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29Si solid state NMR study of tricalcium silicate and cement hydration at high temperature
CEMENT and CONCRETE RESEARCH. Vol. 23, pp. 1169-1177, 1993. Primed in the USA. 0008-8846D3. $6.00+00. Copyright © 1993 Pergamon Press Ltd.
29Si SOLID STATE NMR STUDY OF TRICALCIUM SILICATE AND CEMENT HYDRATION AT HIGH TEMPERATURE
S. Masse, H. Zanni Laboratoire de Physique et M6canique des Milieux H6t6rog~nes - URA CNRS 857 E.S.P.C.I. - 10, rue Vauquelin - 75231 Paris Cedex 05 - FRANCE, and Universit6 Pierre et Made Curie - 4, place Jussieu - 75252 Pads Cedex 05 - FRANCE. J. Lecourtier, J.C. Roussel, A. Rivereau Institut Franqais du P6trole - Bo~te Postale 311 1 et 4, avenue de Bois-Pr6au 92506 Rueil Malmaison Cedex - FRANCE (Commtmicated by M. Moranville-Regourd) (Received January 5, 1993)
ABSTRACI" 29Si high resolution solid state NMR has been used to follow the hydration kinetics of class G Portland cement and of its major component : tricalcium silicate Ca3SiO5 (C3S). Samples were hydrothermally synthetized at temperatures between 60 and 120°C; hydration was stopped at selected reaction times, from 30 minutes to 14 days, by the aceton-ether method of water-removing. 29Si NMR spectra of hydrates clearly show that, in silicate chains, the ratio between the silicon atoms of end groups and those of middle groups depends not only on the time of hydration, but also on the synthesis temperature. RESUME La RMN haute r6solution en phase solide de 29Si a 6t6 utilis6e pour suivre la cin6tique d'hydratation du ciment Portland de classe G ainsi que celle de son constituant principal : le silicate tricalcique Ca3SiO5 (C3S). Les 6chantillons ont 6t6 synth6tis6s dans des conditions hydrothermales ~ des temp6ratures comprises entre 60 et 120°C; rhydratation a 6t6 stopp6e aux temps de r6action souhait6s, allant de 30 minutes h 14 jours, par la m6thode d'entralnement de l'eau ~t l'ac6tone-6ther. Les spectres de RMN de 29Si des hydrates montrent clairement que, dans les cha/nes de silicates, le rapport entre le nombre d'atomes silicium de bouts de cha/ne et celui de milieux de chalne d6pend non seulement du temps d'hydratation, mais aussi de la temp6rature de synth~se. Introduction Oilwell cementing involves the placement of a cement slurry in the annulus between the metal casing and the geological formation. Its principal functions are to isolate the different zones within the wellbore and to support the casing at each stage of drilling. In order to reach safely the target 1169
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depths, the cement slurry must remain pumpable for sufficient time to allow a satisfying placement and remain stable once in place. Then, it must harden within a reasonable time scale and exhibit high strength and low permeability during all the lifetime of the well. The cement slurries have to sustain a wide range of conditions, such as temperatures from 0 to 200°C, pressures as high as 140MPa; according to the individual well conditions, the pumping times go from 2 to 6 hours. In order to improve the qualities of cement casings in deep oil-wells and to get a better knowledge of the hydration kinetics and hydrates structure of cement hydrated under strong conditions especially high temperature - we have undertaken various methods of investigation, such as XRD, DTG, SEM and NMR. In this work, our purpose is to present the first NMR results about cement and C3S hydration at 60, 80, 100 and 120°C. We can refer to other works also devoted to the effect of temperature on hydration (1-3). Parry-Jones et al studied cement hydration using 29Si MAS-NMR techniques first from 20 to 55°C (1) and then from 21 to 80°C (2); Bell et al (3) investigated 29Si MAS and CP-MAS NMR techniques to study hydrothermally synthetized CSH samples between 100 and 200°C. Polymerization effects in synthetic CSH were investigated by MacPhee et al (4) using 29Si MAS and CP-MAS NMR. We can also refer to Taylor and Roy (5) who listed the minerals which can occur into autoclaved cement pastes. As a first investigation, 29Si high resolution solid state NMR has been used to follow the hydration kinetics of class G Portland cement and, in the same way, of its major component, tricalcium silicate Ca3SiO5 (C3S), which represents from 50 to 70% of the ordinary Portland cement. Hydration of tricalcium silicate with water is responsible for the setting and the strength development of hydrated cement, whereas dicalcium silicate C2S is not so reactive. It is the reason why C3S is chosen as a model for studying the silicate phases hydration during cement hydration itself. Nowadays, it is well known that the hydration of cement silicates proceeds as a condensation of the monomeric SiO44- units Qo to higher-condensed silicates Qn, where 1 _
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TABLE 1 Composition of class G Portland cement Component Aluminium Oxyde Iron Oxyde Calcium Oxyde Magnesium Oxyde Potassium Oxyde Sulphur Triox~cde Silicium Oxide Loss on ignition
Formula
Al20~ Fe203 CaO
M#
K20 SO3 SiO2
% in weight 3.5 4.1 65.6 0.9 0.6 2.1 22.0 0.5
