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A reply to the discussion by S. Chatterji of the paper “surface studies of hydrated β-C2S”
CEMENT and CONCRETE RESEARCH. Vol. I I , pp. 297-298, 1981. Printed in the USA. 0008-8846/81/020297/02502.00/0 Pergamon Press, Ltd.
A Reply to the Discussion by S. Chatterji of the paper "Surface Studies of Hydrated ~-C2S"* D. M4n6trier, I. Jawed, T.S. Sun and J. Skalny Martin Marietta Laboratories Baltimore, Maryland 21227 We welcome this opportunity to clarify certainpoints in response to Dr. Chatterji's cormnents on our paper on B-C2S hydration. The followiHg discussion also applies to our earlier work on ESCA and SI~4 studies on early C3S hydration (I). Both of Dr. Chatterji's questions can be answered in the affirmative, with some qualifications. Changing the temperature of hydration does change the Ca/Si ratio at the hydrated C3S surface as it does for 8-C2S. The final ratios are unknown, but the change during hydration is obvious. In a previous ESCA study on C3S hydration (i), we noted a significant difference in the Ca/Si ratio vs hydration time profiles for C3S at two different temperatures, 25 ° and 4°C. For the period investigated (up to 6 hours), the Ca/Si ratio at 25°C continuously decreased whereas, at 4°C, the decrease was almost negligible. We do not have sufficient data to prove it, but we believe the differences to be related to the solubilities of C3S at the two temperatures and to the rate of nucleation of the initially formed hydration products. The solubilities of the hydration products of C3S -- Ca(OH)2 and calcium silicate hydrate (C-S-H) -- also change with temperature. For example, the higher solubility of Ca(OH)2 at low temperatures reduces the probability of its nucleation and precipitation and may account for a lowe9 Ca/Si ratio at 4°C than at 25°C. When the surface of unhydrated C3S is sputtered with an argon beam, the value of the Ca/Si ratio remains at 3. Sputtering the hydrated surface brings this ratio closer to a value of 3. Extrapolation of the curve for Ca/Si ratio for hydrated surfaces vs sputtering depth to zero thickness (i.e., to a value of 2 for the Ca/Si ratio for C2S and 3 for C3S) does not and should not establish whether dissolution of calcium silicates is congruent or incongruent. The hydrated surface is, of course, a mixture of calcium silicate hydrates and Ca(OH)2, but there is only partial surface coverage by the hydration products even after 4-S hours of hydration, as shown by our high resolution S ~ studies (2, 3, 4). The observed Ca/Si ratio is an average value obtained by integrating over the whole specimen, surface. We can conclude , however, from our ESCA measurements that the Ca/Si ratios of CsS and C2S on the hydrated surface were not 3 and 2, respectively, at any time during hydration. We agree with Dr. Chatterji's cogent that diffusion or dissolution of Ca(OH)2 from the hydrated surface must also be contributing to the observed variation of Ca/Si ratio of hydrated layer with depth.
*CCR 1_0_0,42S (1980)
297
298
Vol. I I , No. 2 D. M~n~trier, et al.
Dr. Chatterji's second observation, based on comparison of Figs. 2 and 7 of our paper, is even more obvious from our high-resolution S ~ w o r k , which shows very marked differences in surface morphologies between the early and later stages of hydration of both C25 and C35 (2, 3, 4). We believe these differences in the morphologies and characteristics of the hydration products to be correlated with the differences in their chemical composition, as indicated by the different Ca/Si ratios. The changes in the Ols peak in the F_.SCA spectrum of C25 and C35 during hydration also indicate that the main hydration products formed at later stages are probably very different from those formed on the initial interaction between water and calcium silicate at the interface. This interaction has been termed hydroxylation or water chemisorption by some authors (5,6). References i.
D. Menetrier, I. Jawed, T.S. Sun, and J. Skalny, Cem. Concr. Res. 9, 473 (1979).
2.
D. Mentrier, D. McNamara, I. Jawed, and J. Skalny, Cem. Concr. Res. iO,
107 (1980). 3.
I. Jawed, D. Menetrier, and J. Skalny, Proc. 7th Int. Congr. Chem. Cement, Paris, 1980, Vol. 2, p. II-182 (1980).
4.
D. Menetrier, I. Jawed, T.S. Sun, and J. Skalny, Cem. Concr. Res. iO,
425 (1980). 5.
