraction (XRD)
3.2. Infrared spectroscopy (FTIR) The most relevant signals on the FTIR spectrum for CAC (Fig. 6) are the absorption bands in the region between 850 and 650 cm1. The bands near to 840, 805 and 780 cm1 are attributed to AlO4 groups; the bands around 720, 685, 640 and 570 cm1 are ascribed to AlO6 groups. At low frequencies, under 400 cm1, absorption bands are caused by Ca–O bonds [17,18]. The IR spectrum for the original ash (Fig. 7) shows two main very wide and intense bands which are characteristic of the internal vibrations of TO4 tetrahedra groups (T = Al, Si). The first one shows its maximum around 1095 cm1 and is associated with T–
1600
1600
1400
1400
1200
1200
Int. (counts)
Int. (counts)
Results obtained from the analysis of the fly ash by XRD show the FA basically constituted by a major vitreous phase (halo registered between 2h = 15° and 2h = 35°) and crystalline phases consisted mainly in quartz and mullite (see Fig. 2). The Fig. 3 shows the diffractograms of the six working mixes prepared as specified above and cured for four days and the Table 3 summarize the mineralogical semi-quantitative interpretation, respectively. The main crystalline hydration product of the reactions in the S1–S4 studied systems was ettringite. Apart from ettringite, the sample S4 presented a high portion of non reacted gypsum; presumably an excess of C$ was used in the initial mixture. The samples S5 and S6 – with major portion of CAC – presented minor ettringite content but in addition also presented C2ASH8, C4AHx; and the broad diffraction lines between 2h = 6–16° indicated cal-
cium monosulfoaluminate, hemicarboaluminate and calcium monocarboaluminate (Fig. 4). The diffraction lines for aluminium hydroxide polymorphs are observed only in the diffraction patterns of samples with high CAC content (S5 and S6) – mainly as gibbsite; the higher CAC content the higher gibbsite was estimated. Moreover, the sample S6 contains C3AH6. Nonetheless, there is every indication that regardless of the amount of CAC blended with fly ash and calcium sulphate, most part of the CAC reacted in these systems, since practically no remains of anhydrous calcium aluminates were found. Lamberet [12] in relation with the ternary blend CAC–PC–C$ studies of hydration and durability established that the hydration mechanisms depend on PC/CAC and CAC/C$ ratios. The characteristic feature of these mixture binders was reported to be the formation of supplementary ettringite and the delay in the hydration silicates. In this research, an attempt has been made to estimate the semi-quantitative study of ettringite in the different mixtures by representing the intensity of the maximum diffraction line of ettringite versus CAC/FA and CAC/C$ ratios (Fig. 5). As it can be seen from Fig. 5, there is no direct relation between the hydration products and the CAC/FA ratio used, but there is a tendency to increase the portion of ettringite as FA content is increased. Some relation can be found between the CAC/C$ ratio employed: in general it can be said that as CAC/C$ ratio increase the amount of detected ettringite decrease; this can be expected due to the rich presence of aluminate but poor sulphate phases. An interesting remarkable points are circled and denoted as A and B in the Figures. With respect to ‘‘A point” it can be stated that an increase of CAC and a decrease of FA amount resulted in an important reduction of ettringite; on the other hand, ‘‘B points” presented same CAC/C$ ratio but different portion of FA. Therefore, there is not a simple relation explaining such behaviour; all initial phases are probably having a roll in the hydration reactions and need to be more investigated.
1000 800
A
600
1000 800 600
400
400
200
200
0
2
4
6
8
10
12
14
16
18
20
B
0
2
4
6
8
CAC/FA Fig. 5. I/Io of ettringite 2h = 9.01° diffraction line vs CAC/FA and CAC/C$ ratios.