TABLE 2 Constitution of class G Portland cement Constituent Tricalcium Silicate Dicalcium Silicate Tricalcium Aluminate Tetracalcium Aluminoferrite Gypsum
% in weight 57 24 12
water/C3S ratio of 0,50. The paste specimens were poured into autoclaved stainless-steel cells and heated to 60°C, 80°C, 100°C or 120°C under a pressure of 3,5 bars, which is enough for getting more than the vapor saturated pressure of water at these temperatures. As for the cement samples, hydration of the C3S hydrated samples was stopped, after grinding, by washing the powder with aceton and diethyl ether, selected hydration times were 30 minutes, 3 hours and 14 days. NMR Measurements 29Si experiments were carried out using a Bruker MSL 400 spectrometer for the cement study and a Bruker CXP 300 spectrometer for the C3S study. The broadening due to the chemical shift anisotropy effects can be eliminated by rapidly spinning the sample (-4 kHz) around the "magic angle" (54o44'83 '') with respect to the magnetic field B0. This is the single pulse MAS experiment. For dilute spins such as 29Si (nat. ab. 4.7%), interactions with 1H atoms can be exploited in a "cross polarization" (CP) experiment (11), in which magnetic polarization is transfered from the abundant IH nuclei to the rare 29Si nuclei. Whereas single pulse MAS experiments show resonances from all of the silicon sites, the CPMAS experiments show only resonances from the silicon nuclei coupled to protons and lead to spectra which will exhibit enhanced or attenuated intensities, depending on the cross relaxation between proton and silicon and on IH relaxation times. The Bruker CXP 300 high resolution spectrometer (7.05T magnetic field) is equipped with a double air bearing CP-MAS solid state probe-head. The Bruker MSL 400 high resolution spectrometer (9.395T magnetic field) is equipped with a MAS probe-head. Free induction decays (FIDs) of the 29Si nucleus were recorded at 59.617 MHz on the CXP 300 and at 79.48 MHz on the MSL 400. The pulse width was 51.ts. For single pulse 29Si MAS experiments, the recycle delays were, respectively, 5s and 20s for C3S and for cement; the recycle delay was 3s for 1H-
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29Si CP-MAS experiments. The contact time was 3ms in this case. Each hydrated specimen was packed into a cylindrical double bearing alumina rotor and loaded into the Bruker probe-head. The rotor was spun to -4 kHz using air as the drive and bearing gas. Chemical shift values were calibrated before the experiments using Q8M8 as a solid external reference for 29Si, referred to TMS. The ranges of 29Si chemical shifts in solid state are classified according to a Qn-notation (6), where Q represents the SiO44- unit and n the degree of connectivity of these units; we can refer to Table 3 : TABLE 3 Ranges of 29Si Chemical Shifts of Qn Units in Solid Silicates (6).
Type
Symbol
Monosilicates Disilicates and chain end ~oups Chain middle ~oups Chain branchin~ sites Three-dimensional framework
Range (ppm) -66 to -74 -75 to -82 -85to-89 -95to-100 -103to-115
Qo QI Q2 Q~ Q4
Results and Discussion We present first 29Si NMR spectra of C3S hydrated at 60, 80, 100 or 120°C during 30 minutes, 3 hours or 14 days. Figure 1 and Figure 2 allow a comparison between samples hydrated during 30 minutes at the different temperatures. The MAS experiment (Figure 1) shows the existence of Qo species (from -69 to -74ppm) only. We can refer to the spectrum of the anhydrous C3S at the bottom of Figure 1 and conclude that, at this stage of hydration, we have obtained the characteristic spectrum of the anhydrous phase. That proves the persistence of unreacted anhydrous material at any of the four studied temperatures. The CP-MAS experiment (Figure 2) shows that there is yet QoH (from -69 to
Qo
Q0 NS = ~ .
Ns_NS
120°C . . . . . . . .
0.ooc
:-.--_- =-- -_ __.
NS ~
u
I
I
-60
-70
60_°C
NS NS = ¢ ~
ooc "/ ~
0
o
C
s I
I
-80 -90 ppm
I
I
-100
-110
Figure 1 MAS 29Si NMR spectra of C3S hydrated during 30 minutes.
I -60
I -70
I -80
I -90 ppm
I -100
I -110
Figure 2 CP-MAS 29Si NMR spectra of C3S hydrated during 30 minutes.
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29-Si,SOLIDSTATENMR,HYDRATION
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-74ppm) and Q1 (around -79ppm) species; this kind of Qo H species represents now SiO44tetraedra which are surrounded by water molecules or hydroxyls groups. In fact, these QoH entities react as precursors in the formation of more polymerized species (8) and are representative of an hydration of the C3S surface (10). Figure 3 and Figure 4 are relative to an hydration time of 3 hours. The MAS experiment (Figure 3) shows now Qo, Q1 and Q2 (around -85ppm) species. We can see that the relative amount of Qo species decreases when temperature rises from 60 to 120°C. This is linked to an acceleration of the hydration kinetics with temperature, the Qo anhydrous species being transformed into a Q1-Q2 type calcium silicate hydrate (CSH). Furthermore, the ratio Q2/Q1 increases with temperature. As for an hydration time of 30 minutes (Figure 2), the CP-MAS experiment (Figure 4) shows QoH hydrated species; moreover, we can see now, at every temperature, an hydrated species represented by Q1 and Q2 entities.
