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29Si NMR study of hydration and pozzolanic reactions in reactive powder concrete (RPC)
Magnetic
ELSEVIER
Resonance Imaging, Vol. 14, Nos. 7/8, pp. 891-893, 1996 Copyright 0 1996 Elsevier Science Inc. Printed in the USA. All rights reserved 0730-725X/96 $15.00 + .OO
PI1 SO730-725X( 96) 00174-7
0 Short Communication 29Si NMR
STUDY OF HYDRATION AND POZZOLANIC REACTIONS IN REACTIVE POWDER CONCRETE (RPC)
SAMUEL PHILIPPOT," SYLVIE MASSE,-/- HBLBNE ZANNI,* PEDRO NIETO,* VINCENT MARET,? AND MARCEL CHEYREZY~ *Laboratoire de Physique et de MCcanique des Milieux HCtCrogenes, UR4 CNRS 857, E.S.P.C.I. 10, rue Vauquelin 75231 Paris Cedex 05 et Universite Pierre et Marie Curie, 4, place Jussieu, 75252 Paris Cedex 05, France tDirection Scientifique BOUYGUES,
Challenger, 78061 St. Quentin en Y velines, France
A careful analysis of the 29SiNMR signal of reactive powder concretes, composed of siliceous cement, silica fume, and crushed quartz, has been done in order to determine the hydration conditons on the kinetics of hydration. Copyright 0 1996 Elsevier Science Inc. Keywords:
NMR spectroscopy;
Silicates; Concrete.
NMR
INTRODUCTION
SPECTROSCOPY
It is well known that in the case of spin 4 nuclei, like *‘Si, single-pulse excitation allows one to make a quantitative analysis of the different silicon species coexisting in the sample (i.e., anhydrous cement, silica fume, quartz, CSH) , the peaks areas being proportional to the amounts of *‘Si entities. Using Magic Angle Spinning, only isotropic chemical shift interaction remains, leading to well-resolved peaks in the spectra, the positions of which are characteristic of the different “Si site types. The analysis is based on the Q” classification* where Q represents a SiO”,- unit and the degree of connectivity, n, is related to the oxygen bond number between the SiQi- units. Chemical shift values were calibrated using QsMs [ Si( CH3),]8Si8020 relatively to TMS, the tetramethylsilane Si ( CH3)4. *‘Si NMR experiments were carried out on ASX NMR BRUKER spectrometers operating at 59,62 and 99,35 MHz in fields of 7.04 and 11.7 T, respectively. For a quantitative analysis, three conditions were required: (a) long enough recycle times to ensure the spin relaxation of all the species present in the sample. Therefore, two types of experiments were achieved: one with a long recycle time (2600 s) respecting the quartz relaxation
Reactive Powder Concretes ( RPCs) ’ are characterized by a high silica fume content, the presence of crushed quartz in their formulation, and a very low water to cement ratio (i.e. w/c = 0.15 compared to 0.45 in ordinary cements). These materials exhibit very high mechanical and durability properties, the compressive strength lying between 200 and 800 MPa, depending on temperature of heat treatment applied to concrete before and during its setting period. In RPCs the calcium silicate hydrates (CSH) result from two reactions: the cement hydration reaction and the so-called pozzolanic reaction between silicate ions, produced by dissolution of silica fume in water, and calcium ions coming mainly from calcium hydroxide, (portlandite CH) present in the medium. Cement notation is used: (C = CaO, S = SiOz, H = HzO.) The
CSH stoechiometry and, hence, their microstructure are totally dependent on the various postset heat treatments (20 to 250°C) applied during hydration. Generally, CSH are noncrystalline and NMR spectroscopy is a relevant technique to establish the link between their microstructural properties and their high mechanical properties. In a first approach, we started with a “Si NMR investigation.
time Ti in order to determine the proportion of crushed
quartz entities Q&; another with a shorter recycle time CNRS 857, E.S.P.C.I. 10, me Vauquelin 75231 Paris, Cedex 05 France.
Address correspondence to Samuel Philippot, Laboratoire de Physique et de Mecanique des Milieax Heterogenes, URA 891
Magnetic Resonance Imaging l Volume 14, Numbers 7/8, 1996
892
Fig. 1. (A) 29SiNMR spectrumof RFT anhydrousmixture. MAS-Single PulseExperimentat a frequencyof S9,62MHz. Recycle time: 2600 s. (B) 29Si NMR spectrum of an RPC sample,hydrated at 9O”C-48 h. MAS-Single PulseExperiment at a frequency of 99,3SMHz. Recycle time: 20 s. (C) 29SiNMR spectrumof a RPC sample,hydrated at 250°C during 1 week. MAS-Single PulseExperimentat a frequency of 99,3SMHz. Recycle time: 20 s.