10
CAC/C$
12
14
16
18
20
1536
L. Fernández-Carrasco, E. Vázquez / Fuel 88 (2009) 1533–1538
90
60
a)
55
transmittance (%)
Transmittance (%)
85 80 75 70
50 45 40 35 30 25
65
20
60
15
55
1000
800
600
400
cm-1
2000
1500
500
1000
Fig. 8. FTIR of samples S1–S6.
Wavenumber (cm -1) Fig. 6. IR spectra of CAC.
30
Transmittance (%)
1200
697
25 20
778 796
560
15 460
10
1095
1200
1000
800
600
400
Wavenumbers (cm1) Fig. 7. FTIR of fly ash.
O bond asymmetric stretching vibrations (this band provides information on the degree of crystallinity of a sample), while the other one, centred at 460 cm1, corresponds to T–O bond internal deformation vibrations. The presence of quartz in the original ash gives rise in the IR spectrum to a series of bands located at 1150, 1084, 796–778 (double band), 697, 668, 522 and 460 cm1.The presence of mullite, in turn, is responsible for a series of bands at around 1180–1130 cm1 and 560–550 cm1 (band associated with the octahedral aluminium present in mullite). As these data show, the bands generated by quartz, mullite and the vitreous phase of the ash overlap in the area between 1200 and 900 cm1, where the T–O bond asymmetric stretching vibration appears, generating the wide, intense band [19]. According to J. Bensted [18], the infrared spectra of ettringite C3A 3CS H32 or Ca6[Al(OH)6]2(SO4)3 26H2O present a very strong anti-symmetrical stretching frecuency of the sulphate ion (m3 SO4) centred towards 1120 cm1; this band is indicative of relative isolation of this ion in the hexagonal prism structure. The water absorption bands appear in the region 1600–1700 cm1 (1640 and 1675 cm1 m2 H2O) and above 3000 cm1 (3420 due to m1 H2O and 3635 cm1 of m OHfree). The presence of aluminate bands are near to 550 cm1 (m AlO6) and 855 cm1 (Al–O–H bending). The IR spectrums of S1 to S4 show clearly the ettringite presence (3638, 3525, 3430 and 3430 cm1 and near to 1665, 1110, 988 and 855 cm1); other absorption bands near to 600 and 536 cm1 – are assigned to ettringite too (Fig. 8). The IR spectrum of S1–S3 also presented a very slight absorption bands near to 1025 and 990 cm1 indicating AH3 presence – and not detected
by XRD. Moreover, the IR spectrum of S4 sample presented absorption bands due to gypsum (1690, 1620, 670 cm1 and the absorption band towards to 600 cm1 of major expected intensity also due to the contribution of gypsum). The IR spectrums of systems with major CAC content, S5 and S6, are almost identical (Fig. 8). There were not found absorption bands caused by gypsum or FA. It can be observed in S6 spectrum a weak waveband near to 3665 cm1 characteristic of OH free frequency of cubic calcium aluminate hydrates, C3AH6; that absorption band was not present in the spectrum of S5 sample. Both IR spectrums presented absorption bands towards 3620, 3525 and 3465 cm1 due to aluminium hydroxide, gibbsite. An absorption band towards 3684 cm1 (m-OHfree) could indicate presence of C4AH13 [17] and also an absorption band near 3640 cm1 would indicate ettringite; moreover a band around 3673 cm1 could be due to calcium monocarboaluminate. Nevertheless, we need to take into account that this spectrum area is very difficult to analyse due to the overlapping with the AH3 absorption bands. Most important difference between S5 and S6 spectrums are the relative intensity of the absorption band sited near 1110 cm1 – major in S5 spectrum; an anti-symmetrical stretching frequency of the sulphate ion (m3-SO4) indicates the relative isolation of this ion in the hexagonal prism, although a greater degeneracy of the symmetry would result in more bands in this area of the spectrum of ettringite. The absorption band near 1025 and 970 cm1 are assigned to AH3. At lower frequencies, the aluminate bands towards 790 cm1 (Al–O–H bending) and 530 cm1 (m-AlO6) are not suitable for identification because C3AH6, monosulfo, C4AH13 and ettringite present very close absorption bands. 