Q1 Q2
Q1 Q2 NS -
°C
NS =
~
NS = NS =
~
o
I
I
I
-60
-70
-80
C
I -90 ppm
-
~ t
o
\
I
I
t
I
-100
-llO
-60
-70
Figure 3 MAS 29Si NMR spectra of C3S hydrated during 3 hours.
120°C
-
I
C
-
o
I
I
I
-80ppn,190 -lO0 -110
Figure 4 CP-MAS 29Si NMR spectra of C3S hydrated during 3 hours.
Figure 5 and Figure 6 give informations about the effect of temperature after 14 days. First, Figure 4 shows that Qo anhydrous species persists till 100°C; above 120°C, this remanent anhydrous phase seems to disappear. We can compare the spectra obtained for a sample hydrated at 100°C during 14 days (Figure 5 and Figure 6) with those obtained for a sample hydrated at 120°C during 3 hours (Figure 3 and Figure 4); conclusion is that the general shape is quite the same. So, hydration at 120°C during 3 hours gives the same hydrates structure than hydration at 100°C during 14 days. We can also compare the spectra obtained for a sample hydrated at 100°C during 14 days (Figure 5 and Figure 6) with those obtained for a sample hydrated at 100°C during 3 hours (Figure 3 and Figure 4); it is clear that the amount of Q1 and Q2 entities is becoming greater and greater with time of hydration. Figure 5 allows a study of the temperature dependence of the Q2/Q1 ratio (a calculation of this ratio is in progress). It shows that till 60°C, the Q2 entities are less numerous than the Q1 one's, which was also the case at ambient temperature (8, 9); on the contrary, above 80°C, the Q2 entities become more numerous than the Q1 one's. So, not only temperature accelerates the reaction kinetics in a significative way, but also the length of the polymerized silicate chains grows with temperature, which proves that structural changes occur between 60 and 120°C. We think that such modifications in the hydrates structure can be linked to a change in the Ca/Si ratio; we can refer to Grutzeck and al (12). In our study, Q3 or Q4 entities had never been seen.
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QI ?2
Q1 Q2
NS =
~
0
]
c
NS =
~
°
C
,
I -70
I -8 0
I -90
I -100
I -60
ppm
NS ~
I -ll0
°
I
I
-60
- 70
Figure 5
C
I
I
- 80 -90 ppm
I -100
! -110
Figure 6
MAS 29Si NMR spectra of C3S hydrated during 14 days.
CP-MAS 29Si NMR spectra of C3S hydrated during 14 days.
The CP-MAS qualitative experiment (Figure 6) shows still QoH, Q1 and Q2 entities. It is possible to distinguish at least two kinds of resonances in the range of Q2; this work is in progress, varying the contact-time in the CP-MAS experiment (11). We can now compare these results with those obtained with an actual material : cement. Also, class G Portland cement was hydrated at 60°C, 80°C, 100°C or 120°C under 30 bars during 6 hours (Figure 7) and 4 days (Figure 8). As a reference, we can look at the anhydrous clinker spectrum presented on the bottom of Figure 7. The resolution of the cement NMR signal is poorer compared to those of pure tricalcium silicate; this is due to the presence of several phases and of impurities in
~~ , N,
jS
=
3
0
0120°C
C
,
. . . .
1
. . . .
-80
,
. . . .
I
. . . .
-80 PPN
,
. . . .
I ....
-tO0
Figure 7 MAS 29Si NMR spectra of Class G Portland cement hydrated during 6 hours.
-60
-80 PPN
-t00
Figure 8 MAS 29Si NMR spectra of Class G Portland cement hydrated during 4 days.
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29-Si, SOLIDSTATENMR,HYDRATION
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the material, which involves a line broadening. Nevertheless, we can easily identify three kinds of entities : a Qo anhydrous species, which displays chemical shifts around -69ppm, a Q1 entity around -77ppm and a Q2 entity around -83.5ppm. The position of the greatest resonance on the cement spectrum corresponds to the resonance of the belite (C2S + impurities), which has the slowest kinetics in cement hydration reaction. Whatever the conditions of hydration were, for instance 60°C during 510 days or 4 days at 120°C, we have never observed Q3 or Q4 entities. Figure 7 shows the growth of the Q1 and Q2 entities at a stage of 6 hours. Figure 8 allows the same observation at a stage of 4 days, but the kinetics is very much faster, the Q2 entities growing more than the QI one's above 80°C. The 29Si NMR peaks of each kind of species have been integrated. Figure 9 shows the evolution of each kind of species versus temperature at an hydration stage of 6 hours. We can see that, just after 6 hours of hydration, the Qo monomeric species decrease with temperature, whereas the chain middle groups Q2 increase with it; the dimeric species or chain end groups Q1 seem to be constant whatever temperature is. The general feature is that, as we have concluded for the C3S hydration, the Q1 species are more numerous than the Q2 one's till 60°C, on the contrary to what happens at higher temperatures. The very early stages of cement hydration were studied in detail only at 80°C; it was noticed that the evolution during the first hour of hydration was very slow, showing only the Qo anhydrous species by 29Si MAS-NMR.
8O % 6O
40
20
6O
80
1 O0
12O
temp.