(20 s) respecting the relaxation times of cement, silica fume, and hydrated species to make a more precise analysis of the respective proportions of these entities. (b) fast rotation of the sample to eliminate sidebands in MAS experiments. A spinning speedequal to 7 kHz was used. (c) sufficient acquisition numbers due to the low natural abundance of 29Sinuclei (4.7%). Usually, 30 scans were necessary for the long recycle time experiments and 1000 scans for the short recycle time ones. RESULTS A RPC formulation containing ordinary Portland cement, silica fume, crushed quartz, superplasticizer with
w/c = 0.15, was prepared and submitted to various heat treatments from 20 to 250°C during durations lying from 8 h to 28 days. Then the different samples obtained were examined by NMR. As examples, we present three NMR spectra: first, on Fig. la, the anhydrous mixture spectrum, then, on Fig. lb and c, two typical spectra of samples hydrated at 90°C during 48 h and at 250°C during 1 wk, respectively. The first spectrum, obtained with a long recycle time, shows the contribution of cement silicatesproviding a signal in the Q” range (-71 ppm) and the contribution of quartz and silica fume giving signals in the Q” range (Q$@ thin peak of the quartz, centered at -107 ppm, and Q& rather broad peak of silica fume centered at - 110 ppm) . The spectra of Fig. lb and c were obtained with a short recycle time and did not respect the quartz relaxation time T1. Nevertheless, they give the proportion of the other species: anhydrous cement (Q” at -71 ppm), calcium silicate hydrates CSH (Q’ and Q’ at -79 and -85 ppm), silica fume (Q4 at - 110 ppm) and also a little contribution of Q3 species ( -97 ppm) attributed to xonotlite formation for the treatment at 250°C. Comparisonof Fig. lb and c showsthe role of temperatureand duration of heat treatment on the different species. At 90°C 48 h
the amount of CSH phase is comparable to the amount of not yet hydrated cement and a lot of silica fume is
‘%i NMR study of hydration and pozzolanic reactions l S. PHILLFOT
always present. On the contrary, a rather long treatment at 250°C leads to a large amount of calcium silicate hydrates compared to the remaining at-hydrous phases, cement, and silica fume, which is rather totally consumed. Furthermore, the structure of the CSH is changed and give rise to a big signal centered in the Q’ domain and a little one in the Q’ range. This phase may be composed of a noncrystalline CSH, based on a long chain silicate skeleton and a crystalline hydrate identified as xonotlite by XRD investigation. From the spectra, simulated with the WlNFIT BRUKER NMR program, we could determine the respective proportions of each Q” units and deduce four parameters: percentage of hydration, H = (Q’ + Q* + Q” ) , which describes the proportion of concrete compounds that were hydrated; connectivity degree defined as C = (Q’ + 2Q’ + 3Q’)/(Q’ + Q’ + Q3) and related to the statistical chain length of CSH; pozzolanic activity relative to the consumption of silica fume, PSF = ( Q4s~o - Q4s~)/Q4s~o and that relative to the consumption of quartz PCQ = (Q4cao -- Q4ca)/Q4c~.
ETAL.
893
CONCLUSIONS In conclusion, we may say that silica fume and quartz activities are highly dependent on heat treatment temperature and duration. Microstructural changes in hydrate structures happened, depending on heat treatment. As observed previously3 in the case of pure tricalcium silicate hydration, the average CSH chain length increases with heat treatment temperature and duration and, at the highest heat treatment temperature (250°C)) crystalline hydrates appear, as in hydrothermal synthesis. REFERENCES 1. Richard, P.; Cheyrezy, M. Compositionof reactive powder concretes.Cem. Concr. Res. (to be published). 2. Engelhard,G.; Michel, D. High resolution29SiNMR of silicatesand zeolites.Chichester:J. Wiley; 1987. 3. Masse,S.; Zanni, H.; Lecourtier,J.; Roussel,J.C.; Rivereau, A. “Si solid stateNMR study of tricalcium silicate and cementhydration at high temperature.Cem. Concr. Res.23:1169-1177; 1993.