4. Discussion Typically CAC hexagonal hydrated phases as CAH10 or C2AH8, formed during the normal hydration, were not detected on the studied systems. As reported in the bibliography [20], the hydration of CAC cements is strongly dependent on the temperature, from 5 °C onwards the stable hydrates are C3AH6 and c-AH_3. But, the formation of these hydrates is preceded by the formation of meta-stable hydrates: CAH10, C2AH8 and amorphous phases. These amorphous phases have yet to be properly characterized, but are assumed to be based on anhydrous alumina and are generally called AH3 gel. Cong et al. [21] suggest that at early ages these amorphous phases may have compositions closer to CAH10 and contain aluminium in five fold coordination. It is also previously reported [20] that the conversion of meta-stable hydrates to the stable hydrates may not occur for years in which case, CAH10 and C2AH8 become the stable hydration products. A halo was recorded between 2h = 11–15° in the diffraction patterns of all systems due to an existing microcrystalline or amor-
1537
L. Fernández-Carrasco, E. Vázquez / Fuel 88 (2009) 1533–1538
Al2O3 0.00
CAC
0.6
6 5
CaO/SiO2 CaO/Al2O3 SiO2/Al2O3 SO3/Al2O3 CaO/Al2O3 + SO3
0.8
0.25
0.50
Table 4 Total oxide ratios.
1.0
S1
S2
S3
S4
S5
S6
0.51 0.58 1.13 0.23 0.47
0.70 0.66 0.93 0.21 0.54
1.38 0.93 0.67 0.45 0.64
3.34 1.48 0.44 1.10 0.70
6.95 1.28 0.18 0.17 1.10
7.21 0.89 0.12 0.08 0.82
0.2
0.4
FA
4
3
2 1
0.4 1600
0.75
OPC
0.2
1400 1200
0.25
0.50
0.75
0.0 1.00 SiO2
Fig. 9. Ternary system of the total CaO/SiO2/Al2O3 content.
1000
I/Io
1.00 CaO 0.00
800 600 400
phous material. XRD pattern of fly ash presents also a halo due to vitreous materials (2h = 15–35°). In the diffraction patterns of systems the FA halo is difficult to be evidenced due to the intense diffraction lines of ettringite in the same area. The position of the halo caused by microcrystalline or amorphous AFm phases between 2h = 9–12° is present in samples S5 and S6 and can be assigned by the behaviour of the AFm phase in the Portland Cement [22]. It has been also reported that the presence of monosulphate phases in the system CAC–PC–C$ is due to the limited availability of sulphates [12]. The cubic hydrate C3AH6 – normally developed in the CAC hydrated cements and converted – was detected only in the S6 sample. The studies in relation with the thermodynamic investigation of CaO–Al2O3–CaSO4–H2O system at 25 °C [23] explained that small amounts of sulphate destabilise hydrogarnet, ideally C3AH6, thereby combining much of the available alumina as ettringite rather than as hydrogartnet. The smaller portion on sulphates of sample S6 was not enough to destabilise hydrogartnet phase. The AFm phase of Portland cements refers to a family of calcium aluminates based on the hydrocalumite-like structure of 4CaO Al2 O3 13–19H2O. However OH may be replaced by and CO2 SO2 4 3 . The AFm phase has proven a difficult subject for analysis both because of its low crystallinity, pollytypism and because of variations in composition with corresponding changes to the position and intensity of reflections in its diffraction patterns. It has been reported [23] that at 25 °C stability of AFm phases is much affected by the nature of the anion: carbonate stabilises AFm and displaces OH and SO2 4 at species activities commonly encountered in cement systems. The impact of small amounts of carbonate gained by reaction with the atmosphere on the nature and stability of the AFm phases is noteworthy. In a carbonate-free system, C4AHx will react with monosulphoaluminate to form a solid solution; moreover, as a result of the reaction of monocarboaluminate with C4AHx it will initially cause hemicarboaluminate. The reaction of monocarboaluminate with C4AHx is thermodynamically preferred in relation with the formation of the monosulfoaluminate-C4AHx solid solution series. Thus, while C4AHx is still present, as in the S5 and S6 studied samples, it will react first with monocarboaluminate to form hemicarboaluminate. Moreover, monosulfoaluminate has been calculated to be stable but only above 40 °C – at lower temperatures decompose to AFt, C3AH6 and gibbsite [24]. It has been previously mentioned that the correlation of initial content of phases and developed phases is not simple. Another approach could be done by representing the CaO/SiO2/Al2O3 ternary system (Fig. 9) and try to relate this with the developed phases; Table 4 gives the ratios of oxides (CaO/SiO2, CaO/Al2O3, SiO2/
200 0
0
0.6
0.8
1
1.2
SO3/Al2O3 Fig. 10. I/Io of ettringite 2h = 9.01° diffraction line vs the SO3/Al2O3 ratio.