(°C)
Figure 9 Percentages of Qn species versus temperature at an hydration stage of 6 hours.
In the case of the C3S hydration study, our aim was first to look at the hydrated phase structure of the material composed of Q1-Q2 entities. This phase has a relatively short relaxation time, so that a delay time of 5 sec. between the sequences is enough to obtain the signal of the hydrated species. Unfortunately, in the same place, we have a residue of unhydrated C3S phase, which has a very long relaxation time. If the chosen delay time is too short, this phase has not sufficient time to relax compared to the other part of the material (the hydrated phase) and, then, the proportion between the hydrated and unhydrated phases is modified. In order to be aware of this problem, a careful analysis based on the recycle delay required in 29Si MAS-NMR experiments was achieved. It was shown that a delay time of 5 sec. was too short for providing a quantitative analysis (especially for the anhydrous part of the sample); however, the general feature of the 29Si NMR spectra was not too much modified. The corresponding results will be presented in a next paper.
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Summary and Conclusions Previous works (8, 9, 10) about C3S hydration at room temperature had shown that, first, Qo anhydrous species exists still after two months, and second, that Q2 entities were never more numerous than the Q1 one's. That means that, at room temperature, we form relatively short silicate chains and that the anhydrous phase has not completely reacted after 2 months. As in this case, the C-S-H structure at higher temperature is also based only on Q1 and Q2 entities (we have never seen Q3 and Q4 entities). Furthermore, we have shown that not only the anhydrous phase has quite completely disappeared after 14 days at 120°C, but also that the chains become longer with temperature, the Q2/QI ratio being able to exceed 1 above 80°C at an hydration stage of 14 days. A careful analysis on the decomposition of the spectra is following in order to give the exact values of the Q2/Q1 ratio. The 29Si NMR spectra observed in the case of cement and C3S hydration are very similar, which leads us to conclude that, in the range of temperatures we have investigated, we form the same calcium silicate hydrates when hydrating cement. A temperature rise involves not only a significative acceleration of the hydration reaction kinetics, but also structural changes between 60 and 120°C which are probably linked to a change of the Ca/Si ratio in these compounds. Acknowledgements We are very grateful to Technodes S.A., Group Ciments Franqais, which provided all the tricalcium silicate necessary to this study, and especially C. Vernet for his helpful collaboration. References 1. 2.
3.
4. 5. 6. 7. 8.
G. Parry-Jones, A.J. A1-Tayyib, S.U. A1-Dulaijan and A.I. A1-Mana "29Si MAS-NMR hydration and compressive strength study in cement paste." Cem. & Concr. Res., 19, 228-234 (1989) S.U. A1-Dulaijan, G. Parry-Jones, A.J. A1-Tayyib and A.I. A1-Mana "29Si Magic-Angle-Spinning Nuclear Magnetic Resonance study of hydrated cement paste and mortar." J. Am. Ceram. Soc., 73 [3], 736-39 (1990) G.M.M. Bell, J. Bensted, F.P. Glasser, E.E. Lachowski, D.R. Roberts and M.J. Taylor "Study of calcium silicate hydrates by solid state high resolution 29Si nuclear magnetic resonance." Adv. Cem. Res., 3, n°9, 23-37 (1990) D.E. MacPhee, E.E. Lachowski and F.P. Glasser "Polymerization effects in C-S-H : implications for Portland cement hydration." Adv. Cem. Res., 1, n°3, 131-37 (1988) H.F.W. Taylor and D.M. Roy "Structure and composition of hydrates." 7 th I.C.C.C., vol.1, II-2/1 (1980) G. Engelhardt et D. Michel "High-resolution solid state NMR of silicates and zeolites." John Wiley & Sons (1987), chp 4 M. M~igi, E. Lippmaa, A. Samoson, G. Engelhardt and A.R. Grimmer "Structural studies of silicates by solid-state high-resolution 29Si NMR." J. Am. Chem. Soc., 102, 4889-93 (1980) S.A. Rodger, G.W. Groves, N.J. Clayden and C.M. Dobson
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29-Si, SOLID STATE NMR, HYDRATION
"Hydration of Tricalcium Silicate Followed by 29Si NMR with Cross-Polarization." J. Am. Ceram. Soc., voh71, n°2, 91-96 (1988) 9. R. Rassem, H. Zanni-Th6veneau, I. Schneid and M. Regourd "29Si high-resolution NMR study of tricalcium silicate hydration." J. Chim. Phys., 86, n°6, 1253-64 (1989) 10. R. Rassem, H. Zanni-Th6veneau, C. Vernet, P. Barret, D. Bertrandie, D. Damidot, A. Nonat, D. Heidemann and A.R. Grimmer "An NMR investigation of the C3S hydration in pastes and in stirred diluted suspensions" In Proceedings of the 1st International Workshop on Hydration and Setting : "Hydration and Setting of Cements". Univ. of Bourgogne, Dijon - France (3-5 July 1991), edited by Chapman and Hall (London), 77-85 (1992) 11. R.K. Harris "Nuclear Magnetic Resonance Spectroscopy." Ed. Pitman, 149-152 (1983) 12. M. Grutzeck, A. Benesi and B. Fanning "Silicon-29 Magic Angle Spinning Nuclear Magnetic Resonance study of calcium silicate hydrates." J. Am. Ceram. Soc., 72 [4], 665-68 (1989)