ELSEVIER
Resonance Imaging, Vol. 14, Nos. 7/8, pp. 891-893, 1996 Copyright 0 1996 Elsevier Science Inc. Printed in the USA. All rights reserved 0730-725X/96 $15.00 + .OO
PI1 SO730-725X( 96) 00174-7
0 Short Communication 29Si NMR
STUDY OF HYDRATION AND POZZOLANIC REACTIONS IN REACTIVE POWDER CONCRETE (RPC)
SAMUEL PHILIPPOT," SYLVIE MASSE,-/- HBLBNE ZANNI,* PEDRO NIETO,* VINCENT MARET,? AND MARCEL CHEYREZY~ *Laboratoire de Physique et de MCcanique des Milieux HCtCrogenes, UR4 CNRS 857, E.S.P.C.I. 10, rue Vauquelin 75231 Paris Cedex 05 et Universite Pierre et Marie Curie, 4, place Jussieu, 75252 Paris Cedex 05, France tDirection Scientifique BOUYGUES,
Challenger, 78061 St. Quentin en Y velines, France
A careful analysis of the 29SiNMR signal of reactive powder concretes, composed of siliceous cement, silica fume, and crushed quartz, has been done in order to determine the hydration conditons on the kinetics of hydration. Copyright 0 1996 Elsevier Science Inc. Keywords:
NMR spectroscopy;
Silicates; Concrete.
NMR
INTRODUCTION
SPECTROSCOPY
It is well known that in the case of spin 4 nuclei, like *‘Si, single-pulse excitation allows one to make a quantitative analysis of the different silicon species coexisting in the sample (i.e., anhydrous cement, silica fume, quartz, CSH) , the peaks areas being proportional to the amounts of *‘Si entities. Using Magic Angle Spinning, only isotropic chemical shift interaction remains, leading to well-resolved peaks in the spectra, the positions of which are characteristic of the different “Si site types. The analysis is based on the Q” classification* where Q represents a SiO”,- unit and the degree of connectivity, n, is related to the oxygen bond number between the SiQi- units. Chemical shift values were calibrated using QsMs [ Si( CH3),]8Si8020 relatively to TMS, the tetramethylsilane Si ( CH3)4. *‘Si NMR experiments were carried out on ASX NMR BRUKER spectrometers operating at 59,62 and 99,35 MHz in fields of 7.04 and 11.7 T, respectively. For a quantitative analysis, three conditions were required: (a) long enough recycle times to ensure the spin relaxation of all the species present in the sample. Therefore, two types of experiments were achieved: one with a long recycle time (2600 s) respecting the quartz relaxation
Reactive Powder Concretes ( RPCs) ’ are characterized by a high silica fume content, the presence of crushed quartz in their formulation, and a very low water to cement ratio (i.e. w/c = 0.15 compared to 0.45 in ordinary cements). These materials exhibit very high mechanical and durability properties, the compressive strength lying between 200 and 800 MPa, depending on temperature of heat treatment applied to concrete before and during its setting period. In RPCs the calcium silicate hydrates (CSH) result from two reactions: the cement hydration reaction and the so-called pozzolanic reaction between silicate ions, produced by dissolution of silica fume in water, and calcium ions coming mainly from calcium hydroxide, (portlandite CH) present in the medium. Cement notation is used: (C = CaO, S = SiOz, H = HzO.) The
CSH stoechiometry and, hence, their microstructure are totally dependent on the various postset heat treatments (20 to 250°C) applied during hydration. Generally, CSH are noncrystalline and NMR spectroscopy is a relevant technique to establish the link between their microstructural properties and their high mechanical properties. In a first approach, we started with a “Si NMR investigation.
time Ti in order to determine the proportion of crushed
quartz entities Q&; another with a shorter recycle time CNRS 857, E.S.P.C.I. 10, me Vauquelin 75231 Paris, Cedex 05 France.
Address correspondence to Samuel Philippot, Laboratoire de Physique et de Mecanique des Milieax Heterogenes, URA 891
Magnetic Resonance Imaging l Volume 14, Numbers 7/8, 1996
892
Fig. 1. (A) 29SiNMR spectrumof RFT anhydrousmixture. MAS-Single PulseExperimentat a frequencyof S9,62MHz. Recycle time: 2600 s. (B) 29Si NMR spectrum of an RPC sample,hydrated at 9O”C-48 h. MAS-Single PulseExperiment at a frequency of 99,3SMHz. Recycle time: 20 s. (C) 29SiNMR spectrumof a RPC sample,hydrated at 250°C during 1 week. MAS-Single PulseExperimentat a frequency of 99,3SMHz. Recycle time: 20 s.