Al2O3, SO3/Al2O3 and CaO/Al2O3 + SO3). The ratios of the different oxides present in the initial compositions have no simple relations between them and the products formed. However, it has been found that the ettringite formation is dependent on the ratio sulphate/alumina (Fig. 10); then at early ages the silicates have no significant impact on the developed phases, neither the source of silicates–Portland cement or wastes. This result indicates the availability of use waste replacement in the ternary systems CAC/ silicates/C$. Anyway some studies need to be done in order to evaluate the durability of the waste-ternary systems. 5. Conclusions Finally, the following conclusions can be drawn from the present research: (1) In the studied ternary mixtures and curing conditions described, the typically CAC hexagonal hydrated phases as CAH10 or C2AH8, formed during the normal hydration, were not detected; anyway, a halo recorded for 2h = 11–15° can be noticed in all DRX patterns due to amorphous material. (a) Only with major CAC content, 90%, the cubic calcium aluminate hydrate – C3AH6 -is detected. (b) The conversion process of CAC is avoided in these mixtures. (2) The main hydration product detected in the mixtures, and depending on the ratio SO3/Al2O3, is ettringite. (3) Hydration mechanisms are not clearly depending on FA/CAC ratio but there is a tendency to ettringite content increase with FA content. A dependence of CAC/C$ ratio was found. There is not a simple relationship between raw materials and developed products. (4) It is proved that the substitution of fly ash by Portland cement in the ternary mixtures is an alternative way to develop ettringite based products. (5) The incorporation of fly ashes in these systems contribute to the reduction of waste materials and therefore to a better sustainability development.
1538
L. Fernández-Carrasco, E. Vázquez / Fuel 88 (2009) 1533–1538
Acknowledgements The authors thank the Spanish Ministerio de Ciencia e Innovación and Universitat Politècnica de Catalunya benefited from a Ramón y Cajal contract. Also thanks to Ministerio de ciencia e innovación for the Project BIA00767-2008. Moreover, thanks to Dr. S. Martínez-Ramírez from IETCC (CSIC) for her useful comments. References [1] Kiehl JT, Kevin E. Trenberth. Earth’s annual global mean energy budget (PDF).. Bulletin of the American meteorological society 1997;78(2):197–208. doi:10.1175/1520-0477(1997)0782.0.CO; 2 [Retrieved on 1 May 2006]. [2] Bensted J, Barnes P. Structure and performance of cements. 2nd ed. New York: Spon Press; 2002. [3] Macphee DE. Sustainable cementiteous binders: new chemistries, new performance. Advanced in Cement and Concrete X. Sustainability. In: ECI Engineering Conferences International. Davos, Switherland; 2006. [4] Taylor HFW. Cement chemistry. Thomas Telford; 1997. [5] Krivenko PV. Alkali cements. In: First international conference of alkaline cements and concretes, Ukraine, Kiev; 1994. p. 11–129. [6] Fernández-Carrasco L, Palomo A, Fernández-Jiménez A. Alkali Activation of Pozzolan – Calcium Aluminate Cement Mixtures. In: 12th International congress on the chemistry of cement. Montreal, Canada; 2007. [7] Criado A, Palomo A, Fernandez-Jimenez A. Alkali activation of fly ashes. Part 1: effect of curing conditions on the carbonation of the reaction products. Fuel 2005;84(16):2048–54. [8] Fernandez-Jimenez A, de la Torre AG, Palomo A. Quantitative determination of phases in the alkali activation of fly ash. Part I. Potential ash reactivity. Fuel 2006;85(5–6):625–34. [9] Kovalchuk G, Fernandez-Jimenez A, Palomo A. Alkali-activated fly ash: effect of thermal curing conditions on mechanical and microstructural development – part II. Fuel 2007;86(3):315–22. [10] Chatterji S, Jeffery JW. Studies of early stages of paste hydration of cement compounds: II. J Am Ceram Soc 1963;46(4):187–91.