1177
29Si SOLID STATE NMR STUDY OF TRICALCIUM SILICATE AND CEMENT HYDRATION AT HIGH TEMPERATURE
S. Masse, H. Zanni Laboratoire de Physique et M6canique des Milieux H6t6rog~nes - URA CNRS 857 E.S.P.C.I. - 10, rue Vauquelin - 75231 Paris Cedex 05 - FRANCE, and Universit6 Pierre et Made Curie - 4, place Jussieu - 75252 Pads Cedex 05 - FRANCE. J. Lecourtier, J.C. Roussel, A. Rivereau Institut Franqais du P6trole - Bo~te Postale 311 1 et 4, avenue de Bois-Pr6au 92506 Rueil Malmaison Cedex - FRANCE (Commtmicated by M. Moranville-Regourd) (Received January 5, 1993)
ABSTRACI" 29Si high resolution solid state NMR has been used to follow the hydration kinetics of class G Portland cement and of its major component : tricalcium silicate Ca3SiO5 (C3S). Samples were hydrothermally synthetized at temperatures between 60 and 120°C; hydration was stopped at selected reaction times, from 30 minutes to 14 days, by the aceton-ether method of water-removing. 29Si NMR spectra of hydrates clearly show that, in silicate chains, the ratio between the silicon atoms of end groups and those of middle groups depends not only on the time of hydration, but also on the synthesis temperature. RESUME La RMN haute r6solution en phase solide de 29Si a 6t6 utilis6e pour suivre la cin6tique d'hydratation du ciment Portland de classe G ainsi que celle de son constituant principal : le silicate tricalcique Ca3SiO5 (C3S). Les 6chantillons ont 6t6 synth6tis6s dans des conditions hydrothermales ~ des temp6ratures comprises entre 60 et 120°C; rhydratation a 6t6 stopp6e aux temps de r6action souhait6s, allant de 30 minutes h 14 jours, par la m6thode d'entralnement de l'eau ~t l'ac6tone-6ther. Les spectres de RMN de 29Si des hydrates montrent clairement que, dans les cha/nes de silicates, le rapport entre le nombre d'atomes silicium de bouts de cha/ne et celui de milieux de chalne d6pend non seulement du temps d'hydratation, mais aussi de la temp6rature de synth~se. Introduction Oilwell cementing involves the placement of a cement slurry in the annulus between the metal casing and the geological formation. Its principal functions are to isolate the different zones within the wellbore and to support the casing at each stage of drilling. In order to reach safely the target 1169
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depths, the cement slurry must remain pumpable for sufficient time to allow a satisfying placement and remain stable once in place. Then, it must harden within a reasonable time scale and exhibit high strength and low permeability during all the lifetime of the well. The cement slurries have to sustain a wide range of conditions, such as temperatures from 0 to 200°C, pressures as high as 140MPa; according to the individual well conditions, the pumping times go from 2 to 6 hours. In order to improve the qualities of cement casings in deep oil-wells and to get a better knowledge of the hydration kinetics and hydrates structure of cement hydrated under strong conditions especially high temperature - we have undertaken various methods of investigation, such as XRD, DTG, SEM and NMR. In this work, our purpose is to present the first NMR results about cement and C3S hydration at 60, 80, 100 and 120°C. We can refer to other works also devoted to the effect of temperature on hydration (1-3). Parry-Jones et al studied cement hydration using 29Si MAS-NMR techniques first from 20 to 55°C (1) and then from 21 to 80°C (2); Bell et al (3) investigated 29Si MAS and CP-MAS NMR techniques to study hydrothermally synthetized CSH samples between 100 and 200°C. Polymerization effects in synthetic CSH were investigated by MacPhee et al (4) using 29Si MAS and CP-MAS NMR. We can also refer to Taylor and Roy (5) who listed the minerals which can occur into autoclaved cement pastes. As a first investigation, 29Si high resolution solid state NMR has been used to follow the hydration kinetics of class G Portland cement and, in the same way, of its major component, tricalcium silicate Ca3SiO5 (C3S), which represents from 50 to 70% of the ordinary Portland cement. Hydration of tricalcium silicate with water is responsible for the setting and the strength development of hydrated cement, whereas dicalcium silicate C2S is not so reactive. It is the reason why C3S is chosen as a model for studying the silicate phases hydration during cement hydration itself. Nowadays, it is well known that the hydration of cement silicates proceeds as a condensation of the monomeric SiO44- units Qo to higher-condensed silicates Qn, where 1 _
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TABLE 1 Composition of class G Portland cement Component Aluminium Oxyde Iron Oxyde Calcium Oxyde Magnesium Oxyde Potassium Oxyde Sulphur Triox~cde Silicium Oxide Loss on ignition
Formula
Al20~ Fe203 CaO
M#
K20 SO3 SiO2
% in weight 3.5 4.1 65.6 0.9 0.6 2.1 22.0 0.5
TABLE 2 Constitution of class G Portland cement Constituent Tricalcium Silicate Dicalcium Silicate Tricalcium Aluminate Tetracalcium Aluminoferrite Gypsum