(20 s) respecting the relaxation times of cement, silica fume, and hydrated species to make a more precise analysis of the respective proportions of these entities. (b) fast rotation of the sample to eliminate sidebands in MAS experiments. A spinning speedequal to 7 kHz was used. (c) sufficient acquisition numbers due to the low natural abundance of 29Sinuclei (4.7%). Usually, 30 scans were necessary for the long recycle time experiments and 1000 scans for the short recycle time ones. RESULTS A RPC formulation containing ordinary Portland cement, silica fume, crushed quartz, superplasticizer with
w/c = 0.15, was prepared and submitted to various heat treatments from 20 to 250°C during durations lying from 8 h to 28 days. Then the different samples obtained were examined by NMR. As examples, we present three NMR spectra: first, on Fig. la, the anhydrous mixture spectrum, then, on Fig. lb and c, two typical spectra of samples hydrated at 90°C during 48 h and at 250°C during 1 wk, respectively. The first spectrum, obtained with a long recycle time, shows the contribution of cement silicatesproviding a signal in the Q” range (-71 ppm) and the contribution of quartz and silica fume giving signals in the Q” range (Q$@ thin peak of the quartz, centered at -107 ppm, and Q& rather broad peak of silica fume centered at - 110 ppm) . The spectra of Fig. lb and c were obtained with a short recycle time and did not respect the quartz relaxation time T1. Nevertheless, they give the proportion of the other species: anhydrous cement (Q” at -71 ppm), calcium silicate hydrates CSH (Q’ and Q’ at -79 and -85 ppm), silica fume (Q4 at - 110 ppm) and also a little contribution of Q3 species ( -97 ppm) attributed to xonotlite formation for the treatment at 250°C. Comparisonof Fig. lb and c showsthe role of temperatureand duration of heat treatment on the different species. At 90°C 48 h
the amount of CSH phase is comparable to the amount of not yet hydrated cement and a lot of silica fume is
‘%i NMR study of hydration and pozzolanic reactions l S. PHILLFOT
always present. On the contrary, a rather long treatment at 250°C leads to a large amount of calcium silicate hydrates compared to the remaining at-hydrous phases, cement, and silica fume, which is rather totally consumed. Furthermore, the structure of the CSH is changed and give rise to a big signal centered in the Q’ domain and a little one in the Q’ range. This phase may be composed of a noncrystalline CSH, based on a long chain silicate skeleton and a crystalline hydrate identified as xonotlite by XRD investigation. From the spectra, simulated with the WlNFIT BRUKER NMR program, we could determine the respective proportions of each Q” units and deduce four parameters: percentage of hydration, H = (Q’ + Q* + Q” ) , which describes the proportion of concrete compounds that were hydrated; connectivity degree defined as C = (Q’ + 2Q’ + 3Q’)/(Q’ + Q’ + Q3) and related to the statistical chain length of CSH; pozzolanic activity relative to the consumption of silica fume, PSF = ( Q4s~o - Q4s~)/Q4s~o and that relative to the consumption of quartz PCQ = (Q4cao -- Q4ca)/Q4c~.
ETAL.
893
CONCLUSIONS In conclusion, we may say that silica fume and quartz activities are highly dependent on heat treatment temperature and duration. Microstructural changes in hydrate structures happened, depending on heat treatment. As observed previously3 in the case of pure tricalcium silicate hydration, the average CSH chain length increases with heat treatment temperature and duration and, at the highest heat treatment temperature (250°C)) crystalline hydrates appear, as in hydrothermal synthesis. REFERENCES 1. Richard, P.; Cheyrezy, M. Compositionof reactive powder concretes.Cem. Concr. Res. (to be published). 2. Engelhard,G.; Michel, D. High resolution29SiNMR of silicatesand zeolites.Chichester:J. Wiley; 1987. 3. Masse,S.; Zanni, H.; Lecourtier,J.; Roussel,J.C.; Rivereau, A. “Si solid stateNMR study of tricalcium silicate and cementhydration at high temperature.Cem. Concr. Res.23:1169-1177; 1993.