[11] Brooks SA, Sharp JH. Calcium aluminate cements, ettringite-based cements. In: Manghabhai RJ, editor. London: E. & F. Spon, ISBN 0419 15200 8 (HB); 1990. p. 335–349. [12] Lamberet S. Durability of ternary binders based on Portland cement, calcium aluminate cement and calcium sulphate. These no. 3151, Ècole Polytechnique Fédérale de Lasanne (EPFL) Switzerland; 2005. [13] Giroud G. Expansion des mélanges ternaries (PC, CAC, C$). Projet de diplôme, Laboratorie de Matériaux de Construction, Ècole Polytechnique Fédérale de Lasanne (EPFL) Switzerland; 2005. [14] Mathur PC. Study of Cementitious materials using transmission electron microscopy. These, Laboratorie de Matériaux de Construction, Ècole Polytechnique Fédérale de Lasanne (EPFL) Switzerland; 2007. [15] Glasser FP, Zhang L, Zhou Q. Reactions of aluminate cements with calcium sulphate. In: International conference on calcium aluminate cement, Edinburgh, United Kingdom; 2001. [16] Zhang L, Glasser FP. Investigation of the microstructure and carbonation of CSA-based concretes removed from service. Cement Concrete Res 2005;35:2252–60. [17] Volant J. Etude par spectrométrie infrarouge d´aluminates de calcium hydratés. Thèse de doctorat, Publication du centre d´études et de recherches de l´industrie des Liants Hydrauliques; 1966. [18] Bensted J. An infrared spectral examination of calcium aluminate hydrates and calcium aluminate sulphate hydrates encountered in Portland cement hydration. Alluminati di Calcio, Seminario Internazionale Torino, Italy; 1982. [19] Criado M, Fernández-Jiménez A, Palomo A. Alkali activation of fly ash: effect of the SiO2/Na2O ratio: part I: FTIR study. Micropor Mesopor Mater 2007;106(13):180–91. [20] Scrivener KL, Capmas A. Lea’s Chemistry of Cement and Concrete. Calcium aluminate cements, Arnold; 1988: 709-778 [chapter]. [21] Cong X, Kirkpatrick RJ. Hydration of calcium aluminate cements: a solid-state 27 Al NMR study. J Am Ceram Soc 2005;76(2):409–16. [22] Matschei T, Lothenbach B, Glasser FP. The AFm phase in Portland cement. Cement Concrete Res 2007;37:118–30. [23] Damidot D, Glasser FP. Thermodynamic investigation of CaO–Al2O3–CaSO4– H2O system at 25 °C and the influence of Na2O. Cement Concrete Res 1993;23:221–38. [24] Damidot D, Glasser FP. Thermodynamic investigation of CaO–Al2O3–CaSO4– H2O system at 50 °C and 85 °C. Cement Concrete Res 1992;22:1179–91.