% in weight 57 24 12
water/C3S ratio of 0,50. The paste specimens were poured into autoclaved stainless-steel cells and heated to 60°C, 80°C, 100°C or 120°C under a pressure of 3,5 bars, which is enough for getting more than the vapor saturated pressure of water at these temperatures. As for the cement samples, hydration of the C3S hydrated samples was stopped, after grinding, by washing the powder with aceton and diethyl ether, selected hydration times were 30 minutes, 3 hours and 14 days. NMR Measurements 29Si experiments were carried out using a Bruker MSL 400 spectrometer for the cement study and a Bruker CXP 300 spectrometer for the C3S study. The broadening due to the chemical shift anisotropy effects can be eliminated by rapidly spinning the sample (-4 kHz) around the "magic angle" (54o44'83 '') with respect to the magnetic field B0. This is the single pulse MAS experiment. For dilute spins such as 29Si (nat. ab. 4.7%), interactions with 1H atoms can be exploited in a "cross polarization" (CP) experiment (11), in which magnetic polarization is transfered from the abundant IH nuclei to the rare 29Si nuclei. Whereas single pulse MAS experiments show resonances from all of the silicon sites, the CPMAS experiments show only resonances from the silicon nuclei coupled to protons and lead to spectra which will exhibit enhanced or attenuated intensities, depending on the cross relaxation between proton and silicon and on IH relaxation times. The Bruker CXP 300 high resolution spectrometer (7.05T magnetic field) is equipped with a double air bearing CP-MAS solid state probe-head. The Bruker MSL 400 high resolution spectrometer (9.395T magnetic field) is equipped with a MAS probe-head. Free induction decays (FIDs) of the 29Si nucleus were recorded at 59.617 MHz on the CXP 300 and at 79.48 MHz on the MSL 400. The pulse width was 51.ts. For single pulse 29Si MAS experiments, the recycle delays were, respectively, 5s and 20s for C3S and for cement; the recycle delay was 3s for 1H-
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29Si CP-MAS experiments. The contact time was 3ms in this case. Each hydrated specimen was packed into a cylindrical double bearing alumina rotor and loaded into the Bruker probe-head. The rotor was spun to -4 kHz using air as the drive and bearing gas. Chemical shift values were calibrated before the experiments using Q8M8 as a solid external reference for 29Si, referred to TMS. The ranges of 29Si chemical shifts in solid state are classified according to a Qn-notation (6), where Q represents the SiO44- unit and n the degree of connectivity of these units; we can refer to Table 3 : TABLE 3 Ranges of 29Si Chemical Shifts of Qn Units in Solid Silicates (6).
Type
Symbol
Monosilicates Disilicates and chain end ~oups Chain middle ~oups Chain branchin~ sites Three-dimensional framework
Range (ppm) -66 to -74 -75 to -82 -85to-89 -95to-100 -103to-115
Qo QI Q2 Q~ Q4
Results and Discussion We present first 29Si NMR spectra of C3S hydrated at 60, 80, 100 or 120°C during 30 minutes, 3 hours or 14 days. Figure 1 and Figure 2 allow a comparison between samples hydrated during 30 minutes at the different temperatures. The MAS experiment (Figure 1) shows the existence of Qo species (from -69 to -74ppm) only. We can refer to the spectrum of the anhydrous C3S at the bottom of Figure 1 and conclude that, at this stage of hydration, we have obtained the characteristic spectrum of the anhydrous phase. That proves the persistence of unreacted anhydrous material at any of the four studied temperatures. The CP-MAS experiment (Figure 2) shows that there is yet QoH (from -69 to
Qo
Q0 NS = ~ .
Ns_NS
120°C . . . . . . . .
0.ooc
:-.--_- =-- -_ __.
NS ~
u
I
I
-60
-70
60_°C
NS NS = ¢ ~
ooc "/ ~
0
o
C
s I
I
-80 -90 ppm
I
I
-100
-110
Figure 1 MAS 29Si NMR spectra of C3S hydrated during 30 minutes.
I -60
I -70
I -80
I -90 ppm
I -100
I -110
Figure 2 CP-MAS 29Si NMR spectra of C3S hydrated during 30 minutes.
Vol.23,No.5
29-Si,SOLIDSTATENMR,HYDRATION
1173
-74ppm) and Q1 (around -79ppm) species; this kind of Qo H species represents now SiO44tetraedra which are surrounded by water molecules or hydroxyls groups. In fact, these QoH entities react as precursors in the formation of more polymerized species (8) and are representative of an hydration of the C3S surface (10). Figure 3 and Figure 4 are relative to an hydration time of 3 hours. The MAS experiment (Figure 3) shows now Qo, Q1 and Q2 (around -85ppm) species. We can see that the relative amount of Qo species decreases when temperature rises from 60 to 120°C. This is linked to an acceleration of the hydration kinetics with temperature, the Qo anhydrous species being transformed into a Q1-Q2 type calcium silicate hydrate (CSH). Furthermore, the ratio Q2/Q1 increases with temperature. As for an hydration time of 30 minutes (Figure 2), the CP-MAS experiment (Figure 4) shows QoH hydrated species; moreover, we can see now, at every temperature, an hydrated species represented by Q1 and Q2 entities.