P. Barret, l'Industrie Nationalle i, 3 (1979).
6.
P. Fierens and J. Verhaegen, Silicates Industriels 79, 125 (1974).
A Reply to the Discussion by S. Chatterji of the paper "Surface Studies of Hydrated ~-C2S"* D. M4n6trier, I. Jawed, T.S. Sun and J. Skalny Martin Marietta Laboratories Baltimore, Maryland 21227 We welcome this opportunity to clarify certainpoints in response to Dr. Chatterji's cormnents on our paper on B-C2S hydration. The followiHg discussion also applies to our earlier work on ESCA and SI~4 studies on early C3S hydration (I). Both of Dr. Chatterji's questions can be answered in the affirmative, with some qualifications. Changing the temperature of hydration does change the Ca/Si ratio at the hydrated C3S surface as it does for 8-C2S. The final ratios are unknown, but the change during hydration is obvious. In a previous ESCA study on C3S hydration (i), we noted a significant difference in the Ca/Si ratio vs hydration time profiles for C3S at two different temperatures, 25 ° and 4°C. For the period investigated (up to 6 hours), the Ca/Si ratio at 25°C continuously decreased whereas, at 4°C, the decrease was almost negligible. We do not have sufficient data to prove it, but we believe the differences to be related to the solubilities of C3S at the two temperatures and to the rate of nucleation of the initially formed hydration products. The solubilities of the hydration products of C3S -- Ca(OH)2 and calcium silicate hydrate (C-S-H) -- also change with temperature. For example, the higher solubility of Ca(OH)2 at low temperatures reduces the probability of its nucleation and precipitation and may account for a lowe9 Ca/Si ratio at 4°C than at 25°C. When the surface of unhydrated C3S is sputtered with an argon beam, the value of the Ca/Si ratio remains at 3. Sputtering the hydrated surface brings this ratio closer to a value of 3. Extrapolation of the curve for Ca/Si ratio for hydrated surfaces vs sputtering depth to zero thickness (i.e., to a value of 2 for the Ca/Si ratio for C2S and 3 for C3S) does not and should not establish whether dissolution of calcium silicates is congruent or incongruent. The hydrated surface is, of course, a mixture of calcium silicate hydrates and Ca(OH)2, but there is only partial surface coverage by the hydration products even after 4-S hours of hydration, as shown by our high resolution S ~ studies (2, 3, 4). The observed Ca/Si ratio is an average value obtained by integrating over the whole specimen, surface. We can conclude , however, from our ESCA measurements that the Ca/Si ratios of CsS and C2S on the hydrated surface were not 3 and 2, respectively, at any time during hydration. We agree with Dr. Chatterji's cogent that diffusion or dissolution of Ca(OH)2 from the hydrated surface must also be contributing to the observed variation of Ca/Si ratio of hydrated layer with depth.
*CCR 1_0_0,42S (1980)
297
298
Vol. I I , No. 2 D. M~n~trier, et al.
Dr. Chatterji's second observation, based on comparison of Figs. 2 and 7 of our paper, is even more obvious from our high-resolution S ~ w o r k , which shows very marked differences in surface morphologies between the early and later stages of hydration of both C25 and C35 (2, 3, 4). We believe these differences in the morphologies and characteristics of the hydration products to be correlated with the differences in their chemical composition, as indicated by the different Ca/Si ratios. The changes in the Ols peak in the F_.SCA spectrum of C25 and C35 during hydration also indicate that the main hydration products formed at later stages are probably very different from those formed on the initial interaction between water and calcium silicate at the interface. This interaction has been termed hydroxylation or water chemisorption by some authors (5,6). References i.
D. Menetrier, I. Jawed, T.S. Sun, and J. Skalny, Cem. Concr. Res. 9, 473 (1979).
2.
D. Mentrier, D. McNamara, I. Jawed, and J. Skalny, Cem. Concr. Res. iO,
107 (1980). 3.
I. Jawed, D. Menetrier, and J. Skalny, Proc. 7th Int. Congr. Chem. Cement, Paris, 1980, Vol. 2, p. II-182 (1980).
4.
D. Menetrier, I. Jawed, T.S. Sun, and J. Skalny, Cem. Concr. Res. iO,
425 (1980). 5.
P. Barret, l'Industrie Nationalle i, 3 (1979).
6.
P. Fierens and J. Verhaegen, Silicates Industriels 79, 125 (1974).