Q1 Q2
Q1 Q2 NS -
°C
NS =
~
NS = NS =
~
o
I
I
I
-60
-70
-80
C
I -90 ppm
-
~ t
o
\
I
I
t
I
-100
-llO
-60
-70
Figure 3 MAS 29Si NMR spectra of C3S hydrated during 3 hours.
120°C
-
I
C
-
o
I
I
I
-80ppn,190 -lO0 -110
Figure 4 CP-MAS 29Si NMR spectra of C3S hydrated during 3 hours.
Figure 5 and Figure 6 give informations about the effect of temperature after 14 days. First, Figure 4 shows that Qo anhydrous species persists till 100°C; above 120°C, this remanent anhydrous phase seems to disappear. We can compare the spectra obtained for a sample hydrated at 100°C during 14 days (Figure 5 and Figure 6) with those obtained for a sample hydrated at 120°C during 3 hours (Figure 3 and Figure 4); conclusion is that the general shape is quite the same. So, hydration at 120°C during 3 hours gives the same hydrates structure than hydration at 100°C during 14 days. We can also compare the spectra obtained for a sample hydrated at 100°C during 14 days (Figure 5 and Figure 6) with those obtained for a sample hydrated at 100°C during 3 hours (Figure 3 and Figure 4); it is clear that the amount of Q1 and Q2 entities is becoming greater and greater with time of hydration. Figure 5 allows a study of the temperature dependence of the Q2/Q1 ratio (a calculation of this ratio is in progress). It shows that till 60°C, the Q2 entities are less numerous than the Q1 one's, which was also the case at ambient temperature (8, 9); on the contrary, above 80°C, the Q2 entities become more numerous than the Q1 one's. So, not only temperature accelerates the reaction kinetics in a significative way, but also the length of the polymerized silicate chains grows with temperature, which proves that structural changes occur between 60 and 120°C. We think that such modifications in the hydrates structure can be linked to a change in the Ca/Si ratio; we can refer to Grutzeck and al (12). In our study, Q3 or Q4 entities had never been seen.
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S. Masseet al.
Vol.23, No. 5
QI ?2
Q1 Q2
NS =
~
0
]
c
NS =
~
°
C
,
I -70
I -8 0
I -90
I -100
I -60
ppm
NS ~
I -ll0
°
I
I
-60
- 70
Figure 5
C
I
I
- 80 -90 ppm
I -100
! -110
Figure 6
MAS 29Si NMR spectra of C3S hydrated during 14 days.
CP-MAS 29Si NMR spectra of C3S hydrated during 14 days.
The CP-MAS qualitative experiment (Figure 6) shows still QoH, Q1 and Q2 entities. It is possible to distinguish at least two kinds of resonances in the range of Q2; this work is in progress, varying the contact-time in the CP-MAS experiment (11). We can now compare these results with those obtained with an actual material : cement. Also, class G Portland cement was hydrated at 60°C, 80°C, 100°C or 120°C under 30 bars during 6 hours (Figure 7) and 4 days (Figure 8). As a reference, we can look at the anhydrous clinker spectrum presented on the bottom of Figure 7. The resolution of the cement NMR signal is poorer compared to those of pure tricalcium silicate; this is due to the presence of several phases and of impurities in
~~ , N,
jS
=
3
0
0120°C
C
,
. . . .
1
. . . .
-80
,
. . . .
I
. . . .
-80 PPN
,
. . . .
I ....
-tO0
Figure 7 MAS 29Si NMR spectra of Class G Portland cement hydrated during 6 hours.
-60
-80 PPN
-t00
Figure 8 MAS 29Si NMR spectra of Class G Portland cement hydrated during 4 days.
Vol. 23, No. 5
29-Si, SOLIDSTATENMR,HYDRATION
1175
the material, which involves a line broadening. Nevertheless, we can easily identify three kinds of entities : a Qo anhydrous species, which displays chemical shifts around -69ppm, a Q1 entity around -77ppm and a Q2 entity around -83.5ppm. The position of the greatest resonance on the cement spectrum corresponds to the resonance of the belite (C2S + impurities), which has the slowest kinetics in cement hydration reaction. Whatever the conditions of hydration were, for instance 60°C during 510 days or 4 days at 120°C, we have never observed Q3 or Q4 entities. Figure 7 shows the growth of the Q1 and Q2 entities at a stage of 6 hours. Figure 8 allows the same observation at a stage of 4 days, but the kinetics is very much faster, the Q2 entities growing more than the QI one's above 80°C. The 29Si NMR peaks of each kind of species have been integrated. Figure 9 shows the evolution of each kind of species versus temperature at an hydration stage of 6 hours. We can see that, just after 6 hours of hydration, the Qo monomeric species decrease with temperature, whereas the chain middle groups Q2 increase with it; the dimeric species or chain end groups Q1 seem to be constant whatever temperature is. The general feature is that, as we have concluded for the C3S hydration, the Q1 species are more numerous than the Q2 one's till 60°C, on the contrary to what happens at higher temperatures. The very early stages of cement hydration were studied in detail only at 80°C; it was noticed that the evolution during the first hour of hydration was very slow, showing only the Qo anhydrous species by 29Si MAS-NMR.
8O % 6O
40
20
6O
80
1 O0
12O
temp.
(°C)
Figure 9 Percentages of Qn species versus temperature at an hydration stage of 6 hours.
In the case of the C3S hydration study, our aim was first to look at the hydrated phase structure of the material composed of Q1-Q2 entities. This phase has a relatively short relaxation time, so that a delay time of 5 sec. between the sequences is enough to obtain the signal of the hydrated species. Unfortunately, in the same place, we have a residue of unhydrated C3S phase, which has a very long relaxation time. If the chosen delay time is too short, this phase has not sufficient time to relax compared to the other part of the material (the hydrated phase) and, then, the proportion between the hydrated and unhydrated phases is modified. In order to be aware of this problem, a careful analysis based on the recycle delay required in 29Si MAS-NMR experiments was achieved. It was shown that a delay time of 5 sec. was too short for providing a quantitative analysis (especially for the anhydrous part of the sample); however, the general feature of the 29Si NMR spectra was not too much modified. The corresponding results will be presented in a next paper.
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Vol. 23, No. 5
Summary and Conclusions Previous works (8, 9, 10) about C3S hydration at room temperature had shown that, first, Qo anhydrous species exists still after two months, and second, that Q2 entities were never more numerous than the Q1 one's. That means that, at room temperature, we form relatively short silicate chains and that the anhydrous phase has not completely reacted after 2 months. As in this case, the C-S-H structure at higher temperature is also based only on Q1 and Q2 entities (we have never seen Q3 and Q4 entities). Furthermore, we have shown that not only the anhydrous phase has quite completely disappeared after 14 days at 120°C, but also that the chains become longer with temperature, the Q2/QI ratio being able to exceed 1 above 80°C at an hydration stage of 14 days. A careful analysis on the decomposition of the spectra is following in order to give the exact values of the Q2/Q1 ratio. The 29Si NMR spectra observed in the case of cement and C3S hydration are very similar, which leads us to conclude that, in the range of temperatures we have investigated, we form the same calcium silicate hydrates when hydrating cement. A temperature rise involves not only a significative acceleration of the hydration reaction kinetics, but also structural changes between 60 and 120°C which are probably linked to a change of the Ca/Si ratio in these compounds. Acknowledgements We are very grateful to Technodes S.A., Group Ciments Franqais, which provided all the tricalcium silicate necessary to this study, and especially C. Vernet for his helpful collaboration. References 1. 2.
3.
4. 5. 6. 7. 8.
G. Parry-Jones, A.J. A1-Tayyib, S.U. A1-Dulaijan and A.I. A1-Mana "29Si MAS-NMR hydration and compressive strength study in cement paste." Cem. & Concr. Res., 19, 228-234 (1989) S.U. A1-Dulaijan, G. Parry-Jones, A.J. A1-Tayyib and A.I. A1-Mana "29Si Magic-Angle-Spinning Nuclear Magnetic Resonance study of hydrated cement paste and mortar." J. Am. Ceram. Soc., 73 [3], 736-39 (1990) G.M.M. Bell, J. Bensted, F.P. Glasser, E.E. Lachowski, D.R. Roberts and M.J. Taylor "Study of calcium silicate hydrates by solid state high resolution 29Si nuclear magnetic resonance." Adv. Cem. Res., 3, n°9, 23-37 (1990) D.E. MacPhee, E.E. Lachowski and F.P. Glasser "Polymerization effects in C-S-H : implications for Portland cement hydration." Adv. Cem. Res., 1, n°3, 131-37 (1988) H.F.W. Taylor and D.M. Roy "Structure and composition of hydrates." 7 th I.C.C.C., vol.1, II-2/1 (1980) G. Engelhardt et D. Michel "High-resolution solid state NMR of silicates and zeolites." John Wiley & Sons (1987), chp 4 M. M~igi, E. Lippmaa, A. Samoson, G. Engelhardt and A.R. Grimmer "Structural studies of silicates by solid-state high-resolution 29Si NMR." J. Am. Chem. Soc., 102, 4889-93 (1980) S.A. Rodger, G.W. Groves, N.J. Clayden and C.M. Dobson
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"Hydration of Tricalcium Silicate Followed by 29Si NMR with Cross-Polarization." J. Am. Ceram. Soc., voh71, n°2, 91-96 (1988) 9. R. Rassem, H. Zanni-Th6veneau, I. Schneid and M. Regourd "29Si high-resolution NMR study of tricalcium silicate hydration." J. Chim. Phys., 86, n°6, 1253-64 (1989) 10. R. Rassem, H. Zanni-Th6veneau, C. Vernet, P. Barret, D. Bertrandie, D. Damidot, A. Nonat, D. Heidemann and A.R. Grimmer "An NMR investigation of the C3S hydration in pastes and in stirred diluted suspensions" In Proceedings of the 1st International Workshop on Hydration and Setting : "Hydration and Setting of Cements". Univ. of Bourgogne, Dijon - France (3-5 July 1991), edited by Chapman and Hall (London), 77-85 (1992) 11. R.K. Harris "Nuclear Magnetic Resonance Spectroscopy." Ed. Pitman, 149-152 (1983) 12. M. Grutzeck, A. Benesi and B. Fanning "Silicon-29 Magic Angle Spinning Nuclear Magnetic Resonance study of calcium silicate hydrates." J. Am. Ceram. Soc., 72 [4], 665-68 (1989)
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